# Noise terminology explained Decibels

SPL = Sound Pressure Level (in dB or dB(A))

Frequency weighting, dB(A), dB(C), dB(Z)

dB(A) – weighting factor which takes in consideration the sensitivity of the human hearing. As our body perceives high frequency sounds more disturbing than low frequency sounds, the dB(A) weighting was introduced. This way, a higher dB(A) level always sounds louder for humans than a lower dB(A) level.

dB(C) – weighting gives more emphasis to low frequencies

dB(Z) – is also called unweighted, linear or flat, no weighting is applied

sound weighting graphs decibel

LAmax = The maximum level with A-weighted frequency response in Fast or Slow time constant.
LAmin = The minimum level with A-weighted frequency response in Fast or Slow time constant.
Lpeak = The true peak level in sound pressure (without time constant), typically a Lpeak will be 3 dB higher than Lmax

1/1 octave filtering – frequencies of measured sound divided in octave bands filtering

1/3 octave filtering – frequencies of measured sound divided in third octave bands filtering

Leq = equivalent sound pressure level over a given time, equivalent continuous sound level

moving Leq = running Leq – the running or moving equivalent continuous sound level

L10 – the sound level that is exceeded 10% of the time

L90 – the sound level that is exceeded 90% of the time

Lxx – the statistical value of the sound level that is exceeded xx% of the time

Example of sound level:

 Sound sources (noise)Examples with distance Sound pressure   Level Lp dB(A) SPL Aircraft, 50 m distance 140 dB(A) Threshold of pain ! 130 dB(A) Threshold of severe discomfort. 120 dB(A) Chainsaw, sledgehammer, 1 m distance 110 dB(A) Disco (average), 1 m from speaker 100 dB(A) Big truck, 10 m distance 90 dB(A) Footpath next to a busy road Sound Level where noise induced hearlng loss starts ! 80 – 85 dB(A)80 dB(A) Vacuum cleaner, distance 1 m 70 dB(A) Conversational speech, distance 1 m 60 dB(A) Average home 50 dB(A) Quiet library 40 dB(A) Very quiet bedroom 30 dB(A) Background in recording studio or anechoic room 20 dB(A) Rustling leaves in the distance 10 dB(A) Hearing threshold 0 dB(A)