Chapter 14 Acoustics Flashcards
What are the 3 basic qualities of sound?
1- velocity: depends on the medium in which the sound is traveling and the temperature of the medium
2 - frequency: the number of cycles completed per second and is measured in hertz Hz (higher the frequency, the higher the pitch)
3 - power: the quality of acoustic energy as measured in watts
At what decibel (dB) does sound start to cause pain
130 dB
What decibel (dB) is the threshold of hearing?
0
How many decibel levels needs to change for a change in apparent loudness to be clearly noticeable?
5 levels
What is the difference between transmission loss and noise reduction?
Transmission loss takes into account only the loss through the partition
noise reduction is dependent not only on the transmission loss but also on the area of the partition separating the two spaces and the absorption of the surfaces in the room not making noise
What is STC ?
Sound transmission class: used to rate the transmission loss of construction. The higher the rating, the better the barrier is in stopping sound
Do openings for outlets and doors in a STC rated wall lower the rating?
yes
What are noise criteria curves used for?
To specify the maximum amount of continuous back ground noise allowable in the space
Study table 14.4
What sound absorption coefficient is considered to be reflective? Consider to se sound absorbing?
Coefficient below 0.2 is reflective
Coefficient above 0.2 is absorbing
The coefficients are listed in manufactures technical literature.
What is NRC?
Noise reduction coefficient - the average of a materials absorption coefficient at four frequencies (250, 500,1000,2000 Hz)
What rating system superseeds NRC?
SAA - sound absorption average. Similar to NRC , but the SAA is the average absorption coefficient for the 12 one-third-octave bands from 200Hz to 2500Hz
What average sound absorption coefficient should a room be?
Minimum 0.2 - anything above 0.5 is undesirable
How is the total sound absorption for a room determined?
The sum of all the various individual material absorptions in the room
What is reverberation?
The prolongation of sound as it is repeatedly bounces of hard surfaces
What are the three primary ways interior designers can control sound within space?
Reduce sound level at the source (not always possible)
Modify the spaces sound absorption
Introducing background sounds to mask the unwanted sound
What features can a sound-resistant partition have to that increases it’s STC rating?
Double layer wall board (one or both sides)
Insulation in stud cavity (absorbs more sounds as it travels from one layer to the next)
Resilient channels
What design solutions can be used in an open office plan to achieve speech privacy?
highly absorptive ceilings
sound absorbing space dividers
furniture and fixtures arranged to reduce sound reflection
background sound masking system
What is “ impact noise “ and how is it quantified?
Sound resulting from direct contact of an object with a sound barrier - generally floors (footfall, shuffled furniture, dropped objects etc.)
Quantified by “ impact insulation class” (IIC) number - The higher the IIC rating, the better the floor performs in reducing impact sounds
What is the speech range absorption rating system?
SRA is similar to NRC but the frequency range tested is 500, 1000,2000, 4000 Hz (a range that more closely represents the frequencies of speech)
What effect on hearing does STC rating have on the following?
STC 25
STC 30
STC 35
STC 42-45
STC 46-50
STC 25 - normal speech can barely be heard through the barrier
STC 30 - loud speech can be heard and understood fairly well, normal speech is heard but barely understood
STC 35 - loud speech is not intelligible but can be heard
STC 42-45 - loud speech can only be faintly heard; normal speech cannot be heard
STC 46-50 loud speech is not audible; loud sounds other than speech can only be faintly heard if at all
How is the sound absorption of a material defined?
By the coefficient of absorption, which is the ratio of the sound intensity absorbed by the material to the total intensity reaching the material
The maximum absorption possible is 1
