Chapter 14 Acoustics

Question 1

What are the 3 basic qualities of sound?

Answer 1

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

Question 2

At what decibel (dB) does sound start to cause pain

Answer 2

130 dB

Question 3

What decibel (dB) is the threshold of hearing?

Answer 3

0

Question 4

How many decibel levels needs to change for a change in apparent loudness to be clearly noticeable?

Answer 4

5 levels

Question 5

What is the difference between transmission loss and noise reduction?

Answer 5

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

Question 6

What is STC ?

Answer 6

Sound transmission class: used to rate the transmission loss of construction. The higher the rating, the better the barrier is in stopping sound

Question 7

Do openings for outlets and doors in a STC rated wall lower the rating?

Answer 7

yes

Question 8

What are noise criteria curves used for?

Answer 8

To specify the maximum amount of continuous back ground noise allowable in the space

Question 9

Study table 14.4

Question 10

What sound absorption coefficient is considered to be reflective? Consider to se sound absorbing?

Answer 10

Coefficient below 0.2 is reflective

Coefficient above 0.2 is absorbing

The coefficients are listed in manufactures technical literature.

Question 11

What is NRC?

Answer 11

Noise reduction coefficient - the average of a materials absorption coefficient at four frequencies (250, 500,1000,2000 Hz)

Question 12

What rating system superseeds NRC?

Answer 12

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

Question 13

What average sound absorption coefficient should a room be?

Answer 13

Minimum 0.2 - anything above 0.5 is undesirable

Question 14

How is the total sound absorption for a room determined?

Answer 14

The sum of all the various individual material absorptions in the room

Question 15

What is reverberation?

Answer 15

The prolongation of sound as it is repeatedly bounces of hard surfaces

Question 16

What are the three primary ways interior designers can control sound within space?

Answer 16

Reduce sound level at the source (not always possible)
Modify the spaces sound absorption
Introducing background sounds to mask the unwanted sound

Question 17

What features can a sound-resistant partition have to that increases it’s STC rating?

Answer 17

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

Question 18

What design solutions can be used in an open office plan to achieve speech privacy?

Answer 18

highly absorptive ceilings
sound absorbing space dividers
furniture and fixtures arranged to reduce sound reflection
background sound masking system

Question 19

What is “ impact noise “ and how is it quantified?

Answer 19

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

Question 20

What is the speech range absorption rating system?

Answer 20

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)

Question 21

What effect on hearing does STC rating have on the following?

STC 25
STC 30
STC 35
STC 42-45
STC 46-50

Answer 21

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

Question 22

How is the sound absorption of a material defined?

Answer 22

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