What is Automobile Speedometer

what is automobile speedometerBackgroundA speedometer is a device used to measure the traveling speed of a vehicle, usually for the purpose of maintaining a sensible pace. Its development and eventual status as a standard feature in automobiles led to the enforcement of legal speed limits, a notion that had been in practice since the inception of horseless carriages but had gone largely ignored by the general public. Today, no automobile is equipped without a speedometer intact; it is fixed to a vehicle's cockpit and usually shares a housing with an odometer, which is a mechanism used to record total distance traveled. Two basic types of automobile speedometer, mechanical and electronic, are currently produced.HistoryThe concept of recording travel data is almost as old as the concept of vehicles. Early Romans marked the wheels of their chariots and counted the revolutions, estimating distance traveled and average daily speed. In the eleventh century, Chinese inventors came up with a mechanism involving a gear train and a moving arm that would strike a drum after a certain distance. Nautical speed data was recorded in the 1500s by an invention called the chip log, a line knotted at regular intervals and weighted to drag in the water. The number of knots let out in a set amount of time would determine the speed of the craft, hence the nautical term "knots" still applied today.The first patent for a rotating-shaft speed indicator was issued in 1916 to inventor Nikola Tesla. At that time, however, speedometers had already been in production for several years. The development of the first speedometer for cars is often credited to A. P. Warner, founder of the Warner Electric Company. At the turn of the century, he invented a mechanism called a cut-meter, used to measure the speed of industrial cutting tools. Realizing that the cut-meter could be adapted to the automobile, he modified the device and set about on a large promotional campaign to bring his speedometer to the general public. Several speed indicator concepts were introduced by competing sources at the time, but Warner's design enjoyed considerable success. By the end of World War I, the Warner Instrument Company manufactured nine out of every 10 speedometers used in automobiles.The Oldsmobile Curved Dash Runabout, released in 1901, was the first automobile line equipped with a mechanical speedometer. Cadillac and Overland soon followed, and speedometers began to regularly appear as a factory-installed option in new automobiles. Speedometers in this era were difficult to read in daylight and, with no lamp in the housing, virtually illegible at night. The drive cable in early models was attached to either the front wheels or the back of the transmission, but the integration of the drive cable into the transmission housing wouldn't happen for another 20 years. After that improvement was made, the basic technical design of a speedometer would remain untouched until the advent of the electronic speedometer in the early 1980s.Raw MaterialsMaterials used in the production of speedometers vary with the type of gauge and intended application. Older mechanical models were entirely comprised of steel and other metal alloys, but in later years about 40% of the parts for a mechanical speedometer were molded from various plastic polymers. Newer electronic models are almost entirely made of plastics, and design engineers continually upgrade the polymers used. For example, the case of a speedometer's main assembly is usually made of nylon, but some manufacturers now employ the more water-resistant polybutylene terephthalate (PBT) polyester. The worm drive and magnet shaft are also nylon, as is the speedometer's gear train and spindles. The glass display lens of the recent past is now made of transparent polycarbonate, a strong, flexible plastic that is resistant to heat, moisture, and impact.DesignIn a mechanical speedometer, a rotating cable is attached to a set of gears in the automobile's transmission. This cable is directly attached to a permanent magnet in the speedometer assembly, which spins at a rate proportional to the speed of the vehicle. As the magnet rotates, it manipulates an aluminum ring, pulling it in the same direction as the revolving magnetic field; the ring's movement, however, is counteracted by a spiral spring. Attached to the aluminum ring is the pointer, which indicates the speed of the vehicle by marking the balance between these two forces. As the vehicle slows, the magnetic force on the aluminum ring lessens, and the spring pulls the speedometer's pointer back to zero.Electronic speedometers are almost universally present in late-model cars. In this type of gauge, a pulse generator (or tach generator) installed in the transmission measures the vehicle's speed. It communicates this via electric or magnetic pulse signals, which are either translated into an electronic read-out or used to manipulate a traditional magnetic gauge assembly.The ManufacturingProcessSteel components To form molten steel, iron ore is melted with coke, a carbon-rich substance that results when coal is heated in a vacuum. Depending on the alloy, other metals such as aluminum, manganese, titanium, and zirconium may also be introduced. After the steel cools, it is formed into sheets between high-pressure rollers and distributed to the manufacturing plant. There, the individual parts may be cast into molds or pressed and shaped from bar stock by large rolling machines.Plastic components The various plastics that arrive in an instrument manufacturing station were first created from organic chemical compounds derived from petroleum. These polymers are distributed in pellet form for use in the injection-molding process. To make the small parts for a speedometer assembly, these pellets are loaded into the hopper of a molding machine and melted. A hydraulic screw forces the plastic through a nozzle and into a pre-cast mold, where the plastic is allowed to cool and solidify. The parts are then gathered and transported to assembly stations.Assembly The manner of assembly and degree of human interaction depends on the quality of speedometer. Some inexpensive speedometer systems are made to be "disposable," meaning that the instruments are not built for easy disassembly or repair. In this case, the hardware is fastened using a process called riveting, in which a headed pin is inserted and blunted on the other end, forming a permanent attachment. Higher-end speedometer systems consist of two major assemblies attached by screws; the advantage is that the inner hardware of the gauge is accessible for repair and recalibration. The inner shaft and speedometer assembly are then fused into place with rivets or screws. The permanent magnets used in mechanical speedometers are compressed and molded before arrival at the plant, and therefore only require mounting onto the worm drive. In the case of electronic speedometers, fiberglass-and-copper circuitry is also manufactured by vendors, and does require programming before it is screwed into the larger system. These larger components are transported to a separate assembly station, where they are mounted into the housing with stud-terminal or blade-terminal plastic connectors. Beyond its primary duty as a protective case, the housing also serves as a platform for attaching exterior features such as the dial face, needle, and display window. Again, these processes require automation due to large output, but human effort is needed at every step to inspect and ensure product consistency.Calibration Calibration is the process of determining the true value of spaces in any graduated instrument. It is an especially vital process in the manufacture of speedometers because driver safety is reliant on an accurate readout. In a mechanical gauge, magnetic forces produce the torque that deflects the indicator needle. When calibrating this type of gauge, an electromagnet is used to adjust the strength of the permanent magnet mounted in the speedometer until the needle matches the input from the rotating cable. When calibrating an electronic gauge, adjustments are made when calibration factors are written into the memory of the meter. The system can then refigure the balance between input from the transmission and output of the needle. New automated systems for calibrating both mechanical and electronic speedometers are now available, saving an immense number of the man-hours usually required for this process. A microphone, colloquially called a mic or mike (both pronounced /mak/), is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1876, Emile Berliner invented the first microphone used as a telephone voice transmitter. Microphones are used in many applications such as telephones, tape recorders, hearing aids, motion picture production, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, VoIP, and for non-acoustic purposes such as ultrasonic checking. A Neumann U87 condenser microphone The most common design today uses a thin membrane which vibrates in response to sound pressure. This movement is subsequently translated into an electrical signal. Most microphones in use today for audio use electromagnetic induction (dynamic microphone), capacitance change (condenser microphone, pictured right), piezoelectric generation, or light modulation to produce the signal from mechanical vibration. What is a Microphone? A microphone is an electromechanical device that uses vibration to create an electrical signal proportional to the vibration, which is usually an air pressure wave. There are many different types of microphone, ranging from the old condensers to the modern piezoelectrics.

Microphone History Alexander Graham Bell invented the first microphone in 1876 as part of the telephone. Thomas Edison invented the first carbon microphone in 1886, a significant improvement on Bell's impractical liquid microphone, and the forerunner of the modern microphone. Microphone Types Condenser microphones are a capacitor that has a fixed plate and a moving plate plate connected to a diaphragm. Air vibrations cause the diaphragm plate to move slightly and change the voltage between the plates. The electret microphone is a modern improvement on the old condenser design, and uses a dielectric material that has a permanently static charge, eliminating the need for a power supply to maintain the charge. This allows electrets to be made very small and cheap. Dynamic microphones have a coil connected to a diaphragm that moves between a fixed permanent magnet. Vibration causes the diaphragm and coil to move, inducing a current in the coil proportional to the vibration. It is the opposite process of creating sound with a speaker, and while speakers can be used as microphones, their signal quality is poor. Carbon microphones have a fixed plate and a moving plate connected to a diaphragm. Between the plates are tiny carbon grains that move when the diaphragm is vibrated. This movement changes the total contact surface area of the carbon, which also changes the resistance between the plates. The changing resistance results in voltage changes proportional to the vibration. Ribbon microphones use the movement of a thin metal foil suspended in a magnetic field to create a signal. Piezoelectric microphones convert vibration into mechanical stress to create a charge from the piezoelectric crystal. Sound Direction Microphones are also categorized according to how well they pick up sound from certain directions. Omni-directionals detect sound equally well from all angles, bi-directionals pickup from the front and back but not the sides, and uni-directionals only pick up sound from the front. Microphone Applications Microphones are commonly used in television, radio, concerts, telephones, and public address systems, but also in other unusual applications. They have been used by rescuers to find survivors after disasters, and by police to conduct surveillance. They are used for feedback in noise cancellation systems, and used to detect the vibrations that precede volcanoes and earthquakes.Microphones I. How They Work.A microphone is an example of a transducer, a device that changes information from one form to another. Sound information exists as patterns of air pressure; the microphone changes this information into patterns of electric current. The recording engineer is interested in the accuracy of this transformation, a concept he thinks of as fidelity.A variety of mechanical techniques can be used in building microphones. The two most commonly encountered in recording studios are the magneto-dynamic and the variable condenser designs.THE DYNAMIC MICROPHONE.

In the magneto-dynamic, commonly called dynamic, microphone, sound waves cause movement of a thin metallic diaphragm and an attached coil of wire. A magnet produces a magnetic field which surrounds the coil, and motion of the coil within this field causes current to flow. The principles are the same as those that produce electricity at the utility company, realized in a pocket-sized scale. It is important to remember that current is produced by the motion of the diaphragm, and that the amount of current is determined by the speed of that motion. This kind of microphone is known as velocity sensitive. THE CONDENSER MICROPHONE.

In a condenser microphone, the diaphragm is mounted close to, but not touching, a rigid backplate. (The plate may or may not have holes in it.) A battery is connected to both pieces of metal, which produces an electrical potential, or charge, between them. The amount of charge is determined by the voltage of the battery, the area of the diaphragm and backplate, and the distance between the two. This distance changes as the diaphragm moves in response to sound. When the distance changes, current flows in the wire as the battery maintains the correct charge. The amount of current is essentially proportioinal to the displacement of the diaphragm, and is so small that it must be electrically amplified before it leaves the microphone.A common varient of this design uses a material with a permanently imprinted charge for the diaphragm. Such a material is called an electret and is usually a kind of plastic. (You often get a piece of plastic with a permanent charge on it when you unwrap a record. Most plastics conduct electricity when they are hot but are insulators when they cool.) Plastic is a pretty good material for making diaphragms since it can be dependably produced to fairly exact specifications. (Some popular dynamic microphones use plastic diaphragms.) The major disadvantage of electrets is that they lose their charge after a few years and cease to work.II. SpecificationsThere is no inherent advantage in fidelity of one type of microphone over another. Condenser types require batteries or power from the mixing console to operate, which is occasionally a hassle, and dynamics require shielding from stray magnetic fields, which makes them a bit heavy sometmes, but very fine microphones are available of both styles. The most important factor in choosing a microphone is how it sounds in the required application. The following issues must be considered:Sensitivity.This is a measure of how much electrical output is produced by a given sound. This is a vital specification if you are trying to record very tiny sounds, such as a turtle snapping its jaw, but should be considered in any situation. If you put an insensitive mic on a quiet instrument, such as an acoustic guitar, you will have to increase the gain of the mixing console, adding noise to the mix. On the other hand, a very sensitive mic on vocals might overload the input electronics of the mixer or tape deck, producing distortion. Overload characteristics.Any microphone will produce distortion when it is overdriven by loud sounds. This is caused by varous factors. With a dymanic, the coil may be pulled out of the magnetic field; in a condenser, the internal amplifier might clip. Sustained overdriving or extremely loud sounds can permanently distort the diaphragm, degrading performance at ordinary sound levels. Loud sounds are encountered more often than you might think, especially if you place the mic very close to instruments. (Would you put your ear in the bell of a trumpet?) You usually get a choice between high sensitivity and high overload points, although occasionally there is a switch on the microphone for different situations.Linearity, or Distortion.This is the feature that runs up the price of microphones. The distortion characteristics of a mic are determined mostly by the care with which the diaphragm is made and mounted. High volume production methods can turn out an adequate microphone, but the distortion performance will be a matter of luck. Many manufacturers have several model numbers for what is essentially the same device. They build a batch, and then test the mics and charge a premium price for the good ones. The really big names throw away mic capsules that don't meet their standards. (If you buy one Neumann mic, you are paying for five!)No mic is perfectly linear; the best you can do is find one with distortion that complements the sound you are trying to record. This is one of the factors of the microphone mystique discussed later. Frequency response.A flat frequency response has been the main goal of microphone companies for the last three or four decades. In the fifties, mics were so bad that console manufacturers began adding equalizers to each input to compensate. This effort has now paid off to the point were most professional microphones are respectably flat, at least for sounds originating in front. The major exceptions are mics with deliberate emphasis at certain frequencies that are useful for some applications. This is another part of the microphone mystique. Problems in frequency response are mostly encountered with sounds originating behind the mic, as discussed in the next section.Noise.Microphones produce a very small amount of current, which makes sense when you consider just how light the moving parts must be to accurately follow sound waves. To be useful for recording or other electronic processes, the signal must be amplified by a factor of over a thousand. Any electrical noise produced by the microphone will also be amplified, so even slight amounts are intolerable. Dynamic microphones are essentially noise free, but the electronic circuit built into condensor types is a potential source of trouble, and must be carefully designed and constructed of premium parts.Noise also includes unwanted pickup of mechanical vibration through the body of the microphone. Very sensitive designs require elastic shock mountings, and mics intended to be held in the hand need to have such mountings built inside the shell.The most common source of noise associated with microphones is the wire connecting the mic to the console or tape deck. A mic preamp is very similar to a radio reciever, so the cable must be prevented from becoming an antenna. The basic technique is to surround the wires that carry the current to and from the mic with a flexible metallic shield, which deflects most radio energy. A second technique, which is more effective for the low frequency hum induced by the power company into our environment, is to balance the line:

Current produced by the microphone will flow down one wire of the twisted pair, and back along the other one. Any current induced in the cable from an outside source would tend to flow the same way in both wires, and such currents cancel each other in the transformers. This system is expensive.Microphone LevelsAs I said, microphone outputs are of necessity very weak signals, generally around -60dBm. (The specification is the power produced by a sound pressure of 10 uBar) The output impedance will depend on whether the mic has a transformer balanced output . If it does not, the microphone will be labeled "high impedance" or "hi Z" and must be connected to an appropriate input. The cable used must be kept short, less than 10 feet or so, to avoid noise problems.If a microphone has a transformer, it will be labeled low impedance, and will work best with a balanced input mic preamp. The cable can be several hundred feet long with no problem. Balanced output, low impedance microphones are expensive, and generally found in professonal applications. Balanced outputs must have three pin connectors ("Cannon plugs"), but not all mics with those plugs are really balanced. Microphones with standard or miniature phone plugs are high impedance. A balanced mic can be used with a high impedance input with a suitable adapter.You can see from the balanced connection diagram that there is a transformer at the input of the console preamp. (Or, in lieu of a transformer, a complex circuit to do the same thing.) This is the most significant difference between professional preamplifiers and the type usually found on home tape decks. You can buy transformers that are designed to add this feature to a consumer deck for about $20 each. (Make sure you are getting a transformer and not just an adapter for the connectors.) With these accessories you can use professional quality microphones, run cables over a hundred feet with no hum, and because the transformers boost the signal somewhat, make recordings with less noise. This will not work with a few inexpensive cassette recorders, because the strong signal causes distortion. Such a deck will have other problems, so there is little point trying to make a high fidelity recording with it anyway.III. Pick Up PatternsMany people have the misconception that microphones only pick up sound from sources they are pointed at, much as a camera only photographs what is in front of the lens. This would be a nice feature if we could get it, but the truth is we can only approximate that action, and at the expense of other desirable qualities.

MICROPHONE PATTERNSThese are polar graphs of the output produced vs. the angle of the sound source. The output is represented by the radius of the curve at the incident angle.OmniThe simplest mic design will pick up all sound, regardless of its point of origin, and is thus known as an omnidirectional microphone. They are very easy to use and generally have good to outstanding frequency response. To see how these patterns are produced, here's a sidebar on directioal microphones.Bi-directionalIt is not very difficult to produce a pickup pattern that accepts sound striking the front or rear of the diaphragm, but does not respond to sound from the sides. This is the way any diaphragm will behave if sound can strike the front and back equally. The rejection of undesired sound is the best achievable with any design, but the fact that the mic accepts sound from both ends makes it difficult to use in many situations. Most often it is placed above an instrument. Frequency response is just as good as an omni, at least for sounds that are not too close to the microphone.CardioidThis pattern is popular for sound reinforcement or recording concerts where audience noise is a possible problem. The concept is great, a mic that picks up sounds it is pointed at. The reality is different. The first problem is that sounds from the back are not completely rejected, but merely reduced about 10-30 dB. This can surprise careless users. The second problem, and a severe one, is that the actual shape of the pickup pattern varies with frequency. For low frequencies, this is an omnidirectional microphone. A mic that is directional in the range of bass instruments will be fairly large and expensive. Furthermore, the frequency response for signals arriving from the back and sides will be uneven; this adds an undesired coloration to instruments at the edge of a large ensemble, or to the reverberation of the concert hall.A third effect, which may be a problem or may be a desired feature, is that the microphone will emphasize the low frequency components of any source that is very close to the diaphragm. This is known as the "proximity effect", and many singers and radio announcers rely on it to add "chest" to a basically light voice. Close, in this context, is related to the size of the microphone, so the nice large mics with even back and side frequency response exhibit the strongest presence effect. Most cardioid mics have a built in lowcut filter switch to compensate for proximity. Missetting that switch can cause hilarious results. Bidirectional mics also exhibit this phenomenon.Tighter PatternsIt is posible to exaggerate the directionality of cardioid type microphones, if you don't mind exaggerating some of the problems. The Hypercardioid pattern is very popular, as it gives a better overall rejection and flatter frequency response at the cost of a small back pickup lobe. This is often seen as a good compromise between the cardioid and bidirectional patterns. A "shotgun" mic carries these techniques to extremes by mounting the diaphragm in the middle of a pipe. The shotgun is extremely sensitive along the main axis, but posseses pronounced extra lobes which vary drastically with frequency. In fact, the frequency response of this mic is so bad it is usually electronically restricted to the voice range, where it is used to record dialogue for film and video.Stereo microphonesYou don't need a special microphone to record in stereo, you just need two (see below). A so called stereo microphone is really two microphones in the same case. There are two kinds: extremely expensive professional models with precision matched capsules, adjustable capsule angles, and remote switching of pickup patterns; and very cheap units (often with the capsules oriented at 180 deg.) that can be sold for high prices because they have the word stereo written on them.IV. Typical PlacementSingle microphone useUse of a single microphone is pretty straightforward. Having chosen one with appropriate sensitivity and pattern, (and the best distortion, frequency response, and noise characteristics you can afford), you simply mount it where the sounds are. The practical range of distance between the instrument and the microphone is determined by the point where the sound overloads the microphone or console at the near end, and the point where ambient noise becomes objectionable at the far end. Between those extremes it is largely a matter of taste and experimentation.If you place the microphone close to the instrument, and listen to the results, you will find the location of the mic affects the way the instrument sounds on the recording. The timbre may be odd, or some notes may be louder than others. That is because the various components of an instrument's sound often come from different parts of the instrument body (the highest note of a piano is nearly five feet from the lowest), and we are used to hearing an evenly blended tone. A close in microphone will respond to some locations on the instrument more than others because the difference in distance from each to the mic is proportionally large. A good rule of thumb is that the blend zone starts at a distance of about twice the length of the instrument. If you are recording several instruments, the distance between the players must be treated the same way.If you place the microphone far away from the instrument, it will sound as if it is far away from the instrument. We judge sonic distance by the ratio of the strength of the direct sound from the instrument (which is always heard first) to the strength of the reverberation from the walls of the room. When we are physically present at a concert, we use many cues beside the sounds to keep our attention focused on the performance, and we are able to ignore any distractions there may be. When we listen to a recording, we don't have those visual clues to what is happening, and find anything extraneous that is very audible annoying. For this reason, the best seat in the house is not a good place to record a concert. On the other hand, we do need some reverberation to appreciate certain features of the music. (That is why some types of music sound best in a stone church) Close microphone placement prevents this. Some engineers prefer to use close miking techniques to keep noise down and add artificial reverberation to the recording, others solve the problem by mounting the mic very high, away from audience noise but where adequate reverberation can be found.StereoStereo sound is an illusion of spaciousness produced by playing a recording back through two speakers. The success of this illusion is referred to as the image. A good image is one in which each instrument is a natural size, has a distinct location within the sound space, and does not move around. The main factors that establish the image are the relative strength of an instrument's sound in each speaker, and the timing of arrival of the sounds at the listener's ear. In a studio recording, the stereo image is produced artificially. Each instrument has its own microphone, and the various signals are balanced in the console as the producer desires. In a concert recording, where the point is to document reality, and where individual microphones would be awkward at best, it is most common to use two mics, one for each speaker.

Spaced microphonesThe simplest approach is to assume that the speakers will be eight to ten feet apart, and place two microphones eight to ten feet apart to match. Either omnis or cardioids will work. When played back, the results will be satisfactory with most speaker arrangements. (I often laugh when I attend concerts and watch people using this setup fuss endlessly with the precise placement of the mics. This technique is so forgiving that none of their efforts will make any practical difference.)The big disavantage of this technique is that the mics must be rather far back from the ensemble- at least as far as the distance from the leftmost performer to the rightmost. Otherwise, those instruments closest to the microphones will be too prominent. There is usually not enough room between stage and audience to achieve this with a large ensemble, unless you can suspend the mics or have two very tall stands.Coincident cardioidsThere is another disadvantage to the spaced technique that appears if the two channels are ever mixed together into a monophonic signal. (Or broadcast over the radio, for similar reasons.) Because there is a large distance between the mics, it is quite possible that sound from a particular instrument would reach each mic at slightly different times. (Sound takes 1 millisecond to travel a foot.) This effect creates phase differences between the two channels, which results in severe frequency response problems when the signals are combined. You seldom actually lose notes from this interference, but the result is an uneven, almost shimmery sound. The various coincident techniques avoid this problem by mounting both mics in almost the same spot.This is most often done with two cardioid microphones, one pointing slightly left, one slightly right. The microphones are often pointing toward each other, as this places the diaphragms within a couple of inches of each other, totally eliminating phase problems. No matter how they are mounted, the microphone that points to the left provides the left channel. The stereo effect comes from the fact that the instruments on the right side are on-axis for the right channel microphone and somewhat off-axis (and therefore reduced in level) for the other one. The angle between the microphones is critical, depending on the actual pickup pattern of the microphone. If the mics are too parallel, there will be little stereo effect. If the angle is too wide, instruments in the middle of the stage will sound weak, producing a hole in the middle of the image. [Incidentally, to use this technique, you must know which way the capsule actually points. There are some very fine German cardioid microphones in which the diaphragm is mounted so that the pickup is from the side, even though the case is shaped just like many popular end addressed models. (The front of the mic in question is marked by the trademark medallion.) I have heard the results where an engineer mounted a pair of these as if the axis were at the end. You could hear one cello player and the tympani, but not much else.]You may place the microphones fairly close to the instruments when you use this technique. The problem of balance between near and far instruments is solved by aiming the mics toward the back row of the ensemble; the front instruments are therefore off axis and record at a lower level. You will notice that the height of the microphones becomes a critical adjustment.M.S.The most elegant approach to coincident miking is the M.S. or middle-side technique. This is usually done with a stereo microphone in which one element is omnidirectional, and the other bidirectional. The bidirectional element is oriented with the axis running parallel to the stage, rejecting sound from the center. The omni element, of course, picks up everything. To understand the next part, consider what happens as instrument is moved on the stage. If the instrument is on the left half of the stage, a sound would first move the diaphragm of the bidirectional mic to the right, causing a positive voltage at the output. If the instrument is moved to center stage, the microphone will not produce any signal at all. If the instrument is moved to the right side, the sound would first move the diaphragm to the left, producing a negative volage. You can then say that instruments on one side of the stage are 180 degrees out of phase with those on the other side, and the closer they are to the center, the weaker the signal produced.Now the signals from the two microphones are not merely kept in two channels and played back over individual speakers. The signals are combined in a circuit that has two outputs; for the left channel output, the bidirectional output is added to the omni signal. For the right channel output, the bidirectional output is subtracted from the omni signal. This gives stereo, because an instrument on the right produces a negative signal in the bidirectional mic, which when added to the omni signal, tends to remove that instrument, but when subtracted, increases the strength of the instrument. An instrument on the left suffers the opposite fate, but instruments in the center are not affected, because their sound does not turn up in the bidirectional signal at all.M.S. produces a very smooth and accurate image, and is entirely mono compatabile. The only reason it is not used more extensively is the cost of the special microphone and decoding circuit, well over $1,000.Large ensemblesThe above techniques work well for concert recordings in good halls with small ensembles. When recording large groups in difficult places, you will often see a combination of spaced and coincident pairs. This does produce a kind of chorusing when the signals are mixed, but it is an attractive effect and not very different from the sound of string or choral ensembles any way. When balance between large sections and soloists cannot be acheived with the basic setup, extra microphones are added to highlight the weaker instruments. A very common problem with large halls is that the reverberation from the back seems late when compared to the direct sound taken at the edge of the stage. This can be helped by placing a mic at the rear of the audience area to get the ambient sound into the recording sooner. Studio techniquesA complete description of all of the procedures and tricks encountered in the recording studio would fill several books. These are just a few things you might see if you dropped in on the middle of a session.Individual mics on each instrument.This provides the engineer with the ability to adjust the balance of the instruments at the console, or, with a multitrack recorder, after the musicians have gone home. There may be eight or nine mics on the drum set alone.Close mic placement.The microphones will usually be placed rather close to the instruments. This is partially to avoid problems that occur when an instrument is picked up in two non-coincident mics, and partially to modify the sound of the instruments (to get a "honky-tonk" effect from a grand piano, for instance).Acoustic fences around instruments, or instruments in separate rooms.The interference that occurs when when an instrument is picked up by two mics that are mixed is a very serious problem. You will often see extreme measures, such as a bass drum stuffed with blankets to muffle the sound, and then electronically processed to make it sound like a drum again.Everyone wearing headphones.Studio musicians often play to "click tracks", which are not recorded metronomes, but someone tapping the beat with sticks and occasionally counting through tempo changes. This is done when the music must be synchronized to a film or video, but is often required when the performer cannot hear the other musicians because of the isolation measures described above.20 or 30 takes on one song.Recordings require a level of perfection in intonation and rhythm that is much higher than that acceptable in concert. The finished product is usually a composite of several takes.Pop filters in front of mics.Some microphones are very sensitive to minor gusts of wind--so sensitive in fact that they will produce a loud pop if you breath on them. To protect these mics (some of which can actually be damaged by blowing in them) engineers will often mount a nylon screen between the mic and the artist. This is not the most common reason for using pop filters though:Vocalists like to move around when they sing; in particular, they will lean into microphones. If the singer is very close to the mic, any motion will produce drastic changes in level and sound quality. (You have seen this with inexpert entertainers using hand held mics.) Many engineers use pop filters to keep the artist at the proper distance. The performer may move slightly in relation to the screen, but that is a small proportion of the distance to the microphone. V. The Microphone MystiqueThere is an aura of mystery about microphones. To the general public, a recording engineer is something of a magician, privy to a secret arcana, and capable of supernatural feats. A few modern day engineers encourage this attitude, but it is mostly a holdover from the days when studio microphones were expensive and fragile, and most people never dealt with any electronics more complex than a table radio. There are no secrets to recording; the art is mostly a commonsense application of the principles already discussed in this paper. If there is an arcana, it is an accumulation of trivia achieved through experience with the following problems:Matching the microphone to the instrument.There is no wrong microphone for any instrument. Every engineer has preferences, usually based on mics with which he is familiar. Each mic has a unique sound, but the differences between good examples of any one type are pretty minor. The artist has a conception of the sound of his instrument, (which may not be accurate) and wants to hear that sound through the speakers. Frequency response and placement of the microphone will affect that sound; sometimes you need to exaggerate the features of the sound the client is looking for.Listening the proper way.It is easy to forget that the recording engineer is an illusionist- the result will never be confused with reality by the listener. Listeners are in fact very forgiving about some things. It is important that the engineer be able to focus his attention on the main issues and not waste time with interesting but minor technicalities. It is important that the engineer know what the main issues are. An example is the noise/distortion tradeoff. Most listeners are willing to ignore a small amount of distortion on loud passages (in fact, they expect it), but would be annoyed by the extra noise that would result if the engineer turned the recording level down to avoid it. One technique for encouraging this attention is to listen to recordings over a varitey of sound systems, good and bad. Learning for yourself.Many students come to me asking for a book or a course of study that will easily make them a member of this elite company. There are books, and some schools have courses in recording, but they do not supply the essential quality the professional recording engineer needs, which is experience.A good engineer will have made hundreds of recordings using dozens of different microphones. Each session is an opportunity to make a new discovery. The engineer will make careful notes of the setup, and will listen to the results many times to build an association between the technique used and the sound achieved. Most of us do not have access to lots of professional microphones, but we could probably afford a pair of general purpose cardioids. With about $400 worth of mics and a reliable tape deck, it is possible to learn to make excellent recordings. The trick is to record everything that will sit still and make noise, and study the results: learn to hear when the mic is placed badly and what to do about it. When you know all you can about your mics, buy a different pair and learn those. Occasionally, you will get the opportunity to borrow mics. If possible, set them up right alongside yours and make two recordings at once. It will not be long before you will know how to make consistently excellent recordings under most conditions.

Peter Elsea 1996

StethoscopeFrom Wikipedia, the free encyclopediaJump to: navigation, search

Modern stethoscopeThe stethoscope (from Greek , of , stthos - chest and , skop - examination) is an acoustic medical device for auscultation, or listening to the internal sounds of an animal body. It is often used to listen to heart sounds. It is also used to listen to intestines and blood flow in arteries and veins. Less commonly, "mechanic's stethoscopes" are used to listen to internal sounds made by machines, such as diagnosing a malfunctioning automobile engine by listening to the sounds of its internal parts. Stethoscopes can also be used to check scientific vacuum chambers for leaks, and for various other small-scale acoustic monitoring tasks.History

Early stethoscopesThe stethoscope was invented in France in 1816 by Ren-Thophile-Hyacinthe Laennec at the Necker-Enfants Malades Hospital in Paris.[1] It consisted of a wooden tube and was monaural. His device was similar to the common ear trumpet, a historical form of hearing aid; indeed, his invention was almost indistinguishable in structure and function from the trumpet, which was commonly called a "microphone". In 1851, Arthur Leared invented a binaural stethoscope, and in 1852 George Cammann perfected the design of the instrument for commercial production, which has become the standard ever since. Cammann also authored a major treatise on diagnosis by auscultation, which the refined binaural stethoscope made possible. By 1873, there were descriptions of a differential stethoscope that could connect to slightly different locations to create a slight stereo effect, though this did not become a standard tool in clinical practice.Rappaport and Sprague designed a new stethoscope in the 1940s, which became the standard by which other stethoscopes are measured,consisting of two sides, one of which is used for the respiratory system, the other is used for the cardiovascular system. The Rappaport-Sprague was later made by Hewlett-Packard. HP's medical products division was spun off as part of Agilent Technologies, Inc., where it became Agilent Healthcare. Agilent Healthcare was purchased by Philips which became Philips Medical Systems, before the walnut-boxed, $300, original Rappaport-Sprague stethoscope was finally abandoned ca. 2004, along with Philips' brand (manufactured by Andromed, of Montreal, Canada) electronic stethoscope model. Today there are still cardiologists who consider the original Rappaport-Sprague to be the finest acoustic stethoscope. Rappaport-Sprague copies made in China currently retail for about US$20.00. The Rappaport-Sprague model stethoscope was heavy and short (18"-24") with an antiquated appearance recognizable by their two large independent latex rubber tubes connecting an exposed-leaf-spring-joined-pair of opposing "f"-shaped chrome-plated brass binaural ear tubes with a dual-head chest piece.Several other minor refinements were made to stethoscopes, until in the early 1960s Dr. David Littmann, a Harvard Medical School professor, created a new stethoscope that was lighter than previous models and had improved acoustics.[2] In the late 1970s, 3M-Littmann introduced the tunable diaphragm: a very hard (G-10) glass-epoxy resin diaphragm member with an overmolded silicone flexible acoustic surround which permitted increased excursion of the diaphragm member in a "z"-axis with respect to the plane of the sound collecting area. The left shift to a lower resonant frequency increases the volume of some low frequency sounds due to the longer waves propagated by the increased excursion of the hard diaphragm member suspended in the concentric acountic surround. Conversely, restricting excursion of the diaphragm by pressing the stethoscope diaphragm surface firmly against the anatomical area overlying the physiological sounds of interest, the acoustic surround could also be used to dampen excursion of the diaphragm in response to "z"-axis pressure against a concentric fret. This raises the frequency bias by shortening the wavelength to auscultate a higher range of physiological sounds. 3-M Littmann is also credited with a collapsible mold frame for sludge molding a single column bifurcating stethoscope tube [3] with an internal septum dividing the single column stethoscope tube into discrete left and right binaural channels (AKA "cardiology tubing"; including a covered, or internal leaf spring-binaural ear tube connector).In 1999, Richard Deslauriers patented the first external noise reducing stethoscope, the DRG Puretone. It featured two parallel lumens containing two steel coils which dissipated infiltrating noise as inaudible heat energy. The steel coil "insulation" added .30lb to each stethoscope. In 2005, DRG's diagnostics division was acquired by TRIMLINE Medical Products.[4] Between 1998-2007 Marc Werblud, a disabled paramedic/medical student created a lightweight 32" long acoustic noise cancelling stethoscope which improved sound quality, and reduced neck strain. The acoustic properties of the specific materials used to make stethoscope components were first tested to determine their 'resident frequency'. The results of individual acoustical component materials tests revealed how their collective interactions determine the instrument's dominant tonal character and frequency response of the stethoscope, yielding several high fidelity and acoustic noise cancelling stethoscope models. Some models weighed as little as 133 grams (4.7 oz) - half the weight of common cardiology stethoscopes from the 1960s and 1970s. The new models also included a unique set of stethoscope diaphragms which increased frequency response, and could be sanitarily changed for each patient.Until his death in 2007, Georgetown University Professor W. Proctor Harvey (b. 1917) was the name most synonymous with the stethoscope and considered the nation's most skilled practitioner of auscultation, the ability to detect cardiac ailments by listening to the sounds of the heart. Dr. Harvey's incredible gift was being able to make sound clinical diagnoses from basic clinical examinations and the bedside using only an acoustic stethoscope. Dr. Harvey elevated the discipline of cardiovascular diagnosis to an art form. He taught differential auscultation using classical music to train a generation of clinicians to diagnose the heart by first learning to hear the individual instrument voices within a symphony. Harvey invented acoustic stethoscopes under the Tycos brand name notably, the Harvey Triple-head; and the "stethophone", the first electronic amplification auscultation device.[citation needed][edit] Current practice

Dresden, DDR, 1973Stethoscopes are often considered as a symbol of the doctor's profession, as doctors are often seen or depicted with a stethoscope hanging around their neck.[edit] Types of stethoscopes[edit] Acoustic

Acoustic StethoscopeAcoustic stethoscopes are familiar to most people, and operate on the transmission of sound from the chest piece, via air-filled hollow tubes, to the listener's ears. The chestpiece usually consists of two sides that can be placed against the patient for sensing sound a diaphragm (plastic disc) or bell (hollow cup). If the diaphragm is placed on the patient, body sounds vibrate the diaphragm, creating acoustic pressure waves which travel up the tubing to the listener's ears. If the bell is placed on the patient, the vibrations of the skin directly produce acoustic pressure waves traveling up to the listener's ears. The bell transmits low frequency sounds, while the diaphragm transmits higher frequency sounds. This 2-sided stethoscope was invented by Rappaport and Sprague in the early part of the 20th century. One problem with acoustic stethoscopes was that the sound level is extremely low. This problem was surmounted in 1999 with the invention of the stratified continuous (inner) lumen, and the kinetic acoustic mechanism in 2002. Acoustic stethoscopes are the most commonly used. A recent independent review evaluated 12 common acoustic stethoscopes on the basis of loudness, clarity, and ergonomics. They did acoustic laboratory testing and recorded heart sounds on volunteers. The results are listed by brand and model. [5][edit] ElectronicAn electronic stethoscope (or stethophone) overcomes the low sound levels by electronically amplifying body sounds. However, amplification of stethoscope contact artifacts, and component cutoffs (frequency response thresholds of electronic stethoscope microphones, pre-amps, amps, and speakers) limit electronically amplified stethoscopes' overall utility by amplifying mid-range sounds, while simultaneously attenuating high- and low- frequency range sounds. Currently, a number of companies offer electronic stethoscopes.Electronic stethoscopes require conversion of acoustic sound waves to electrical signals which can then be amplified and processed for optimal listening. Unlike acoustic stethoscopes, which are all based on the same physics, transducers in electronic stethoscopes vary widely. The simplest and least effective method of sound detection is achieved by placing a microphone in the chestpiece. This method suffers from ambient noise interference and has fallen out of favor. Another method, used in Welch-Allyn's Meditron stethoscope, comprises placement of a piezoelectric crystal at the head of a metal shaft, the bottom of the shaft making contact with a diaphragm. 3M also uses a piezo-electric crystal placed within foam behind a thick rubber-like diaphragm. Thinklabs' Rhythm 32 inventor, Clive Smith uses an Electromagnetic Diaphragm with a conductive inner surface to form a capacitive sensor. This diaphragm responds to sound waves identically to a conventional acoustic stethoscope, with changes in an electric field replacing changes in air pressure. This preserves the sound of an acoustic stethoscope with the benefits of amplification.Because the sounds are transmitted electronically, an electronic stethoscope can be a wireless device, can be a recording device, and can provide noise reduction, signal enhancement, and both visual and audio output. Around 2001, Stethographics introduced PC-based software which enabled a phonocardiograph, graphic representation of cardiologic and pulmonologic sounds to be generated, and interpreted according to related algorithms. All of these features are helpful for purposes of telemedicine (remote diagnosis) and teaching.[edit] Noise reductionMore recently, ambient noise filtering has become available in some electronic stethoscopes, with 3M's Littmann 3000 and Thinklabs ds32a offering methods for eliminating ambient noise. In acoustic stethoscopes ambient noise filtering is available in TRIMLINE Puretone (DRG, R. Deslauriers) external noise reducing models.[edit] Recording stethoscopesSome electronic stethoscopes feature direct audio output that can be used with an external recording device, such as a laptop or MP3 recorder. The same connection can be used to listen to the previously-recorded auscultation through the stethoscope headphones, allowing for more detailed study for general research as well as evaluation and consultation regarding a particular patient's condition and telemedicine, or remote diagnosis.[edit] Fetal stethoscopeA fetal stethoscope or fetoscope is an acoustic stethoscope shaped like a listening trumpet. It is placed against the abdomen of a pregnant woman to listen to the heart sounds of the fetus. The fetal stethoscope is also known as a Pinard's stethoscope or a pinard, after French obstetrician Adolphe Pinard (1844-1934).[edit] MaintenanceThe flexible vinyl, rubber, and plastic parts of stethoscopes should be kept away from solvents, including alcohol and soap. Solvents can have detrimental effects, including accelerating the natural aging process by dissolving the plasticizers that keep these parts flexible and looking new. In addition, when they are manufactured stethoscopes with two-sided chestpieces are lubricated where the chestpiece rotates around the stem and need to be re-lubricated periodically, just like any other machine. If these moving parts are not lubricated, they grind together and ruin the fine tolerances required for the proper acoustic performance of the stethoscope. Cleaning the stethoscope will also remove lubricants, making periodic lubrication essential. Most lubricants must be kept away from rubber, vinyl, and plastic parts.Stethoscope Definition The stethoscope is an instrument used for auscultation, or listening to sounds produced by the body. It is used primarily to listen to the lungs, heart, and intestinal tract. It is also used to listen to blood flow in peripheral vessels and the heart sounds of developing fetuses in pregnant women.

Purpose A stethoscope is used to detect and study heart, lung, stomach, and other sounds in adult humans, human fetuses, and animals. Using a stethoscope, the listener can hear normal and abnormal respiratory, cardiac, pleural, arterial, venous, uterine, fetal and intestinal sounds.

Demographics All health care providers and students learn to use a stethoscope.

Description Stethoscopes vary in their design and material. Most are made of Y-shaped rubber tubing. This shape allows sounds to enter the device at one end, travel up the tubes and through to the ear pieces. Many stethoscopes have a two-sided sound-detecting device or head that listeners can reverse, depending on whether they need to hear high or low frequencies. Some newer models have only one pressure-sensitive head. The various types of instruments include: binaural stethoscopes, designed for use with both ears; single stethoscopes, designed for use with one ear; differential stethoscopes, which allow listeners to compare sounds at two different body sites; and electronic stethoscopes, which electronically amplify tones. Some stethoscopes are designed specifically for hearing sounds in the esophagus or fetal heartbeats.

Diagnosis/Preparation Training

Stethoscope users must learn to assess what they hear. When listening to the heart, one must listen to the left side of the chest, where the heart is located. Specifically, the heart lies between the fourth and sixth ribs, almost directly below the breast. The stethoscope must be moved around. A health care provider should listen for different sounds coming from different locations. The bell (one side of the head) of the instrument is generally used for listening to low-pitched sounds. The diaphragm (the other side of the head) of the instrument is used to listen to different areas of the heart. The sounds from each area will be different. "Lub-dub" is the sound produced by the normal heart as it beats. Every time this sound is detected, it means that the heart is contracting once. The noises are created when the heart valves click to close. When one hears "lub," the atrioventricular valves are closing. The "dub" sound is produced by the pulmonic and aortic valves. Other heart sounds, such as a quiet "whoosh," are produced by "murmurs." These sounds are produced when there are irregularities in the path of blood flow through the heart. The sounds reflect turbulence in normal blood flow. If a valve remains closed rather than opening completely, turbulence is created and a murmur is produced. Murmurs are not uncommon; many people have them and are unaffected. They are frequently too faint to be heard and remain undetected.

The lungs and airways require different listening skills from those used to detect heart sounds. The stethoscope must be placed over the chest, and the person being examined must breathe in and out deeply and slowly. Using the bell, the listener should note different sounds in various areas of the chest. Then, the diaphragm should be used in the same way. There will be no wheezes or crackles in normal lung sounds.

Crackles or wheezes are abnormal lung sounds. When the lung rubs against the chest wall, it creates friction and a rubbing sound. When there is fluid in the lungs, crackles are heard. A high-pitched whistling sound called a wheeze is often heard when the airways are constricted.

When the stethoscope is placed over the upper left portion of the abdomen, gurgling sounds produced by the stomach and small intestines can usually be heard just below the ribs. The large intestines in the lower part of the abdomen can also be heard. The noises they make are called borborygmi and are entirely normal. Borborygmi are produced by the movement of food, gas or fecal material.Definition: Speaker sensitivity is a measurement of the amount of sound output derived from a speaker with one watt of power input from an amplifier. Sensitivity is usually measured with a microphone connected to a sound level meter placed one meter in front of the speaker. Speaker sensitivity is used to determine the amount of power necessary to drive or operate a speaker. For more information, refer to thMeaning:telephoneEarphone that converts electrical signals into soundsClassified under:Nouns denoting man-made objectsSynonyms:telephone receiver; receiverHypernyms ("telephone receiver" is a kind of...):earphone; earpiece; headphone; phone (electro-acoustic transducer for converting electric signals into sounds; it is held over or inserted into the ear)Hyponyms (each of the following is a kind of "telephone receiver"):headset (receiver consisting of a pair of headphones)Holonyms ("telephone receiver" is a part of...):phone; telephone; telephone set (electronic equipment that converts sound into electrical signals that can be transmitted over distances and then converts received signals back into sounds)HistoryMain articles: History of the telephone and Timeline of the telephoneCredit for the invention of the electric telephone is frequently disputed, and new controversies over the issue have arisen from time-to-time. As with other great inventions such as radio, television, light bulb, and computer, there were several inventors who did pioneering experimental work on voice transmission over a wire and improved on each other's ideas. Innocenzo Manzetti, Antonio Meucci, Johann Philipp Reis, Elisha Gray, Alexander Graham Bell, and Thomas Edison, among others, have all been credited with pioneering work on the telephone. An undisputed fact is that Alexander Graham Bell was the first to be awarded a patent for the electric telephone by the United States Patent and Trademark Office (USPTO) in March 1876.[1] That first patent by Bell was the master patent of the telephone, from which all other patents for electric telephone devices and features flowed.The early history of the telephone became and still remains a confusing morass of claims and counterclaims, which were not clarified by the huge mass of lawsuits that hoped to resolve the patent claims of many individuals and commercial competitors. The Bell and Edison patents, however, were forensically victorious and commercially decisive.A Hungarian engineer, Tivadar Pusks quickly invented the telephone switchboard in 1876, which allowed for the formation of telephone exchanges, and eventually networks. [2]Further information: Invention of the telephone,Elisha Gray and Alexander Bell telephone controversy,andCanadian Parliamentary Motion on Alexander Graham BellBasic principles

1896 Telephone from Sweden.A traditional landline telephone system, also known as "plain old telephone service" (POTS), commonly handles both signaling and audio information on the same twisted pair of insulated wires: the telephone line. Although originally designed for voice communication, the system has been adapted for data communication such as Telex, Fax and Internet communication. The signaling equipment consists of a bell, beeper, light or other device to alert the user to incoming calls, and number buttons or a rotary dial to enter a telephone number for outgoing calls. A twisted pair line is preferred as it is more effective at rejecting electromagnetic interference (EMI) and crosstalk than an untwisted pair.The telephone consists of an alerting device, usually a ringer, that remains connected to the phone line whenever the phone is "on hook", and other components which are connected when the phone is "off hook". These include a transmitter (microphone), a receiver (speaker) and other circuits for dialing, filtering, and amplification. A calling party wishing to speak to another party will pick up the telephone's handset, thus operating a button switch or "switchhook", which puts the telephone into an active (off hook) state by connecting the transmitter (microphone), receiver (speaker) and related audio components to the line. This circuitry has a low resistance (less than 300 Ohms) which causes DC current (48 volts, nominal) from the telephone exchange to flow through the line. The exchange detects this DC current, attaches a digit receiver circuit to the line, and sends a dial tone to indicate readiness. On a modern telephone, the calling party then presses the number buttons in a sequence corresponding to the telephone number of the called party. The buttons are connected to a tone generator circuit that produces DTMF tones which end up at a circuit at the exchange. A rotary dial telephone employs pulse dialing, sending electrical pulses corresponding to the telephone number to the exchange. (Most exchanges are still equipped to handle pulse dialing.) Provided the called party's line is not already active or "busy", the exchange sends an intermittent ringing signal (about 90 volts AC in North America and UK and 60 volts in Germany) to alert the called party to an incoming call. If the called party's line is active, the exchange sends a busy signal to the calling party. However, if the called party's line is active but has call waiting installed, the exchange sends an intermittent audible tone to the called party to indicate an incoming call.The phone's ringer is connected to the line through a capacitor, a device which blocks the flow of DC current but permits AC current. This constitutes a mechanism whereby the phone draws no current when it is on hook, but exchange circuitry can send an AC voltage down the line to activate the ringer for an incoming call. When a landline phone is inactive or "on hook", the circuitry at the telephone exchange detects the absence of DC current flow and therefore "knows" that the phone is on hook with only the alerting device electrically connected to the line. When a party initiates a call to this line, and the ringing signal is transmitted. When the called party picks up the handset, they actuate a double-circuit switchhook which simultaneously disconnects the alerting device and connects the audio circuitry to the line. This, in turn, draws DC current through the line, confirming that the called phone is now active. The exchange circuitry turns off the ring signal, and both phones are now active and connected through the exchange. The parties may now converse as long as both phones remain off hook. When a party "hangs up", placing the handset back on the cradle or hook, DC current ceases to flow in that line, signaling the exchange to disconnect the call.Calls to parties beyond the local exchange are carried over "trunk" lines which establish connections between exchanges. In modern telephone networks, fiber-optic cable and digital technology are often employed in such connections. Satellite technology may be used for communication over very long distances.In most telephones, the transmitter and receiver (microphone and speaker) are located in the handset, although in a speakerphone these components may be located in the base or in a separate enclosure. Powered by the line, the transmitter produces an electric current whose voltage varies in response to the sound waves arriving at its diaphragm. The resulting current is transmitted along the telephone line to the local exchange then on to the other phone (via the local exchange or a larger network), where it passes through the coil of the receiver. The varying voltage in the coil produces a corresponding movement of the receiver's diaphragm, reproducing the sound waves present at the transmitter.A Lineman's handset is a telephone designed for testing the telephone network, and may be attached directly to aerial lines and other infrastructure components.Early development

Early telephone with hand cranked generator. 1844 Innocenzo Manzetti first mooted the idea of a speaking telegraph (telephone). 26 August 1854 Charles Bourseul publishes an article in a magazine L'Illustration (Paris): "Transmission lectrique de la parole" [electric transmission of speech]. 26 October 1861 Johann Philipp Reis (18341874) publicly demonstrated the Reis telephone before the Physical Society of Frankfurt 22 August 1865, La Feuille d'Aoste reported It is rumored that English technicians to whom Mr. Manzetti illustrated his method for transmitting spoken words on the telegraph wire intend to apply said invention in England on several private telegraph lines. 28 December 1871 Antonio Meucci files a patent caveat (n.3335) in the U.S. Patent Office titled "Sound Telegraph", describing communication of voice between two people by wire. 1874 Meucci, after having renewed the caveat for two years, fails to find the money to renew it. The caveat lapses. 6 April 1875 Bell's U.S. Patent 161,739 "Transmitters and Receivers for Electric Telegraphs" is granted. This uses multiple vibrating steel reeds in make-break circuits. 11 February 1876 Gray invents a liquid transmitter for use with a telephone but does not build one. 14 February 1876 Elisha Gray files a patent caveat for transmitting the human voice through a telegraphic circuit. 14 February 1876 Alexander Bell applies for the patent "Improvements in Telegraphy", for electromagnetic telephones using undulating currents. 19 February 1876 Gray is notified by the U.S. Patent Office of an interference between his caveat and Bell's patent application. Gray decides to abandon his caveat. 7 March 1876 Bell's U.S. patent 174,465 "Improvement in Telegraphy" is granted, covering "the method of, and apparatus for, transmitting vocal or other sounds telegraphically by causing electrical undulations, similar in form to the vibrations of the air accompanying the said vocal or other sound." 10 March 1876 The first successful telephone transmission of clear speech using a liquid transmitter when Bell spoke into his device, Mr. Watson, come here, I want to see you. and Watson heard each word distinctly. 30 January 1877 Bell's U.S. patent 186,787 is granted for an electromagnetic telephone using permanent magnets, iron diaphragms, and a call bell. 27 April 1877 Edison files for a patent on a carbon (graphite) transmitter. The patent 474,230 was granted 3 May 1892, after a 15 year delay because of litigation. Edison was granted patent 222,390 for a carbon granules transmitter in 1879. Early commercial instruments

Modern emergency telephone powered by sound alone.Early telephones were technically diverse. Some used a liquid transmitter, some had a metal diaphragm that induced current in an electromagnet wound around a permanent magnet, and some were "dynamic" - their diaphragm vibrated a coil of wire in the field of a permanent magnet or the coil vibrated the diaphragm. The dynamic kind survived in small numbers through the 20th century in military and maritime applications where its ability to create its own electrical power was crucial. Most, however, used the Edison/Berliner carbon transmitter, which was much louder than the other kinds, even though it required an induction coil, actually acting as an impedance matching transformer to make it compatible to the impedance of the line. The Edison patents kept the Bell monopoly viable into the 20th century, by which time the network was more important than the instrument.Early telephones were locally powered, using either a dynamic transmitter or by the powering of a transmitter with a local battery. One of the jobs of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century, "common battery" operation came to dominate, powered by "talk battery" from the telephone exchange over the same wires that carried the voice signals.Early telephones used a single wire for the subscriber's line, with ground return used to complete the circuit (as used in telegraphs). The earliest dynamic telephones also had only one port opening for sound, with the user alternately listening and speaking (or rather, shouting) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but also more expensive.At first, the benefits of a telephone exchange were not exploited. Instead telephones were leased in pairs to a subscriber, who had to arrange for a telegraph contractor to construct a line between them, for example between a home and a shop. Users who wanted the ability to speak to several different locations would need to obtain and set up three or four pairs of telephones. Western Union, already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco, and Bell was not slow in appreciating the potential.Signalling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator, by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell, first operated over a second wire, and later over the same wire, but with a condenser (capacitor) in series with the bell coil to allow the AC ringer signal through while still blocking DC (keeping the phone "on hook"). Telephones connected to the earliest Strowger automatic exchanges had seven wires, one for the knife switch, one for each telegraph key, one for the bell, one for the push button and two for speaking.Rural and other telephones that were not on a common battery exchange had a magneto or hand-cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the operator.

A U.S. candlestick telephone in use, circa 1915.In the 1890s a new smaller style of telephone was introduced, packaged in three parts. The transmitter stood on a stand, known as a "candlestick" for its shape. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook." Previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user was less likely to leave the phone "off the hook". In phones connected to magneto exchanges, the bell, induction coil, battery and magneto were in a separate bell box called a "ringer box." [3] In phones connected to common battery exchanges, the ringer box was installed under a desk, or other out of the way place, since it did not need a battery or magneto.Cradle designs were also used at this time, having a handle with the receiver and transmitter attached, separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular.Disadvantages of single wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and, for long distance telephones, four-wire circuits. Users at the beginning of the 20th century did not place long distance calls from their own telephones but made an appointment to use a special sound proofed long distance telephone booth furnished with the latest technology.What turned out to be the most popular and longest lasting physical style of telephone was introduced in the early 20th century, including Bell's Model 102. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use sat in a cradle in the base unit. The circuit diagram of the Model 102 shows the direct connection of the receiver to the line, while the transmitter was induction coupled, with energy supplied by a local battery. The coupling transformer, battery, and ringer were in a separate enclosure. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1-10 times for each digit, and the hook switch (in the center of the circuit diagram) disconnected the line and the transmitter battery while the handset was on the cradle.After the 1930s, the base also enclosed the bell and induction coil, obviating the old separate ringer box. Power was supplied to each subscriber line by central office batteries instead of a local battery, which required periodic service. For the next half century, the network behind the telephone became progressively larger and much more efficient, but after the dial was added the instrument itself changed little until touch tone replaced the dial in the 1960s.Digital telephonyMain article: Digital TelephonyThe Public Switched Telephone Network (PSTN) has gradually evolved towards digital telephony which has improved the capacity and quality of the network. End-to-end analog telephone networks were first modified in the early 1960s by upgrading transmission networks with T1 carrier systems. Later methods such as SONET and fiber optic transmission further advanced digital transmission. Although analog carrier systems existed, digital transmission allowed lower cost and more channels multiplexed on a single transmission medium. Today the end instrument remains analog but the analog signals are typically converted to digital signals at the (Serving Area Interface (SAI), central office (CO), or other aggregation point. Digital loop carriers (DLC) place the digital network ever closer to the customer premises, relegating the analog local loop to legacy status.IP telephony

Hardware-based IP phone.Internet Protocol (IP) telephony (also known as Voice over Internet Protocol, VoIP), is a disruptive technology that is rapidly gaining ground against traditional telephone network technologies. As of January 2005, up to 10% of telephone subscribers in Japan and South Korea have switched to this digital telephone service. A January 2005 Newsweek article suggested that Internet telephony may be "the next big thing." [1] As of 2006 many VoIP companies offer service to consumers and businesses.IP telephony uses an Internet connection and hardware IP Phones or softphones installed on personal computers to transmit conversations encoded as data packets. In addition to replacing POTS (plain old telephone service), IP telephony services are also competing with mobile phone services by offering free or lower cost connections via WiFi hotspots. VoIP is also used on private networks which may or may not have a connection to the global telephone network.IP telephones have two notable disadvantages compared to traditional telephones. Unless the IP telephone's components are backed up with an uninterruptible power supply or other emergency power source, the phone will cease to function during a power outage as can occur during an emergency or disaster, exactly when the phone is most needed. Traditional phones connected to the older PSTN network do not experience that problem since they are powered by the telephone company's battery supply, which will continue to function even if there's a prolonged power black-out. A second distinct problem for an IP phone is the lack of a 'fixed address' which can impact the provision of emergency services such as police, fire or ambulance, should someone call for them. Unless the registered user updates the IP phone's physical address location after moving to a new residence, emergency services can be, and have been, dispatched to the wrong locationStethoscope Anatomy

3M Littmann Stethoscope Cardiology III

1- HeadsetThe headset is the metal part of the stethoscope onto which the tubing is fitted. The headset is made up of the two eartubes, tension springs, and the eartips. All Littmann stethoscope headsets are set at an anatomically correct angle so that they fit correctly into the wearers ear canals. The wearer can adjust the tension to a comfortable level by pulling the eartubes apart to loosen the headset or crossing them over to tighten.

2- EartipThe Cardiology III Stethoscope is fitted with 3M Littmann Snap-tight soft-sealing eartips. Soft-sealing eartips offer increased comfort, seal and durability, and feature a surface treatment that increases surface lubricity and reduces lint and dust adhesion. Snap-tight soft-sealing eartips are available in small and large sizes in black and grey colours. The Cardiology III Stethoscope comes with an extra set of soft-sealing eartips plus a pair of firm grey eartips. The firm eartips are available in small and large sizes, grey colour.

3-EartubeThe eartube is the part to which the eartips are attached. The Cardiology III Stethoscope is fitted with a ribbed eartube. Note: all Littmann stethoscopes manufactured after 1994 are fitted with a ribbed eartube that gives a Snap-tight fit between the eartube and eartips.

4 - Tunable Diaphragm

A traditional stethoscope consists of a bell and a diaphragm. The bell is used with light skin contact to hear low frequency sounds and the diaphragm is used with firm skin contact to hear high frequency sounds. Littmann stethoscopes patented tunable diaphragm technology alternates between bell and diaphragm modes with a simple pressure change on the chestpiece. Use light contact to hear low frequency sounds. Press firmly for high frequency sounds. The small side of the Cardiology III Stethoscope can be converted to a traditional bell. The tunable diaphragm can easily be replaced with the nonchill bell sleeve that is included with each stethoscope.

5 - StemThe stem connects the stethoscope tubing to the chestpiece. On the Cardiology III Stethoscope the stem is used to index, or open, the side of the stethoscope that the practitioner wants to use.

6 - TubingThe Cardiology III Stethoscope has double lumen tubing if you were to view a cross-section of the tubing you would see two openings. The tubing on all Littmann stethoscopes is manufactured from polyvinyl chloride (PVC). The tubing does not contain either natural rubber latex or dry natural rubber.

7 - ChestpieceThe chestpiece is the part of the stethoscope that is placed on the location where the user wants to hear sound. The chestpiece of the Cardiology III Stethoscope is an innovative design that offers a patented tunable diaphragm on each side of the chestpiece. The large side can be used for adult patients, while the small side is especially useful for paediatric or thin patients, around bandages and for carotid assessment.Anatomy of a 3M Littmann Cardiology III Stethoscope

Headset: The headset is the metal part of the stethoscope onto which the tubing is fitted. The headset is made up of the two ear tubes, tension springs, and the eartips. All Littmann stethoscope headsets are set at an anatomically correct angle so that they fit correctly into the wearer's ear canals. The wearer can adjust the tension to a comfortable level by pulling the eartubes apart to loosen the headset or crossing them over to tighten.Chestpiece: The chestpiece is the part of the stethoscope that is placed on the location where the user wants to hear sound. The chestpiece of the Cardiology III Stethoscope is an innovative design that offers a patented tunable diaphragm on each side of the chestpiece. The large side can be used for adult patients, while the small side is especially useful for pediatric or thin patients, around bandages and for carotid assessment.Eartip: The Cardiology III Stethoscope is fitted with 3M Littmann Snap-tight soft-sealing eartips. Soft-sealing eartips offer increased comfort, seal and durability, and feature a surface treatment that increases surface lubricity and reduces lint and dust adhesion. Eartube: The eartube is the part to which the eartips are attached. The Cardiology III Stethoscope is fitted with a ribbed eartube. Note: all Littmann Stethoscopes manufactured after 1994 are fitted with a ribbed eartube that gives a "Snap-tight" fit between the eartube and eartips.Tunable Diaphragm: A traditional stethoscope consists of a bell and a diaphragm. The bell is used with light skin contact to hear low frequency sounds and the diphragm is used with firm skinn contact to hear high frequency sounds. Littmann stethoscope's patented tunable dipahragm technology alternates between bell and diaphragm modes with a simple pressure change on the chestpiece. Use light contact to hear low frequency sounds. Press firmly for high frequency sounds.The small side of the Cardiology III Stethoscope can be converted to a traditional bell. The tunable diaphragm can be easily replaced with the nonchill bell sleeve that is included with each stethoscope.Stem: The stem connects the stethoscope tubing to the chestpiece. On the Cardiology III Stethoscope the stem is used to index, or open, the side of the stethoscope that the practitioner wants to use.Tubing: The Cardiology III Stethoscope has double lumen tubing - if you were to view a cross section of the tubing you would see two openings. The tubing on all LIttmann stethoscopes is manufactured from polyvinyl chloride (PVC). The tubing does not contain either natural rubber latex or dry natural rubber (with the exception of the 3M Littmann Anesthoscope).