Chapter 14: Acoustics

Question 1

what are the thresholds of human hearing in db

Answer 1

0 is nothing and 130 is pain

Question 2

a change in how many decibels is noticeable

Answer 2

5 db

Question 3

a change in 10 decibels is how much louder or quieter

Answer 3

twice as loud or half as loud

Question 4

what frequencies are humans the most sensitive too

Answer 4

3000-4000 hertz

Question 5

is the human ear more sensitive to low or high frequencies

Answer 5

less sensitive to low frequencies

Question 6

two major problems in controlling noise in a space

Answer 6

prevent or minimizing the transmutation of the sound from one space to another, and reducing the noise within the space

Question 7

how is sound transmission mainly slowed down from space to space

Answer 7

by the mass of the partition followed by the rigidity of the wall. Less rigid = more absorption and less transmitting

Question 8

what does stc rating stand for and what does it do

Answer 8

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

Question 9

what is an stc rating so that loud speech is not intelligible but can be heard

Answer 9

35

Question 10

how do you measure how sound absorbent a material is

Answer 10

by its coefficient of absorption.

coefficient below 0.2 is reflective

coefficient above 0.2 is sound absorbing

Question 11

what is the preferred decibels to have in:

1. large office
2. apartment

Answer 11

1. 35-40

2. 20-30

Question 12

what is the NRC for sound absorbtion

Answer 12

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

Question 13

what is the NRC rating for gwb walls

Answer 13

0.05

Question 14

Name some rules of thumb when designing for noise reduction in a room

Answer 14

• 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.

Question 15

how to control noise within a space

Answer 15

1. reducing the level of loudness of the sound source
2. modifying the absorption in the space
3. adding white noise to mask the unwanted sound

Question 16

how to increase a walls STC rating

Answer 16

1. add mass to the wall with either more gwb layers or using a masonry wall
2. place insulation in the wall cavity
3. use resilient channels on one side of the partition to furr out the gwb.

Question 17

how do you deal with doors in sound walls

Answer 17

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.

Question 18

what is impact noise, how do you rate it, and how to do you minimize it

Answer 18

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

Question 19

when space planning, how can you plan to increase acoustical performance

Answer 19

1. plan similar areas next to each other
2. use buffer spaces like closets and halways to separate noise producing spaces
3. stagger doorways in halls
4. minimize common wall between spaces
5. avoid room shapes that reflect sound like round rooms

Question 20

name three ceiling sound controlling ratings

Answer 20

1. NRC- noise reduction coefficient (between 0 and 1.0)
2. SRA- speech range absorption
3. CAC- ceiling attenuation class- transmission loss between two closed rooms beside each other through the ceiling

Question 21

what is a typical NRC rating for ceiling tiles

Answer 21

0.85

Question 22

what are sounds 3 basic qualities

Answer 22

velocity
frequency
power

Question 23

what is noise reduction in regards to acoustics

Answer 23

focuses on preventing the noise from TRANSMITTING from one space to another

Question 24

what is the rating of the coefficient of absorption for a reflective material and for a absorptive material

Answer 24

above .2 is absorptive and below .2 is reflective

Question 25

what is SAA in regards to acoustics

Answer 25

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

Question 26

which sound test would you use for controlling sound within a space

Answer 26

NRC