In this example the cooling tower has been relocated to give a separation of noise source to the listener of 300ft. plus a screen of 15 db± value.
Noise level of cooling
tower at 3ft.
Attenuation with distance
of 300ft.
Screen value of 15 db
Allowable noise level
=
= 105 dba
40 db
=
15 db
=
50 dba
MICROBAR
0.0002
90
80
70
60
RE
80
PRESSURE
LEVEL
50
40
30
N C CURVES
[NC-70
-NC-60
NC-50
NC-40
CNC-30
-NC-20
BUS
A building with a room facing the main street is situated on the 6th floor and has an allowable noise level of 30 dba. What TL does the exterior wall have to meet.
Heavy traffic (dominated
by autobus) at 75ft. ±
Allowable noise level
.. required TL of exterior wall
www
Check wall design requirement of 45 dba against possible helicopter noise
source.
Helicopter noise level
at say 500ft. (check)
db to be added to allowable
noise level when not continuous say .005 (check)
SOUND
20
20
APPROXIMATE THRESHOLD
OF
HEARING
FOR
CONTINUOUS
NOISE
10
20 75
75
150
300
150
300
600
600 1 200
1 200 2400
2400
4800
4800 10 000
FREQUENCY
BAND
-
CYCLES
PER SECOND
10. TABLE OF RECOMMENDED MAXIMUM CONTINUOUS NOISE LEVELS FOR SATISFACTORY USE OF SPACE
Bibliography
Knudsen & Harris
Acoustical Designing in Architecture Wiley & Sons, New York, 1950
Geiger
Noise Reduction Manual
University of Michigan Press, Ann Arbour Mich. 1956
Harris
Handbook of Noise Control
McGraw-Hill, New York, 1957
= 75 dba
Space
= 30 dba
designation
NC level from graph
meter
reading
Auditoria
Concert halls. NC 20
25 dba
45 dba
Legitimate
25
30
theatres.
Cinemas,
30
35
lecture halls.
Public buildings
=
= 78 dba
Museums, post
offices, Banking halls etc.
40
45
Beranek
Restaurants etc.
Restaurants and
cocktail lounges.
40
45
Cafeterias and night clubs.
45
50
Clothing stores
Noise Reduction
McGraw-Hill, New York, 1960
Committee on the Problem of Noise
Noise Final Report
London: Her Majesty's Stationery Office
Parkin & Humphreys
Acoustics Noise & Buildings
and high class
35
40
Faber, London, 1969
shops. Small shops. Sport activities
Noise Control Magazine
45
50
Publication of the Acoustical Society of
America
− 45 + 35 db – OK
=
9. NOISE CRITERIA CURVES
(NC). Noise criteria
curves are
employed for a more accurate specifi- cation of the desired amount of back- ground noise levels for various occu- pancies. The curves allow plotting of the specific TL value of enclosing structures as opposed to the single average of a dba number. Where noise criteria are established check 'in situ' with a noise level meter using the A scale (dba) with a +5 added.
The data which has been presented is typical and has been assembled from many sources. The next article will cover specifications and supervision for enclosures requiring above average noise protection.
Shops
Bowling alleys and gymnasia. Swim. pools.
Transportation Ticket sales offices Lounges and
50
Doelle
40
45
Acoustics in Architectural Design
50
55
National Research Council, Canada, 1965
Solutions to Noise Control Problems
Owens-Corning Fiberglass, 1964
35
40
Pappas & Associates
Methods for the Control of Noise Sources
45
50
waiting areas
Report No. 329-188. Montreal, 1964
16
Far East BUILDER, July 1970