resounance of sound,generation of sound waves,propogation of sound

1. •All sound sources have M A S S and E L A S T I C I T Y.
•Sound needs a medium, it cannot propagate in a vacuum.
•Medium (e.g. air molecules) also have M A S S and E L A S T I C I T Y.
•Speed of Sound determined by the properties of the Medium, not by Frequency or Amplitude
Sound source

2. Generation of Sound Waves:
Sound waves are generated by any vibrating body.
For example :
1.when a violin string vibrates upon being bowed or plucked, its
movement in one direction pushes the molecules of the air before it,
crowding them together in its path. When it moves back again past its
original position and on to the other side, it leaves behind it a nearly
empty space.
2.Generation of sound in Drums:

3. Propagation of Sound:
* When sound is generated in a place, it can move or spread in all direction
by air is called as propagation of sound.
some of the sound propagation principles:
 The propagation of sound energy through a media
via sound waves i.e. compression and rarefaction of
sound waves.
 The propagation of sound depends up on the
frequency of sound source and the capacity of
listener ear drum.
 The propagation of sound depends up on the
weather conditions like air temperature, presence of
moisture, air velocity etc.
 The propagation of sound depends up on the
topographical features like ground cover, hills and
obstacles between the source and receivers, type of
space like open or closed.

4. Propagation of sound:

5. Transmission of sound:
Transmission of sound in building design refers
to a number of processes by which sound can
be transferred from one part of a building to
another. Typically these are:
*Airborne transmission
*Impact transmission
*Flanking transmission
*Impact transmission:
A typical example would be the sound of
footsteps in a room being heard in a room
below.
*Flanking transmission:
*Airborne transmission:

6. Reception of Sound :
In order to hear a sound, the auditory system must accomplish three basic tasks.
First, it must deliver the acoustic stimulus to the receptors; second, it must convert
the stimulus from pressure changes into electrical signals; and third, it must process
these electrical signals so that they can efficiently indicate the qualities of the sound
source, such as frequency (pitch), amplitude (loudness, volume), and location.
The human ear can be divided into three functional segments:
The outer ear: collects sound energy from the environment and sends it to the
eardrum
The middle ear: transduces the mechanical pressure signals from the ear drum into
electrical signals
The inner ear: interprets the electrical signals from the middle ear using hair cells

7. Frequency :
The number of cycles per second (Hertz) (abbreviated as, hz) of anything that
oscillates is called the "frequency". The electricity of an AC wall outlet is said to
have a frequency of 60 Hertz as it cycles negative then positive 60 times each
second.
*A low frequency sound has a low pitch, like the rumble of a big truck.
*A high-frequency sound has a high pitch, like a whistle or siren.

8. Wavelength of Sound:
It is the distance a sound wave traveling during one cycle of vibration or
wavelength is the distance between adjacent regions where identical conditions of
particle displacement occur.
For example:
*sound will scatter (bounce) off a flat object that is several wavelengths long in a
specular (mirror-like) manner. If the object is much smaller than a wavelength, the
sound will simply flow around it as if it were not there.
*If we observe the behaviour of water waves we can clearly see this behaviour.
Ocean waves will pass by small rocks in their path with little change, but will
reflect off a long breakwater or similar barrier.
*Bats, which use echolocation to find their prey, must
transmit frequencies as high as 100,000 Hz to scatter off a 2 mm (0.1 in) mosquito.

9. shows typical values of the wavelength of
sound in air at various frequencies.

10. f = 1 ÷ T
T = 1 ÷ f
f = frequency
[Number of Oscillations per Second]
T = Period
[Time taken to complete one Cycle]
P E R I O D a n d F R E Q U E N C Y
W A V E L E N G T H a n d F R E Q U E N C Y
WL = 340 ÷ f
f = 340 ÷ WL
WL = Length of Sound Wave
340 = Speed of Sound per Second
[Variables such as atmosphere,
humidity, temperature, and medium
(e.g., gas, liquid, solid) can affect
speed of sound]

11. Velocity of Sound:
*The speed at which the sound travels is called as velocity of sound Velocity of
sound primarily depends on the elasticity and density of the medium.
*The velocity of sound
depends upon nature and
temperature of medium
through which it travels.
The velocity of sound can
be measured by meter per
second. See the velocity of
sound through different
medium given bellow.

12. Sound intensity :
Sound intensity also known as acoustic intensity is defined as the sound power
per unit area. The SI unit of sound intensity is the watt per square metre(W/m2).
The usual context is the noise measurement of sound intensity in the air at a
listener's location as a sound energy quantity.
Sound intensity, denoted I, is defined by
where p is the sound pressure; v is the particle velocity.

13. Inverse square law:
For a spherical sound wave, the intensity in the radial direction as
a function of distance r from the centre of the sphere is given by
where
P is the sound power;
A(r) is the area of a sphere of radius r.
Thus sound intensity decreases as 1/r2 from the centre of the
sphere:
This relationship is an inverse square law.

14. Invers square law
F R E E F I E L D
S O U N D
F I E L D
•Any acoustic field that is
free of reflective surfaces
•The sound pressure will
decrease 6.02 dB for
every doubling of distance
•Any field that has reflective
surfaces.
•Virtually all acoustic fields
are sound fields.
•The inverse square law
doesn’t hold because of
reflection and diffraction of
sound waves.
*An Anechoic Chamber is commonly used to
conduct acoustics experiments in nominally
"free field" conditions

15. INVERSE SQUARE LAW

16. WAVE TERMINOLOGIES X - AXIS Y - AXIS
Time
• Period
Amplitude
• Peak to peak
• Peak
Wave Length
Sine wave period

17. Decibel :
The decibel (dB) is a logarithmic unit used to express the ratio of two
values of a physical quantity, often power or intensity. One of these
values is often a standard reference value, in which case the decibel is
used to express the level of the other value relative to this reference. The
number of decibels is ten times the logarithm to base 10 of the ratio of
two power quantities or of the ratio of the squares of two field
amplitude quantities. One decibel is one tenth of one bel, named in
honour of Alexander Graham Bell; however, the bel is seldom used.

19. Decibel addition:
You can either use logarithmic calculators to add together two decibel values or
you can use this table of corrections as described below. For noises that are more
than 10 dB apart the addition of the lower level to the higher one will have a
negligible effect on the resultant level so can be ignored. Corrections are shown for
two noises up to 15 dB apart in the table below.
Example :
One machine on its own measures 84 dB(A) at a certain position. At the same
position a second machine measures 79 dB on its own. What will the effect be of
measuring both noises at the same time?
Method :
Difference between the two noise levels is 5 dB so the correction from the table
below is 1.2 dB. Add this to the higher noise level so the overall measured level for
both machines running at the same time will be 85.2 dB.

21. Decibel subtraction:
You can either use logarithmic calculators to subtract two noise levels or you can
use the following table of corrections. The table below shows the corrections for
differences between noise levels up to 15 dB apart.
Example :
When trying to establish what the level is of a piece of noisy equipment it is
difficult to measure it without all the background being present. A solution is to
measure the noise levels with the background only and then with the
background and the noise source switched on and running. Subtracting the
background level from the total level will give the level of the noisy piece of
equipment on its own. Total noise level is 85 dB and the background alone is 78
dB.
Method :
The difference between the total noise level and the background noise level
alone is 7 dB. Therefore, the difference to be subtracted from the higher total
noise is 1 dB, which makes the true noise of the equipment to be 84 dB on its
own.

23. LAW OF INERTIA: (Newton’s 1st Law of Motion)
•Everybody continues its state of motion or
rest in absence of an external force
•It is the tendency of objects to keep moving
in a straight line at constant linear velocity
ELASTICITY:
•Tendency of solid materials to return to
their original shape after being deformed
FORCE:
•Any influence that causes an object to
undergo a certain change, either
concerning its movement, direction, or
geometrical construction
DAMPING:
•An influence within or upon an oscillatory
system that has the effect of reducing,
restricting or preventing its oscillations