SYSTEMS - ACCOUSTICS

Question 1

Attenuation

Answer 1

reduction of sound

Question 2

Decibel threshold of human hearing, pain-point

Answer 2

db, unit of sound intensity.

0 dB threshold of human hearing,

130 dB threshold of pain

Question 3

Acoustic Frequency

Answer 3

number of pressure fluctuations or cycles occurring in one second, expressed in hertz hz

Question 4

Noise Isolation Class NIC

Answer 4

Single number rating of noise reduction expressing the actual degree of sound control between two adjoining areas measured at various frequency levels (pitches), on-site in a building and is commonly referred to as a “Field Test”. The higher the number the better the control.

Question 5

Noise reduction coefficient NRC

Answer 5

NRC is a single number value ranging from 0.0-1.0 that describes the average sound absorption performance of a material.

An NRC of 0.0 indicates the object does not attenuate mid-frequency sounds, but rather reflects sound energy. measured at the 4 1/3 octave band frequency of 250, 500, 1000, and 2000 Hz

Question 6

Phon

Answer 6

unit of loudness level

Question 7

Sabin

Answer 7

unit of absorption.

Can be expressed as a coefficient, with a

value of 1.00 representing a material that absorbs 100% of the energy,

and a value of 0.00 meaning all the sound is reflected

Question 8

Sound Transmission Class STC

Answer 8

average of barriers ability to reduce sound over several frequency bands.

The higher the STC rating the better the better it’s ability to control sound transmission

Question 9

Transmission loss TL

Answer 9

difference in decibels between 2 rooms with a barrier Transmission loss varies with frequency being tested.

Question 10

Sound - Inverse square law

Answer 10

intensity of sound at any given point is inversely proportional to the square of the distance from the source of sound

I1 / I2 = R2² / R1²

Question 11

Sound - Power P

Answer 11

quantity of acoustical energy is measured in watts.

In free space, the point source emits waves in all directions equally, so sound intensity at a given point in the distance of R from the source is equal to the source power divided by the area of a sphere (A=4πr²)

Question 12

Additions of decibels - Difference 0-1 Db

Answer 12

add 3 db to higher value

Question 13

Additions of decibels - Difference 2-3 Db

Answer 13

add 2 db to higher value

Question 14

Additions of decibels - Difference 4-8 Db

Answer 14

add 1 db to higher value

Question 15

Additions of decibels - Difference 9- or more Db

Answer 15

dd 0 db to higher value

Question 16

Additions of arbitrary number N of sources of identical value - formula

Answer 16

DB_total = DB_source + 10 log N

F.e. Office contains eight machines each produces 73DB of sound

73 DB +10 log 8 = 82 db

Question 17

how many Noise Criteria in Concert halls, opera, recording studio

Answer 17

15 to 20 NC in DB

Question 18

how many Noise Criteria in Bedrooms

Answer 18

20 to 30 NC in DB

Question 19

how many Noise Criteria in Office

Answer 19

30 to 40 NC in DB

Question 20

how many Noise Criteria in Kitchens, mech shops

Answer 20

45-55 NC in DB

Question 21

stc rating 25

Answer 21

normal speech can clearly be heard through barrier

Question 22

stc rating 35

Answer 22

loud speech is not intelligible but can be heard

Question 23

stc rating 45-50

Answer 23

loud speech is not audible sounds other in speech can only be heard faintly if it all

Question 24

Reverberation time Auditorium

Answer 24

1.5 SEC

Question 25

Reverberation time Offices

Answer 25

0.6 SEC

Question 26

Reverberation time broadcast studios

Answer 26

0.4 SEC

Question 27

SIL Speech interference level 30 to 40 dB

Answer 27

communication in normal voice possible

Question 28

SIL Speech interference level 60 to 70 dB

Answer 28

Communication with raised voice satisfactory 1-2‘, phone use difficult

Question 29

SIL Speech interference level 80 to 85 dB

Answer 29

Communication slightly difficult with shouting

Question 30

Sound - what is Noise Criteria NC

Answer 30

NC - level is a standard describing relative loudness of a space with a range of frequencies

Question 31

reverberation time cathedral

Answer 31

2.4 seconds

Question 32

reverberation time recording or broadcasting studio.

Answer 32

0.5 seconds

Question 33

reverberation time small theater, a lecture or conference room, or other fairly intimate space.

Answer 33

1.1 seconds

Question 34

reverberation time noise perception

Answer 34

5 seconds

Question 35

sound control plan

Answer 35

A sound control plan would take room noise, speech privacy, impact noise, and mechanical noise into consideration. It would not take specific issues such as music or loud conversations into consideration.

Question 36

At which decibel level is speech privacy not possible.

Answer 36

At a decibel level above 30db, speech privacy is not possible.

Question 37

Q. Which is the decibel level of background noise?

Answer 37

35db

Question 38

An architect is designing a new subdivision on a large plot of land adjacent to a commuter train route. What is the most effective option for mitigating off-site noise intrusion from a nearby train route?

Answer 38

The best approach is to adjust the grading to deaden the noise. Sound barriers do not have enough mass to effectively deaden the noise from a train route. Vegetation makes a poor sound screen. If uninterrupted, sound can travel a great distance.