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 which 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 = R2^2 / R1^2

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 I at given point in the distance of R from the source is equal to the power divided by the area of a sphere (A=4πr^2)

Question 12

Sound - Frequency FORMULA

Answer 12

Frequency F - Number of cycles completed per sound, measured in hertz - 1 hz equals 1 cycle / sec F = c / w Frequency = velocity / wavelength

Question 13

velocity of sound c

Answer 13

depends on medium and temperature of medium. Air approx. 1130 ft/sec

Question 14

Additions of decibels - Difference 0-1 Db

Answer 14

add 3 db to higher value

Question 15

Additions of decibels - Difference 2-3 Db

Answer 15

add 2 db to higher value

Question 16

Additions of decibels - Difference 4-8 Db

Answer 16

add 1 db to higher value

Question 17

Additions of decibels - Difference 9- or more Db

Answer 17

dd 0 db to higher value

Question 18

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

Answer 18

DBtotal = DBsource + 10 log N F.e. Office contains eight machines each produces 73DB of sound 73 DB +10 log 8 = 82 db

Question 19

Noise reduction def & formula

Answer 19

Arithmetic difference in decibels between intensity levels in two rooms separated by barrier of given transmission loss Nr = tl + 10log A/S noise reduction = Transmission loss + 10log * sabins / area

Question 20

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

Answer 20

15 to 20 NC in DB

Question 21

how many Noise Criteria in Bedrooms

Answer 21

20 to 30 NC in DB

Question 22

how many Noise Criteria in Office

Answer 22

30 to 40 NC in DB

Question 23

how many Noise Criteria in Kitchens, mech shops

Answer 23

45-55 NC in DB

Question 24

stc rating 25

Answer 24

normal speech can clearly be heard through barrier

Question 25

stc rating 35

Answer 25

loud speech is not intelligible but can be heard

Question 26

stc rating 45-50

Answer 26

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

Question 27

Reverberation time Auditorium

Answer 27

1.5 SEC

Question 28

Reverberation time Offices

Answer 28

0.6 SEC

Question 29

Reverberation time broadcast studios

Answer 29

0.4 SEC

Question 30

SIL Speech interference level 30 to 40 dB

Answer 30

communication in normal voice possible

Question 31

SIL Speech interference level 60 to 70 dB

Answer 31

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

Question 32

SIL Speech interference level 80 to 85 dB

Answer 32

Communication slightly difficult with shouting

Question 33

Sound - what is Noise Criteria NC

Answer 33

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

Question 34

reverberation time cathedral

Answer 34

2.4 seconds

Question 35

reverberation time recording or broadcasting studio.

Answer 35

0.5 seconds

Question 36

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

Answer 36

1.1 seconds

Question 37

reverberation time noise perception

Answer 37

5 seconds

Question 38

sound control plan

Answer 38

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 39

At which decibel level is speech privacy not possible.

Answer 39

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

Question 40

Q. Which is the decibel level of background noise?

Answer 40

35db

Question 41

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 41

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.