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ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
BASIC CONCEPTS IN ARCHITECTURAL ACOUSTICS
ENVIRONMENTAL CONTROL III
(ACOUSTICS AND NOISE CONTROL)
DEPARTMENT OF ARCHITECTURE.
FEDERAL UNIVERSITY OF TECHNOLOGY, AKURE
ONDO STATE.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Outline• Introduction• The Nature of Sounds• Properties of Sound• Propagation of Sound• Sound Power and Intensity• Effects of Barrier on Sound• Conclusion
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Acoustics is the science of sound and it
covers two areas, those of room acoustics
and control of noise.
Noise is unwanted or damaging sound
which interferes with what people are trying
to do, or sound which has an adverse effect
on health and safety.
Introduction
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Introduction
This lecture covers basic
architectural
acoustics including the properties
and nature of
sound, the terms used to describe
sound waves,
and the relationship between sound
pressure,
sound intensity and sound power.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Nature of Sound
Sound is a disturbance, or wave
which
moves through a physical
medium (such as
air, water, or metal) from a source
to cause
the sensation of hearing in
animals.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound waves
Sound waves are longitudinal
waves
originating from a source and
conveyed by
a medium. They are characterized
by
velocity (v), frequency (f),
wavelength (٨),
and amplitude (a).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound waves
Compression in sound waves is
a region
of raised pressure.
Rarefaction in sound waves is a
region of
lowered pressure.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound waves
Figure 1: Compression And Rarefaction Of Sound By A Vibrating
Tuning Fork.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound waves
Figure 2: Visual ization of sound rarefaction and compression in a
coi led spring.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound waves
Figure 3: Sound wave i l lustration.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Frequency range of sound
Sounds produced by various sources can
range from frequencies below 20Hz to
20,000Hz and above.
Infrasound are sounds with frequencies
below 20Hz.Ultrasound are sounds with
frequencies above 20,000Hz.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
Audible sounds range from the threshold
of audibility to the threshold of pain.
The threshold of audibility is the lower
Limit of hearing and it has a standard value
of 1 picowatt per metre square (1pW/m²).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The threshold of pain is the upper
Limit of hearing and it has a standard value
of 1 watt per metre square (1W/m²).
Sounds below the lower limit of hearing
are inaudible while the those above the
upper limit may cause pain or even damage
the human ear.
The Audible range of sound
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
Figure 4: Audible range of sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
Figure 5: Audible range of sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
The sound level or decibel scale is the logarithm
of the ratio of measured sound intensity to the
intensity at the threshold
of audibility.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
The loudness of a sound is determined by referring
to the loudness or phon scale which shows sounds of
various levels and frequencies which are perceived as
of the same sound loudness.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
Figure 6: Equal loudness contours.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
The Audible range of sound
Figure 7: Psychological and physiological eff ects of sounds
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Wave length
This is the distance between two
successive pressure peaks. Its
symbol is ٨ and it is measured in
units of metres (m).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Period
This is the time taken for one
vibration cycle. Its symbol is T
and it is measured in units of
seconds (s).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Frequency
This is the number of vibration cycles per
seconds. Its symbol is F and it is measured in
units of Hertz (Hz).
For the relationship between frequency and
period,
F=1/T
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Speed or wave velocity
This is the speed with which sound travels
through a medium. Its symbol is C and it is
measured in units of metres per seconds
(m/s).
For the relationship between the speed
(C), frequency (F) and wave length (٨ ),
C=F ٨
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 8: Variation of speed of sound with the medium of transmission. .
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Factors that affect the speed of sound
through a medium
•Elasticity of the medium
•Density of the medium
•Temperature of the medium
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Amplitude
This indicates the intensity of sound. Its
symbol is I and it is measured in units of
watts per metres square (W/m²).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 9: Amplitude i l lustration.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
The inverse square law of sound states that the
intensity of sound in a free field is indirectly
proportional to the square of the distance from the
source.
This infers that there is a decrease in the intensity
of sound the farther the observer is from the source.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 10: The inverse square law.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 11: Amplitude i l lustration.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Pitch
This is the property of sound that is perceived as highness and lowness depending on the rapidity of the vibrations producing it . It is measured in cycles per second
(cps).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 12: Pitch i l lustration.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Sound pressure
This is the force per unit area and it gives the magnitude of the sound wave. Its symbol is p and it is measured in
units of Pascal (Pa).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
The pressure changes produced by a sound wave are also known as sound pressure.
Compared with atmospheric pressure on which they are superimposed (about 100,000 pascals), they are very small (between 20
micropascals and 200 pascals).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 13:Changes in sound pressure over t ime.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 14:Sound pressure superimposed on atmospheric
pressure.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 15:Relationship between sound pressure and sound frequency
in a pure tone.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
Figure 16:The characteristics of Machine noise.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Inside a room, close to a source like a machine, the direct sound dominates, and the sound pressure may vary significantly with just small changes in
position.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
This area is called the near field and its extent is about twice the dimension of the machine or one wavelength of the sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
The area beyond the near field is called the far field made up of two sections,
•The free field
•The reverberant field
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
In the free field the direct sound still dominates and the sound pressure level decreases by 6 dB for each doubling of distance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
In the reverberant field the reflected sound adds to the direct sound and the decrease per doubling of distance of the sound pressure level will be less
than 6 dB.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Figure 17: The near fi eld and far fi eld of sound. Source: National Institute for Occupational Health and Safety
(1988).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Figure 18: Decrease in sound intensity for a point source with
doubling of distance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Spherical wave fronts
These are produced when sound spreads out from a point source in a free space. The wave fronts are spherical and the sound
pressure level decreases 6 dB for each doubling of distance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Figure 19: Decrease in sound intensity for an omnidirectional
point source.source.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Cylindrical wave fronts
These are produced when sound spreads out from a line source (such as a road with constant traffic or a pipe carrying fluid). The
waves are cylindrical and the sound pressure level decreases 3 dB for each doubling of distance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Figure 20: Decrease in sound intensity for a l ine source with
doubling of distance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Figure 21: Decrease in sound pressure level for a l ine source.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
•Perpendicular wave fronts
These are produced when sound spreads out from a plane source (such as close to a large vibrating panel or sound travelling down
a duct). The waves are perpendicular and the sound pressure does not decrease with distance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Propagation of Sound
Figure 22: Perpendicular wave fronts.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Properties of Sound
The above relationships hold true only in ideal conditions. Decrease in sound levels depends on
•Absorption by air and moisture ;
•Wind and temperature gradients;
•Absorption of the ground; and
•Reflection and absorption by obstacles .
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound Intensity
•Sound Power
This is the fundamental property of the source of sound that depicts the energy emitted by a sound source per unit time. Its symbol
is W and it is measured in units of Watts (w).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound Intensity
A source that emits power equally in all directions is called an omnidirectional source. Any other source is called a directional source.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound
Intensity
Figure 23: Decrease in sound pressure level for an omnidirectional
point source .
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound Intensity
•Sound Intensity
Sound intensity at a point in the surrounding medium is the power passing through a unit area. Its symbol is I and it is measured in
units of watts per metre square (W/m²).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound Intensity
For an omnidirectional point source the sound power is spread over the surface of the sphere.
S=4pr².
Hence the sound intensity is given by
I=W/4r²
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound Intensity
The relationship between sound intensity and sound pressure is given as
I=p² / rc
This equation is for plane waves. However, away from a point source, spherical waves approximate plane
waves.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Sound Power and Sound IntensityI is the sound intensity in watts per metre square (w/m²),
p is the sound pressure in pascals (pa),
r is the density of the medium in kilogram per metres cube (kg/m³), and
c is the speed of sound in metres per second
(m/s).
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
When a sound wave encounters an obstacle such as a barrier or a wall, its propagation will be affected in one of three ways
•reflection
•diffraction
•refraction
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
•Reflection
This occurs when the dimensions of an obstacle are larger than the wave length of the sound. In this case, the sound wave behaves like a light
ray and for an obstacle with a flat surface, the reflected ray will leave the surface at the same angle as the incident wave.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
Figure 24: Refl ection of sound .
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
•Refraction
This occurs when a sound wave enters a different medium at an angle. The bending of sound wave is due to the differing speed of travel of the
sound wave in the two media.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
Figure 25: Refraction of sound with no temperature inversion .
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
Figure 26: Refraction of sound with temperature inversion .
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
•Diffraction
This occurs when the dimensions of an obstacle are of the same order or less than the wavelength of the sound. In case the edge of the
obstacle acts like a source of sound itself and the sound ray appears to bend around the edge.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Effects of Barriers on Sound
Figure 27: Diff raction of sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Transmission of sound
This refers to the ways in which sound can be transmitted which could be in form of structure borne sound, impact sound, and
airborne sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
Structure borne sound refers to the transmission of sound involving the re-emission of sound via vibration of the
molecules of a barrier in the path of the sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
Impact sound refers to the transmission of sound via mechanical means.
Airborne sound simply refers to the transmission of sound through air.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Absorption of sound
This refers to the product of the absorption coefficient and the area of a given surface. It is measured in the open window unit which is
equivalent to the absorption of a square metre opening with zero reflectance.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
The Absorption coefficient is an indication of the sound that is not reflected and is thus an indication of both the sound absorbed and transmitted.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
Figure 28: Transmission and absorption of sound.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
An ability of an obstacle to block the transmission of sound depends on its structure which indicates its transmission loss rating.
Hence, stiff, heavy materials like concrete have high transmission loss. Soft porous materials like cell foams are not good at
blocking the transmission of sound but are good absorbers.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Masking of sound
This refers to the acoustic shadow effect of screens or barriers in the path of sound which differs in accordance with the frequency
and wave length of the sound and the dimension of the barriers.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
This effect disappears when the wave length of the sound is more than the dimension of the barrier in a direction perpendicular to the sound path.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
Figure 29: Acoustic shadow at high frequencies.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Sound Insulation
This refers to the reduction of sound transmission of airborne sounds through walls, floors, and partitions. It is achieved by using
elements with an adequate transmission coefficient or sound reduction index.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
The transmission coefficient is a decimal fraction expressing the proportion of sound energy emitted.
The sound reduction index or transmission loss defines the reduction effect of an element and it is expressed in decibels.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Reverberation
This is the persistence of sound in an enclosed space as a result of repeated reflection or scattering after the sound source has
stopped.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Reverberation Time
This is number of seconds required for the energy of the reflected sound in a room to diminish to one-millionth of the original energy it
had. It can also be defined as the number of seconds required for the sound pressure level to diminish to 60 decibels below its initial value.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Transmission and Absorption of Sound
•Echoes
This is a distinct repetition of the direct sound. Its effect may be observed by making a short sound such as a clap, in a large room.
ARC 507: Environmental Control III (Acoustics and Noise Control)Department of Architecture, Federal University of Technology, Akure, Nigeria
Conclusion
The basic concepts in architectural acoustics, the nature of sound and its physical properties as discussed in this lesson help in providing an understanding
for dealing with the problems of noise.