SOURCE PROPERTIES
1 Power and spectrum
I.
TRANSMISSION PATH
1 Effect of ceiling
and floor
RECIPIENT EFFECTS
1 Annoyance
2 Intermittence
3 Directionality
Fig. 1. Structure of acoustic design problem
2 Communication
2 Effect of walls
and vertical surfaces
3 Privacy
3 Effect of screens
4 Distraction/
Arousal
INTENSITY LEVEL, dB, AT 1 METRE
60
ம்
INTENSITY LEVEL, dB, AT 1 METRE
125
250
500
1000 FREQUENCY, Hz
2000
4000
125
250
500 1000 FREQUENCY, Hz
(a) ELECTRIC TYPEWRITER
(b) AVERAGE SPEECH
2000
Fig. 2a & b. Octaye band intensity levels at 1m for electric typewriter and average speech
-10dB-
20dB
-30dB
-10-
20-
-30
-20-
-10
Low frequency
-OdB-
Fig. 3a. Directionality of typewriter noise
-10dB
-20dB
de
-20dB-
High frequency
-10dB-
Low frequency
-OdB-
Fig. 3b. Directionality of average human voice
18
High frequency
frequency.
frequency
High frequency
-10-
4000
frame-work of the problem, the struc- ture of which is illustrated in Fig. 1. We need information concerning the pro- perties of the sound source; we need to know how the sound is attenuated as it travels from source to recipient, and we need to know how the recipient will respond to the sound when it arrives.
The situation is complicated by the fact that we have to consider both communication and noise: speech be- tween two people needs to be clearly heard by them, but the same speech constitutes noise to a third person who may be distracted or annoyed by it.
At the same time, the noise pro- duced by ventilator outlets, office machinery and so on, needs to be kept at the correct level, to provide privacy through the masking of speech with- out becoming annoying.
Noise sources
Considering first the properties of office noise sources, we can list three pieces of required information: (1) The power of the source in each of the different bands of the frequency spec- trum. (2) The amount of time per day for which the source operates. (3) The directional properties of the source in each of the different bands of the fre- quency spectrum.
The first two pieces of information are required for normal office design, and are readily available. Figs. 2a and 2b give data on the octave band inten- sity levels at 1m for an electric type- writer and the human voice, respec- tively. It should be borne in mind though that office machines chosen for use in a landscaped office will be selected for their quietness, and that office personnel are influenced by the improved environment so as to act in a quieter manner.
The third item is not normally re- quired, but may readily be obtained
Far East BUILDER, December 1970
INTENSITY LEVEL
D.
Source
R.S.