Architectural acoustic notes

Architectural Acoustics Notes compiled by Jaikumar Ranganathan,Designer,India Page 1
Architectural Acoustics

Architectural Acoustics
COURSE STRUCTURE:
UNIT I - FUNDAMENTALS
Sound waves, frequency, intensity, Wave length, measure of sound,
decibel scale, speech and music frequencies, human ear characteristics-
tone Structure.
UNIT- II SOUND TRANSMISSION AND ABSORPTION
Outdoor noise levels, acceptable indoor noise levels, sonometer,
determinate of a given building material, absorption co-efficient
and measurements, choice of absorption material, resonance,
reverberation,echo,exercises involving reverberation time and
absorption co-efficient.
UNIT III NOISE CONTROL AND SOUND ABSORPTION
Types of noises, transmission of noise, transmission loss,
noise control and sound insulation, remedial measures and
legislation
UNIT IV CONSTRUCTIONAL MEASURES
Walls/Partitions, floors/ ceilings,windows/doors,fittings and gadjets,
machine mounting and insulation of machinery
UNIT V ACOUSTICS AND BUILDING DESIGN.
Site selection, Shape, Volume, treatment for interior spaces,
basic principles in designing open air theatres, cinemas,
broad casting studios, Concert halls, Class rooms, Lecture halls
and theatres.

Basics in Acoustics
# Acoustics is a branch of physics and is the study of sound
# A scientist who works in the field of acoustics is an acoustician.
The application of acoustics in technology is called acoustical
engineering. There is often much overlap and interaction between
the interests of acousticians and acoustical engineers.
# Acoustics is the science concerned with the production, control,
transmission, reception, and effects of sound. Its origins began
with the study of mechanical vibrations and the radiation of these
vibrations through mechanical waves, and still continues today.
Divisions of Acoustics
* Acoustical measurements and instrumentation
* Acoustic signal processing
* Aeroacoustics: study of aerodynamic sound
* Architectural acoustics: study of sound waves distribution in
variously shaped enclosed or partly enclosed spaces with effects
of sound waves on objects of different shapes which are in their
way.Mostly concentrated on how sound and buildings interact,
including the behavior of sound in concert halls and
* Bioacoustics: study of the use of sound by animals such as whales,
dolphins, bats etc.
* Biomedical acoustics: study of the use of sound in medicine,
for example the use of ultrasound for diagnostic
* Environmental noise: study of the sound propagation in the human
environment, noise health effects and noise mitigation analysis.
* Psychoacoustics: study of subjective reaction of living beings to
sound, hearing, perception, and localization

* Physiological acoustics: study of the mechanical, electrical
and biochemical function of hearing in living organisms. auditoriums but also
in office buildings, factories and homes.
* Physical acoustics: study of the detailed interaction of sound
with materials and fluids and includes, for example,
thermoacoustics (the interaction of sound and heat).
* Speech communication: study of how speech is produced,
the analysis of speech signals and the properties of speech
transmission, storage, recognition and enhancement.
* Structural acoustics and vibration: study of how sound and
mechanical structures interact; for example, the transmission
of sound through walls and the radiation of sound from
vehicle panels.
* Transduction: study of how sound is generated and measured by
loudspeakers, microphones, sonar projectors, hydrophones, ultrasonic
transducers and sensors.
* Ultrasonics: study of high frequency sound, beyond the range of
human hearing.
* Musical acoustics: study of the physics of musical instruments.
* Underwater acoustics: study of the propagation of sound in water.
* Nonlinear Acoustics

Sound
# Sound expresses an auditory sensation passing through
the ear and created by fluctuations in air pressure.
These fluctuations are usually set up by some vibrating
object, for example, the plucked string of a guitar or
a struck tuning fork
# Sound is a disturbance of mechanical energy that
propagates through matter as a wave. Sound is characterized
by the properties of waves, which are frequency, wavelength,
period, amplitude, and speed.
Sound waves
Sound wave motion is created by outward-traveling layers
of compression and rarefaction of the air particles, this is,
by pressure flucuations.
The air particles that transmit sound waves do not change
their normal positions; they vibrate only about their
equilibrium positions,whichpositions when no sound waves
are transmitted.The pressure fluctuations are superimposed
on the more or less steady atmospheric pressure and
are picked up by the ear.

Speed of sound
The speed at which sound travels depends on the medium through
which the waves are passing, and is often quoted as a fundamental
property of the material. In general, the speed of sound is proportional
to the square root of the ratio of the elastic modulus (stiffness) of the
medium and its density. Those physical properties and the speed of
sound change with ambient conditions. For example, the speed of sound
in air and other gases depends on temperature. In air, the speed of sound
is approximately 344 m/s, in water 1500 m/s and in a bar of steel 5000 m/s.
The speed of sound is also slightly sensitive to the sound amplitude,
resulting in nonlinear propagation effects, such as the weak production
of harmonics and the mixing of tones.
Frequency
Sine waves of various frequencies; the bottom waves have higher frequencies
than those above
Frequency is the measurement of the number of occurrences of a
repeated event per unit of time. It is also defined as the rate of change
of phase of a sinusoidal waveform.
Frequency (f) is the number of cycles that the periodic signal
completes in one second. The unit of the frequency is Hz (Hertz)

The upper and the lower limits of the audible frequency range
(generally considered 16 Hz to 20,000 Hz) depend on many factors
such as the setup of the measurements and the age of the listeners.
The human hearing system (the ears and the related perception system in
the brain) is more sensitive to frequencies in the range of 1000 Hz-4000 Hz
The higher the frequency the wider the range. A unit was defined
to describe the concept of these frequency ranges. This unit is
called octave which is the interval between two frequencies
having a ratio of 2:1.
wavelength is the distance betweenrepeating units of a propagating
wave of a given frequency

Sound pressure
The fluctuation in the atmospheric pressure caused by the vibration of
air particles due to a sound wave is called sound Pressure.
Sound pressure level
As the human ear can detect sounds with a very wide range of amplitudes,
sound pressure is often measured as a level on a logarithmic decibel scale.
Sound intensity is defined as the sound power per unit area.
Sound Pressure levels of representative soundsand noises.

The ear consists of three basic parts - the outer ear, the middle ear, and the inner
ear. Each part of the ear serves a specific purpose in the task of detecting and
interpreting sound. The outer ear serves to collect and channel sound to the
middle ear. The middle ear serves to transform the energy of a sound wave into
the internal vibrations of the bone structure of the middle ear and ultimately
transform these vibrations into a compressional wave in the inner ear. The inner
ear serves to transform the energy of a compressional wave within the inner ear
fluid into nerve impulses which can be transmitted to the brain.

Sound Measurement
Laboratory and Field Measurements
Laboratory Measurements
Laboratory measurements are used to determine specific properties of a material
or to make a complete investigation of it in order to establish acoustic data or a
quality standard. They are also used to ensure that the quality of a material or a
sample of building element meets international standards or local
regulations.The test room suite of a laboratory is constructed very carefully to
avoid any possible flanking transmission.Thus,when sound insulation tests are
performed, practically all the energy in the receiving room is transmitted
through the partition under test.

Field Measurements
There are so many possible transmission paths of sound in a building and
so many factors influencing the acoustic quality of the construction that the
only way of determining whether the building meets the legal requirements is
to make measurements "in situ" in the actual building.In most cases, a part
of the sound produced in a room is transmitted indirectly via flanking elements
or acoustic "leaks" into adjacent rooms. The sound insulation of building
elements is therefore generally lower in situ than in the laboratory. Therefore,
care should be taken when selecting building materials to include a safety factor
in the calculation of the forecasted sound insulation of building constructions.

Elimination of Defects
The basic defects attributable to room geometry have been touched in a
previous lecture and consist of echoes, sound concentrations, sound shadowing,
distortions, coupled spaces and room resonance.
1. Echoes
These are probably the most serious and most common defect. They occur
when sound is reflected off a boundary with sufficient magnitude and delay to
be perceived as another sound, distinct from the direct sound. As a rule, if the
delay is greater than 1/25 sec (14m) for speech and 1/12 sec (34m) for music
then that reflection will be a problem.
Solution: Either alter the geometry of the offending
surface or apply absorber or diffusion.
(Flutter and picket fence echoes.)
2. Sound concentration
Sometime referred to as 'hot-spots', these are caused by focussed reflections off
concave surfaces. The intensity of the sound at the focus point is unnaturally
high and always occurs at the expense of other listening areas.
Solution: Treat with absorber or diffusers, better still, redesign
it to focus the sound outside or above the enclosure.
3. Sound shadowing
Most noticeable under a balcony, it is basically the situation where a significant
portion of the reflected sound is blocked by a protrusion that itself doesn't
contribute to the reflected component. In general, avoid balconies with a depth
exceeding twice their height as they will cause problems for the rear-most seats
beneath them.
Solution: Redesign the protruding surface to provide reflected
sound to the affected seats or get rid of the protrusion.

4. Distortions
These occur as a result of wildly varying absorption coefficients at different
frequencies. This applies an undesirable change in the quality and tone
colouration (of frequency distortions) to sound within the enclosure.
Solution: Balance the absorption coefficients of acoustical
finishes over the whole audible range.
5. Coupled spaces
When an auditorium is connected to an adjacent space which has a substantially
different RT, the two rooms will form a coupled space. As long as the airflow is
unrestricted between the two spaces, the decay of the most reverberant space will
be noticeable within the least reverberant. This will be particularly disturbing to
those closest to the interconnection.
Solution: Add some form of acoustic separation (a screen or a door) or match
the RT of both rooms.
6. Room resonance
Room resonance is similar to distortions in that it causes an undesirable tone
colouration, however, room resonance results from particularly emphasised
standing waves, usually within smaller rooms. This is a significant concern when
designing control rooms and recording studios.
Solution: Apply subtle changes in overall shape of the room or find out which
surfaces are contributing and use large sound diffusers.

ACOUSTICS AND BUILDING DESIGN.
Site selection, Shape, Volume, treatment for interior spaces,
basic principles in designing open air theatres, cinemas,
broad casting studios, Concert halls, Class rooms, Lecture halls
and theatres.

Acoustical Requirementsin Auditorium Design
OUTLINE OF ACOUSTICAL REQUIREMENTS
The following are the requirements for good hearing conditions in an auditorium:
 There should be adequate loudness in every part of the auditorium, particularly the
remote seats.
 The sound energy should be uniform distributed (diffused) in the room.
 Optimum reverberation characteristics should be provided in the auditorium to
allow the most favorable reception of the program material by the audience and the
most efficient presentation of the program by the performers.
 The room should be free of such acoustical defects as echos,long-delayed reflections,
flutter echoes, sound concentrations,distortion, sound shadow, and room resonance.
 Noises and vibrations which would interfere with listening or performing should be
excluded or reasonably reduced in every part of the room.
Adequate Loudness
The problem of providing adequate loudness, particularly in Medium-size and large
auditoriums, results from the energy losses of the traveling sound waves and from excessive
absorption by the audience and room contents ( upholstered seats, carpets, draperies,etc).
Sound energy losses can be reduced and adequate loudness can be reduced and adequate
loudness can be provided in the following ways
The auditorium should be shaped so that the adequate is as close to the sound
source as possible,thereby reducing the distance the sound must travel. In larger
auditoriums use of a balcony brings more seats closer to the sound source.

Fan-shaped plan with balcony

Rectangular plan without balcony

The sound source should be raised as much as feasible in order to secure a free flow
of direct sound waves (those traveling directly from the sound source without
reflection) to every listener
When listeners are exposed to ample direct sound waves, loudness benefits
The floor where the audience is seated should be properly ramped, or
raked, because sound is more readily absorbed when it travels over the
audience at gazing incidence.
The gradient along the aisles of sloped auditorium floors should be not
more than 1 in 8; however requirements of local building codes should be
consulted.

The method of raking a auditorium
 Establishing the slope of a floor that simultaneously provides good
vertical sight lines and a satisfactory flow of direct sound waves to the
listeners
 It has been assumed that the arrival point of sight (APS) is located on the
stage floor 4 ft (122 cm) from the edge of the stage. This will usually
result in a floor which is too steep,with the well-known result of excessive
room height. A more gentle slope can be achieved by considering any of
the following compromises.
1) raising the APS to a higher level if this is acceptable
2) Adequate reducing the value of x
3) observing two-row vision (instead of one-row vision, which
permits unobstructed view over the heads of the spectators in
the row immediately ahead) and staggering the seats to allow
a view between the heads of the spectators in the row immediately
in front.
 The usual steep rakes of balconies, applied primarily for visual reasons,
normally create satisfactory conditions for the reception of direct sound
waves.

Properly located ceiling reflectors, with the progressively increasing Sound reflections
towards the remote seats, effectively contribute to Adequate loudness.
 The sound source should be closely and abundantly surrounded with large
sound- reflective surfaces (plaster, gypsum board, plywood, rigid plastic
boards, etc.) in order to supply additional reflected sound energy to every
portion of the audience area, particularly to the remote seats.
 The reflectors must be layed out in such a fashion that the initial time-
delay gap between direct and first reflected sound is relatively short,
possibly not exceeding 30 milliseconds. The angle of the reflective
surfaces must be established by the law of sound reflection

 The floor area and volume of the auditorium should be kept at a
reasonable minimum, thereby shortening the distance that direct and
reflected sounds must travel.
Recommended volume-per-seat values for various types of Auditoriums
Type of Auditorium Volume per audience seat,
Cu ft (Cu m)
Min Opt Max
Room for speech 80(2.3) 110(3.1) 150(4.3)
Concert halls 220(6.2) 275(7.8) 380(10.8)
Multipurpose Auditorium 180(5.1) 250(7.1) 300(8.5)
Motion –Picture theaters 100(2.8) 125(3.5) 180(5.1)
 Parallelism between opposite ( horizontal or vertical) sound-reflective
boundary surfaces, particularly close to the sound source, should be
avoided, to eliminate undesirable back reflections to the sound source.

RECOMMENDATIONS FOR DESIGN OF OPEN AIR THEATRE:
 The site should be carefully selected in view of effects of topographical
and atmospherical conditions (wind,temperature,etc.) and of exterior
noise sources upon the propagation and reception of sound
 The basic shape, size, and capacity of the seating area should be
determined to ensure satisfactory speech intelligibility throughout the
entire audience area. The distance of the seats from the sound source
should be kept at a reasonable minimum, with strict economy in the
layout of aisles and gangways.
 An Attempt should be made to accommodate the maximum amount of
reflective surfaces close to the sound source. A reflective and diffusive
enclosure (band shell), to direct the reflected sound waves both toward
the audience and back to the performers will be of great advantage. A
paved space, an artificial brook, or other reflective surface between stage
and audience will improve hearing conditions.
 The platform should be well elevated and the seating area steeply
banked, with increased rake toward the rear, to provide the maximum
amount of direct sound for the entire audience
 Back reflections converging upon the platform from the concentric
benches, particularly noticeable with partially or totally unoccupied
seating area, should be eliminated.
 Nearby reflective surfaces of existing buildings should be carefully
checked for echoes or harmful reflections.
Note: If audience capacity exceeds about 500, a high-quality sound
amplification system should be installed. Its layout and volume should be such
that the audience is unaware of its existence.

Acoustical considerations in the Architectural Design of Musical Auditoriums
 Since no music hall is built for one specific type or style of music, the RT
must be a meticulously established compromise. A carefully controlled
RT will increase fullness of tone and will help loudness, definition, and
diffusion.However, the establishing of an ideal RT alone is no guarantee
that a hall will be acoustically excellent for the performance of music; it is
a contributing factor only.
 Definition will be satisfactory if the initial time-Delay gap does not
exceed 20 msec; if the direct sound is loud enough relative to the
reverberant sound, that is, listeners are reasonably close to the sound
source; and if there is no echo.
 Providing an adequate supply and distribution of bass tones over a large
audience area( above 2500 seats) is a serious acoustical problem, in part
because the fundamentals of several musical instruments are relatively
week and most of the time only their harmonics are heard.
 To achieve uniform quality of sound over the entire seating area
balconies should not protrude too deeply into the air space of the room;
listeners should have unobstructed sight lines so that they receive ample
direct sound, the should be of reasonable size and proportion, and
concave enclosures should be avoided
 Echo will be particularly noticeable if the RT is short and diffusion is
inadequate. The longer the RT in a room, the less trouble can be expected
from echo. The longer RT will cover up the single intrusions of an echo.
In checking echo-producing spots, it should always be borne in mind that
the acoustical design of rooms is a three dimensional problem.

 The frequencies of sounds involved in the acoustics of music halls
extend over a considerable wide range than those for speech, from about
30 Hz for certain musical instruments to about 12,000 Hz, including
those high-frequency components of musical sounds which characterize
some musical instruments.
 Particular attention is required to control noises and vibrations
originating from the heating, ventilation and air –conditioning system;
from nearby spaces; mechanical and electrical rooms; and from surface,
underground, and air transportation.

Masking Noise
In many situationsnoise control problems can be solved by drowning out
( or Masking) unwanted noises by electronically created background
noise. This artificial noise is often referred to as acoustical perfume,
although the term acoustical deodorant would be more appropriate. This
process suppresses minor intrusions which might interrupt the recipients’
privacy.
In designing offices the provision of a relatively high but acceptable
degree of background noise is essential in order to mask undesirable office
noises created by typewriters, telephones, office machines, or loud
conversation and to provide a reasonable amount of privacy.
In team teaching classrooms the sounds produced by several learning
groups and spread in various directions cancel each other out to a certain
extent and create a particular type of masking noise which seems to be
acceptable to the occupants.
Noise from ventilating systems, from a uniform flow of traffic, or from
general office activities contributes to an artificial masking noise.
Appropriately selected and well-distributed background music can also be
considered as a type of masking noise.

NOISE CONTROL AND SOUND ABSORPTION
Types of noises, transmission of noise, transmission loss,
noise control and sound insulation, remedial measures and
legislation
CONSTRUCTIONAL MEASURES
Walls/Partitions, floors/ ceilings,windows/doors,fittings and gadjets,
machine mounting and insulation of machinery

Environmental Noise Control
Noise is unwanted sound. However this can be subjective: some sounds are
considered noise by some but not by others, e.g. certain music, church bells,
sounds of playing children, birds, wind, sea, etc. Noise can also be any un-
meaningful or unintended sound
Noise Sources
The main sources of noise in Environmental noise Control can be classified in
two groups;
Interior noises, originating from people, house-hold equipment or machinery
within a building. Partition Walls,floors,doors and windows must provide
adequate Protection against these noises inside the buildings.
Outdoor noises, originating from traffic, transportation,industry, exposed
mechanical equipment in buildings,construction sites, road repairs, sports and
other outdoor activities, and advertising.
Noise in buildings is usually assigned to one of three classes:
Airborne sound
Sound such as voices, TV or stereo sounds. The source does not strike or
vibrate against the structure of the building.
Structure-borne sound
Sound that is generated when some object in contact with the structure vibrates
and so generates noise. Examples: elevators, washing machine, plumbing noise.
Impact sound
Sound that is generated when some object strikes the structure of the building.
Examples: door slamming, a hammer blow, footsteps.

Source of Airborne sounds
Source of Structure-borne & Impact Sounds.
Transmission of air-borne noises in a building

Remedial Treatment: Walls
 build a studwork frame, attached to the ceiling and floor but not fixed to
the original wall
 hang mineral wool inside the cavity, and tack between the studs or to a
batten on the wall
 line the studwork with two layers of plasterboard, making sure the joints
between the sheets in the first and second layer do not coincide
 seal perimeter and all other sound paths with flexible sealant

Remedial Treatment: Ceilings
 attach wall plates to the walls to give the shortest room span and run new
ceiling joists between them
 fix mineral wool between the new ceiling joists, or drape it over them
 line with two plasterboard layers, making sure the joints between the
sheets in the first and second layer do not coincide
 seal perimeter and all other sound paths with flexible sealant

Remedial Treatment: Floors
Floating floor
A Floating Floor is a floor that does not need to be nailed or glued to the sub
floor. A sprung floor is a special type of floating floor designed to enhance
sports or dance performance. In general though the term refers to a floor used
to reduce noise or vibration
A domestic floating floor might be constructed over an existing floor and
consist of a glass fibre, felt or cork layer for sound insulation with neoprene
pads holding up a wood floor. There is a gap between the floor and the walls to
decouple them and allow for expansion, this gap will be covered with skirting
boards or mouldings

Principal types of Urban Noises
 Traffic and transportation noise (automobiles, trucks, motorcycles,
streetcars, trains, diesel engines, subways, watercraft, aircraft, etc.)
 Industrial noise (factories, workshops, plants, cooling towers, air
conditioners, etc.)
 Noise created by people (sports and other outdoor activities, open-air
performances, etc.)
 By following town and community planning methods with desirable
degree of noise abatement in mind.
 By establishing and enforcing Zoning regulations and antinoise by-laws
and restricting maximum permissible noise levels, particularly in
residential areas
 By requiring manufacturers of noisy mechanical and electrical equipment
to test their products and supply noise ratings for them.
 By educating members of city administrations (legislators, council
members, employees, etc.) to observe noise-control principles.
 By encouraging the public to complain about objectionable noises through
all possible channels of communication ( by complaints to the police,
letters to newspapers, airport authorities, through appeals to radio and
television stations, etc.)
 By educating the public to realize that a number of noise sources capable
of causing great annoyance, irritable, and distress can be eliminated by
careful planning and foresight and on a personal level by courtesy and
consideration.

Traffic Noise at a given point can be reduced by
Reducing the speed of the vehicle
Reducing the number of stops along the route
Restricting the time during which the vehicle is creating noise
Reducing the number of vehicles
Traffic Noise Index (TNI)
Traffic Noise Index (TNI) takes into account:
 Intensity levels and characteristics of noise,
 The effect on people and the social nuisance created and
 The considerable difference in the degree to which human beings tolerate
noise.

Noise Control through Architectural Design
Sensible architectural planning with attention to sound-control requirements is
the most economical approach to effective noise control in buildings.
Quiet and noisy quarters should be grouped and separated from each
other horizontally and vertically by means of adequately sound-insulation
walls and floors or by rooms not particularly susceptible to noises, such as
entry, corridor, and staircase.
A living room in one apartment should not be adjacent to a bedroom in
another apartment. Bedrooms and living rooms in horizontal or vertical
pairs of dwelling units should be adjacent to and above one another. If
this layout is not feasible, the wall or floor construction separating the
dwelling units must provide a higher sound Insulation.
Bedrooms should be located in a relatively quiet part of the building and
should not be adjacent to elevator shafts or mechanical rooms or overlook
traffic lines or driveways.
Bathrooms should be efficiently separated acoustically from living rooms
and should not be planned over living rooms or bedrooms, whether of the
same dwelling or another. Bathroom fixtures should not be installed along
walls which separate living room and bath room.
Doors leading to bedrooms and bathrooms should have a reasonable
sound insulation. They should have solid-core panels and be gasketed all
around.

A staircase should not be adjacent to abedroom. Treads of a staircase
should be covered with soft materials to avoid footstep noises.
Uninterrupted rows of balconies along the exterior walls of buildings
should be avoided. Terraces should be recessed into the building, at an
adequate distancefrom each other.
A vertically staggered layout of apartments should be avoided, because
noises from a single source can penetrate several dwelling units at the
same time. Also, common walls between vertically staggered dwelling
units transmit footstep noises more easily into an adjacent unit than
floors alone.
Windows should be laid out so as to minimize cross talk from one
apartment to another.
A design that disregards the above requirements and yet is intended to
produce a soundproof building will have to use expensive sound-
insulating walls and floors

Sound Insulation Construction
 Sound insulation against Air borne sound
* Sound Transmission Loss (TL)
* Measurement of Transmission Loss
* Sound transmission class (STC)
* Noise Reduction of partitions
 Insulation against Structure borne (Impact) noise
Insulation against Structure borne (Impact) noise
Insulation against Structure borne (Impact) Noise
can be achieved by the use of:
 Soft floor finish (Carpet, Cork, Vinyl, rubber, etc.)
 Floating floor
 Resilient ( antivibration ) mounts
 Resiliently suspended solid ceiling

Sound Insulation:
It is important to avoid confusion between sound absorption and sound
insulation.
(a) Sound absorption is the prevention of reflection of sound or alternatively, a
reduction in the sound energy reflected by the surfaces of a room.
(b) Sound insulation is the prevention of transmission of sound or alternatively,
a reduction of sound energy transmitted into an adjoining air space.
Two types of sound insulation are to be dealt with in building construction:
(a) Airborne Sound Insulation : the insulation against noise originating in air,
e.g. voices, music, motor traffic, wind.
(b) Impact Sound Insulation : the insulation against noise originating directly
on a structure by blows or vibration e.g. footsteps above, furniture being moved,
drilling and hammering the structure.
 Sound insulation against Air borne sound
* Sound Transmission Loss (TL)
* Measurement of Transmission Loss
* Sound transmission class (STC)
* Noise Reduction of partitions
 Insulation against Structure borne (Impact)noise

Sound Transmission Loss (TL)
The sound transmission loss, or simply transmission loss (TL), of a partition,
stated in decibels, is a measure of its sound insulation. It is equal to the number
of decibels by which sound energy incident on the partition is reduced in
passing through the structure.
The numerical value of the TL depends only on the construction of the
partition and varies with the frequency of the sound. It is independent of the
acoustical properties of the two spaces separated by the partition.
The TL of a partition can be determined in an acoustical laboratory or in the
field as follows: a steady sound is generated in the source room at one side of
the partition to be tested ; the sound levels are then measured at both sides of
the partition, that is, in both source room and receiving room. The TL of the
partition is determined from the difference between the measured sound levels
on both sides of the partition

Measurement of Transmission Loss
Measurement of the TL are made at several test frequencies between 125 and
4000 Hz. The TL of the test panel is given by the formula
TL = L1 –L2 + 10 log s – 10 log A2
Where L1 = average sound pressure level in sourceroom,dB
L2 = average sound pressure level in receiving room,dB
S = area of the test panel , sq ft ( sq m)
A2 = total absorption of receiving room, sq-ft sabins (sq-m sabins)
Sound transmission class (STC)
Sound Transmission Class (or STC) is a widely used** integer-number rating of
how well a building partition attenuates airborne sound.
STC is used to rate interior partitions, ceilings/floors, doors, windows and
exterior wall configurations in the USA. See ASTM International Classification
E413 and E90. Outside the USA, the Sound Reduction Index (SRI) ISO
standard is used.

Noise Reduction of partitions
Noise Reduction (NR) is moregeneral term thanTL for specifying sound
insulation between rooms because it takes into account the effects of the various
transmission paths between sourceroom and receiving room and also the
acoustical properties of these rooms
NR expressed in decibels, is given by
NR = L1 – L2 or NR = TL + 10 log A2 / S
Where L1 = average sound pressure level in sourceroom,dB
L2 = average sound pressure level in receiving room,dB
TL = Transmission loss of partition, dB
S = area of partition , sq ft ( sq m)
A2 = total absorption of receiving room, sq-ft sabins
( sq-m sabins)

Architectural acoustic notes

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