Sub : Physics Sub code:

Topics and Sub-topics

Acoustics:

- Characteristics of musical sound

- Loudness
- Characteristics of sound and absorption(without Sabine formula)
- Absorption coefficient
- Acoustics of buildings – Factors affecting building and their remedies
Ultrasonic

- Production: Magnetostriction and piezoelectric methods

- Applications : SONAR, NDT through ultrasonic, Medical Applications

Learning Outcomes
- define sound as longitudinal waves propagating in medium and classify types of sound and
its properties.
- analyze Music and Noise with measurement techniques and further classifications.
- know about Ultrasound and its generation bymechanical and electrical methods.
- enumerate various methods fordetection of ultrasonic sound.
- enumerate simple application of ultrasound: detection, ranging, mechanical devices, medical
fields, and ultrasonic testing methods (NDT) and its outcomes.

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A periodic disturbance produced in a medium or a space is known as wave.

They are classified in following categories

(1)Mechanical Waves

(2)Electromagnetic Waves

(3)Matter Waves

GECR/GEN/PHYSICS/PKR/SEM1 & 2 /202425

 Transverse Waves
Disturbance are at right angle
to the direction of propagation

Longitudanal Waves
If the particles of medium
are displaced in direction of
propagation
“SOUND WAVES”

Basics of Sound waves

Sound Waves Mechanical Waves
“Sound is a mechanical wave that is an oscillation of pressure transmitted through some medium
(like air or water), composed of frequencies within the range of hearing

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases,
liquids, and solids including vibration, sound, ultrasound and infrasound

Acoustics
 CLLASICFICATION OF SOUND BASED ON FREQUENCY

Sound waves can be classified based on frequency in three groups.

1. Infrasonic sound waves (f<20 Hz )

2. Audible sound waves (20 Hz< f < 20 KHz)
3. Ultrasonic sound waves ( f > 20 KHz)

 Sound waves with frequencies lying in the range of 20 Hz to 20 KHz

known as Audible sound waves,
 Sound waves with frequency less than 20 Hz is known as infrasonic
sound waves
 Sound waves with frequency more than 20 KHz is known as
Ultrasonic Sound Waves

Explain the method to determine the absorption coefficient of material.

( 02 march 2010) Or
Explain the method to determine the absorption coefficient of material.
GECR/GEN/PHYSICS/PKR/SEM1 & 2 /202425
( 02 march 2010)Or
What is the absorption coefficient? Explain how to determine the
absorptioncoeffiecient. (03
january 2010)
Ans.:05:
ABSORPTION COEFFICENT.
o Absorption coefficient is a ratio of sound energy absorbed by a
material to the total sound energy incident on it.

∴ Absorption Coefficient (  ) =
.

If there different materials in a hall,then the total sound absorption

by the different materials is given by
A = a1+a2+a3+a4+……………………
A =  1 s1+  2 S2+  3 S3+  4 S4+……………………

A = ∑  n𝑠n
Where  1 ,  2,  3,  4 , are absorption coefficients of materials with
areas S1,S2,S3.
o Sabine chose an area of 1m2 open window to be the standard unit
of absorption. Because all the sound energy falling on it, pass
through, so it can be said that sound energy is completely
absorbed by it.
o So a unit area of open window is selected as the standard which is
an “Ideal absorber of sound”
o Thus the unit of absorption is the Open Window Unit.(O.W.U.) also
known as a ”sabine”

Reverberation and Reverberation Time

o Sound produce by a source is remains for some time even after the
source has stoped to produce the sound, This effect of sound waves
are known as a Reverberation

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 o Person inside the room or a hall continues to receive the successive
reflections of progressively decreasing Intensities.

o Time taken by the sound waves to fall below the minimum audibility
level even after the source of sound stopped to produce it ,this time
period is known as Reverberation of Time.

Sound undergoes by a
multiple reflection by
walls, floor and ceiling
and directly towards the
listeners which produce
reverberation effect.

QUE: 09 : SABINE FORMULA (02 MARKS)

SABINE’S FORMULA
o Sabine defined the reverberation time as, the time taken by the sound
intensity to fall to one millionth of its original intensity after the
source stopped emitting sound.
o The reverberation time is given by
,
T ∝ ,

∙
T = where K is Pro.lity const.

.
T= where A = ∑  n𝑠n

Where, V is the volume of the hall.

A is the Total sound absorption
a is the absorption coefficient of various materials.

GECR/GEN/PHYSICS/PKR/SEM1 & 2 /202425

 S is the surface area.
Que:06: Discuss the various factors affecting the acoustics of buildings
and give their remedies. ( March 2009 03 marks)
Or
State any five factors affecting the acoustics of the building and
give at least two remedies for each. (March 2009 marks 05)
Or
Give four factors which affect acoustics of building.
( June 2010 1 marks)
Or
Explain the various factors affecting the acoustics of building and
give their remedies. (04 january 2010)
Or
Explain factor affecting acoustics of the building. (03 June 2009)

Ans: 06:
The various factors affecting the acoustics of building with their
remedies are as under.
1. Reverberation Time.
2. Loudness.
3. Echo.
4. Echelon effect.
5. Resonance.
6. Noise.

(1) Reverberation Time

- Reverberation is the persistence of prolongation of sound in a hall even
after the source stopped to produce it.
- The reverberation time is the time taken by the sound to fall below the
minimum audibility level.
- In order to have a good acoustics effect, the reverberation time has to be
maintained at optimum value, if the reverberation time is to small,
Theloudness becomes inadequate. As a result, the sound may not reach the
listener.

- Remedies

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- (1) By providing window and openings.
- (2) By having full capacity of audience in the hall or room.
- (3) By using heavy curtains with folds.
- (4) By covering the floor with carpets.
- (5) By decorative the walls with beautiful pictures.
- (6) By covering the ceiling and walls with good sound absorbing
material like, fiber board, roofing etc.
- The reverberation time is depends on the size of the hall and the quality of
sound.

(2) Loudness

- The uniform distribution of loudness in a hall or a room is an important

factor for satisfactory hearing. The loudness may get reduces due to the
excess of sound absorbing materials used inside the hall or room.
Remedies
If the loudness of sound is not adequate, the loudness can be increased by
adopting the following methods.
- (1) By using suitable absorbents at the place where the feel loudness to be
high. As a result, the distribution of loudness becomes uniform.
- (2) By constructing low ceilings for the reflection of sound towards the
listener.
- (3) By using the large sounding board behind the speaker and facing the
audience.
- (4) By using public address system like loudspeakers.

(3) Echo
- An echo is heard due to reflection of sound from a distant sound reflecting
object.
- If the time interval between the direct sound and reflected sound us less
than 1/15th of a second, the reflected sound is helpful in increasing the
loudness. But, those sounds arriving later than this cause confusion.

GECR/GEN/PHYSICS/PKR/SEM1 & 2 /202425

- Remedy
- An echo can be avoided by covering long distance walls and high ceiling
with suitable sound absorbing material. This prevents the reflection of
sound.

(4) Echelon effect

- It refers to the generation of a new separate sound due to multiple echo’s.
Any regular reflecting surface is said to produce the echelon effect. This
echelon effect affects the quality of the original sound
Remedy
- The remedy to avoid echelon effect is to cover such surfaces with sound
absorbing materials.

(5) Resonance

- Resonance occurs due to matching of frequency. In case, if the window

panels and sections of wooden portions have not been tightly fitted they
may start vibrating creating an extra sound in addition to the sound
produced in the hall or room.
- Remedy
- The resonance may be avoided by fixing the window panels properly. Any
other vibrating object which may produce resonance can be placed over a
suitable sound absorbing material.

(6) Noise
- The hall or room should be properly insulated from external and internal
noises.
- In general, there are three types of noises.
- A. airborne noise
- B. structure borne noise
- C. inside noise
- Remedies

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- The hall can be made air conditioned. By using doors and windows with
separate frames having proper sound insulating material between them.

REQUIRMENT OF GOOD ACOUSTICS CONDITIONS

a hall or an auditorium is said to be acoustically good if they satisfy the
following conditions.
a. The quality of the sound is uniform throughout the entire hall.
b. There should not be any overlapping of sound.
c. The loudness of the sound is uniform throughout the hall.
d. The presence or absence of audience can not affect the quality of
sound.
e. Resonance effect should be avoided.
f. The hall should have a proper reverberation time.
g. The external noise should not disturb quality of sound inside
the hall or auditorium.
h. There should not be echelon effect.

Note: Acoustic Grating method is not added. And examples…..Thanks

GECR/GEN/PHYSICS/PKR/SEM1 & 2 /202425