Chapter 14 - Acoustics Flashcards
Sound has three basic qualities
velocity, frequency, and power
velocity
depends on medium in which the sound is traveling
temperature of the medium
frequency
number o cycles completed per second
frequency is measured in
Hertz (hz)
1 hz equals
1 cycle per second
high-pitched sounds have ____ frequencies| bass notes have ______ frequencies
higher| lower
power (in acoustics)
quality of acoustic energy
power (in acoustics ) is measured in
watts
the ______ (unit) is used in acoustic descriptions and calculations
decibel
the decibel relates actual ___ _____ to ___
actual sound intensity to the way humans experience sound
__ db is the threshold of human hearing| __ __ __ db is the threshold of pain
0 dB| 130 dB
Changes in intensity level / change in apparent loudness
1 db
almost imperceptible
Changes in intensity level / change in apparent loudness
5 db
clearly noticeable
Changes in intensity level / change in apparent loudness
10 db
twice or half as loud
Changes in intensity level / change in apparent loudness
18 db
very much louder or quieter
Changes in intensity level / change in apparent loudness
20 db
four times or one-fourth as loud
a healthy young person can hear the range of about ____-__0,000 Hz
20 - 20,000
Human are most sensitive to the Hz range of
3,000 to 4,000
There are two basic problems in controlling noise
- preventing or minimizing the transmission of sound from one space to another
- reducing the noise within a space
Transmission of sound is primarily retarded by ________. what is also important?
the mass of the partition
stiffness, or rigidity, of the partition
there are two important concepts in noise reduction
- transmission loss
- actual noise reduction between two spaces
____ takes into account only the loss through the partition
transmission loss
____ is dependent not only on transmission loss but also on the area of the partition separating the two spaces and the absorption of the surfaces in the quiet room
noise reduction
how can noise reduction be improved?
- increasing the transmission loss of the partition
- by increasing the absorption in the “quiet” room
- by decreasing the area of the common wall between the rooms
- some combo the above
To simplify the selection of wall construction and other building components, a single-number rating called the _____ is often used to rate the transmission loss of construction.
sound transmission class (STC)
the higher the STC, the _______
better the barrier is in stopping sound
25 STC =
normal speech can be heard clearly through barrier
30 STC =
lounge speech can be heard and understood| normal speech can be heard by not understood
35 STC =
loud speech is not intelligible
42-45 STC =
loud speech can only be faintly heard
46-50 STC =
loud speech not audible; sound sounds other than speech can only be heard faintly
low STC to high STC
25-50
- control unwanted sound reflections (noise)
- improve speech privacy
- decrease or increase reverberation
sound absorption is used to do 3 things:
the absorption of a material is defined by the coefficient of ____________. This ratio is
absorption
ratio of sound intensity absorbed by the material to the total intensity reaching the material
coefficient below ____ is considered reflective
coefficient above ____ is considered absorbing
.2
.2
the coefficient of absorption, for convenience, is translated into a single number. This coefficient is referred to as _______.
noise reduction coefficient (NRC)
vinyl tile on concrete NRC| 5/8” suspended acoustic tile NRC
.05| .90
Each doubling of the amount of absorption in a room results in a noise reduction of only _____
3 dB–hardly noticeable
To make any difference in the noise reduction within a space, the total absorption must be increased by at least _______
three times to change the reduction by 5 dB, which is noticeable
Although absorptive materials can be placed anywhere, ______ treatment for sound absorption is more effective in large rooms, while _____ treatment is more effective in small rooms.
ceiling
wall
__________ is the prolongation of sound as it repeatedly bounces off hard surfaces.
reverberation
technically, reverberation time is the time it takes the sound level to _________
decrease 60 dB after the source has stopped producing the sound
three primary ways sound can be ___________ within a space:
- by reducing the level of loudness of the sound voice
- by modifying the absorption in the space
- by introducing nonintrusive background sound to mask the unwanted sound
controlled
Walls and floors are generally rated with their ______ values
STC
The higher the STC the _____.
better the barrier is at reducing transmitted sound
What type of glass in a door provides better STC?
laminated glass
_____, or sound resulting from direct contact of an object with a sound barrier, can occur on any surface, but it generally occurs on a floor and ceiling assembly
impact noise
What is one of the most important ceiling ratings for sound?
NRC (noise reduction coefficient)
Absorptive ceiling tiles normally have an NRC range of ___ to _____
.65-.90
What is a rating similar to the NRC which is often used for ceiling tiles?
SRA speech range absorption singe number rating. range more closely represents the frequencies of speech and may be a better rating to use in evaluating and selecting ceiling tiles
third rating method for ceiling tiles is _____
CAC ceiling attenuation class
What is CAC?
single-number measure of the transmission loss through ceiling tiles between two closed rooms where there is no wall or other barrier above the suspended ceiling
