Deck 8: Acoustical Properties of Materials

Question 1

Compared to a lightweight building element, a heavyweight element is generally a poor transmitter of airborne sound.

Answer 1

False

Question 2

The pitch of a sound is related to

A)sound energy.
B)sound frequency.
C)sound speed.
D)all of the above.
E)none of the above.

Answer 2

B

Question 3

What does the frequency of sound measure? What is the unit of measurement of frequency?

Answer 3

Sound waves create back- and- forth vibrations of air particles. Frequency measures the number of vibrations of air particles in one second. Its unit is cycles/second, also called Hertz (Hz).

Question 4

The wavelength of sound at a frequency of 1,000 Hz is approximately

A)2 ft.
B)1 ft.
C)10 ft.
D)0 ft.
E)5 ft.

Question 5

Sound transmission class (STC)is a measure of the

A)sound- insulating property of a material with respect to airborne sound.
B)sound- insulating property of a material with respect to structure- borne sound.
C)sound- reflecting property of a material.
D)sound- absorbing property of a material.

Question 6

Sound speed in air is approximately

A)1,100 ft/s.
B)500 ft/s.
C)1,000 ft/s.
D)10 ft/s.
E)100 ft/s.

Question 7

Most of the noise produced in a busy restaurant or dining hall is

A)structure- borne sound.
B)airborne sound.

Question 8

The noise- reduction coefficient (NRC)of a material is evaluated between the frequency range of 250 Hz and 2 kHz because

A)most of the sound energy in the noise produced in buildings lies in the given frequency range.
B)most of the sound energy in human speech lies in the given frequency range.
C)the human ear is insensitive to noise outside the above frequency range.
D)it is virtually impossible to evaluate this property outside the above frequency range.
E)none of the above.

Question 9

A sound barrier with an STC of 50 will generally

A)not block music but will block speech sufficiently to be heard only by a curious listener.
B)block all speech and music, however loud.
C)block loud speech but not loud music.
D)block loud music but not loud speech.

Question 10

A resilient clip consists of a small light- gauge steel member with a rubber pad fastened to it.

Question 11

A resilient channel is used to attenuate airborne sound, whereas a resilient clip is used to attenuate structure- borne sound.

Question 12

For a party wall between two dwelling units, such as two apartments, the building codes require its minimum STC value to be

A)55.
B)50.
C)65.
D)100.
E)75.

Question 13

A commonly used porous sound absorber is

A)gypsum board.
B)oriented strandboard.
C)aluminum foil.
D)fiberglass.
E)microperforated plastic.

Question 14

Sound that is audible to human beings has a frequency lying between

A)20 Hz and 20 kHz.
B)100 Hz and 800 Hz.
C)2 kHz and 20 kHz.
D)50 Hz and 50 kHz.
E)200 Hz and 20 kHz.

Question 15

The sound created by human speech is

A)structure- borne sound.
B)airborne sound.
C)both A and B.
D)neither A nor B.

Question 16

Cycles per second is also called a

A)hulen.
B)pascal.
C)newton.
D)hertz.
E)none of the above.

Question 17

The NRC of a material lies between

A)0 and 10.
B)1 and 100.
C)0 and 100.
D)1 and 10.
E)none of the above.

Question 18

The wavelength of sound at a frequency of 100 Hz is approximately

A)5 ft.
B)10 ft.
C)0 ft.
D)2 ft.
E)1 ft.

Question 19

The measure that is used for structure- borne sound insulation is

A)impact insulation class.
B)transmission loss.
C)impact isolation index.
D)structural insulation index.

Question 20

The three important properties of sound waves are sound frequency, f, wavelength of sound, h, and the speed of sound, c. What is the relationship between them?

Question 21

What is a resilient channel made of and what is its purpose?

Question 22

What is the speed of sound in air?

Question 23

The International Building Code requires minimum STC 50 for a party wall between two dwelling units (condominiums or apartments). In terms of the transmission of speech or music through the wall, what will STC 50 provide?

Question 24

In architectural acoustics, we distinguish between airborne sound and structure- borne sound. Place the followin sounds in one of the above two categories.
Sound from the speaker in an auditorium Sound from hailstorm on an auditorium roof
Sound from the footsteps of a person walking on the floor Sound from someone knocking on an entry door of a house Sound from the orchestra in a concert hall

Question 25

Is STC related to airborne sound or structure- borne sound?

Question 26

The International Building Code requires minimum STC 50 for a party wall separating two dwelling units (condominiums or apartments). With this STC value, loud speech is heard across the party wall with some effort and music is heard easily. As a consulting acoustician, what STC value would you recommend to the architect/project owner for the party walls in an upscale condominium project?

Question 27

What is the typical center- to- center spacing of resilient channels?

Question 28

The addition of a resilient floor covering, such as vinyl tiles, improves the structures- borne sound insulation of a wood joist floor. Will the vinyl tiles also improve the airborne sound insulation of a floor?

Question 29

Does the sound absorption coefficient of a material, a, vary with frequency? What is the unit of measurement of
a? What are the theoretical minimum and maximum values of a?

Question 30

Which wall assembly will provide a higher sound transmission loss (TL):
(a)6- 1/2- in.- thick concrete wall or (b)a 6- 1/2- in.- thick stud wall comprising 1- 1/2 in. × 5- 1/2 in. wood studs covered on each side with 1/2- in.- thick gypsum board? Give reason(s)for your answer.

Question 31

What is the minimum building code- required STC value for a party wall separating two dwelling units (condominiums or apartments)?

Question 32

Explain what sound transmission class (STC)is.

Question 33

What is impact insulation class, IIC? What is its unit of measurement?

Question 34

What is noise reduction coefficient, NRC? What is the unit of measurement of NRC? What are the theoretical minimum and maximum values NRC?

Question 35

Does the transmission loss (TL)of an assembly vary with sound frequency?

Question 36

STC represents the equivalent of average transmission loss (TL)of an assembly. The unit of measurement of TL is decibel (dB). Is the unit of measurement of STC also dB or different?

Question 37

What is the approximate range of frequencies (h)in human speech and their corresponding wavelengths? For all practical purposes, the speed of sound in air may be assumed = 1,000 ft/s in place of its exact value of 1130 ft/s.

Question 38

The ear's perception of the loudness of sound, commonly called sound level, is measured by the decibel (dB)scale. What is the approximate sound level in conversational speech at 1 m away from a speaker? Sound level in shouting speech at 1m from a speaker? Sound level that causes pain in the ear?

Question 39

Explain what transmission loss (TL)is. What is its unit of measurement?

Question 40

Which wall assembly will provide a higher sound transmission loss (TL):
(a)a 6- 1/2- in.- thick stud wall comprising 1- 1/2 in. × 5- 1/2 in. wood studs covered on each side with 1/2- in.- thick gypsum board or
(b)same as wall type (a)but the air space between studs is filled with fiberglass? Give reason(s)for your answer.

Question 41

All building materials absorb sound to some degree. So, what is a sound- absorbing material?