Acoustics+Ppt

PRESENTED BY:PRESENTED BY:

NITYA JAIN A2315808023NITYA JAIN A2315808023

MANSI JAIN A2315808015MANSI JAIN A2315808015

R.G. SINDHU A2315808034R.G. SINDHU A2315808034

PRESENTATION ON PRESENTATION ON

ACOUSTICSACOUSTICS

Acoustics is defined as the science of sound and it discusses the origin, propagation and auditory sensation of sound. A sound is produced due to the vibrations produced and transmitted in the material medium i.e.; air

Sound is a travelling wave which is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently

strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.PROPERTIES OF SOUND 1.PRESSURESound pressure is defined as the difference between the average local pressure of the medium outside of the sound wave in which it is traveling through (at a given point and a given time) and the pressure found within the sound wave itself within that same medium.

2. INTENSITY AND LOUDNESS Intensity of sound is defined as the amount or flow of wave energy crossing per unit time through a unit area taken perpendicular to the direction of propagation.Loudness of a sound corresponds to the degree of sensation depending on the intensity of sound and the sensitivity of ear-drums. According to Weber and Fechner’s law.. The magnitude of any sensation is proportional to the logarithm of the physical stimulus that produces it. OR loudness is directly proportional to the logarithm of intensity. L1 α log10 I1 L 2 α log10I 2 The Intensity level L is given by difference of the two equations above L=k log10 I1/I2If k=1, the difference in loudness is expressed in BELS. This unit is rather large. Shorter practical unit is DECIBEL. 1bel = 10dB

SOUNDSOUND

3.FREQUENCY AND PITCH OF SOUND-

Frequency or the pitch is defined as the number of cycles which a sounding body makes in each unit of time. Greater the frequency, higher is the pitch. The frequency scale covers a wide range varying from 20 cycles per second to 1500 cycles per second.

The pitch of a sound is how high or low the sound is. A high sound has a high pitch and a low sound has a low pitch. When plucked, a short string gives a higher-pitched sound than a long string. When banged, a tight drum skin gives a higher-pitched sound than a loose drum skin.

Conditions for good acoustics of a hall• The initial sound from the source should be adequate

intensity so that it can be heard throughout the hall. For halls of big size, suitable sound amplification system should be installed.

• The sound produced should be evenly spread in the hall so that sound foci and dead spots are avoided.

• The boundary surfaces of the hall should be so designed that there are no echoes.

• The boundary surfaces of the hall should be properly designed so that the unwanted sound is absorbed.

• In case of conference halls, the acoustics of the halls should be designed in such a way that they ensure proper conditions for listening, assuming that a person may speak or listen from any corner in the hall.

• In case of music halls, the treatment should be such that the initial sound reaches the audience with the same intensity and frequency.

GENERAL PRINCIPLES AND FACTORS IN ACOUSTICAL DESIGN:--Site selection and planning.--Dimensions--Shape--Seats and setting arrangement-- Treatment of interior surfaces--Seats and seating arrangement--Reverberation and sound absorption

Most of the common building materials absorb sound to a small extent and hence, for better acoustical requirement, some other materials are to be

incorporated on the surfaces of the room. Such materials are known as the absorbent materials and they help a great deal in making the room

acoustically good.

The important facts in connection with absorbent materials are as follows:The noise level of the room provided with absorbent materials is

considerably reduced.

In the hall treated with absorbent materials, the speech can be heard clearly and music can be fully enjoyed.

All the absorbent materials are found to be soft and porous. The absorbing capacity of the absorbent materials depends on the

thickness of the material, its density and frequency of sound.

The acoustic properties of the absorbent materials are considerably changed by the their modes of fixing.

Great care should be exercised while prescribing the covering for an absorbent material so as to improve its appearance. The improper covering

destroys the absorbent properties of the material.

SOUND ABSORBING MATERIALS AND CONSTRUCTIONS

Sound Absorbing foamsComposite sandwich barrier/foam productDampening sheet and sound paint are all used in a diverse range of industries.

The requirements of a good acoustical material are as follows:

It should be durable and should not be liable to be attacked by insects, termites.It should be easily available at a reasonable cost.

It should be efficient available over a wide range of frequencies.It should be fire-resistant.

It should be non-hygroscopic and heat insulating.It should be self-supporting and should be capable of easy fixing.

It should give pleasing appearance after fixing.It should be high coefficient of absorption.

It should have sufficient structural strength.

Following are some of the common types of absorbent materials:

HairfeltAcoustic plasterAcoustical tilesStrawboardPulp boards

Compressed fiberboardCompressed wood particle board

Perforated plywoodWood wool boardQuilts and mats

ACOUSTICAL DEFECTS The acoustical design of an enclosed space is preliminary governed by the behavior of the reflected sound.

When the reflected sound wave reaches the ear just when the original sound from the same source has been already reached, an echo is produced and it thus indicates the repetition of a sound by reflection of sound waves from a surface.The heavy rolling sound of a thunder is due to successive reflections from a number of reflecting surfaces like clouds, mountains, various strata of air, etc.

Common acoustical defects1. Reverberation

2. Formation of echoes

3. sound foci

4. Dead spots

5. Insufficient loudness

6. Exterior noise

The immediate effect of multiple reflections is an increase in the sound intensity caused by the reflections. A listener will hear the direct sound arriving at the ear along with all of the multiple reflections. Thus the combined loudness of the direct sound and the reflected sound will be greater than the direct sound alone.

Reverberation time in seconds

Acoustics

0.50 to 1.50 Excellent

1.50 to 2.00 Good

2.00 to 3.00 Fairly Good

3.00 to 5.00 Bad

Above 5.00 Very bad

REVERBERATION TIME AND ACOUSTICS

TRANSMISSION OF SOUND♫ When sound is produced in a room it proceeds outward in spherical waves until it

strikes the boundary of the room .♫ Thereafter, the sound waves are reflected, transmitted and absorbed in varying

amounts depending upon the characteristics of the wall of the room. (thickness, weight, material of wall, nature of its surface)

Noise is transmitted in the following ways:a. Through airb. By vibrations of structural membersc. Through structural members

SOUND INSULATIONSOUND INSULATIONIt is the measure by which transmission of sound from inside to outside or from one room to another is prevented

TRANSMISSION LOSSES♪The reduction in the intensity of air-borne sound, that takes place during its transmission from the source to the recipient.

♪Transmission loss is numerically equivalent to the loss in the intensity of the sound expressed in decibels.

METHODS OF SOUND INSULATIONMETHODS OF SOUND INSULATION

BUILDINGS

Good planning in respect of the location of building as well as the placement of quiet and noisy areas in the building itself play an important role in noise transmission.

• WALLSWALLS

The sound insulation rating of a wall is generally governed by the net sound transmission loss it provides and also the efficiency with which it serves as a barrier for speech sound. Wait of the wall is the governing factor in wall insulation. A solid one brick thick wall plastered on both sides, proves quiet effective as a sound insulating partition wall has an average reduction of 50db.

Wall construction used for sound insulation is of 3 types:

1. Rigid homogenous wall

♦ Rigid wall consists of stone , brick or concrete masonry construction, well plastered on one or both sides.

♦ Sound insulation thus increases with the increase in the thickness of the wall.

♦ Highly uneconomical and bulky after certain limit.

2. Partition walls of porous materials♦ Rigid porous materials insulation increases about 10% higher than the non-porous.♦ Non-rigid porous materials offer low sound insulation but can be used in combination

with the rigid materials

3. Double wall partition

♦ Consists of plaster boards or fibre boards on both the faces, with sound absorbing blanket in between

♦ Staggered wooden studs are provided as support.

4. Cavity wall construction

♦ This can be made to have increased insulation value by filling the cavity with some resilient material.

♦ The cavity should be at least 5cm in width and the two wall leaves should be tied by use of only light butterfly wall ties

♦ Partition walls having the value of transmission loss of 45db or less are considered adequate for separating critical areas of adjacent dwellings.

• FLOORS AND ROOFSFLOORS AND ROOFS

Transmission of sound takes place more easily through floors. Sound proofing can be achieved by:

1.Use of resilient surface materials on floors

♦Providing thin concrete and then providing soft floor finish or covering with linoleum, insulation board, cork, asphalt mastic.♦No appreciable effect on air-borne sound.

2. Concrete floor floating construction.Material like quilted mineral or glass wool is laid over the R.C.C. floor or roof.

3. Timber floor.Employing mineral or glass wool quilt.

4. Skirting.The larger the contact area it provides between floor and wall, lower the insulation.Lower edge is chamfered to reduce the contact area.

Superior Soundproofing

Insulated engineered floor truss system to reduce floor squeaks and vertical sound transmission- There is 22 inches of space in between that is filled with cellufibre that blocks and shield sound transfer! Double staggered stud party walls between suites, including insulation and sound bar technology to minimize horizontal sound transfer- the flooring has gaps in between suites so sound is not carried from one suite to the other from the walls! Cast iron plumbing stacks to reduce plumbing noise-because cast iron is so much heavier than other materials the steel holds in the noise!