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Terms in this set (78)
is a science which deals with the production, control, transmission, reception and effects of sound in an enclosed space
is the human ear's response to pressure fluctuations in the air caused by vibrating objects.
Sound travels in space by a phenomenon called
-is similar to the motion of a ripple produced by dropping a pebble into a water pond
Types of Sound
1. FREQUENCY (f)
2. SPEED (c)
3. WAVELENGTH (λ)
Physical Quantities of Sound
the number of sound ripples generated in unit time.
frequency of the wave
The number of cycles that the air particles move back and forth in one second in a sound wave is called
-its unit is cycles per second whcih is also termed hertz (Hz) after the Austrian physicist Heinrich Hertz (1857-94).
cycles per second (c/s)
1. 63 Hz
2. 125 Hz
3. 250 Hz
4. 500 Hz
5. 1 kHz
6. 2 kHz
7. 4 kHz
8. 8 kHz
Eight frequency bands, or octaves, are considered in room acoustics with the following center frequencies:
1. 63 Hz
2. 125 Hz
3. 250 Hz
1. 500 Hz
2. 1 kHz
1. 2 kHz
2. 4 kHz
3. 8 kHz
c = f λ
c = speed in meters per time
f = frequency in cycles per time
λ = meters
The wavelength and the frequency of sound are related to each other as shown in the equation:
is defined as the amount of sound power falling on (or passing through, or crossing) a unit area.
unit of power
watt per square meter (W/m2)
unit of sound intensity
threshold of audibility
intensity that corresponds to the sensation of pain in the human ear is approximately 10 W/m2.
Characteristics of sound
is a measure of the intensity of sound and is expressed in decibels (dB). It is a quantity called the sound intensity level (IL).
Unit of loudness
is the frequency of sound wave perceived by the human ear. A high-pitched sound means that it has a high frequency. The female voice is slightly higher pitched than the male voice.
1. Prolonged Reverberation
4. Flutter Echo
5. Undue Focusing of Sound
Principal Acoustical Defects of Rooms
long reverberation time (RT) due to large amounts of highly reflective surfaces and/or to large volume of space which will take considerable time for reflected sound to die out.
distinct reflection of original sound which results when the path of reflected sound is 20 m (65 ft) or more than the path of direct sound. If the difference is less than 20 m, the reflected sound will reinforce the direct sound which is desirable.
It is recommended that the surfaces of the front part of an auditorium must be highly reflective to reinforce direct sound and throw it to the rear of the room. On the other hand, the rear must be highly absorptive so the delayed direct sound will the absorbed and not be reflected to the front.
is the reinforcement of certain sound frequencies due to sympathetic vibrations. This is especially the case in enclosed rooms with highly reflective surfaces. The effect would be to emphasize certain frequencies at the expense of others, which is undesirable for balance desired in rooms intended for music.
a rapid but repetitive succession of sounds caused by highly reflective parallel surfaces (wall to wall, or ceiling to floor).
Undue Focusing of Sound
is caused by concave surfaces which causes sound to converge at certain points with resulting loss of energy in other parts of the room.
the fraction of the incident sound energy absorbed by a surface.
a sealed room in which all the surfaces are designed to completely absorb all sound produced in the room.
a reduction in sound level. Sound attenuation in air-conditioning is specified in terms of dB per meter.
transfer of noise from a space surrounding the duct into the duct through duct walls.
transfer of noise from the interior of a duct through duct walls into a space outside the duct.
a room containing an unusually large amount of sound absorption..
a unit of measurement for sound pressure level, sound intensity level or sound power level.
a change in the direction of propagation of sound as a result of bending caused by a barrier in the path of a sound wave.
diffuse sound (field)
a sound field in which the sound comes in equal intensity from all directions.
the sound that arrives at a receiver along a direct line from the source without reflection from any surface.
a sound that has been reflected with sufficient time delay.
exterior background noise in a neighborhood (ie. traffic, aircraft).
faithful reproduction of a sound source.
a rapid but repetitive succession of sound from a sound source usually occurring as a result of multiple reflections in a space with hard, flat and parallel walls.
the number of full cycles per second measured.
noise caused by the collision of two objects.
a sound that is below the human audible frequency, below 20 Hz.
a sound which is discontinuous or fluctuates to such an extent that at times its sound pressure level falls below a measurable level.
inverse square law
a law which states that the sound intensity in a free field varies inversely with the square of the distance from the source.
a lack of acoustical connection.
a small opening in a barrier that allows airborne sound to pass through.
a room containing an unusually small amount of sound absorption.
an auditory sensation that depends on sound pressure level and the frequency of sound.
the increase in the threshold of audibility of a sound that is required so that the sound can be heard in the presence of another sound.
noise isolation class (NIC)
a single number rating derived from the measured value of noise reduction between two rooms.
noise reduction (NR)
the reduction in sound pressure level of noise.
noise reduction coefficient (NRC)
a single number rating derived from measured values of sound absorption coefficients of a material at 250, 500, 1000 and 2000 Hz.
outdoor-indoor transmission class (OITC)
a weighted single number rating of the sound reduction effectiveness of a partition that separates an indoor space from the outside.
a listener's perception of the frequency of a pure tone.
a measure of the sound reflective property of a surface.
the relatively large amplitude of vibration produced when the frequency of the source of sound is equal to the natural frequency of a room.
reverberant sound field
a sound field created by repeated reflections of sound from the boundaries in an enclosed space.
the continuation of sound in an enclosed space after the initial source has been terminated.
reverberation time (RT)
the time it takes for sound intensity to decay by 1 millionth of its steady state value after the sound source has been terminated.
a unit of measure of sound absorption.
an irregular diffraction of sound in many directions.
the ability of a barrier to prevent sound from reaching a receiver.
sound intensity (SI)
the average rate of sound energy flow through a unit area in a given direction.
sound intensity level (SIL)
a quantity expressed in decibels of airborne sound.
a small space that works as a buffer between a source room and a receiving room.
fluctuating pressure of sound superimposed on the static air pressure.
sound pressure level
see sound intensity level
sound transmission class (STC)
a single number rating of the sound insulation rating of a partition.
sound propagated through a solid structure.
the ratio of transmitted sound energy to incident sound energy
transmission loss (TL)
is the measure of sound insulation of a partition.
distance between two adjacent compressions or rarefactions in a sound wave.
a noise whose energy is uniform over a wide range of frequencies. This is analogous to the term "white light", which consists of almost equal amount of light of different wavelength (colors). A white noise sounds hissy.
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