Home Theater Calibration Guide

8/8/2019 Home Theater Calibration Guide

1/56

Home Theater

CalibrationGuide

2003 AudioControl. All rights reserved.


2/56


3/56

Room Acoustics

page-3

IntroductionIn the real world,anyspace in which you want to install loud-speakers can be a bad space in some way. The only perfectrooms, acoustically speaking, are anechoic test chambers;and unless your customer is very, very weird, it is unlikely

you will be installing a theater in such a space.

Room AcousticsLets first review the basic physics that determine how soundworks and the affects of a room on sound waves, to under-stand the kind of problems you are likely to face.

The human ear perceives sound because it is re-sponding to both the physical vibration of themolecules that make up air, and the pressurechanges (waves) produced by sound wavesmoving through the ears various passages andmechanisms.

All mammalian ears respond in a similar fashion(although their range of frequency sensitivity varies substan-tially) to the vibration and detect it as frequency. They alsorespond to the pressure and detect it as level or intensity.

All sound producing devices produce a series of waves inthe air, water, steel or anything but a vacuum. Rememberthere is no sound in outer space.

Figure 1 Sound waves eminate

from a central point like a stone

being tossed in a pond.

Figure 2 Energy produced

by loudspeakers or any other

source will reflect from all

surfaces of a room.

Room Acoustics

Section I


4/56Room Acoustics

A Rooms Effect On Sound WavesAs shown in figures 2 and 3, sound waves react with everysurface, barrier or boundary they encounter. There are onlytwo possible reactions - reflection or absorption.

If the energy contained in the waves is absorbed it will betransformed (according to the laws of physics) into anotherform of energy - usually heat. Surfaces that are absorptive,such as fiberglass, draperies or curtains, reduce the amountof energy in the system

Surfaces that reflect, or refract the energy waves (most solid,hard surfaces) will produce a series of counter-waves of en-ergy. There are always multiple reflections, at differing anglesin every reflective situation.

For our purposes we are concerned with only those reflectivewaves that can produce energy peaks or dips in the per-ceived frequency response of the sound system in the room.

Remember that despite what you may read or have beentold elsewhere - all rooms are bad in some way. Every spacehas its own unique set of problems, and therefore all roomsforce some set of audio performance compromises to bemade.

Figure 3 When reflections occur,

they may cause cancellation of the

original energy wave producing

nulls, especially noticeable

at low frequencies in various

positions within the room.

Section I


5/56

Room Acoustics

page-5

Room Modes and WavelengthsRoom resonances (also called standing waves or roommodes) are one of the most significant problems affectingperceived sound quality and loudspeaker spectral presen-tation. These resonances are caused by reflected energy

bouncing around the room from the various surfaces, (walls,ceilings, floor, etc.)

Remember thatthe perceived sound quality of the systemis what the customer is judging and how your work will beviewed. Regardless of what type or brand of equipment youinstall, its price or reputation; the overall systems perfor-mance in the customers space is what makes you a hero orgets you the call from their attorney!

Given that all rooms have some acoustical problems, the twokey questions we need to answer are:

1. How bad, and where, will the problems produced by theresonances and reflections be?

2. What other acoustic problems are present within thespace?

In order to obtain a preliminary answer to question numberone, and frame the overall problem we have to do somesimple math.

No groaning please, its all just straightforward long division!

So. . . f = speed of sound in ft/s = ( then 2x, 3x, 4x)

2 x length in feet

fis the frequency of the standing wave mode.

1130 is the speed of sound in air at normal temperature (70F [21 C])

Note: the formula works the same way for metric dimensions

Room Acoustics

Section I


6/56Room Acoustics

Every room will have length, width, and height modes, pluseach mode will then have orders.

What are orders? Orders are the relative number of a particu-lar resonance.

This is usually expressed using a three coordinate (x, y, z)

structure and three numbers (i.e. 1,0,0 represents the firstorder mode along the x axis of the room and so forth.)

For the most part, the modes we are concerned with willbe first, second and third order axial (length, width, height)ones.

The likelihood of a fourth order mode being at a frequencyand of a level to be an issue is relatively small. You can calcu-late a mode of any order using the following formula.

For example if the room is 15 feet long the math would be:

f = 1130/30 which produces a first order mode of: 37.66

Hz.

Thus, we should expect standing waves around 40 Hz or thelower limit of many subwoofers to show up.

Wavelength - The Key to Finding Modes:Remember all sound waves have a WAVELENGTH.

To get the wavelength of a particular frequency you can lookit up - the tables are in dozens of reference books or... sim-

ply divide the speed of sound by the frequency.

Using the frequency derived from the formula on the previ-ous page you would divide 1130 by 38 Hz. You should get29.7 or roughly 30 feet. This means that the wavelength isalmost twice our example 15 foot room length. This is a badthing.

Knowing the wavelength will help you quickly predict poten-tial standing wave or mode problems in any space whosedimensions you have.

For example, if your room dimensions are some even frac-tion of any low frequency (under 200 Hz) wavelength (, ,etc.) you are looking at a standing wave problem.

The only question is how much, where and how audible.

Section I


7/56

Room Acoustics

page-7

If you are looking at plans of a new house, or plans for therenovation of an older structure look VERY CAREFULLYat thedimensional rations for the space(s) you may have to dealwith.

It will pay you to remember thatall mode phenomena will

produce a first minimum (null) at precisely1

4 the wavelengthfrom the reflecting surface or in the case noted above around3.75 feet - one fourth of the way down the room and anotherat12 and34 of the distance

In our example, this means it is VERY likely that the seatingarea will be in a pressure maximum or peak at this frequency,as well as all of its relatives, i.e. 76Hz, 114Hz, 152 Hz andso forth.

In plain English, this means you are going to have a LOT OFBASS around the probable seating position.

You can do this type of calculation and determination for anyroom - even rooms that exist only on paper.

Getting this information in advance of any construction canhelp you and your client avoid potentially incurable problemsbefore the first nail is driven.

Knowing this information and the equivalent distances (feetor meters) will allow you to quickly determine how bad theroom is likely to be.

(Note: You need to know how much trouble you are facinggoing into any project- since it is unlikely you will be dealingwith a good to excellent room to start with.)

Confirming the MathOnce you have done the math and gotten a rough idea ofwhat you might expect in a room, you must actually mea-sure the space as built.

This is because the predictive math will only give you anapproximation of what will happen in a precisely rectangular

space with perfectly flat walls, and uncontaminated reflec-tions. If you ever find a room that matches the drawings, putthe construction contractor on a lifetime retainer.

Room Acoustics

Section I


8/56Room Acoustics

Multi-channel Audio CompromisesWe have been looking at this issue so far as if there is onlyone sound source in the room. In a residential entertainmentspace, this is, to say the least, unlikely.

Therefore you must also recognize that the acoustic prob-lems will always be worse for multi-channel - 5.1, 6.1, 5.2,6,2, 7.1 type installations - than for any mono or stereosetup, because you have more sources; and therefore, moreenergy being introduced into the space.

These additional sources automatically produce higher overalllevels, and in particular more low frequency energy, the spe-cific spectral area where most of the worst problems occur.

Section I


9/56

Room Acoustics

page-9

Section II

Room DesignResidential Entertainment SpaceRoom Design and Setup GuidelinesRealistically, every room you encounter will need some formof correction to be fully functional as a high performance au-

dio or theater environment.

You can, to a certain extent, maximize any rooms potentialand minimize your probable difficulties by following some ba-sic design and setup guidelines at the outset of any project.

Please remember these are only GUIDELINES, not rules!Every room and every system is different, with their ownunique problems.

Room Design Basics

The first thing to recognize is that all room dimensions areratios. There are good and bad ratios as well as good andbad shapes for rooms. Square rooms and rooms with equallength walls are generally VERY BAD ideas.

Ratios that are multiples of each other - i.e. a length that isexactly twice the width or height are BAD because they willcreate families of room resonances/modes.

For example, a room that is 20 feet long, 10 feet wide and10 feet high is VERY BAD.

Why?

Because any modes created by the 10 foot dimensions willhave an acoustical family member created by the 20 foot di-mension and because you have two identical dimensions anyproblems will be multiplied by a factor of two as well.

These family members will be VERY close in frequency tothe original modes. When you get clusters of modes nearbyto each other in frequency i.e. within 10 Hz of each other,things go from bad to really awful very quickly.

There are no fixed in concrete rules here, but generally,ratios that come out looking like (L X W X H) 2.0 / 1.0 / 1.0are bad.

Room dimension ratios that come out unevenly, for example2.4 / 1.1 / 1.0 are much better, since the mode distributionwill not have as many grouped frequency clusters. [Please


10/56Room Acoustics

note that there will still be clusters but they will be spread out

more evenly across the frequency spectrum, and thus createless of a problem.]

Seating LocationsYour seating location options are going to be determined pri-marily by the video devices screen size and location.

There are specific rules for distance from the screen (opti-mally 5 to 8 times picture height; with a minimum of 1.5 to2 times picture height if resolution enhancement is used) ,but your projects particular conditions may make it difficultto achieve these distances.

You must be extremely careful to insure that your chosen/

dictated seating location does not fall in a low frequency

NULL.

Why is a NULL so much worse than a peak??

Its really simple if you remember what we discussed earlierin the section on modes and standing waves. You can cor-rect for peaks using equalization to remove energy from thesystem, but you CANNOT fix nulls.

If you are really lucky, you can get both optimal viewingdistance and seating right on the edge of a peak. If you do,thank the home theater gods and have a cold beverage!!!!!.

Speaker PlacementThe key point to remember about speaker placement is- equal distance. The closer you can get to having the LCRspeakers equidistant from the wallet seat the better you are.The same applies to each pair of surrounds.

If you are setting up a 5.1 system, you are better off locatingthe surrounds to the sides and slightly to the rear of the seat-ing location than directly in the rear. This will provide moreenvelopment from the surrounds. If you are using bi-polarTHX surrounds this is a critical element of a successful sys-

tem.In more complex systems, position is also critical to ensurean even soundfield, and as smooth an overall coverage pat-tern as possible.

Room Design

Section II

14 12 34

14

12

34

Room Mode Placement


11/56

Room Acoustics

page-11

However, if you cannot position the speakers at the optimumphysical location dont panic! You have a clever trick upyour sleeve. The AudioControl DIVA gives you the option tomove speakers electronically to their optimal position.

This can greatly help you in compensating for interior decora-

tors and less than ideal positions. More on that later.In summary try to position your speakers to surroundthe seating area as evenly as possible. Also as noted below- ALWAYS take attendance before enclosing or otherwise per-manently mounting the speakers. This allows you to ensureeveryone is working correctly while you can still get at thespeakers easily.

What We Need to KnowTo find out what has to be done and how to do it, you need

to ask and answer, as precisely as possible the followingquestions:

1. What are the obvious physical issues that can affect audioperformance? - i.e. windows, construction type, spatial/di-mensional ratios, and furniture - yes, furniture.

2. What measurable problems can be detected, and how badare they? This includes what may be obvious issues suchas :

A: Is everything connected properly and operating as

expected?B: Are all devices in the correct polarity and connected to

the right outputs?

C: Are any speakers wounded - that is, are the outputcharacteristics of all similar devices actually similar?

3. Of the problems we have, how do we address each one?Even more significantly, which ones CANNOTbeaddressed?

Room Design

Section II


12/56Room Acoustics

Here is a reflected view room layout showing lengthand width and height.The dimensions are:

Width __________Feet

Length _________Feet

Height _________Feet

Practice using the basic math we just discussed:

Using the formula: f= speed of sound in ft. per second2x the dimension in feet, calculate the first order roommodes for this space.

1st order length mode = f ________________ Hz

1st order width mode = f ________________ Hz

1st order height mode = f ________________ Hz

Now calculate the second order modes by multiplying youranswers to the 1st order calculation by two.

2nd order length mode= f ________________ Hz

2nd order width mode= f ________________ Hz

2nd order height mode= f ________________ Hz

Room Design

Section II


13/56

Room Acoustics

page-13

Room Design

Section II

Divide the speed of sound [1130ft/s] by the frequency or1130f [in Hz] which will give you the wavelength in feet

Calculate the wavelengths for each of the six modes youobtained.

1st order length mode wavelength = __________________ft.

1st order width mode wavelength = __________________ft.

1st order height mode wavelength = __________________ft.

2nd order length mode wavelength = _________________ft.

2nd order width mode wavelength = __________________ft.

2nd order height mode wavelength = _________________ft.


14/56Room Acoustics


15/56

Room Acoustics

page-15

Section III

System AnalysisSystem Analysis ToolsNow its time to:

Measure Twice - Then we will need to EQ only once

To make the most of your correction capabilities you must first

accurately establish the rooms acoustic signature.

This means you must both measure from multiple points and inmultiple ways, and compare your actual data to the predictionsyou did. If there is a significant difference between them, thenyou did something wrong.

Acoustic Spaces:There are two ways to view any acoustical environment - from afrequency perspective and from a time perspective. These twoviews are the essence of the Fast Fourier Transform mathematicsthat allows data from one domain to be convolved and convert-ed into data for the other.

To examine the frequency perspective of an acoustic space youwill need to measure it with a Real Time Spectrum Analyzer.

How an RTA Works - The AudioControl SA-3052The microphone that comes with the SA-3052 RTA measures pres-sure changes caused by the sound waves. The analyzer convertsthese pressure changes to AC voltage and then displays them in 13

octave bandwidths on the screen.When utilizing a test tone of known (or predictable)amplitude (volume) in each band, the screen thendisplays the relative amplitude of each 13 octave bandof the frequency spectrum.

Pink noise is the recommended test signal toconduct this measurement because it is readilyavailable from the pink noise generator in the SA-3052 and it provides the proper combination of spectral widthand amplitude- thats the right bandwidth of frequencies at the

right level.

All RTAs display steady state( data that is not sensitive to any-thing in the time domain), broadband information, giving youan overall picture of the spectral/frequency environment in thespace being measured.

AudioControl SA-3052


16/56Room Acoustics

To insure that you have an accurate picture you must takeRTA measurements from multiple points within the listeningarea.

This averaging method removes certain kinds of non-equaliz-able data from the spectral portrait which emerges when

you are done. But remember, that such averaged data canalso hide nearby problems. This is why you need to look atboth the individual measurements and the averaged dataover a length of time.

Features of the SA-3052 RTA1. LED DISPLAY: The left portion of the display shows theone-third octave energy content of the input signal from 25Hz to 20 kHz.

2. POWER SWITCH: Depressing the power switch turns the

SA-3052 on or off.3. ON/CHARGE LED: The dual-color ON/CHARGE indicatorilluminates green during normal operation of the SA-3052.

[While operating the SA-3052 on the rechargeable batteries,a flashing green ON/CHARGE light indicates that the batteriesneed recharging. When plugged in and turned off, the ON/CHARGE light is red, and by flashing or staying on, indicatesthe amount of charge the batteries have. A longer flash indi-cates more charge is needed.] When not using yourSA-3052, keep it plugged in.

4. SPL: Momentarily pressing the SPL push-button switchturns the SPL bargraph display in the right side of the displaywindow on and off. Pressing and holding the SPL push-buttonactivates the full-screen digital SPL display.

5. DISPLAY SPEED: The display speed push-button switch islocated underneath the SPL switch and to the left of the FAST,MED, and SLOW LEDs. The lighted LED to the right of theswitch indicates the decay time of the display.

6. MEMORY: The SA-3052 can store up to six different fre-

quency response curves in its internal memory. Press theMEMORY button to select which memory to store or recall.The associated LED indicators show which memory is cur-rently being displayed. Up to six previously stored curvesmay be averaged together. The result is stored in memoryregister SIX.

Section III

System Analysis


17/56

Room Acoustics

page-17System Analysis

Section III

System Analysis7. STORE/FREEZE: The STORE/FREEZE switch freezes thedisplay and stores the contents of the display in the memoryindicated by the MEMORY LEDs. Pressing and holding theSTORE/FREEZE pushbutton activates the averaging function.The calculated average is stored in memory register six.

8. RECALL RTA: The RECALL-RTA push-button switch alter-nately selects between the normal real-time analyzer modeand the memory-recall mode.

The associated LEDs indicate the selected mode. Pressingand holding the RECALL-RTA switch activates the peak-holdfunction. The analyzer now displays the highest peaks of theinput signal on a real-time basis.

9. PINK NOISE: The internal pink noise generator is an accu-rate, digital laboratory-grade test source. The signal level atthis connector is controlled by the knob to its immediate left.

The pink noise generator has sufficient output to drive virtu-ally any speaker or passive crossover directly.

10. dB PER STEP: This switch sets the resolution of thespectrum analyzer portion of the display. The setting repre-sents the value of each LED in the display.

11. dB INPUT SENSITIVITY: The dB INPUT SENSITIVITY controland switch selects the reference level of the curve shown inthe display window. The control to the right of the input selec-tor switch is a fine adjustment and alters the range selectedby the switch over a range of +/-10 dB.

12. INPUT 3: Accommodates a 1/4inch tip-ring-sleeve phonojack used for connecting tobalanced and unbalancedsources.

13. INPUT 2: This acceptsa standard audio RCA con-nector that allows for con-necting almost any audio

source to this input.14. INPUT 1: This ac-commodates a +12 volt,phantom powered, bal-anced microphone input. SA-3052 Front Panel


18/56Room Acoustics

White buttons for

Automatic test

HELP for info

ENTER for menu

On the back of the SA-3052 is the printer interface (whichconnects to any IBM-compatible printer) and the print button.

Iasys HT - The Tool To Create PerfectionIasys HT allows you to look into spectral issues with muchmore detail due to its higher resolution. It provides timebased information and equalizable spectra data that can givea you a major head start toward determining where yourproblems are and what you can do about them.

Features of the Iasys HT1. Inputs Input 1 is where the microphone supplied with theIasys (the CM-10) plugs in. We do not recommend any othermicrophone. Input 2 is reserved for future, to be defined,applications and expansions. The Speaker Level input is formonitoring of the speaker level signal during the limiter test.

2. Output From here Iasys puts out a variety of test tones.This connects to the HT-100 to route signals.

3. Automatic Tests The gray and two blue buttons to theright of the inputs are for the automatic tests of Iasys. Fromthese tests, you get answers on how to set the tools notedby the label of the buttons. That is, for setting delay times,you select the delay button. Push any of these gray buttonsand Iasys will give you instructions on what to do next.

Iasys HT Front Panel

Section III

System Analysis

Iasys HT-100


19/56

Room Acoustics

page-19System Analysis

Section III

System Analysis

Balance Levels:FRONT REAR

SIDESUB L C R L R L R

Accurate Level Setting

Delay Test RecordsBank 1 in MSEC

S: 21.74+ LR: 25.14-L: 22.05+ RR: 24.65+R: 23.35+ LS: 23.41-C: 25.53+ RS: 22.47+

feet msec

Precise Distance Measurement

Frequency Response20.00 kHz > -15 dBu

--dB rel 85 db SPL

One-Third Octave RTA

112 Octave Equalizable Spectra

EQ Spectra RecordsBank 2A

Sweep Tones for Finding Rattles

Sweep Output

40 Hz --2.50kHz

10 sec/swp -10dBu

SPL: 85 dB

4. Display Screen The display is the gas plasma type forcomfortable viewing in most light conditions and extremelygood visibility from side angles.

5. Octave Selects and Soft Keys Below the display screenare dark gray buttons, each for an octave center point. These

are quite useful to go quickly to a frequency. They are used inmore tests than we can mention here, and are usually ap-plied in conjunction with the wheel for fine tuning. The but-tons right below the screen with the arrow above, are usedto select on-screen options.

6. Help After pressing the Help button, press any other but-ton for a brief explanation of the function of that other but-ton. To exit help, press Quit.

7. Manual Tests Pure sine wave, sweep sine wave and pinknoise with real time analyzer are the manual tests available

from the same labeled buttons on the lower right of Iasys HT.The wheel is used after selecting either frequency or levelto fine tune those aspects. For the sweep, the octave selectbuttons program the start and stop points of the sweep.

8. Function Keys F1 through F4 are special keys whichnow and in the future take on different functions in differenttests. The adjacent red light is on when any of these buttonsis active.

9. Wheel With the wheel you can scroll through numbers,memories, or other functions. When the wheel is active, asmall circle (

) shows in the upper right hand corner of the

display.

10. Enter and Quit The Quit button always functions andyou should use it any time you want to stop or back out of afunction. Enter is used with the special functions menu.

How Iasys HT Helps Create Magic1. Accurate equalization

2. Shows what is correctable

3. Precise level setting

4. Exact signal alignment (delay)

5. Pinpoint resonances and rattles

6. Fuzzy logic intelligent testing

7. No computer or software hassles


20/56Room Acoustics


21/56

Room Acoustics

page-21

Theater CalibrationProper measurements, coupled with a tool such as DIVA (withits extensive array of filters, delay and signal processing) canprovide all the ELECTRONICtools you might require to correctthose problems.

We must remember that we are dealing with both physicalacoustics issues and those that can be dealt with using elec-tronic correction.

RULE NUMBER 1: There is no type of electronic correction/EQthat will fix all problems

Or to put it another way: You cannot fix bad loudspeakers,impossible room acoustics, or non-equalizable spectral issueswith any type of electronic correction.

Often the only available solution is ... explosives!! Or morerealistically, sometimes you just have to walk away from aroom.

This is why it is absolutely crucial that you verify from actualmeasurements where your problems really are, and whatthey are. This is the only way you can determine whether ornot the problem is addressable with electronic correction.

Now - Lets Measure!(NOTE: Make printouts or record EVERYTHING on paper for ref-

erence. Keeping an acoustic signature file of every job allowsyou to go back and re-create what you did, and also showwhat youve done.)

You will need to collect and save the following from both anRTA and Iasys:

1. Wallet Seat data

2. Surrounding seating plane data

3. Seating ring data (at least three points)

By doubling up here you insure that:A: You dont miss anything important

B: You build in a cross-check of the data you get

Examine the data, both the individual responses and aver-aged responses, and look for significant peaks and or dips inthe overall response. Significant means atleast 3 dB.

Theater Calibration

Section IV

Theater Calibration

Speakers

Seating Ring Wallet Seat

Speakers


22/56Room Acoustics

If these changes are wide from an octave standpoint ( 1.5octaves or more), they may not be serious. If they are verysharp ( lets say 5-10Hz wide), they may not be fixable oraudible.

What you want to look for are the big hills or deep valleys.

Once weve completed the measurement/equalization pro-cess, which will enable you to tune the rooms acousticsignature to be as accurate as feasible, then we can examinethe creative options you can employ to enhance and expandthe possibilities.

Later in this manual you will find an extended discussion ofsetup procedures, a checklist and some additional guide-lines. It is strongly recommended that you review theseEVERY time you do a job.

For now you need to recognize that there are five basic signalprocessing areas you will have to examine, adjust and LISTENto:

1. Sub-woofer to main system crossover splicing

2. Internal main/surround speaker crossovers (if beingdone electronically)

3. Delay setting and time/distance relationships

4. General systems equalization (customer happy EQ)

5. System dynamics - limiting and compression

Note: This list assumes the gain levels are already properlyadjusted and matched. See Iasys section for level matichinginformation.

Theater Calibration

Section IV


23/56

Room Acoustics

page-23Theater Calibration

Sound System Analysis with the RTAThe basic steps for analyzing any space with an RTA are:

1. Using a microphone stand, place the microphone fromthe analyzer in the head position of the primary listener.

2. Play pink noise through the system at the normallistening level (85dB is the recognized roomcalibration setpoint).

3. With the dB Per Step switch in the 3 position and thedisplay speed in the Med mode, make certain that allof the LEDs in the display fall within the 12dB rangeof the display.

4. Switch the display speed to Slow, and start takingyour measurements across the seating plane - remem-ber you will need three or more measurements for any

seating area. Store your measurements in the memo-ries and note what memory represents what seatingposition.

Remember, when equalizing, the result you are after is notnecessarily a flat curve across the center of the screen, buta smooth curve in which there are no variations exceeding3dB between any two adjacent bands.

Remember, we recommend using both an RTA and the IasysHT system because they supply different types of informa-

tion.

Sub-woofer to Main System Crossover SplicingThe fundamental issue with this parameter is to ensure asmooth and seamless splice between the upper end of thesubwoofers output and the lower end of the main systemscapability. If youve got this right you will not be able to tellwhen the transition occurs or precisely where the subwooferis. If you can hear either of these parameters you need to goback and make further adjustments.

Section IV

Theater Calibration

SA-3052


24/56Room Acoustics

Internal Main/Surround Speaker Crossovers(If Being Done Electronically)

If you are using DIVA or another device to create the cross-overs for the main loudspeaker system, you need to insurethat the LCR speakers are exactly the same acoustically (if the speakers are the same). You will want to match thecrossovers as precisely as feasible to avoid shifting speechwhen it moves across the frontal presentation plane. Thisis a VERY delicate adjustment and should be avoided unlessthe speakers require an external crossover. Normally the fac-tory supplied crossover is tuned to produce optimum resultsfrom the particular drivers.

NOTE: Using Iasys HT, you can verify the energy centers (asshown earlier) to confirm that the LCR speakers are operatingproperly and are acoustically similar.

Delay Setting and Time/Distance RelationshipsThis is one of the creative areas, where your ears and yourbrain will work together to help you find the best combina-tion. In essence you want to make the room appear as largeas feasible, the sound field as even as possible, and producethe most spatiality from the system as possible. This is anART, and you need to practice to get it right.

You must begin, however, by precisely positioning the speak-ers in space so that they are all equidistant from your se-lected TIME ZERO point which is normally the center channel.Iasys HT is the ideal tool for this job, and it can provide all thedata you need to get this done quickly and accurately.

After getting all signals to arrive together, you can then movethem to where you want them to be.

General Systems Equalization(Customer Happy EQ)This is the LAST step in any setup process. It is where you

usually apply 1/3 octave type EQ (available on all channels inDIVA) to produce you chosen house curve or a curve youfeel will make the customer happy.

Theater Calibration

Section IV


25/56

Room Acoustics

page-25

This step should NOT be used to correct for loudspeakeranomalies or other problems. That should be addressed withthe PARAMETRIC EQ tools as discussed above and againlater on.

Be VERY VERY careful to apply identical EQ to any PAIRS of

loudspeakers - that is Front L/R; Side L/R; or Surround L/R. Ifyou do not you will cause image shifting and create a wholelot of trouble for yourself.

Dynamics Processing - Limiting and CompressionDIVA offers you a unique opportunity to affect the audiosignal, because it provides both limiting and compressionoptions. You can, using these tools, efficiently manage thedynamic range of the signals reaching the power amplifierinputs and ultimately, loudspeakers.

Applying these tools is a complex process and should bedone with a gentle hand and careful listening. We stronglyrecommend you experiment with this option a lot, before at-tempting to use it in the field.

A basic rule of thumb is to apply these options ONLY to thesubwoofer and center channel.

Later on in this manual is a complete discussion of thesesignal processing options. It should be read carefully beforeattempting to use any of the dynamics management toolsavailable in DIVA.

You should first try the factory presets, as these have beenoptimized for most applications.

Theater Calibration

Section IV

Theater Calibration


26/56Room Acoustics


27/56

Room Acoustics

page-27

Section V

Equalization

EqualizationEqualization TerminologyEqualizers are the single most cost effective improvement toany quality audio system.

Some Key terms:

Amplitude - A measure of the strength of a signal.

Bandpass - A combination of a lowpass and highpass filter.

The bandpass filter has rapidly decreasing output above orbelow its -3dB frequencies. (see below) The bandpass filtersused in most equalizers for tonal correction have bell-shapedcurves. Another type of bandpass filter has rather straightskirts, and a flat response characteristic in its passband (thearea between the lower and upper -3dB points).

Bandwidth - A measure of the amount of the audio spectrum

affected by the equalizer. Bandwidth is usually measured infractions of an octave across the -3dB points. (see Figure 4)

Center - The frequency at which the output signal from theequalizer is at its maximum cut or boost.

Equalizer - An electronic filter network that effects the trans-mission of alternating current with respect tofrequency.

Octave - A musical term representing a pitchratio of 2:1. Thus, A-440 (A above middle-C on

a piano, or 440 Hz) is one octave lower than A-880.

Q - Similar to bandwidth, Q is the quality factorof a filter. It is calculated as the center frequencydivided by the bandwidth.

Skirt - The skirts of a filter are those frequenciesthat lie above and below the center frequency.

Figure 4 - The shape of a typicalbandpass filter (1/3 octave type)


28/56Room Acoustics

Section V

Types of EqualizersThere are many equalization products on the market.

Although there will be alleged unique capabilities, and oftenclaims that appear to violate the known laws of physics andpossibilities using electronic components made in this uni-verse, the reality is fairly simple. ALL equalization products onthe market today are based on one of two core types of filterimplementations:

Graphic: Graphical layout of controls, fixed center frequen-cies and bandwidths, variable amplitude. e.g. DIVA and otherAudioControl EQs

Parametric: Variable Bandwidth, Amplitude, and Frequency.e.g. DIVA.

A key point to remember when applying any type of equaliza-

tion or correction:

If we optimize the on-axis response of the reproduction sys-tem, the off-axis response will be as good as it gets.

What to do and How to do itOnce you have both calculated and measured the space todetermine what the rooms acoustic characteristics are, hereis a step by step procedure that should produce the bestresults available for any space:

1. Insure that you have properly measured the distancesfrom the center of the seating area or wallet seat to eachspeaker precisely (that is to the inch/cm). If you are usingIasys this data has been calculated precisely for you.

Never-the-less you should repeat and re-verify your datato insure it is accurate to the final loudspeaker positionsin the room. Better yet, have someone else do it to crosscheck your measurements.

2. Getting the basic loudspeaker array distances exactly cor-rect is VITAL to making any other adjustment and to insur-ing that all your work will result in positive changes.

(Remember 12" = approx. 1 millisecond. . .1 microsec-ond = .012 millisecond)

Equalization


29/56

Room Acoustics

page-29Equalization

Section V

Equalization3. Set all decoder delays as per manufacturers instructions.If the system incorporates a DIVA unit, you can set thechannel delays to far more precision using microsecondsteps.

In this case, DO NOT set any delay in the decoder; or, use

it only for basic delay and add the precision needed usingDIVA.

Now - Check timing and delay setting using Iasys HT.

4. Correct until you have it as accurate as feasible.

Remember flight-time as processed with Iasys HT is farmore accurate than any tape measure to seat distances.

Using Diva to Create the Best Room/Sonic

Presentation and Impact PossibleFirst remove any major LF bumps or problems.These will likely be masking other problems. THIS IS A CUTONLY PROCEDURE. You want to take energy OUT of the sys-tem to reduce or remove the excess.

DO this in small steps 1-2 dB maximum per pass to allow forboth listening tests and re-measurement to verify your affect.

Measure again. Repeat !



Once LF issues have been resolved to produce the best pos-sible (THIS DOES NOT MEAN FLAT) spectra and level, look atthe Center channel for dialog intelligibility, and at LCR for evenspectra.

In the center channel look for the smoothest possible re-sponse from 100 to 3kHz - 4kHz - the speech band.

Also, look for any real peaks below or above those frequen-

cies and gently reduce them.Look at LCR to SUB splice and surround to LCR spectral bal-ance.

Apply graphic or parametric EQ to remove problems.


30/56Room Acoustics

General Equalization GuidelinesThe overall goal of equalizing any sound system is to have asmooth transition from one frequency to the next with varia-tions of no greater than 3 dB. Do not attempt to use anyequalizer to re-invent the laws of physics and try and make a

speaker do something it cant.

Although the audio police will not hold you accountable, youshould follow some guidelines when it comes to makingequalization corrections:

1. Your equalization curve should always start by beingsome position of the inverse of what your analyzerdisplays.

2. If the analyzer shows a 3 dB bump a given frequency,you should cut the frequency 2 dB for starters.

3. Cut the peaks

4. Use extreme care when boosting any dip in factnever boost at all unless you have a lot of experiencewith the system and the hardware.

5. Try to keep your EQ applications to less than 3 dB.

6. After making initial equalization adjustments, re-analyze the system and adjust again if necessary.

7. If your left and right speakers are mounted symmetri-

cally you can measure and equalize them together.8. When in doubt, re-analyze and re-equalize a particular

speaker or group of speakers.

LCR SpeakersIn this step, you will want to measure the frequency re-sponse of each speaker at each listening position; and, thenaverage them together to achieve a spatial average of thelistening room.

Set the SA-3052 in the 2 dB per step division with the speedset at averaging(20 second averaging).

The volume level should be set at a reference position ofapproximately 75dB (THX reference level to a maximum of90dB to avoid loudspeaker damage.) Pink noise should beused as test material.

Section V

Equalization


31/56

Room Acoustics

page-31

Starting with the center channel, use the following proce-dures:

1. Take a measurement in each seating position and storethem in memories #1 through #5 of the analyzer.

2. Average the measurements of each seating location

into memory #6

3. Following the Equalization Guidelines, make theappropriate equalization corrections to the frequencyresponse.

4. After making equalization corrections, repeat the aboveprocedures.

After you have completed the above steps, repeat them forthe left and right channels.

Disconnect the channels you are not equalizing by unplug-ging the connectors for the appropriate amplifiers.

Subwoofer EqualizationTo measure and equalize the subwoofer you will want to fol-low the same procedures as you do for the LCR speakers.However, because of the numerous fluctuations caused bypink noise at lower frequencies it will not be necessary totake subwoofer measurements at all of the various seatinglocations.

Splicing the SubwooferGiven the numerous possible speaker locations, there tendsto be an occurrence of peaks or dips at the point where thesubwoofer and the main LCR speakers energy output over-laps commonly called - THE CROSSOVER FREQUENCY. It isimportant to smooth out this transition point.

Center Splice: Disable all channels, except for the subwooferand center channel. Play pink noise through them and usethe center channel equalization controls to smooth out thesplice between the subwoofer and the center channel.

L & R Splice: Disable all channels except for the left & rightmains and the subwoofer. Play pink noise through them anduse the left & right channel equalization controls to splice inthe subwoofer.

Equalization

Section V

Equalization


32/56Room Acoustics

Chop Off the Peaks - Never Fill the ValleysYou can use more than minus 6dB if need, but use caution,there may be an easier physical way to reduce some of yourproblem.

Once you have worked through the subwoofers, Centerchannel and L/R systems examine the spectral data from thesurround.

Look for BIG peaks and gently soften them if possible.

Delay and Psycho-AcousticsHow to use DIVA to change apparent room size, and, howto apparently position a center channel speaker up or down;front or back using the channel delay in DIVA .

First: There is no such thing as time delay in audio without

the use of a micro black hole to alter time.

What DIVA and all other delay units supply is signal delay.

The ear/brain processor equates delay with distance and theimpression of spaciousness or ambiance.

Thats why all studio engineers apply some pre-delay to thesends for reverb units and often add additional delay to thereturns.

You can use delay to do something similar.

Now you will understand why it was so important to get theactual position of the speakers calibrated so precisely.

Because ... we can move them electronically.

For example:

If you have a 7.1 system which uses both side and rearspeakers, you can by increasing the delay to the side speak-ers move the apparent position of the side walls of the roomaway from the listener, or by decreasing the relative ratiosthe reverse.

By increasing the delay to the rear speakers, you can pushthe rear wall back.

Section V

Real

Room

Apparent Room

Equalization


33/56

Room Acoustics

page-33

Here are some examples for a medium size room

Side add 10 ms = 10 feet

Rear add 12 ms = 12 feet

Finally . . . Conduct a Listening Test

The two commandments of equalization that cannot be ig-nored are:

1. Always, always, always conduct numerous listening

tests throughout the process to insure that what you

are doing is actually having a beneficial effect.

2. Never, never, never do equalization without also

listening to the system with the EQ in and the EQ out to

compare.

Given the tools now have available, you can electronically

correct a significant portion of the equalizable problems. Withthe proper application of the right kind of acoustical treatmentyou can tackle many of the others.

Remember choosing and using the right tool for the job cango a long way to improving the acoustic performance of anyroom, and thus the performance of the sound system youput in that room.

Equalization

Section V

Equalization


34/56Room Acoustics


35/56

Room Acoustics

page-35The Art of Listening

Section VI

The Art of ListeningThe Art of ListeningThe Emotional Power of SoundListening to and experiencing an audio environment is aunique and intense multi-level encounter.

Stephen Handel, Professor of Psychology at the University ofTennessee, put it as well as anyone has in the Preface to hiswonderful book called Listening(The MIT Press, 1993):

Listening puts me in the world. Listening gives me a

sense of emotion, a sense of movement, and a sense

of being there that is missing when I am (just) looking. I

am more frightened by thunder than by lightning, even

though I know that thunder is harmless and lightning is

deadly. I feel far more isolation living with ear plugs,

than living with blinders. Listening is centripetal, it pulls

you into the world. Looking is centrifugal, it separates

you from the world .

Lets understand precisely what Handel is saying. If the audiosystems re-creationcapability is working correctly, it can andshouldpull the listener into the presentation with the powerto make them believe that they are There , wherever theremay be.

To do this, the there must be perceived to be real enoughto place the listener in the scene or story with enough

strength to make them forget that they care actually sittingsomeplace else.


36/56Room AcousticsThe Art of Listening

The Almost Lost DataEvery time you hear an audio system (especially a multi-channel one) you are, without formally recognizing the pro-cess, being provided with a huge amount of information onthat systems specific attributes and capabilities.

Unfortunately, you will actually use and process only a smallportion of what you are hearing, primarily because you arenot listening for the rest of the information.

The industry has over the years used a variety of hardwaretypes and analysis approaches such as the AudioControl3052 RTA or the AudioControl IasysHT System, to measureand determine audio system performance. Because thesemethods produce for the most part totally objective, accu-rate* and repeatable data that has no subjective compo-nent , we have been trained to and accepted the concept of

relying almost totally on our test equipment to tell us whatwe are hearing.

(* The accuracy of the data gathered by any measurementsystem is very much dependant on the care and precisiontaken during the measurement process. Good technologycan most certainly produce bad data.)

But, no matter how sophisticated that instrumentation maybe or how expert the operator none of those systems can(as yet) measure, compile or quantify to the same degree

of precision the complex psychoacoustical aspects that areinherent in the way the ear/brain system processes sound.

It is critical to understanding the listening process to recog-nize that unless your ear/brain system is impaired in someway, 100% of the time you are awake and aware, your earsare delivering a flood of information to your brain about whatkind of space you are in by constantly painting a complexsonic landscape in full 3D and covering a full 360 degrees.

In created physical spaces such as residential entertainmentrooms or motion picture theaters, you are receiving input

from the complex speaker/room combination about whatkind of perceivable acoustical reality that system is creat-ing in that particular space.

Section VI

The Art of Listening

The AudioControl Iasys HT

measurement system provides

the most comprehensive data setavailable that shows an association

with how and what we hear,

because it uses fuzzy logic and

recognizes the time-based nature

of sound within a space as does

the human hearing system.


37/56

Room Acoustics

page-37The Art of Listening

But, if you just look at just the numbers from your measure-ment systems, you may not recognize how much informa-tion you are either ignoring or discarding.

You can look at this disparity by recognizing that if you justuse the pure data alone, you are taking your High Definition,full color, 3D, 360 degree virtual reality and limiting it in everyparameter to a less detailed lower resolution image of thesame scene. Its the difference between the Star Trek Holo-Deck and todays simulation rides.

You are not using a good deal of the available information be-cause you have never been trained to listen for it and exploitthe information that is sitting there in plain view if you willpardon the pun.

Do not misunderstand this point. I am not in any way sug-gesting that you give up instrumentation and use only the

cognitive, psychoacoustical and to a degree subjective infor-mation (although I constantly read articles and reviews thatseem to indicate that the author has done precisely that).

While that approach will allow you to use very inventivedescriptive verbiage, without the scientific information youcannot really use the other data as effectively and you haveno objective foundation upon which to position the otherinformation.

It is crucial to recognize that the approach described below isNOT a case of either - or.

It is a methodology that combines the recognized and re-spected instrumentation produced information and the stuffyou were not using, to give you a much more powerful ana-lytical tool to use in determining the quality and performanceof audio systems.

Why do we need to do this? Because it is the ears (and thelistening experience they produce) of your customer that willmake the final judgment on your work.

Section VI



38/56Room Acoustics

Section VI


Judging the Reality Creation QuotientIn combining the information from both the objective dataand the listening experience, what we are trying to judge isthe effectiveness of the efforts of a speaker/room combina-tion in re-creating the audio reality envisioned by those who

conceived/created the particular soundtrack, recording orperformance.

How Can You Do this Efficiently and Accurately?Well, at least for the moment there is no quick, easy one-hour class/course you can take to teach you how to do this.However, I can provide you with some guidelines and meth-ods to help you get started. I must emphasize that the onlyway you will become truly proficient at this is to practice,practice, practice.

Only over time can you train your ears and your brain tolisten through the system to hear the cues that will tell youwhat you want to know.

To give you a start, we will explore what you can do to add toyour capabilities and offer some basic tips on how to do this.

The first and most critical step in building up your abilityto use your listening skills is learning how to breakdown asoundtrack or other source into its component pieces andunderstand how they must fit back together to deliver theaudio experience with its maximum power and believability.

While you can use almost any recorded sound source to dothis, motion picture soundtracks provide, in our experience,the best sources.

Why Should You use Soundtracks and What YouShould Be Listening ForWhy do soundtracks offer the best source options? Becausethose soundtracks are created from a set of componentpieces, with the deliberate goal of producing a specific real-

ity, a willing suspension of audio disbelief . The complexinterweaving of literally hundreds of sounds in the process ofcombining dialog, music and effects into a seamless audioenvironment produces the space that the



39/56

Room Acoustics

page-39

Section VI


picture and story occupy. Thatspace is what allows thesoundtrack to put/pull the listeners into the movie.

When listening critically to a sound track to judge systemperformance, you must of course observe the accuracy ofthe music reproduction, and the naturalness of the dialog.

These elements are crucial to the overall experience. Themeasured data you produce about loudspeaker spectral ac-curacy using such tools as the AudioControl 3052 RTA andIasys measurement systems, plus a good careful listen toa variety of program material, will give you significant infor-mation about how well any system is going to handle thesetasks.

How even is the response? How un-colored is the deliveredsoundfield at the listening positions?

Any real problems in those areas will show up almost imme-

diately in a lack of musicality to the score or an unnaturalnessof the dialog, and of course should also be evident in yourmeasured data.

QUICK REFERENCE LIST OFWHAT TO LISTEN FOR: SPACE The concept of space refers to the ability of

the reproduction system to produce a convincing sense ofthe ambiance of the physical place(s) represented by theon screen image or the acoustical ambiance of the spacewhere a recording was produced in the case of performingarts sources without picture.

ACCURACY While this can be a highly subjective pa-rameter, the measurements collected on system perfor-mance using appropriate tools are the basis for determin-ing if a system is producing a smooth even soundfieldwithin the space. Subjectively it is essential to verify thatthe speaker system is not producing any output that is notwithin the original signal (see colored/uncolored below).

DIALOG Dialog is the core element for any motion pic-ture presentation. The Center channel speaker is produc-ing almost all of this information. Insuring that the speechsounds natural and is accurate to the actor/actressesactual presentation is essential. They must



40/56Room Acoustics

Section VI


sound real and not constrained or thin. Dynamic rangeand clarity are also key parameters to check.

COLORED/UNCOLORED Coloration is caused by the ad-dition of unwanted harmonics or resonances to the originalsignal. These may be produced by the loudspeaker itself,

or the speaker room combination. You must know whatsomething is supposed to sound like to determine color-ation. Listening to your selected test material on a goodsystem is the best way to establish these benchmarks.

NATURALNESS This is a largely subjective parameter.However if voices or ambiance do not seem real andunforced then they are probably not natural either.

Its All in the DetailsThe best way to use this listening technique is to pick one or

two film segments (see below) and listen to them on sev-eral systems that you know to be best in class. You need topick just a few chapters (we recommend no more than twoor three 5-6 minute segments) from each film and listen tothem repeatedly to establish a benchmark of what they aresupposed to sound (and by the way look) like.

Once you have this benchmark embedded in your brain youshould be able to play those same segments on any systemyou are testing or calibrating and get immediate data on thatsystems performance status.

This method has been used for decades by live sound engi-neers who play a few of their favorite cuts from their testCDs every time they set up a system.

This gives them both a feel for how the system is perform-ing within the specific space, and also a good indication asto whether or not the basic system parameters are withinspec.; as well as a quick and easy check to insure that thehardware is all working properly.



41/56

Room Acoustics

page-41

Section VI


Field of DreamsThe first is Field of Dreams - Collectors edition. I use Chap-ters 2 and 7. Chapter 2 takes place in the cornfield, whereKevin Costner is walking through the corn and hears the ifyou build it voice for the first time. The detail I look for is

the rustling of the corn as he walks, the sound of the shovelhitting the dirt, the distant squeak of the porch swing wherethe wife and child are slowly rocking back and forth, the icein their drinks, their footsteps on the porch as they walk intothe house.

All these sounds are positioned across the LCR sound stage,with the voice coming from both the LCRs and the sur-rounds. The amount of detail in this seen is immense, in-cluding insect sounds, and wind, all designed to create thatsummer afternoon cornfield/farmhouse place.

If the system is properly set up all of this information willbe there. If not, much of it will be buried and lost. Positionalinformation like the fact that the wife/child/swing are all cen-ter left to match the camera shot, will also be smeared andindistinct. This scene lets me determine if the system isproperly equalized, delayed and level balanced, because if itsnot, all of this stuff collapses and the ambiance is not cre-ated.

Chapter seven starts in the farmhouse living room with Cost-ner and Amy Madigan discussing if they can keep the farm.

The daughter enters the room and tells Costner that Daddy,theres a man on your lawn- announcing the first appear-ance of Shoeless Joe Jackson.

Costner gets up walks across the floor, out on to the porch,across the porch to turn on the three light poles, down thesteps across the yard, onto the gravel and then on to thegrass of the baseball diamond. Again there is a huge amountof subtle detail like the various sounds Costners shoes makeas they change surfaces, and motion he makes as he walksacross the front sound stage, the sharp clicks of the light

switches, the squeaky swing of the screen door, and so forth.



42/56Room Acoustics

Section VI


As in Chapter 2, the detail makes the scene real and brings itto life. If you have calibrated and balanced the system prop-erly the soundtrack should pull you right onto that porch, andwith Costner as he walks out to the diamond. It still sendschills down my spine when it works right, and it should dothis for you too - if the system is accurate.

In investigating this soundtrack, and asking questions ofsome of the people involved, I was told that there were over100 sound elements used to make these scenes real, andeach has a specific place in space and sound to contribute.If they all mesh correctly you will not want to stop the disc- you will fall into the movie- which is of course exactly thegoal.

CRIMSON TIDEAnother excellent, if totally different film is Crimson Tide

- Chapters 12-15 or 18 and 19. Here the goal is to put youon this nuclear missile boat, under high stress, as the cap-tain and crew deal with internal conflicts and their orders tofire missiles. The detail used to create the ambiance insidethis sub, and the dozens of small sounds contributing tothis space such as beeping sonar, communications warn-ing tones, clicks from internal speaker systems and micro-phones, breaking plastic sounds as the officers open theircode authenticator packs, combination locks on safes, keysjangling, the dramatic shift in ambiance from inside to out-

side the sub as torpedoes are detected and fired, and soforth all combine to produce a very intense, very high ten-sion scene.

On a fair to good system the scenes will be interesting, buton a great system properly set up these scenes are abso-lutely compelling, holding you riveted to the screen and mak-ing you believe totally that you are standing in that controlroom.



43/56

Room Acoustics

page-43

Section VI

The Art of Listeningw

DRAGONHEARTAnother excellent clip is Chapter 12 The Old Code fromDragonheart with the voice of Sean Connery as the dragon.Make sure you get and use the anamorphic widescreen(2.35:1)version. This also makes an excellent screen image

size/location tester. In this screen the dragon flies around theroom while speaking and beating its wings. Moving acrossthe LCR stage and around through the surrounds and back.

If the system is set up correctly the wing beats slide seam-lessly and smoothly from speaker to speaker and the wholeambiance rotates with the on screen image of the dragon.There is also substantial low frequency content added intothe voice so it also tests your main system to subwoofersplice and subwoofer accuracy and tone. The voice should besolid and very heavy with out boominess.

U571This film contains a number of segments that can be used.Chapter 4, Chapter 6 ( the rain) Chapter 8, and the nowsemi-famous Chapters 14/15 containing the depth charg-ing sequences. The depth charge scenes not only providea good check of the systems overall dynamic capability andreality creation quotient, but also allow you to see how wellthe system handles both soft (dialog passages) and loud(explosions in rapid sequence) .

The rain in Chapter 6 is a fine test for surround ambiancecreation and a systems overall ability to create a sense ofthere as was discussed earlier.

Every time I use these scenes, in classes or on jobs, I knowif things are working properly because people stop what theyare doing and become glued to the movie.



44/56Room Acoustics

Section VI


Often there will be a physical jerk or snap in their bodylanguage when the stop button is pushed and all of a suddenthe place they are shifts instantly from the picture back tothe reality of the room we are in. This tells me that we havesuccessfully re-created the acoustical space intended, andthat detail is coming through to make everything seem real

.

What Are You Shooting For?It may be difficult to understand what happens until it hap-pens to you, but when it does, you will never look at yoursystems the same way again.

We encourage you to experiment for yourself and find whatworks for you, but remember if you dont disappear intothe movie, if the listening experience is not centripetal anddoesnt pull you in then, there are probably things wrong with

the acoustical envelope you are producing that are interferingwith your ability to fool the ear/brain into believing it is some-place else.

There is an element of art and magic to this process, andonce you get it to work for you, it will allow you to reallyshowcase your systems to their utmost ability. Enjoy theride!!!!!

( NOTE: Another version of this material appeared as anarticle in the October 2001 issue of Residential Systems

Magazine and in training materials prepared for Audio ControlIndustrial .)



45/56

Room Acoustics

page-45

Section VI


Listening for the Details Before

Left

Center

Right

SurroundLeft

SurroundRight

Film: ______________________________

For each film we demonstrate before we calibratethe system:

1. Did what you hear positionally match what was on thescreen? yes or no

2. Write in each loudspeaker box what you heard comingfrom that position in the room.



46/56Room Acoustics

Section VI


Listening for the Details After

SurroundLeft

SurroundRight

Film: ______________________________

Left

Center

Right

For each film we demonstrateafter we calibratethe system:

1. Did what you hear positionally match what was on thescreen yes or no

2. Write in each loudspeaker box what you heard comingfrom that position in the room.



47/56

Room Acoustics

page-47

Section VII

Creating Magic

Creating MagicCreating MagicHowever - Misapplication will always make things worse !

The same methodology can be used on center channelspeakers to control apparent position.

The key point to remember here is APPARENT position.

The brain can be fooled into accepting locations that are notprecisely matched to the physical positions.

Careful and judicious use of delay can both correct forphysical abnormalities in the room and allow you to create aunique acoustic space for each client, tailored to their ownmental map of what the space could sound like. You can,within certain limits, actually re-do the room to make a newspace from the old.

Additionally, differing delay patterns and lengths can beprogrammed in and saved into memory to be triggered bydifferent modes on the decoder such as stadium spacesfor sports, etc. Even the most sophistical processors algo-rithms can be enhanced by tailored delay processing.

Subwoofers and Rooms - Creating ImpactThe first thing to understand about subwoofers is that theyare designed to work into some specific room volume.

If the subwoofer is THX certified, its recommended room vol-ume is part of the spec. If not, most manufacturers specifythis information.

It is VITAL to know exactly how much room volume yoursubwoofer(s) are facing.

That number is the sum of:

The actual room volume of your theater space

Any additional coupled spaces such as hallways, adja-cent rooms not completely sealed off by a

door, and so forth.For example if your theater space has a cubic volume of1500 feet (length x width x height), and the sub you chooseis designed to work into room volumes of 800 square feet(common for small subs) you will need TWO subs to coverthe space.


48/56Room Acoustics

Creating Magic

Section VII

However if the theater room is coupled to a hallway of 250cubic feet, and a den through an archway of an additional1000 cubic feet, your subwoofers are looking at a cumulativevolume of 2750 cubic feet so you will need FOUR subwoof-ers to provide enough output to produce bass in the actualcubic volume you have.

Be CAREFUL here- customers expect BASS and you can eas-ily destroy a small sub trying to fill a large space.

DIVA , unique amongst all room correction tools, providescompressors and a limiter on its subwoofer outputs whichcan be used to protect subs, as well as shape and controlthe sound of subwoofers.

This is in addition to the equalization provided, which can beused to both correct problems and tune the subs sound tothe room, client and program material. Remember you have

memories in DIVA, so your subs can have many sounds.

You can use the Compression, Limiting and EQ in DIVA astools to create a sub sound or manage Bass impact andpresentation in any space.

The best way to understand this is, to hear it; so lets do alittle listening first and then we can discuss what is happen-ing and why.

Compression changes the overall dynamic ratio of any signalby making the loud parts softer and the soft parts louder.

The RATIO used reflects the relative change being made- the higher the number [x] over the 1 (x /1 the more com-pression is being applied.

Thus, a compression ratio of 2:1 is much gentler than a ratioof 10:1.

Limiting is sort of selective compressor in that it only affectsthe top or high level portion of a signal. Limiters essentiallyprevent a signal from getting any louder than a pre-set point.

They can do this all at once (a brick-wall) or gradually starting

at some pre-determined threshold point.

The subjective quality of either process is entirely dependanton its time constants or the amount of time it takes for thedevice to attack the signal, and release the signal fromelectronic bondage.


49/56

Room Acoustics

page-49Misc

Section VII

Creating MagicDIVA provides factory presets (developed by Technology Vi-sions for/with Audio Control) for these function which is whereyou should ALWAYS start.

Make any changes in very small amounts and listen carefullybefore making any addition changes.

Selling Calibration and EqualizationThey key to getting your customers to accept this option,and for you to be able to sell and profit from the service is toplant the seed VERY early on.

You should point out that EVERY system can benefit from thisprocess, because no room is perfect. Additionally you shouldmake sure they recognize that, and that every room in whichthe programming they will enjoy is produced has had beencalibrated, equalized and measured intensively to insure its

accuracy.They should take advantage of your ability to provide thesame scientific analysis and calibration to get the most outof their space.

Remember equalization will enhance system performance,provide flexibility for various programming sources (using therecallable pre-sets in DIVA) and insure optimal enjoyment ofevery programming source.

Your customers simply want the system to sound good - TO

THEM, and you have the tools to provide precisely that. Yourcompetitors probably do not!

You can give them whatever they want (within reason and theknown laws of physics) and for the money provide a muchbetter performing, more stabile, more consistent sonic stagethat anyone else.

SELL that idea!

The objection you are likely to encounter are easy to over-come if you can demonstrate the difference you can make.

You must not only tell them what you can do, you must letthem HEAR the difference.

To do that you need to build up a library of selected demon-stration software.

This should NOT be explosions and screaming jet fighters,


50/56Room Acoustics

Creating Magic

Section VII

although a bit of that is always fun. It should be selected 2-3 minute clips that you can run in a before and after modeshowcasing your skills and the capabilities of the hardware.

Here is a short list of the discs I like to use.

You should spend time to add to this your own favorites,

ones you can talk about and demo with.

You must insure enough variety to appeal to all customertypes, both male and female.

(All these are DVDs)

FIELD OF DREAMSCRIMSON TIDESESSIONS AT WEST 54TH STREETU-571DRAGONHEART

EAGLESFLEETWOOD MAC- THE DANCEHUNT FOR RED OCTOBERALWAYSMETALLICAT-2 - 2000 RE-MASTERED EDITION (METAL BOX)JAMES TAYLOR LIVE AT THE BEACON THEATER

Finally . . . Conduct a Listening TestThe two commandments of system calibration that cannot

be ignored are:Always, always, always conduct numerous listening teststhroughout the process to insure that what you are doing isactually having a beneficial effect.

Never, never, never do any equalization without also listeningto the system with the EQ in and the EQ out to compare.

Given the tools now have available, you can electronicallycorrect a significant portion of the equalizable problems. Withthe proper application of the right kind of acoustical treatment

you can tackle many of the others.Remember choosing and using the right tool for the job cango a long way to improving the acoustic performance of anyroom, and thus the performance of the sound system youput in that room.


51/56

Room Acoustics

page-51Checklist

Section VIII

ChecklistROOM MEASUREMENT ANDCALIBRATION CHECKLISTUsing the SA-3052 Real Time Spectrum Analyzer

1. Take attendance using pink noise

2. Look at frequency response to check if they are similar.

3. Use tape measure to set delays.

4. Look at frequency response and set equalization.

5. Check subwoofer splice

6. Listen and enjoy.

Using the the Iasys HT and the Diva

1. Place microphone in the money position.

During the testing, make sure the microphone stays in thisposition.

2. Play Pink Noise, take attendance.

The purpose here is to make sure all speakers are working,that the connections go to the correct speaker and to see ifthere are any significant inconsistencies between speakers. Ifeverything is perfect the first time, youare one of the lucky few.

3. Make sure there are no rattles.Use the sine sweep at

high volume and listenfor distortion as itsweeps. Tighten thesweep frequenciesto home in on theproblem area. As youget close, changeto the constant sineoutput, then use thewheel to move smallamounts. Most likelythere will be rattles inscreen covers, lightfixtures and the like.


52/56Room Acoustics

4. Run Delay test on each speakerPick an empty memory within Iasys HT or empty a memoryvia the main menu. Press DELAY/POLARITY and follow theinstructions.

The HT-100 will route the signal to the correct output. You will

need to run these automatic tests on each speaker. Whilethis will take some time, you need only start the test foreach speaker, then the Iasys HT will do the rest.

5. Check Energy Center for speaker consistencyAfter running all delay tests, press RECALL and Iasys HT willdisplay the energy centers for all speakers. Like speakers,e.g. left and right front, surrounds, should have energy cen-ters within one-sixth octave. This is a great test for findinginconsistent or wounded speakers. Finding a problem nowwill save much grief later. See octave chart on page 52.

6. Set all SPL levels equalPress CROSSOVER button until the pink noise is cycling toall the different speakers via the HT-100. Using the Diva, setthe gain levels so that the SPL in each channel is identical.While simple, this is a very important step for a great sound-ing system.

7. Adjust delays for Left, Right, Center, Subwoofer, sides

and back.

Select DELAY/POLARITY. Look at the Delay information and besure that all the Polarities are correct. If not, this is the time

to fix them.

Then push the DELAY button another time. The new informa-tion is relative delays calculated from the farthest speaker.With Diva, set the delays as noted on the Iasys HT. In Diva,adding overall delays will not change the relative delays.Now that we have done a fair bit of adjusting with Diva, this isa good time to save into a memory just to be safe.

8. Adjust equalizer using Equalizable SpectraEqualizable Spectra will be in the Iasys HT memory for eachchannel from the Delay and Coherence tests. Set the equal-

izer based on these memories, paying special attention tothe missing data parts of the frequency spectrum.

Checklist

Section VIII

IMPORTANT NOTE:

At the end of each delay test,push the COHERENCE button andlet Iasys HT do a full sweep beforepushing QUIT.


53/56

Room Acoustics

page-53

Do the major adjustments then use the one-third octave ana-lyzer via the PINK noise to check the results. If you want to seethe one-twelfth octave response, you will need to re-run thedelay test for that channel, then as that test concludes switchto the sweeping more of the equalizable spectra.

Use PAUSE not QUIT if you want to stop the noise and thencontinue as that will keep you from having to re-run the delaytest again.

9. Check Subwoofer spliceCheck to make sure at the frequency of the subwoofer cross-over, there is not a peak or dip in the response. You will needto play the speakers physically closer to the subwoofer(s)using the noise/RTA and manual selects of the HT-100, thenlook at the frequency response. Since the delays are setright, this might not be as much a problem as without thedelays.

10. Select Subwoofer mode on DivaHard is a good choice for most movies as it is tweaked for ac-tion and effects. Normal is better for just music as discussedin the Diva manual.

11. Add extra Delay to side and back speakers for effectSee the recommendations early in this manual. Try it and youwill be amazed at the improvement.

12. Add Delay time per individual preference to Left and

Right which brings forward CenterThis one is individual preference but in the authors opinionmakes the images on the screen more 3D as the sound fromthe Center speaker arrives just slightly ahead of the Left andRight speakers.

13. Listen

14. Season to tasteMore side or rear delay? With the Diva, this is easy to addand listen as you go. Change the equalization to the ownerspreference? Again, this is easily done. Remember to save

into permanent memory on the Diva more often than youthink is necessary.

15. EnjoyAt this point, the system should be Magic. Use the Bypassfeature of the Diva to hear the differences.

Checklist

Section VIII

Checklist


54/56Room Acoustics

Octave Chart

Frequency distribution ofcommon musical instruments


55/56

Room Acoustics

page-55

Frederick AmpelTechnology Visions

9512 West 93rd StreetOverland Park, Kansas 66212-4801 USAPhone: 913 492 3047Fax: 913 492 6226

Email: [email protected]

References:

1. The Audio Dictionary, second edition, G.D.White2. Home THX Room Equalization Manual, revised 1.5 Lucasfilm, Ltd

3. Home Theater Acoustical Problems and Equalization Solutions, Fred Ampel/AudioControl

4. Learning to Listen, Residential Systems Magazine, October 2001

Special thanks to Fred Ampel of Technology Visionsfor his efforts towards creating this guide.

22410 70th Avenue West

Mountlake Terrace, WA 98046425-775-8461 Fax [email protected]


56/56

Home Theater Calibration Guide

Documents