SlideShare a Scribd company logo
Architectural Acoustics
Dr. Priyanka Tabhane
Classical ray theory/Growth of a sound intensity in
live room
• If a source of sound is operated continuously, it is
seen that only absorption either in the medium or at
the surrounding surface, will prevent the intensity
from becoming infinitely large.
• In a small or a medium sized enclosure absorption in
the medium is negligible so that both the rate at
which acoustic intensity increases and its final
magnitude are controlled by absorption power of the
bonding surface.
• If the absorptive power is large, intensity quickly
reaches its ultimate value.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• On the other hand if the absorptive power is small the
growth is slow and considerable time will pass on
before the ultimate intensity is attained. Such types of
room are known as live rooms. A live room has a long
reverberation time and a dead room has a short
reverberation time.
• When the source of sound is started in a live
room, reflection at the wall produce a sound energy
distribution that become more and more uniform with
increasing time.
• If the source of the sound is pure tone of just one
frequency, a standing wave pattern may be set up in
the room and large fluctuations in the intensity will
then be observed from point to point.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Now, we will derive the relationship between energy
flow or intensity and energy density for such energy
distributed sound energy.
Consider figure (a) in which ΔS is an element of wall
surface and dV is an element of volume in the medium
at distance r from ΔS where r makes an angle θ with
normal to ΔS.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Let, average acoustic energy density be ‘E’ which is
assumed to be throughout the region.
∴ Acoustic energy present in dV = EdV.
The surface area of sphere of radius r surrounding
dV=4 π r2
Projected area of ‘ΔS’ on any portion of this sphere
= ΔS cos θ
∴
ΔS cos θ
4 π r2 = fraction of energy in ‘dV’ that will strike
‘ΔS’ by direct transmission.
∴ energy from ‘dV’ that strikes directly ‘ΔS’
is ΔE = EdVΔS cos θ
4 π r2 -----------(1)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Now assume that, figure (b) the volume element ‘dV’ is a
part of hemispherical shape of radius ‘r’ and thickness ‘dr’
centred upon ‘ΔS’.
The acoustic energy ‘ΔE’ Contributed to ‘ΔS’ by this entire
shell can be obtained by considering the energy is arrives
from any direction with equal probability ie. by considering
circular zone of radius ‘rsinθ’ , for which θ is constant and
then integrating over the entire surface of the shell.
Now the volume ‘dV’ of this zone is, dV= 2 πr sinθ rdrdθ
And so that integration from θ=0 to π/2, gives
ΔE=
EΔSdr
2 0
π/2
sin θ cos θ dθ
ΔE=
EΔSdr
4
------(2)
∵ 0
π/2
sin θ cos θ dθ = ½
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Since this energy arrives during the time interval
Δt= dr/c, the rate at which sound energy falls on ‘ΔS’ from all
direction is
ΔE/Δt = EcΔS/4 --------(3)
= (Ec/4) x per unit area
Therefore, the intensity ‘I’ of such diffuse sound at walls =
I= Ec/4 -------(4)
Now if α1, α2 .... are the respective absorption coefficient
representing the fraction of randomly incident energy
absorbed by the different materials of areas S1, S2… forming
the interior walls of the room as well as any other absorbing
surface.
Therefore, rate at which the energy is being absorbed by the
surfaces = (Ec/4) x (α1 S1 + α2 S2+ …)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Defining total absorption A of a live room as
A= ∑ α1 S1 + α2 S2+ …
∴ Rate of absorption is
𝐸𝑐𝐴
4
------ (5)
equation (5) give rate at which sound energy is absorbed
at bounding surfaces of the room.
If V (dE/dt) is the rate at which the absorption of sound
increases in the medium throughout the interior of the
room and ‘W’ is the rate at which the sound is being
produced.
Then the fundamental differential equation governing the
growth of sound energy E in a live room can be given as
𝑉
𝑑𝐸
𝑑𝑡
+
𝐴𝑐𝐸
4
= 𝑊 −−−− −(6)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
assuming the sound source to have been started at time
t=0
the solution of equation (6) is
𝐸 =
4𝑊
𝐴𝑐
1 − 𝑒−
𝐴𝑐𝑡
4𝑉 −−− −--(7)
therefore equation (4) becomes
𝐼 =
𝑊
𝐴
1 − 𝑒−
𝐴𝑐𝑡
4𝑉 ---------(8)
E in terms of mean square acoustic pressure ‘P2’ Can be
given as
E =
𝑃2
𝜌𝑐2 i.e. 𝑃2 = 𝐸𝜌𝑐2
i.e. 𝑃2 =
4𝑊𝜌𝑐
𝐴
1 − 𝑒−
𝐴𝑐𝑡
4𝑉 ------------(9)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
If ‘A’ is small the time constant is large And relatively long
time will be required for the intensity to approach its
ultimate/final/maximum value. ie.
I∞ =
𝑊
𝐴
⸫ Ultimate value of energy density will become
E∞ =
4𝑊
𝐴𝑐
—---(10)
and the ultimate value of mean square pressure will be
P∞ =
4𝑊𝜌𝑐
𝐴
equation (10) indicates that final energy density is
independent of volume and shape of the hall but depends
only on total absorption A.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Decay of sound in live room
The Decay of uniformly distributed diffused sound in a
live room can be obtained by considering that the
source of sound has been stopped and therefore by
considering that the rate at which sound energy Is
being produced in the hall W=0.
In equation
𝑉
𝑑𝐸
𝑑𝑡
+
𝐴𝑐𝐸
4
= 𝑊
𝑉
𝑑𝐸
𝑑𝑡
+
𝐴𝑐𝐸
4
= 0 ------------(1)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
assuming that the source is shut off at time t = 0 and letting
E0 represents assumed uniformly distributed energy density. At
this instant as t increases solution
𝐸 = 𝐸0 𝑒−
𝐴𝑐𝑡
4𝑉 ------------(2)
similarly the intensity at any time t is related to initial intensity
I0
𝐼 = 𝐼0 𝑒−
𝐴𝑐𝑡
4𝑉 —-----------------(3)
now considering change in intensity level in dB
∆𝐼𝐿 = 10 𝐿𝑜𝑔
𝐼
𝐼0
= 10 Log 𝑒−
𝐴𝑐𝑡
4𝑉
∆𝐼𝐿 = −
1.087 𝐴𝑐𝑡
𝑉
------(4)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
The intensity level in a live room and correspondingly
the sound pressure level decreases with elapsed time
at constant decay rate D in decibel per second can be
given as
𝐷 =
1.087 𝐴𝑐𝑡
𝑉
----------(5)
Defining reverberation time T according to Sabine
as, time required for a level of sound in a room to
decay by 60 dB, then
𝑇 =
60
𝐷
=
60𝑉
1.087𝐴𝑐
=
55.2𝑉
𝐴𝑐
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Expressing the volume ‘V’ in cubic meters, area ‘S’ in square
meters, ‘A’ in Sabine and using ‘c’ velocity of sound in fluid
343m/s, above equation becomes,
𝑇 =
0.161 𝑉
𝐴
-------(6)
In English units, expressing the volume ‘V’ in feet, area ‘S’ in
square feet , ‘A’ in Sabine and using ‘c’ velocity of sound in
fluid 1125ft/s, above equation becomes,
𝑇 =
0.049 𝑉
𝐴
Equation 6 clears that reverberation time is directly
proportional to volume of hall V and is inversely
proportional to total absorption in the hall A. Reverberation
time T of a live room can be calculated at once if its volume
and total absorption are known.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Further RT can be changed by insertion or
removal of absorptive materials at the walls
and so the magnitude of RT of a live room is
subject to precise control.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Decay of sound in dead room
• In equation of RT, 𝑇 =
0.161 𝑉
𝐴
-----1, of a live room it
was assumed that the number of reflections
occurring during the growth or decay of sound as
well as fractional amount of energy reflected at each
reflection was sufficient to provide uniform energy
density distribution.
• The equation for growth and decay of sound in live
room are not applicable to dead room where
absorption coefficient of the materials is unity. In
dead rooms the reflected energy must be zero.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
The only energy present is that of direct wave diverging
from sound source. Under these conditions RT must be
zero whereas eq 1 gives finite value of 0.161V/S where
S is the area of interior surface of room. Similarly, this
eq also gives incorrect results as the average sound
absorption coefficient exceeds 0.2.
A new approach to this problem was given by Eyring,
who considered the multiplicity of reflections from the
walls as equivalent to set of image sources, all of which
come into existence as real source starts.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
The increase in acoustic energy at any point then consists
of accumulation of successive increment from true
source, first order reflection images whose strengths are
(1-α) .W, second order reflection images whose strengths
are (1- α)2 .W, etc until all the image sources of any
appreciable strength have made their contribution.
The decay in energy, when the true source in the room
stopped, results from successive losses of acoustic
radiation first from the source, then from first order
images, then the second order images etc. the equation
for growth in acoustic energy density can be given as,
𝐸 =
4𝑊
−𝑐𝑆 ln(1−∝)
1 − exp
𝑐𝑆 ln(1−∝)
4𝑉
-------(2)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
In equation 2, total room absorption is given by ,
A = -S ln(1 −∝) -------3
Where ln(1 −∝) is the absorption coefficient and S is
total area of interior surface of room.
The eq for decay of sound energy in such room is given by
𝐸 = 𝐸0 exp
𝑐𝑆 ln(1 −∝) 𝑡
4𝑉
−−−− −(4)
The decay rate in dB per second is given by
𝐷 = −
1.087 𝑐𝑆 ln(1−∝)
𝑉
-------------(5)
RT for such dead room is expressed as
𝑇 = −
0.161 𝑉
𝑆 ln(1−∝)
----------- (6)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Measurement of Reverberation time
Reverberation time of an enclosure is the time in
seconds required to reduce the intensity from a level
60 DB above the threshold of audibility
𝑇 =
0.161𝑉
𝐴
Where V= volume of the hall
A= total capability of absorbing acoustic energy or total
absorption A= ∑ (α1S1 + α2S2 + ….)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
The derivation of reverberation time is based on the
concept of ray acoustic in which sound energy from
source in the room is assume to travel outward from
source along diverging rays. At each encounter with
boundaries of the room, rays are partially reflected and
partially absorbed.
After large number of successive reflections of the
sound in the room may be assumed to become diffused
i.e. average energy density E is then same throughout
the entire volume of the hall and all directions of
propagation are equally probable.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
When a simple source of sound is present in an
enclosed space, sound rays originating from the
source are partially reflected each time they strike
the walls and consequently waves proceeding
along direct sound ray to any particular point in the
room are followed by multitude of reflected rays. It
is assumed that phases and amplitude of these
reflected rays are randomly distributed and cancel
out due to negligible destructive interference. For
any given enclosure, intensity gain is proportional
to reverberation time.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Hence, large reverberation time is desirable if the
source of sound is to be audible everywhere.
• if a sound source is now shut off, the reception
of sound by direct ray path ceases after the
lapse of short time interval, t = d/c, where d is
the distance from source to point of
observation and c if the velocity of sound in
air. Reflected wave continue to be received in the
form of rapid succession of randomly oriented
waves of gradually decreasing intensity.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Sound absorption materials and their uses
Common building materials absorb sound only to a small
extent.
Therefore, to meet the acoustical demands, materials with
better sound absorption property are to be incorporated in
the halls.
Such materials having more capacity to absorb the incident
sound are called absorbent or acoustical materials.
In general, the acoustical materials are soft and porous.
They work on the principle that the sound waves penetrate
into the pores and the sound energy is converted into other
forms of energy.
The absorbing capacity of the material depends upon the
thickness of the material, its density and on the frequency of
the incident sound waves.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Sound absorbers can be broadly classified as porous materials,
resonant panels, cavity resonators and composite types
Porous material:
• Frictional losses contribute to absorption in porous materials. The
sound waves cause the air particles to vibrate down in the pores
and the resulting losses converts some of the sound energy into
heat energy.
• Materials like tiles plaster, wood, carpets, wool are Porous within
viscous losses converts a caustic energy into heat.
• The absorption in such material is strong function of frequency.
• absorption power increases with increasing material thickness.
• Low frequency absorption can be increased by mounting the
material away from the wall.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Resonant panels:
• Non perforated panels of wood, pressed wood fibres, and
plastic etc., comprise diaphragm type of absorber. They are
mounted on solid backing but are separated from it by air
space.
• When sound wave impinge on the panel, the panel vibrates
under the influence of an incident sound and panel
converts some of incident acoustic energy into heat.
• These absorbers are effective at low frequencies. addition
of Porous absorbers in space between panel and the wall
increases efficiency of low-frequency absorbers.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
University of Lowa, United State
Cavity resonator (Helmholtz resonator):
• Cavity resonator consists of confined volume of air connected
to the room by narrow opening.
• It acts as Helmholtz resonator, absorbing efficiently in narrow
band of frequencies near its resonance.
• These absorbers may be in the form of individual element
such as concrete block with slotted cavity.
• Other form consists of perforated panels and wood lattices
spaced away from solid backing with absorption blanket in
between.
• A perforated panel is equivalent to a great number of
acoustically resonant systems.
• It can be designed to absorb sound of any frequency.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Composite absorbers:
This category combine the function of above three
absorbers.
They of a perforated panel fixed over an air space
containing a porous absorber.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Effective absorption coefficients
Values also depend on mounting and thickness of material
Application of sound absorbers
Reverberation control
One of the main application of sound absorbing material is to
reduce reflected sound energy in the room and reduce the
reverberation and sound level. The amount of reverberation in the
space depends on the size of the room and amount of sound
absorption. This kind of absorber is commonly used in restaurants
and railway station to increase speech intelligibility by reducing the
noise.
Noise reduction in factories & large rooms
Other application of sound absorber is to control noise level in
working environment or factories to protect the hearing loss of the
workers by adding SAM on the walls or by putting ear plugs or
heavy headphones on the ears of workers. The noise exposure is
decreased to save level of human ear. The treatment method to
solve this problem is to reduce the RT with in the space.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Noise control in critical listening space
Resonant and Helmholtz absorbers are used for mass spring
system with damping to provide absorption at resonant frequency
of the system. Eg. Narrow short openings in the large room or
storage area or mills with the hanging propeller.
Echo controlling auditorium and lecture hall
Echo’s are heard due to the phenomenon of reflection of sound
waves. To hear the echo clearly the reflection object must be more
than 17.2 mts away from the source. SAM are commonly used to
absorb the late arriving reflected sound in the auditorium. A late
arriving reflected sound appears as an echo if its level is above
reverberation level. By adding sound absorbing material in
auditorium and lecture hall one can optimally reduce the echo in
audience area.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Absorption in sound insulation
Porous absorbers are commonly used to prevent a resonance of
air cavity of light weight construction based on partition with an
air gap. This will provide sound insulation building system to
protect noise entering the room.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Public Address System PAS
Music Sound System for auditorium
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
1. Howlround
One of the most obvious faults in public address system is that
they are too loud, improvement is often possible by turning
down the loudspeaker volume, this makes listening more
tolerable to public and also reduces risk of howl round.
Howlround is caused by acoustic feedback energy from the
loudspeaker to microphone or energy returned by reflections
from the walls of the hall. The sound from the loudspeakers
should not reach microphone. It may result in loud howling
sound.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
2. Selection of Microphone:
While installing a public address system direct activity pattern of
the microphone, position of the loudspeaker and reflectivity of
the walls should be kept in mind. A directional microphone is
much more useful than Omni directional one. Modern moving
coil, cardioid are specially designed for public address work. In
using cardioids, the loudspeaker should be placed in front of the
platform raised above the head of the audience and tilted so
that the sound is directed on the centre of the audience
area. This not only put the sound where it is wanted but the
audience due to their clothing absorbs sound energy and it helps
to prevent feedback. But if the loudspeaker output cannot be
raised to a sufficient level without instability, the reflectivity of
the walls should be considered.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• In many halls the walls are so hard plastered that it gives no
absorption at all. If possible some heavy curtains or similar
material should be hung over a fair amount of all surfaces.
• When the audience is present in an auditorium, there are
several difficulties. Firstly the audience have to be able to
hear what is happening near the microphone. Secondly in
many types of program it is necessary to pick up reaction of
audience and this means slinging microphone overheads of
the audience with the risk of howl round. Use of audience
microphone can reduce this to a minimum.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
3.Distribution of Sound Intensity: Instead of installing one or
two powerful loudspeakers near the stage alone, audio power
should be divided between several loudspeakers to spread it
right up to the farthest point. This covers every specified area.
• Directional loudspeakers- The sound radiated from the
loudspeaker can be confined to a narrow angle that can avoid
sound finding its way back to the microphone or on to the
walls. Distribution of sound from ordinary loudspeaker
mounted on a cabinet is very dependent on the
frequency. The variation of directivity of frequency is
a drawback to good public address system. The distribution
of frequency can cause trouble due to howlround. By using
several loud speakers high frequency can be distributed more
evenly over a wider area. This could also reduce the possibility
of howlround and the distribution of sound will be more even.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Line source loudspeakers-
line source loudspeakers consists of
series of loudspeakers mounted in the
line or immediately adjusted to each
other so that they can form a column
facing in one direction. This is the
immediate improvement to increase the
direct sound reaching the audience and
to reduce the reverberant sound.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Orientation of speakers: The loudspeakers should be oriented
as to direct the sound towards the audience and not towards
walls. The loudspeakers should preferably be placed a meter
off the floor, so that their axes are about the height of the
ears of the listeners.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Reverberation (Echo): Install several small power
loudspeakers at various points to get rid of problem of
overlapping of sound waves in the auditorium, rather than
using single power high power unit. There are two major
faults with many public address systems, the tendency of
instability or howl round and lack of intelligibility.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Impedance Matching: Matching of total loudspeaker
impedance with output impedance of amplifier is necessary
for maximum transfer of energy from amplifier to
loudspeakers.
• Frequency shift: PAS in the room or hall act as a coupling
between loudspeaker and the microphone. The amount of
shift given to the loudspeaker is 2-3 cycles and achieved by
using modulation technique so that the output signal is same
as input signal but is slightly shifted in frequency. The level of
loudspeaker output can be raised by several decibels before
howlround occurs.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Grounding: Chassis, shields of equipment's, and coaxial cables
should be properly earthed.
• Ambient Noise: Use noise cancellation microphones to
eliminate ambient noise.
• Intelligibility: The loudspeakers should not be located beyond
16 meter apart, 10 meter separation is considered quite well.
If they are more than 16 meter apart, the delayed sound from
loudspeakers impairs intelligibility, when delay is 45 ms or
more.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
PA system for an Auditorium Having Large Capacity:
• Loudspeaker system, wide range 40-120db (20 – 16 kHz).
• Columns of loudspeakers with good bass & treble response
should be mounted facing the front on either side of stage.
• If hall is wide, a small column may also be mounted in the
centre of the front line.
• Another pair of small columns, slightly inclined may be placed
at about 1/3 then 2/3 down the hall from front.
• A separate mixer unit is desirable, with tape/CD player and at
least six microphone inputs. The amplifier should be 50-100W.
Standby amplifier is desirable.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Underwater acoustics
Velocity of sound in sea water
In fresh water velocity of sound is a function of temperature only while
in sea water two additional factors influence the velocity of sound .
Salinity and change in pressure associated with changes in depth are
important factors that affect the velocity of sound in sea water. Each of
these factors tends to increase the velocity and their composite effect is
being represented by empirical formula
c = 1449+ 4.6t +0.055t2 + 0.0003 t3 + (1.39 – 0.012t)(S-3S)+0.017 d
where
c – velocity in m/s
t – temperature of water in oC
S- salinity in parts per 1000
d- depth below the surface in meters.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• Above equation is accurate to within about 1m/s for those
condition of temperature, salinity and pressure commonly
occurring in various oceans.
• Velocity of sound in surface sea water having temperature
13oC and salinity of 35 parts per thousand is 1449m/s as
contrasted with 1403m/s for fresh water under similar
condition of temperature and pressure.
• Density of sea water having pressure, temperature and
salinity given above is 1024kg/m3 and the corresponding
standard characteristics impedance ρo = 1.54x106 kg/m2s.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Sound Transmission losses in sea water
If the water composing the oceans were both unbounded and
homogeneous, only absorption and divergence would contribute
to decrease in pressure level as a sound beam propagates away
from its source. Let us consider that a wave diverging spherically
in such a medium maybe represented by equation
P2=P1(r1/r2)e-α(r2-r1) --------(1)
Where P2 and P1 are acoustic pressure measured respectively at
the distance r2 and r1 from apparent centre of origin of wave and
α is absorption constant of medium. On applying 20 log to both
sides of equation (1)
20 log P2 = 20 log P1 + 20 log (r1/r2) – 8.7 α (r2-r1)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Replacing ‘8.7α’ by ‘a’ absorption constant in Decibel per meter
and rearranging above equation we get
20 log P1 - 20 log P2 = 20 log (r2/r1) + a (r2 - r1) -------(2)
Now let us define transmission loss ‘H’ as decrease in sound
pressure level as wave is propagated from r1 to r2.
LHS of equation 2 represents transmission loss in decibel that is
H = 20 log (r2/r1) + a (r2 - r1)
referring transmission losses to given distance ‘r’ as being
relative to sound pressure level existing at 1m from the effective
centre of sound source. The sound transmission losses from
reference distance of 1 m to any distance ‘r’ is then given by
H = 20 log r + a r ----------(3)
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
Curve showing dependence of transmission loss on distance and frequency at 50C.
• Inspection of curve A shows that at low frequency of 1 kHz,
the entire transmission loss is caused by spherical divergence
of sound beam.
• However, as the frequency range increases curve B, at
frequency of 3 kHz, and curve C, at frequency of 10 kHz,
shows that absorption loss become greater and greater.
• Low frequencies must be used if sound energy is to be
transmitted through sea water to great distance with
minimum transmission loss.
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University
• When sound transmission loss measurements are made in
ocean, they are frequently observed to be at considerable
variance.
• Factors contributing to this variance includes additional
divergence or partial convergence caused by
refraction, destructive and constructive interference associated
with multipath types of propagation including reflections from
the surface and the bottom of the sea, diffraction and
scattering caused by presence of in homogeneities in water.
• The oceans are so variable in their characteristics that it is
customary is to lump together contributions of above factors
into a single term ‘A’, known as transmission anomaly.
• The total transmission loss in decibel is then given
• H = 20 log r + a r + A
Dr. Priyanka Tabhane
Department of Physics,
RTM Nagpur University

More Related Content

Similar to Architectural acoustics, underwater acoustics

Ultrasound
UltrasoundUltrasound
Ultrasound
alanssari277
 
Black Body Radiation
Black Body RadiationBlack Body Radiation
Black Body Radiation
M.G. College, Armori
 
Beth Baguley-Learning Objective-LO4-Feb 22nd
Beth Baguley-Learning Objective-LO4-Feb 22ndBeth Baguley-Learning Objective-LO4-Feb 22nd
Beth Baguley-Learning Objective-LO4-Feb 22nd
Beth Baguley
 
Beth Baguley - Learning Objective - Feb 22nd - LO4
Beth Baguley - Learning Objective - Feb 22nd - LO4Beth Baguley - Learning Objective - Feb 22nd - LO4
Beth Baguley - Learning Objective - Feb 22nd - LO4
Beth Baguley
 
Paper einstein
Paper einsteinPaper einstein
Paper einstein
Ricardo Alonso
 
Thermal radiation presentation
Thermal radiation presentationThermal radiation presentation
Thermal radiation presentation
rajan prasad
 
Chapter 6 Lecture- Electrons in Atoms
Chapter 6 Lecture- Electrons in AtomsChapter 6 Lecture- Electrons in Atoms
Chapter 6 Lecture- Electrons in Atoms
Mary Beth Smith
 
Fundamentals of modern physics
Fundamentals of modern physicsFundamentals of modern physics
Fundamentals of modern physics
Praveen Vaidya
 
Fundamental of Noise.ppt
Fundamental of Noise.pptFundamental of Noise.ppt
Fundamental of Noise.ppt
SharanabasappaDegoan
 
1 black body
1 black body1 black body
1 black body
Atanu Kat
 
MET 214 Module 8
MET 214 Module 8MET 214 Module 8
MET 214 Module 8
Ibrahim AboKhalil
 
Noise 2.0
Noise 2.0Noise 2.0
Noise 2.0
bhavyaw
 
Laser and its applications1
Laser and its applications1Laser and its applications1
Laser and its applications1
rahulbarfi
 
Optical Spectroscopy
Optical SpectroscopyOptical Spectroscopy
Optical Spectroscopy
cdtpv
 
Medical Equipment Section1
Medical Equipment Section1Medical Equipment Section1
Medical Equipment Section1
cairo university
 
Noise presentation.pptx
Noise presentation.pptxNoise presentation.pptx
Noise presentation.pptx
SaadiAlNaseri
 
Ch 7 physical optics final
Ch 7 physical optics finalCh 7 physical optics final
Ch 7 physical optics final
animesh samundh
 
Basic physics of ultrasound.JH
Basic physics of ultrasound.JHBasic physics of ultrasound.JH
Basic physics of ultrasound.JH
hari baskar
 
sound level meter octave band ananlyser.pptx
sound level meter octave band ananlyser.pptxsound level meter octave band ananlyser.pptx
sound level meter octave band ananlyser.pptx
priyankatabhane
 
WavesStatistics.pdf
WavesStatistics.pdfWavesStatistics.pdf
WavesStatistics.pdf
cfisicaster
 

Similar to Architectural acoustics, underwater acoustics (20)

Ultrasound
UltrasoundUltrasound
Ultrasound
 
Black Body Radiation
Black Body RadiationBlack Body Radiation
Black Body Radiation
 
Beth Baguley-Learning Objective-LO4-Feb 22nd
Beth Baguley-Learning Objective-LO4-Feb 22ndBeth Baguley-Learning Objective-LO4-Feb 22nd
Beth Baguley-Learning Objective-LO4-Feb 22nd
 
Beth Baguley - Learning Objective - Feb 22nd - LO4
Beth Baguley - Learning Objective - Feb 22nd - LO4Beth Baguley - Learning Objective - Feb 22nd - LO4
Beth Baguley - Learning Objective - Feb 22nd - LO4
 
Paper einstein
Paper einsteinPaper einstein
Paper einstein
 
Thermal radiation presentation
Thermal radiation presentationThermal radiation presentation
Thermal radiation presentation
 
Chapter 6 Lecture- Electrons in Atoms
Chapter 6 Lecture- Electrons in AtomsChapter 6 Lecture- Electrons in Atoms
Chapter 6 Lecture- Electrons in Atoms
 
Fundamentals of modern physics
Fundamentals of modern physicsFundamentals of modern physics
Fundamentals of modern physics
 
Fundamental of Noise.ppt
Fundamental of Noise.pptFundamental of Noise.ppt
Fundamental of Noise.ppt
 
1 black body
1 black body1 black body
1 black body
 
MET 214 Module 8
MET 214 Module 8MET 214 Module 8
MET 214 Module 8
 
Noise 2.0
Noise 2.0Noise 2.0
Noise 2.0
 
Laser and its applications1
Laser and its applications1Laser and its applications1
Laser and its applications1
 
Optical Spectroscopy
Optical SpectroscopyOptical Spectroscopy
Optical Spectroscopy
 
Medical Equipment Section1
Medical Equipment Section1Medical Equipment Section1
Medical Equipment Section1
 
Noise presentation.pptx
Noise presentation.pptxNoise presentation.pptx
Noise presentation.pptx
 
Ch 7 physical optics final
Ch 7 physical optics finalCh 7 physical optics final
Ch 7 physical optics final
 
Basic physics of ultrasound.JH
Basic physics of ultrasound.JHBasic physics of ultrasound.JH
Basic physics of ultrasound.JH
 
sound level meter octave band ananlyser.pptx
sound level meter octave band ananlyser.pptxsound level meter octave band ananlyser.pptx
sound level meter octave band ananlyser.pptx
 
WavesStatistics.pdf
WavesStatistics.pdfWavesStatistics.pdf
WavesStatistics.pdf
 

More from priyankatabhane

Speech, hearing, noise, intelligibility.pptx
Speech, hearing, noise, intelligibility.pptxSpeech, hearing, noise, intelligibility.pptx
Speech, hearing, noise, intelligibility.pptx
priyankatabhane
 
Microphone- characteristics,carbon microphone, dynamic microphone.pptx
Microphone- characteristics,carbon microphone, dynamic microphone.pptxMicrophone- characteristics,carbon microphone, dynamic microphone.pptx
Microphone- characteristics,carbon microphone, dynamic microphone.pptx
priyankatabhane
 
Loudspeaker- direct radiating type and horn type.pptx
Loudspeaker- direct radiating type and horn type.pptxLoudspeaker- direct radiating type and horn type.pptx
Loudspeaker- direct radiating type and horn type.pptx
priyankatabhane
 
Environmental acoustics- noise criteria.pptx
Environmental acoustics- noise criteria.pptxEnvironmental acoustics- noise criteria.pptx
Environmental acoustics- noise criteria.pptx
priyankatabhane
 
Environmental Acoustics- Speech interference level, acoustics calibrator.pptx
Environmental Acoustics- Speech interference level, acoustics calibrator.pptxEnvironmental Acoustics- Speech interference level, acoustics calibrator.pptx
Environmental Acoustics- Speech interference level, acoustics calibrator.pptx
priyankatabhane
 
Fundamentals of Ultrasonic waves and applications
Fundamentals of Ultrasonic waves and applicationsFundamentals of Ultrasonic waves and applications
Fundamentals of Ultrasonic waves and applications
priyankatabhane
 
ultrasonics.pptx
ultrasonics.pptxultrasonics.pptx
ultrasonics.pptx
priyankatabhane
 
Lec 4 digital electronics - interated circuit technology -characteristics o...
Lec 4   digital electronics - interated circuit technology -characteristics o...Lec 4   digital electronics - interated circuit technology -characteristics o...
Lec 4 digital electronics - interated circuit technology -characteristics o...
priyankatabhane
 
Lec 3 digital electronics- read only memory
Lec 3  digital electronics- read only memoryLec 3  digital electronics- read only memory
Lec 3 digital electronics- read only memory
priyankatabhane
 
Lec 2 digital electronics - random access memory
Lec 2  digital electronics - random access memoryLec 2  digital electronics - random access memory
Lec 2 digital electronics - random access memory
priyankatabhane
 
Lec 1 digital electroinics - memory array, write read operations
Lec 1   digital electroinics - memory array, write read operationsLec 1   digital electroinics - memory array, write read operations
Lec 1 digital electroinics - memory array, write read operations
priyankatabhane
 

More from priyankatabhane (11)

Speech, hearing, noise, intelligibility.pptx
Speech, hearing, noise, intelligibility.pptxSpeech, hearing, noise, intelligibility.pptx
Speech, hearing, noise, intelligibility.pptx
 
Microphone- characteristics,carbon microphone, dynamic microphone.pptx
Microphone- characteristics,carbon microphone, dynamic microphone.pptxMicrophone- characteristics,carbon microphone, dynamic microphone.pptx
Microphone- characteristics,carbon microphone, dynamic microphone.pptx
 
Loudspeaker- direct radiating type and horn type.pptx
Loudspeaker- direct radiating type and horn type.pptxLoudspeaker- direct radiating type and horn type.pptx
Loudspeaker- direct radiating type and horn type.pptx
 
Environmental acoustics- noise criteria.pptx
Environmental acoustics- noise criteria.pptxEnvironmental acoustics- noise criteria.pptx
Environmental acoustics- noise criteria.pptx
 
Environmental Acoustics- Speech interference level, acoustics calibrator.pptx
Environmental Acoustics- Speech interference level, acoustics calibrator.pptxEnvironmental Acoustics- Speech interference level, acoustics calibrator.pptx
Environmental Acoustics- Speech interference level, acoustics calibrator.pptx
 
Fundamentals of Ultrasonic waves and applications
Fundamentals of Ultrasonic waves and applicationsFundamentals of Ultrasonic waves and applications
Fundamentals of Ultrasonic waves and applications
 
ultrasonics.pptx
ultrasonics.pptxultrasonics.pptx
ultrasonics.pptx
 
Lec 4 digital electronics - interated circuit technology -characteristics o...
Lec 4   digital electronics - interated circuit technology -characteristics o...Lec 4   digital electronics - interated circuit technology -characteristics o...
Lec 4 digital electronics - interated circuit technology -characteristics o...
 
Lec 3 digital electronics- read only memory
Lec 3  digital electronics- read only memoryLec 3  digital electronics- read only memory
Lec 3 digital electronics- read only memory
 
Lec 2 digital electronics - random access memory
Lec 2  digital electronics - random access memoryLec 2  digital electronics - random access memory
Lec 2 digital electronics - random access memory
 
Lec 1 digital electroinics - memory array, write read operations
Lec 1   digital electroinics - memory array, write read operationsLec 1   digital electroinics - memory array, write read operations
Lec 1 digital electroinics - memory array, write read operations
 

Recently uploaded

Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...
Sérgio Sacani
 
Holsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdf
Holsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdfHolsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdf
Holsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdf
frank0071
 
gastroretentive drug delivery system-PPT.pptx
gastroretentive drug delivery system-PPT.pptxgastroretentive drug delivery system-PPT.pptx
gastroretentive drug delivery system-PPT.pptx
Shekar Boddu
 
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...
PsychoTech Services
 
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆
Sérgio Sacani
 
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptx
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptxTOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptx
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptx
shubhijain836
 
Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...
Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...
Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...
frank0071
 
BIOTRANSFORMATION MECHANISM FOR OF STEROID
BIOTRANSFORMATION MECHANISM FOR OF STEROIDBIOTRANSFORMATION MECHANISM FOR OF STEROID
BIOTRANSFORMATION MECHANISM FOR OF STEROID
ShibsekharRoy1
 
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Compositions of iron-meteorite parent bodies constrainthe structure of the pr...
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...
Sérgio Sacani
 
Microbiology of Central Nervous System INFECTIONS.pdf
Microbiology of Central Nervous System INFECTIONS.pdfMicrobiology of Central Nervous System INFECTIONS.pdf
Microbiology of Central Nervous System INFECTIONS.pdf
sammy700571
 
AJAY KUMAR NIET GreNo Guava Project File.pdf
AJAY KUMAR NIET GreNo Guava Project File.pdfAJAY KUMAR NIET GreNo Guava Project File.pdf
AJAY KUMAR NIET GreNo Guava Project File.pdf
AJAY KUMAR
 
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...
Creative-Biolabs
 
23PH301 - Optics - Unit 1 - Optical Lenses
23PH301 - Optics  -  Unit 1 - Optical Lenses23PH301 - Optics  -  Unit 1 - Optical Lenses
23PH301 - Optics - Unit 1 - Optical Lenses
RDhivya6
 
23PH301 - Optics - Unit 2 - Interference
23PH301 - Optics - Unit 2 - Interference23PH301 - Optics - Unit 2 - Interference
23PH301 - Optics - Unit 2 - Interference
RDhivya6
 
Reaching the age of Adolescence- Class 8
Reaching the age of Adolescence- Class 8Reaching the age of Adolescence- Class 8
Reaching the age of Adolescence- Class 8
abhinayakamasamudram
 
LEARNING TO LIVE WITH LAWS OF MOTION .pptx
LEARNING TO LIVE WITH LAWS OF MOTION .pptxLEARNING TO LIVE WITH LAWS OF MOTION .pptx
LEARNING TO LIVE WITH LAWS OF MOTION .pptx
yourprojectpartner05
 
Polycythemia vera_causes_disorders_treatment.pptx
Polycythemia vera_causes_disorders_treatment.pptxPolycythemia vera_causes_disorders_treatment.pptx
Polycythemia vera_causes_disorders_treatment.pptx
muralinath2
 
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at  𝐳 = 2.9  wi...Discovery of An Apparent Red, High-Velocity Type Ia Supernova at  𝐳 = 2.9  wi...
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...
Sérgio Sacani
 
HUMAN EYE By-R.M Class 10 phy best digital notes.pdf
HUMAN EYE By-R.M Class 10 phy best digital notes.pdfHUMAN EYE By-R.M Class 10 phy best digital notes.pdf
HUMAN EYE By-R.M Class 10 phy best digital notes.pdf
Ritik83251
 
Farming systems analysis: what have we learnt?.pptx
Farming systems analysis: what have we learnt?.pptxFarming systems analysis: what have we learnt?.pptx
Farming systems analysis: what have we learnt?.pptx
Frédéric Baudron
 

Recently uploaded (20)

Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...
 
Holsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdf
Holsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdfHolsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdf
Holsinger, Bruce W. - Music, body and desire in medieval culture [2001].pdf
 
gastroretentive drug delivery system-PPT.pptx
gastroretentive drug delivery system-PPT.pptxgastroretentive drug delivery system-PPT.pptx
gastroretentive drug delivery system-PPT.pptx
 
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...
 
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆
 
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptx
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptxTOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptx
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptx
 
Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...
Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...
Juaristi, Jon. - El canon espanol. El legado de la cultura española a la civi...
 
BIOTRANSFORMATION MECHANISM FOR OF STEROID
BIOTRANSFORMATION MECHANISM FOR OF STEROIDBIOTRANSFORMATION MECHANISM FOR OF STEROID
BIOTRANSFORMATION MECHANISM FOR OF STEROID
 
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Compositions of iron-meteorite parent bodies constrainthe structure of the pr...
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...
 
Microbiology of Central Nervous System INFECTIONS.pdf
Microbiology of Central Nervous System INFECTIONS.pdfMicrobiology of Central Nervous System INFECTIONS.pdf
Microbiology of Central Nervous System INFECTIONS.pdf
 
AJAY KUMAR NIET GreNo Guava Project File.pdf
AJAY KUMAR NIET GreNo Guava Project File.pdfAJAY KUMAR NIET GreNo Guava Project File.pdf
AJAY KUMAR NIET GreNo Guava Project File.pdf
 
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...
 
23PH301 - Optics - Unit 1 - Optical Lenses
23PH301 - Optics  -  Unit 1 - Optical Lenses23PH301 - Optics  -  Unit 1 - Optical Lenses
23PH301 - Optics - Unit 1 - Optical Lenses
 
23PH301 - Optics - Unit 2 - Interference
23PH301 - Optics - Unit 2 - Interference23PH301 - Optics - Unit 2 - Interference
23PH301 - Optics - Unit 2 - Interference
 
Reaching the age of Adolescence- Class 8
Reaching the age of Adolescence- Class 8Reaching the age of Adolescence- Class 8
Reaching the age of Adolescence- Class 8
 
LEARNING TO LIVE WITH LAWS OF MOTION .pptx
LEARNING TO LIVE WITH LAWS OF MOTION .pptxLEARNING TO LIVE WITH LAWS OF MOTION .pptx
LEARNING TO LIVE WITH LAWS OF MOTION .pptx
 
Polycythemia vera_causes_disorders_treatment.pptx
Polycythemia vera_causes_disorders_treatment.pptxPolycythemia vera_causes_disorders_treatment.pptx
Polycythemia vera_causes_disorders_treatment.pptx
 
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at  𝐳 = 2.9  wi...Discovery of An Apparent Red, High-Velocity Type Ia Supernova at  𝐳 = 2.9  wi...
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...
 
HUMAN EYE By-R.M Class 10 phy best digital notes.pdf
HUMAN EYE By-R.M Class 10 phy best digital notes.pdfHUMAN EYE By-R.M Class 10 phy best digital notes.pdf
HUMAN EYE By-R.M Class 10 phy best digital notes.pdf
 
Farming systems analysis: what have we learnt?.pptx
Farming systems analysis: what have we learnt?.pptxFarming systems analysis: what have we learnt?.pptx
Farming systems analysis: what have we learnt?.pptx
 

Architectural acoustics, underwater acoustics

  • 2. Classical ray theory/Growth of a sound intensity in live room • If a source of sound is operated continuously, it is seen that only absorption either in the medium or at the surrounding surface, will prevent the intensity from becoming infinitely large. • In a small or a medium sized enclosure absorption in the medium is negligible so that both the rate at which acoustic intensity increases and its final magnitude are controlled by absorption power of the bonding surface. • If the absorptive power is large, intensity quickly reaches its ultimate value. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 3. • On the other hand if the absorptive power is small the growth is slow and considerable time will pass on before the ultimate intensity is attained. Such types of room are known as live rooms. A live room has a long reverberation time and a dead room has a short reverberation time. • When the source of sound is started in a live room, reflection at the wall produce a sound energy distribution that become more and more uniform with increasing time. • If the source of the sound is pure tone of just one frequency, a standing wave pattern may be set up in the room and large fluctuations in the intensity will then be observed from point to point. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 4. Now, we will derive the relationship between energy flow or intensity and energy density for such energy distributed sound energy. Consider figure (a) in which ΔS is an element of wall surface and dV is an element of volume in the medium at distance r from ΔS where r makes an angle θ with normal to ΔS. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 5. Let, average acoustic energy density be ‘E’ which is assumed to be throughout the region. ∴ Acoustic energy present in dV = EdV. The surface area of sphere of radius r surrounding dV=4 π r2 Projected area of ‘ΔS’ on any portion of this sphere = ΔS cos θ ∴ ΔS cos θ 4 π r2 = fraction of energy in ‘dV’ that will strike ‘ΔS’ by direct transmission. ∴ energy from ‘dV’ that strikes directly ‘ΔS’ is ΔE = EdVΔS cos θ 4 π r2 -----------(1) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 6. Now assume that, figure (b) the volume element ‘dV’ is a part of hemispherical shape of radius ‘r’ and thickness ‘dr’ centred upon ‘ΔS’. The acoustic energy ‘ΔE’ Contributed to ‘ΔS’ by this entire shell can be obtained by considering the energy is arrives from any direction with equal probability ie. by considering circular zone of radius ‘rsinθ’ , for which θ is constant and then integrating over the entire surface of the shell. Now the volume ‘dV’ of this zone is, dV= 2 πr sinθ rdrdθ And so that integration from θ=0 to π/2, gives ΔE= EΔSdr 2 0 π/2 sin θ cos θ dθ ΔE= EΔSdr 4 ------(2) ∵ 0 π/2 sin θ cos θ dθ = ½ Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 7. Since this energy arrives during the time interval Δt= dr/c, the rate at which sound energy falls on ‘ΔS’ from all direction is ΔE/Δt = EcΔS/4 --------(3) = (Ec/4) x per unit area Therefore, the intensity ‘I’ of such diffuse sound at walls = I= Ec/4 -------(4) Now if α1, α2 .... are the respective absorption coefficient representing the fraction of randomly incident energy absorbed by the different materials of areas S1, S2… forming the interior walls of the room as well as any other absorbing surface. Therefore, rate at which the energy is being absorbed by the surfaces = (Ec/4) x (α1 S1 + α2 S2+ …) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 8. Defining total absorption A of a live room as A= ∑ α1 S1 + α2 S2+ … ∴ Rate of absorption is 𝐸𝑐𝐴 4 ------ (5) equation (5) give rate at which sound energy is absorbed at bounding surfaces of the room. If V (dE/dt) is the rate at which the absorption of sound increases in the medium throughout the interior of the room and ‘W’ is the rate at which the sound is being produced. Then the fundamental differential equation governing the growth of sound energy E in a live room can be given as 𝑉 𝑑𝐸 𝑑𝑡 + 𝐴𝑐𝐸 4 = 𝑊 −−−− −(6) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 9. assuming the sound source to have been started at time t=0 the solution of equation (6) is 𝐸 = 4𝑊 𝐴𝑐 1 − 𝑒− 𝐴𝑐𝑡 4𝑉 −−− −--(7) therefore equation (4) becomes 𝐼 = 𝑊 𝐴 1 − 𝑒− 𝐴𝑐𝑡 4𝑉 ---------(8) E in terms of mean square acoustic pressure ‘P2’ Can be given as E = 𝑃2 𝜌𝑐2 i.e. 𝑃2 = 𝐸𝜌𝑐2 i.e. 𝑃2 = 4𝑊𝜌𝑐 𝐴 1 − 𝑒− 𝐴𝑐𝑡 4𝑉 ------------(9) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 10. If ‘A’ is small the time constant is large And relatively long time will be required for the intensity to approach its ultimate/final/maximum value. ie. I∞ = 𝑊 𝐴 ⸫ Ultimate value of energy density will become E∞ = 4𝑊 𝐴𝑐 —---(10) and the ultimate value of mean square pressure will be P∞ = 4𝑊𝜌𝑐 𝐴 equation (10) indicates that final energy density is independent of volume and shape of the hall but depends only on total absorption A. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 11. Decay of sound in live room The Decay of uniformly distributed diffused sound in a live room can be obtained by considering that the source of sound has been stopped and therefore by considering that the rate at which sound energy Is being produced in the hall W=0. In equation 𝑉 𝑑𝐸 𝑑𝑡 + 𝐴𝑐𝐸 4 = 𝑊 𝑉 𝑑𝐸 𝑑𝑡 + 𝐴𝑐𝐸 4 = 0 ------------(1) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 12. assuming that the source is shut off at time t = 0 and letting E0 represents assumed uniformly distributed energy density. At this instant as t increases solution 𝐸 = 𝐸0 𝑒− 𝐴𝑐𝑡 4𝑉 ------------(2) similarly the intensity at any time t is related to initial intensity I0 𝐼 = 𝐼0 𝑒− 𝐴𝑐𝑡 4𝑉 —-----------------(3) now considering change in intensity level in dB ∆𝐼𝐿 = 10 𝐿𝑜𝑔 𝐼 𝐼0 = 10 Log 𝑒− 𝐴𝑐𝑡 4𝑉 ∆𝐼𝐿 = − 1.087 𝐴𝑐𝑡 𝑉 ------(4) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 13. The intensity level in a live room and correspondingly the sound pressure level decreases with elapsed time at constant decay rate D in decibel per second can be given as 𝐷 = 1.087 𝐴𝑐𝑡 𝑉 ----------(5) Defining reverberation time T according to Sabine as, time required for a level of sound in a room to decay by 60 dB, then 𝑇 = 60 𝐷 = 60𝑉 1.087𝐴𝑐 = 55.2𝑉 𝐴𝑐 Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 14. Expressing the volume ‘V’ in cubic meters, area ‘S’ in square meters, ‘A’ in Sabine and using ‘c’ velocity of sound in fluid 343m/s, above equation becomes, 𝑇 = 0.161 𝑉 𝐴 -------(6) In English units, expressing the volume ‘V’ in feet, area ‘S’ in square feet , ‘A’ in Sabine and using ‘c’ velocity of sound in fluid 1125ft/s, above equation becomes, 𝑇 = 0.049 𝑉 𝐴 Equation 6 clears that reverberation time is directly proportional to volume of hall V and is inversely proportional to total absorption in the hall A. Reverberation time T of a live room can be calculated at once if its volume and total absorption are known. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 15. • Further RT can be changed by insertion or removal of absorptive materials at the walls and so the magnitude of RT of a live room is subject to precise control. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 16. Decay of sound in dead room • In equation of RT, 𝑇 = 0.161 𝑉 𝐴 -----1, of a live room it was assumed that the number of reflections occurring during the growth or decay of sound as well as fractional amount of energy reflected at each reflection was sufficient to provide uniform energy density distribution. • The equation for growth and decay of sound in live room are not applicable to dead room where absorption coefficient of the materials is unity. In dead rooms the reflected energy must be zero. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 17. The only energy present is that of direct wave diverging from sound source. Under these conditions RT must be zero whereas eq 1 gives finite value of 0.161V/S where S is the area of interior surface of room. Similarly, this eq also gives incorrect results as the average sound absorption coefficient exceeds 0.2. A new approach to this problem was given by Eyring, who considered the multiplicity of reflections from the walls as equivalent to set of image sources, all of which come into existence as real source starts. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 18. The increase in acoustic energy at any point then consists of accumulation of successive increment from true source, first order reflection images whose strengths are (1-α) .W, second order reflection images whose strengths are (1- α)2 .W, etc until all the image sources of any appreciable strength have made their contribution. The decay in energy, when the true source in the room stopped, results from successive losses of acoustic radiation first from the source, then from first order images, then the second order images etc. the equation for growth in acoustic energy density can be given as, 𝐸 = 4𝑊 −𝑐𝑆 ln(1−∝) 1 − exp 𝑐𝑆 ln(1−∝) 4𝑉 -------(2) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 19. In equation 2, total room absorption is given by , A = -S ln(1 −∝) -------3 Where ln(1 −∝) is the absorption coefficient and S is total area of interior surface of room. The eq for decay of sound energy in such room is given by 𝐸 = 𝐸0 exp 𝑐𝑆 ln(1 −∝) 𝑡 4𝑉 −−−− −(4) The decay rate in dB per second is given by 𝐷 = − 1.087 𝑐𝑆 ln(1−∝) 𝑉 -------------(5) RT for such dead room is expressed as 𝑇 = − 0.161 𝑉 𝑆 ln(1−∝) ----------- (6) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 20. Measurement of Reverberation time Reverberation time of an enclosure is the time in seconds required to reduce the intensity from a level 60 DB above the threshold of audibility 𝑇 = 0.161𝑉 𝐴 Where V= volume of the hall A= total capability of absorbing acoustic energy or total absorption A= ∑ (α1S1 + α2S2 + ….) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 21. The derivation of reverberation time is based on the concept of ray acoustic in which sound energy from source in the room is assume to travel outward from source along diverging rays. At each encounter with boundaries of the room, rays are partially reflected and partially absorbed. After large number of successive reflections of the sound in the room may be assumed to become diffused i.e. average energy density E is then same throughout the entire volume of the hall and all directions of propagation are equally probable. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 22. When a simple source of sound is present in an enclosed space, sound rays originating from the source are partially reflected each time they strike the walls and consequently waves proceeding along direct sound ray to any particular point in the room are followed by multitude of reflected rays. It is assumed that phases and amplitude of these reflected rays are randomly distributed and cancel out due to negligible destructive interference. For any given enclosure, intensity gain is proportional to reverberation time. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 23. • Hence, large reverberation time is desirable if the source of sound is to be audible everywhere. • if a sound source is now shut off, the reception of sound by direct ray path ceases after the lapse of short time interval, t = d/c, where d is the distance from source to point of observation and c if the velocity of sound in air. Reflected wave continue to be received in the form of rapid succession of randomly oriented waves of gradually decreasing intensity. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 24. Sound absorption materials and their uses Common building materials absorb sound only to a small extent. Therefore, to meet the acoustical demands, materials with better sound absorption property are to be incorporated in the halls. Such materials having more capacity to absorb the incident sound are called absorbent or acoustical materials. In general, the acoustical materials are soft and porous. They work on the principle that the sound waves penetrate into the pores and the sound energy is converted into other forms of energy. The absorbing capacity of the material depends upon the thickness of the material, its density and on the frequency of the incident sound waves. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 25. Sound absorbers can be broadly classified as porous materials, resonant panels, cavity resonators and composite types Porous material: • Frictional losses contribute to absorption in porous materials. The sound waves cause the air particles to vibrate down in the pores and the resulting losses converts some of the sound energy into heat energy. • Materials like tiles plaster, wood, carpets, wool are Porous within viscous losses converts a caustic energy into heat. • The absorption in such material is strong function of frequency. • absorption power increases with increasing material thickness. • Low frequency absorption can be increased by mounting the material away from the wall. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 26. Resonant panels: • Non perforated panels of wood, pressed wood fibres, and plastic etc., comprise diaphragm type of absorber. They are mounted on solid backing but are separated from it by air space. • When sound wave impinge on the panel, the panel vibrates under the influence of an incident sound and panel converts some of incident acoustic energy into heat. • These absorbers are effective at low frequencies. addition of Porous absorbers in space between panel and the wall increases efficiency of low-frequency absorbers. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 27. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University University of Lowa, United State
  • 28. Cavity resonator (Helmholtz resonator): • Cavity resonator consists of confined volume of air connected to the room by narrow opening. • It acts as Helmholtz resonator, absorbing efficiently in narrow band of frequencies near its resonance. • These absorbers may be in the form of individual element such as concrete block with slotted cavity. • Other form consists of perforated panels and wood lattices spaced away from solid backing with absorption blanket in between. • A perforated panel is equivalent to a great number of acoustically resonant systems. • It can be designed to absorb sound of any frequency. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 29. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 30. Composite absorbers: This category combine the function of above three absorbers. They of a perforated panel fixed over an air space containing a porous absorber. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 31. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University Effective absorption coefficients Values also depend on mounting and thickness of material
  • 32. Application of sound absorbers Reverberation control One of the main application of sound absorbing material is to reduce reflected sound energy in the room and reduce the reverberation and sound level. The amount of reverberation in the space depends on the size of the room and amount of sound absorption. This kind of absorber is commonly used in restaurants and railway station to increase speech intelligibility by reducing the noise. Noise reduction in factories & large rooms Other application of sound absorber is to control noise level in working environment or factories to protect the hearing loss of the workers by adding SAM on the walls or by putting ear plugs or heavy headphones on the ears of workers. The noise exposure is decreased to save level of human ear. The treatment method to solve this problem is to reduce the RT with in the space. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 33. Noise control in critical listening space Resonant and Helmholtz absorbers are used for mass spring system with damping to provide absorption at resonant frequency of the system. Eg. Narrow short openings in the large room or storage area or mills with the hanging propeller. Echo controlling auditorium and lecture hall Echo’s are heard due to the phenomenon of reflection of sound waves. To hear the echo clearly the reflection object must be more than 17.2 mts away from the source. SAM are commonly used to absorb the late arriving reflected sound in the auditorium. A late arriving reflected sound appears as an echo if its level is above reverberation level. By adding sound absorbing material in auditorium and lecture hall one can optimally reduce the echo in audience area. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 34. Absorption in sound insulation Porous absorbers are commonly used to prevent a resonance of air cavity of light weight construction based on partition with an air gap. This will provide sound insulation building system to protect noise entering the room. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 35. Public Address System PAS Music Sound System for auditorium Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 36. 1. Howlround One of the most obvious faults in public address system is that they are too loud, improvement is often possible by turning down the loudspeaker volume, this makes listening more tolerable to public and also reduces risk of howl round. Howlround is caused by acoustic feedback energy from the loudspeaker to microphone or energy returned by reflections from the walls of the hall. The sound from the loudspeakers should not reach microphone. It may result in loud howling sound. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 37. 2. Selection of Microphone: While installing a public address system direct activity pattern of the microphone, position of the loudspeaker and reflectivity of the walls should be kept in mind. A directional microphone is much more useful than Omni directional one. Modern moving coil, cardioid are specially designed for public address work. In using cardioids, the loudspeaker should be placed in front of the platform raised above the head of the audience and tilted so that the sound is directed on the centre of the audience area. This not only put the sound where it is wanted but the audience due to their clothing absorbs sound energy and it helps to prevent feedback. But if the loudspeaker output cannot be raised to a sufficient level without instability, the reflectivity of the walls should be considered. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 38. • In many halls the walls are so hard plastered that it gives no absorption at all. If possible some heavy curtains or similar material should be hung over a fair amount of all surfaces. • When the audience is present in an auditorium, there are several difficulties. Firstly the audience have to be able to hear what is happening near the microphone. Secondly in many types of program it is necessary to pick up reaction of audience and this means slinging microphone overheads of the audience with the risk of howl round. Use of audience microphone can reduce this to a minimum. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 39. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 40. 3.Distribution of Sound Intensity: Instead of installing one or two powerful loudspeakers near the stage alone, audio power should be divided between several loudspeakers to spread it right up to the farthest point. This covers every specified area. • Directional loudspeakers- The sound radiated from the loudspeaker can be confined to a narrow angle that can avoid sound finding its way back to the microphone or on to the walls. Distribution of sound from ordinary loudspeaker mounted on a cabinet is very dependent on the frequency. The variation of directivity of frequency is a drawback to good public address system. The distribution of frequency can cause trouble due to howlround. By using several loud speakers high frequency can be distributed more evenly over a wider area. This could also reduce the possibility of howlround and the distribution of sound will be more even. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 41. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 42. • Line source loudspeakers- line source loudspeakers consists of series of loudspeakers mounted in the line or immediately adjusted to each other so that they can form a column facing in one direction. This is the immediate improvement to increase the direct sound reaching the audience and to reduce the reverberant sound. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 43. • Orientation of speakers: The loudspeakers should be oriented as to direct the sound towards the audience and not towards walls. The loudspeakers should preferably be placed a meter off the floor, so that their axes are about the height of the ears of the listeners. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 44. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 45. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 46. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 47. • Reverberation (Echo): Install several small power loudspeakers at various points to get rid of problem of overlapping of sound waves in the auditorium, rather than using single power high power unit. There are two major faults with many public address systems, the tendency of instability or howl round and lack of intelligibility. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 48. • Impedance Matching: Matching of total loudspeaker impedance with output impedance of amplifier is necessary for maximum transfer of energy from amplifier to loudspeakers. • Frequency shift: PAS in the room or hall act as a coupling between loudspeaker and the microphone. The amount of shift given to the loudspeaker is 2-3 cycles and achieved by using modulation technique so that the output signal is same as input signal but is slightly shifted in frequency. The level of loudspeaker output can be raised by several decibels before howlround occurs. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 49. • Grounding: Chassis, shields of equipment's, and coaxial cables should be properly earthed. • Ambient Noise: Use noise cancellation microphones to eliminate ambient noise. • Intelligibility: The loudspeakers should not be located beyond 16 meter apart, 10 meter separation is considered quite well. If they are more than 16 meter apart, the delayed sound from loudspeakers impairs intelligibility, when delay is 45 ms or more. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 50. PA system for an Auditorium Having Large Capacity: • Loudspeaker system, wide range 40-120db (20 – 16 kHz). • Columns of loudspeakers with good bass & treble response should be mounted facing the front on either side of stage. • If hall is wide, a small column may also be mounted in the centre of the front line. • Another pair of small columns, slightly inclined may be placed at about 1/3 then 2/3 down the hall from front. • A separate mixer unit is desirable, with tape/CD player and at least six microphone inputs. The amplifier should be 50-100W. Standby amplifier is desirable. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 51. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 52. Underwater acoustics Velocity of sound in sea water In fresh water velocity of sound is a function of temperature only while in sea water two additional factors influence the velocity of sound . Salinity and change in pressure associated with changes in depth are important factors that affect the velocity of sound in sea water. Each of these factors tends to increase the velocity and their composite effect is being represented by empirical formula c = 1449+ 4.6t +0.055t2 + 0.0003 t3 + (1.39 – 0.012t)(S-3S)+0.017 d where c – velocity in m/s t – temperature of water in oC S- salinity in parts per 1000 d- depth below the surface in meters. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 53. • Above equation is accurate to within about 1m/s for those condition of temperature, salinity and pressure commonly occurring in various oceans. • Velocity of sound in surface sea water having temperature 13oC and salinity of 35 parts per thousand is 1449m/s as contrasted with 1403m/s for fresh water under similar condition of temperature and pressure. • Density of sea water having pressure, temperature and salinity given above is 1024kg/m3 and the corresponding standard characteristics impedance ρo = 1.54x106 kg/m2s. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 54. Sound Transmission losses in sea water If the water composing the oceans were both unbounded and homogeneous, only absorption and divergence would contribute to decrease in pressure level as a sound beam propagates away from its source. Let us consider that a wave diverging spherically in such a medium maybe represented by equation P2=P1(r1/r2)e-α(r2-r1) --------(1) Where P2 and P1 are acoustic pressure measured respectively at the distance r2 and r1 from apparent centre of origin of wave and α is absorption constant of medium. On applying 20 log to both sides of equation (1) 20 log P2 = 20 log P1 + 20 log (r1/r2) – 8.7 α (r2-r1) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 55. Replacing ‘8.7α’ by ‘a’ absorption constant in Decibel per meter and rearranging above equation we get 20 log P1 - 20 log P2 = 20 log (r2/r1) + a (r2 - r1) -------(2) Now let us define transmission loss ‘H’ as decrease in sound pressure level as wave is propagated from r1 to r2. LHS of equation 2 represents transmission loss in decibel that is H = 20 log (r2/r1) + a (r2 - r1) referring transmission losses to given distance ‘r’ as being relative to sound pressure level existing at 1m from the effective centre of sound source. The sound transmission losses from reference distance of 1 m to any distance ‘r’ is then given by H = 20 log r + a r ----------(3) Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 56. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University Curve showing dependence of transmission loss on distance and frequency at 50C.
  • 57. • Inspection of curve A shows that at low frequency of 1 kHz, the entire transmission loss is caused by spherical divergence of sound beam. • However, as the frequency range increases curve B, at frequency of 3 kHz, and curve C, at frequency of 10 kHz, shows that absorption loss become greater and greater. • Low frequencies must be used if sound energy is to be transmitted through sea water to great distance with minimum transmission loss. Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University
  • 58. • When sound transmission loss measurements are made in ocean, they are frequently observed to be at considerable variance. • Factors contributing to this variance includes additional divergence or partial convergence caused by refraction, destructive and constructive interference associated with multipath types of propagation including reflections from the surface and the bottom of the sea, diffraction and scattering caused by presence of in homogeneities in water. • The oceans are so variable in their characteristics that it is customary is to lump together contributions of above factors into a single term ‘A’, known as transmission anomaly. • The total transmission loss in decibel is then given • H = 20 log r + a r + A Dr. Priyanka Tabhane Department of Physics, RTM Nagpur University