SYSTEMS - ACCOUSTICS Flashcards
Attenuation
reduction of sound
Decibel threshold of human hearing, pain-point
db, unit of sound intensity.
0 dB threshold of human hearing,
130 dB threshold of pain
Acoustic Frequency
number of pressure fluctuations or cycles occurring in one second, expressed in hertz hz
Noise Isolation Class NIC
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.
Noise reduction coefficient NRC
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
Phon
unit of loudness level
Sabin
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
Sound Transmission Class STC
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
Transmission loss TL
difference in decibels between 2 rooms with a barrier Transmission loss varies with frequency being tested.
Sound - Inverse square law
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
Sound - Power P
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)
Additions of decibels - Difference 0-1 Db
add 3 db to higher value
Additions of decibels - Difference 2-3 Db
add 2 db to higher value
Additions of decibels - Difference 4-8 Db
add 1 db to higher value
Additions of decibels - Difference 9- or more Db
dd 0 db to higher value
Additions of arbitrary number N of sources of identical value - formula
DBtotal = DBsource + 10 log N
F.e. Office contains eight machines each produces 73DB of sound
73 DB +10 log 8 = 82 db
how many Noise Criteria in Concert halls, opera, recording studio
15 to 20 NC in DB
how many Noise Criteria in Bedrooms
20 to 30 NC in DB
how many Noise Criteria in Office
30 to 40 NC in DB
how many Noise Criteria in Kitchens, mech shops
45-55 NC in DB
stc rating 25
normal speech can clearly be heard through barrier
stc rating 35
loud speech is not intelligible but can be heard
stc rating 45-50
loud speech is not audible sounds other in speech can only be heard faintly if it all
Reverberation time Auditorium
1.5 SEC
Reverberation time Offices
0.6 SEC
Reverberation time broadcast studios
0.4 SEC
SIL Speech interference level 30 to 40 dB
communication in normal voice possible
SIL Speech interference level 60 to 70 dB
Communication with raised voice satisfactory 1-2‘, phone use difficult
SIL Speech interference level 80 to 85 dB
Communication slightly difficult with shouting
Sound - what is Noise Criteria NC
NC - level is a standard describing relative loudness of a space with a range of frequencies
reverberation time cathedral
2.4 seconds
reverberation time recording or broadcasting studio.
0.5 seconds
reverberation time small theater, a lecture or conference room, or other fairly intimate space.
1.1 seconds
reverberation time noise perception
5 seconds
sound control plan
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.
At which decibel level is speech privacy not possible.
At a decibel level above 30db, speech privacy is not possible.
Q. Which is the decibel level of background noise?
35db
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?
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.
