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8/14/2019 Acoustic 1

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OPP. OLD INCOME TAX OFFICE ,HISSAR ROAD M -9812193781

unique Technical InstituteACOUSTIC

Acoustic : I t is defined as the branch of physics which deals with generation of

sound waves

Acoustic of Building : the branch of science which deals with the design and

construction of halls ,theatre,and house with best sound effect.

Sound: it is defined as effect which are pleasant to listen ,that is called musical

sound and which are not pleasant to our ear is called noise.Characteristics of musical sound : 1. Intensity or Loudness 2 . Pitch 3 quality

1. Intensity : It is defined as the amount of sound energy crossing per unit area

amount a point in one second is called intensity.

It is a physical quantity that can be measured. The sensation produced in the ear whichenable us to distinguish between a Loud sound and a faint sound is called Loudness .

It has been that; Loudness depend upon (1) Intensity of sound (2) sensitiveness of ear

According to Weber law Loudness (s) is directly proportional to Logarithms of Intensity.S Log I

S =k log I ; where k is constant, suppose the loudness is S forIntensity I and so for intensity IoS=k log I ; so = k log Io

The intensity level is difference in loudness L = S-So = k log I-k log Io

L =k log I/Io bell

L= 10 k log I/Io if k=1; as I/Io = 1.26

2. PITCH: It is defined as the sound which tell us the difference between shrill and

flat sound .pitch always depend on frequency .it does not depend on loudness

.Higher the frequency ,Higher the pitch

3 Quality: It enables us to distinguish between two sounds having the same loudness and

pitch. It depends on the overtones on the basis of Quality ,we can recognize any onewithout seeing him.

ABSORPTION COEFFICIENT: It is defined as ratio of sound energy by the surface to

the total incident sound energy on the surfaceA= sound energy absorbed by the surface

Total energy incident on the surface

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An open window can be acts as perfect absorber because all the waves pass withoutreflection

REVERBERATION : The prolongation of audible sound in a hall after the surface

has stopped emitting sound is called reverberation.

REVERBERATION Time : It is time for Which sound persist until it can be comes

inaudible .

Sabine Formula: It is defined as the time taken by the sound intensity to fall to itsone millionth part after the source stop sounding .

T= 0.16V/ asWhere T is reverberation time, v is volume of room

S is area and a is coefficient of absorption, as is total sum of absorption of surface

METHOD TO CONTROL Reverberation.1. Providing a few open window : The open window are perfect absorber of incident

sound .so open window used for control the R T

2. Covering the walls and floor with absorbing materials.3. Heavy curtains : These materials are also help in absorbing of sound and time of

reverberation can be adjusted by heavy curtains .

4. The presence of audience in the hall also make a lot of difference.FACTOR S : 1. It is sensation that enables us to hear. The acoustic of building mainly

depends on Loudness .it can be improved by using large parabolic reflector boards .The

loudspeaker should be fixed a little above the heads of audience.

2 FOCUSSING: The curved surface should be designed carefully to ensure evendistribution.

3 EXTRA SOUND: It is that sound which is present outside the hall. It should be

avoidable ,because if extraneous sound is greater than inner sound ,then it isnot useful.

4 Absorbing material: /The absorbing material can absorb the sound which

are produced in hall .so the use of uphold stared chair in hall to avoid the

effect of variations the no: of audience .The seat in the hall should beelevated gradually to provided free flow of sound.

5. Echo: Echo is repetition of sound, to avoid confusion between echo and original

sound the surface producing echo must be covered with material.6. Reverberation time : It should be minimum

7. Quality: The property of device to produce a original sound in all its detail is

called fidelity or Quality.




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unique Technical Institute8. Echo lean Effect: If there is regular structure similar to stairs or set of railing

in hall , the sound produced in front of such a structure is musical sound This

effect is called echo lean effect.

ULTRASONIC

Ultrasonic: The sound frequencies having more than 20 kHz are known as. Ultrasonic: The sound which are produced less than 20 kHz are called infra sonic .

Audible sound: The range between 20 Hz to 20 kHz is called audible sound.

Production of ultrasonic: There are two method (1) Magneto striction (2) piezoelectricoscillator

MAGNETOSTRICTION:

PRINCIPAL: According to this effect , If a Ferro magnetic material in the form of bar

is subjected to alternating magnetic field .The bar expands and contracts in length

alternately . the frequency of expansion or contraction is twice the frequency ofalternating magnetic field .That is produced with the help of oscillatory circuit ,due

to this ,it comes in ultrasonic waves

.CONSTRUCTION: X Y Is a ferromagnetic bar that is clamped in middle .L1 and L2 are two coils

surrounding the bar x y. An ac of high

Frequency is passed through coil L1 from oscillator .DueTo this magnetic is set up which makes the bar magnetized

And demagnetized with a.c. Current .Due to this bar expand

And contracts simultaneously and produce high vibration

Frequency .This is maintained by coupling effect betweenL1, L2.




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unique Technical InstituteAccording to principal to magnetostriction,

The length of rod increase and decrease and high

Frequency set up when these frequency increases up to 20 kHz this is called ultrasonic

PIEZO ELCTRIC : According to this , If one pairs of opposite faces of a certain

types of a crystal is subjected to mechanical pressure , the other pairs of oppositefaces develops equal and opposite charge . It is called piezoelectric effect .The

material are used for this quartz ,tourmaline and Rochelle salt .

Construction: Q is thin slice of quartz crystal cut with its opposite facesperpendicular to optic axis. The crystal is placed between the metal plate A and B. when

two opposite faces of quartz crystal are subjected alternately voltage ,the other pair ofopposite experience stress and strain . It continuously contract and expands. These

produce wave more than 20 kHz are ultrasonic n = m/2t where m =1,2, is according to variation modes. And t is thickness.

DETECTION OF ULTRASONIC:

1.Piezoelectric detection : It consist of quartz crystal when waves are allowed to fallon one pair of opposite face of crystal .the changes are developed and amplify to

confirm that wave are ultrasonic. ]

2. Thermal detection: It is based on change in resistance o heating .In a thermal detector,a fine platinum wire fixed at both end is used . the wire begins to vibrate rapidly

causing heating and cooling at nodes and antinodes .The resistance will change on

heating and detected ultrasonic.APPLICATION: 1. Drilling: IT is used to bore holes in steel and other material. Due tooscillation.

2. cold welding : The process of joining two different metal permanently without any

involvement of heat is called cold welding .The difference is that tool bit at the end ofthe drill by hammer .Two pieces are placed together below the hammer and ultrasonic

source is applied therefore pieces will be press and will be joined together

3. ULTRASONIC CLEANING : When ultrasonic are passed through liquid ,it get

violent shaken due to super position of waves .it is device consist of ultrasonic

transducer driven by oscillator .

The object to be placed is either kept hanging.When ultrasonic waves are produced in water

, the job gets strong force to remove its unwanted

Particle .The ultrasonic force looses the particle.

4 SONAR: It is sound navigation and ranging which is used for detection of submarines.The ultrasonic waves are used for detection the depth of sea water and also obstacle




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unique Technical Instituteon the sea. D=ct/2 where d is depth and c is velocity of medium and t is time taken tocomplete one full cycle.



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