Ch 20 Acoustics Flashcards
Sound has three basic qualities:
velocity, frequency, power
this depends on the medium in which the sound is travelling and the temperature of the medium
velocity
the number of cycles completed per second and is measured in hertz
frequency
the quality of acoustic energy as measured in watts
power
By definition, ___ dB is the threshold of human hearing, and ___ dB is the threshold of pain.
0 —– 130
A healthy young person can hear sounds in the range of about __ to __.
20Hz — 20000Hz
There are two basic problems in controlling noise:
preventing the transmission of sound from one space to another and reducing the noise within a space
takes into the account only the loss through the partition
transmission loss
dependent on the area of the partition separating the two spaces and the absorption of the surfaces in the quiet room
noise reduction
a single number rating used to the transmission loss of construction
sound transmission class (STC)
The ___ the STC rating, the better the barrier is in stopping sound
higher
A material with a coefficient below __ is considered to be reflective and one with a coefficient above __ is considered sound absorbing.
0.2 —- 0.2
used to control unwanted sound reflection improves speech privacy and decrease or increase reverberation
sound absorption
the ratio of the sound intensity absorbed by the material to the total intensity reaching the material. ranges from 0 - 1.
coefficient of absorption
Although absorptive materials can be placed anywhere, ___ for sound absorption is more effective in large rooms, while ____ is more effective in small rooms.
ceiling treatment —— wall treatment
the average of a material’s absorption coefficients at the four frequencies of 250, 500, 1000, and 2000 Hz, rounded to the nearest multiple of 0.05
noise reduction coefficient (NRC)
The recommended time for speech reverberation in offices and small rooms is __ to __ seconds, while for auditrium it is __ to __.
- 3 - 0.6 seconds for small rooms
1. 5 - 1.8 for large spaces
The average absorption coefficient of a room should be at least __. An absorption above __ is usually not desirable or economically justifiable.
0.20, 0.50
These 3 methods can be used to build a sound-resistant partition:
add mass to the wall, add insulation between studs and resilient channels on one side of the partition
the prologation of sound as it repeatedly bounces off hard surfaces
reverberation
These are the 3 primary ways sound can be controlled within a space:
by reducing the level of loudness of the sound source, by modifying the absorption of the space and by introducing non-intrusive background noise
There are 5 important factors in designing for speech privacy in an open area. All must be present to achieve the optimum acoustic environment
ceiling must be highly absorptive, area must include space dividers to reduce transmission, other surfaces should be designed to not reflect sound, if possible activities should be distanced to take advantage of normal attenuation of sound with distance and properly designed background masking systems
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 is called
impact noise
These 6 ideas help minimize acoustic problems in interior space planning:
plan similar use areas next to each other, use buffer spaces such as closets, stagger doorways across the corridor, try to locate furniture so that areas producing noise are not close to the wall, minimize the area of the common wall and avoid room shapes that reflect or focus sound
a piece of hardware that drops a seal from the door to the floor or threshold as the door closes
automatic door bottom
a single number rating of a floor/ceiling’s impact sound performance
insulation class (IIC)
the _ the IIC rating, the better the floor performs in reducing impact sounds in the test frequency range
higher
a single number rating of the average sound absorption of a material over a limited frequency range including 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz rounded to the nearest multiple of 0.05
noise reduction coefficient (NRC)
single number rating but the frequency range includes 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz.
speech range absorption (SRA)
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
ceiling attenuation class (CAC)
a single number summation of how effective a ceiling is in absorbing sound reaching it form over low partitions
articulation class
measures the performance of all the elements of a particular configuration working together. predicts the intelligibility of speech for a group of talkers and listeners
articulation index
