32

Rules of Thumb (cont.)

Noise Criteria

Graph sound pressure level for each octave band on NC curve. Highest curve intercepted is NC level of sound source. See

Noise Criteria Curves

., page 34.

Sound Power and Sound Power Level

Difference between sound pressure levels

dB to add to highest sound pressure level

0 3.01 2.52 2.13 1.84 1.55 1.26 1.07 0.88 0.69 0.5

10+ 0

Sound Power (Watts)Sound Power

Level dBSource

25 to 40,000,000 195 Shuttle Booster rocket100,000 170 Jet engine with afterburner

10,000 160 Jet aircraft at takeoff1,000 150 Turboprop at takeoff

100 140 Prop aircraft at takeoff10 130 Loud rock band

1 120 Small aircraft engine0.1 110 Blaring radio0.01 100 Car at highway speed

0.001 90Axial ventilating fan (2500 m

3

h) Voice shouting0.0001 80 Garbage disposal unit0.00001 70 Voice—conversational level

0.000001 60 Electronic equipment cooling fan

0.0000001 50 Office air diffuser0.00000001 40 Small electric clock0.000000001 30 Voice - very soft whisper

System Design Guidelines

33

Sound Pressure and Sound Pressure Level

Room Sones —dBA Correlation†

† From ASHRAE 1972 Handbook of Fundamentals

Sound Pressure (Pascals)

Sound Pressure Level dB

Typical Environment

200.0 140 30m from military aircraft at take-off

63.0 130 Pneumatic chipping and riveting (operator’s position)

20.0 120 Passenger Jet takeoff at 100 ft.

6.3 110 Automatic punch press (operator’s position)

2.0 100 Automatic lathe shop0.63 90 Construction site—pneumatic drilling0.2 80 Computer printout room0.063 70 Loud radio (in average domestic room)0.02 60 Restaurant0.0063 50 Conversational speech at 1m0.002 40 Whispered conversation at 2m0.00063 300.0002 20 Background in TV recording studios0.00002 0 Normal threshold of hearing

150

1009080706050

40

30

20

10950 60 70 80 90 100

dBA = 33.2 Log (sones) + 28, Accuracy ± 2dBA

Sound Level dBA

Lo

ud

nes

s, S

on

es

10

System Design Guidelines