This document discusses acoustics and ultrasonics. It begins by defining acoustics and listing some of its applications in engineering fields. Sound is classified based on frequency into infrasound, audible sound, and ultrasound. Musical sounds are defined as pleasing sounds produced by instruments, while noise produces unpleasant sounds. Sabine's reverberation formula is explained, which gives the reverberation time based on room volume, absorption coefficient, and surface area. The absorption coefficient of a material is defined. Factors affecting building acoustics like reverberation time, loudness, echo, and resonance are also mentioned.

1. Miss Krishna Pathak-17
Miss Honey Mangukiya-18
Mr. Nikhil Bohra-19
Mr. Mahek Pavthawala-20
Miss Shruti Vankawala-21
Mr. Shivam Kumar-22
Miss Prexa Vasia-23
Chapter 3 Acoustics & Ultrasonic
Sarvajanik Collage of Engineering &
Tecnology,Surat

2. Introduction , Classification and
Characteristics Of Sound
 Acoustics is the science of sound which deals with the
properties of sound waves , their origin , propagation
and their action on obstacles.
 Acoustics are applied in all fields. Some of the
important applications in field of engineering are
electro engineering , instruments acoustics &
architectural acoustics.
 Architectural acoustics deals with the design &
construction of music halls & sound recording to
provide audible sound to the audience.
 Sound is an sensible vibration that can detect by
human ears.

3. Introduction , Classification and
Characteristics Of Sound
 On basis of frequency f sound waves are classified
into three types :
1. Infrasound (f < 20 Hz)
2. Audible Sound ( 20 Hz< f < 20 kHz )
3. Ultrasound ( f > 20 kHz)
 Infrasound is which sound having frequencies less
than 20 Hz which is not audible .
 Audible sound is which sound have frequencies in
between of 20 Hz & 20 kHz which is audible by
human ears.
 Ultrasound is which sound have frequencies greater
than 20 kHz which is not audible.

4. Classification Of Sound
 The audible sound is generally classified into two
categories :
1. Musical Sound
2. Noise
 Musical Sound : Which audible sound have
pleasing effect on ears are musical sounds. Like
sound produce by musical instruments as guitar ,
sitar , piano , violin , flute , etc .

5. Classification Of Sound
 Noise : Which audible sound produce a
unpleasant sound & has bad effect on ears is
noise . Like sound produced by the flying
aeroplane , road traffic , cracker , etc .

6. Sabine’s Reverberation Formula
 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.
 The reverberation time is given by
T = 0.167V
EaS
Where V is the volume of the hall.
a is the absorption coefficient.
S is the surface area.

7. Introduction Of Absorption
Coefficient
 The sound absorption coefficient ‘ a ’ of a
material is defined as the ratio of sound energy
absorbed by it to the total sound energy incident
on it.
Absorption Coefficient = Sound energy absorbed by the surface
Total sound energy incident on it
 It is defined as the reciprocal of the area of the
sound absorbing material which absorbs the same
amount of sound energy as that of 1 square
meter of an open window.

8. Factors Affecting Acoustics Of Building And
Their Remedies
 The various factors affecting the acoustics of building such
as reverberation time , loudness , focusing , echo , echelon
effect , resonance & noise with their remedies are
explained below .