Glossary - BRUEL & KJAER HF HATS 5128 User Manual

Decibel (dB)
The measurement unit for expressing the relative intensity of sound. A direct
application of linear scales (in Pa) to the measurement of sound pressure leads to
large and unwieldy numbers. As the ear responds logarithmically rather than linearly
to stimuli, it is more practical to express acoustic parameters as a logarithmic ratio of
the measured value to a reference value. This logarithmic ratio is called a decibel or
dB. The advantage of using dB can be clearly seen in the illustration that follows. Here,
the linear scale with its large numbers is converted into a manageable scale from 0 dB
at the threshold of hearing (20 Pa) to 130 dB at the threshold of pain (100 Pa).
Our hearing covers a surprisingly wide range of sound pressures – a ratio of over a
million to one. The dB scale makes the numbers manageable
Take-off Take-off
Rock group Rock group
Normal traffic Normal traffic
Conversation Conversation
Library Library
Bedroom Bedroom
Appendix B
Sound pressure (µPa) Sound pressure (µPa) Sound pressure level (dB) Sound pressure level (dB)
140 140
100,000,000 100,000,000
130 130
(from 25 25 m) m) (from
Firecrackers Firecrackers
120 120
10,000,000 10,000,000
110 110
100 100
1,000,000 1,000,000
90 90
Noisy workplace Noisy workplace
80 80
100,000 100,000
70 70
Office Office
60 60
10,000 10,000
50 50
40 40
1,000 1,000
30 30
20 20
100 100
10 10
20 20 0

Glossary

Pneumatic hammer Pneumatic hammer
Living room Living room
Woods Woods
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