Chapter 14: Acoustics Flashcards
what are the thresholds of human hearing in db
0 is nothing and 130 is pain
a change in how many decibels is noticeable
5 db
a change in 10 decibels is how much louder or quieter
twice as loud or half as loud
what frequencies are humans the most sensitive too
3000-4000 hertz
is the human ear more sensitive to low or high frequencies
less sensitive to low frequencies
two major problems in controlling noise in a space
prevent or minimizing the transmutation of the sound from one space to another, and reducing the noise within the space
how is sound transmission mainly slowed down from space to space
by the mass of the partition followed by the rigidity of the wall. Less rigid = more absorption and less transmitting
what does stc rating stand for and what does it do
sound transmission class
rates the transmission loss of construction. the higher the number the better the barrier is. if it’s a stc of 35 it means it takes 35 decibels from the noisy room through the barrier
what is an stc rating so that loud speech is not intelligible but can be heard
35
how do you measure how sound absorbent a material is
by its coefficient of absorption.
coefficient below 0.2 is reflective
coefficient above 0.2 is sound absorbing
what is the preferred decibels to have in:
- large office
- apartment
- 35-40
2. 20-30
what is the NRC for sound absorbtion
noise reduction coefficient.
average of a material’s absorption coefficients at the four frequencies of 250, 500, 1000 & 2000 hz
0 is no sound absorption and 1.0 is total absorption
what is the NRC rating for gwb walls
0.05
Name some rules of thumb when designing for noise reduction in a room
- avoid rooms with hard reflective surfaces on all 6 surfaces
- the NRC rating should be at least 0.20
- by doubling the amount of absorption in a room only results in a 3db change which isn’t really noticeable. you’d need to triple it to make a noticeable difference
- ceiling treatments for absorption are the most effective in large rooms and wall treatments are more effective in small rooms.
how to control noise within a space
- reducing the level of loudness of the sound source
- modifying the absorption in the space
- adding white noise to mask the unwanted sound
how to increase a walls STC rating
- add mass to the wall with either more gwb layers or using a masonry wall
- place insulation in the wall cavity
- use resilient channels on one side of the partition to furr out the gwb.
how do you deal with doors in sound walls
perimeter of the door completely sealed with weather stripping specifically designed for sound sealing
add automatic door bottom
use a really heavy door- solid core wood is best.
what is impact noise, how do you rate it, and how to do you minimize it
rate it with the ICC- impact insulation class
easiest way to increase impact sounds on a floor is to add carpet
can also- add suspended ceiling below the floor, float a finished floor on resilient pads, put insulation in the airspace between the floor and ceiling below
when space planning, how can you plan to increase acoustical performance
- plan similar areas next to each other
- use buffer spaces like closets and halways to separate noise producing spaces
- stagger doorways in halls
- minimize common wall between spaces
- avoid room shapes that reflect sound like round rooms
name three ceiling sound controlling ratings
- NRC- noise reduction coefficient (between 0 and 1.0)
- SRA- speech range absorption
- CAC- ceiling attenuation class- transmission loss between two closed rooms beside each other through the ceiling
what is a typical NRC rating for ceiling tiles
0.85
what are sounds 3 basic qualities
velocity
frequency
power
what is noise reduction in regards to acoustics
focuses on preventing the noise from TRANSMITTING from one space to another
what is the rating of the coefficient of absorption for a reflective material and for a absorptive material
above .2 is absorptive and below .2 is reflective
what is SAA in regards to acoustics
sound absorption average- lower rater = more reflective
published in product literature often. same type of scale of coefficient of absorption
0= reflective 1= total absorption
which sound test would you use for controlling sound within a space
NRC
