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Sound Levels

Sound pressure level (SPL) or sound level is a logarithmic measure of sound pressure relative to a reference value. It is measured in decibels (dB). The commonly used "zero" reference sound pressure in air is 20 $\mu$ Pa RMS, the threshold of human hearing (at 1 kHz). It decides how much intensity the sound is having compared to the reference intensity!
If we label Pref as the pressure of sound of an audible sound and P as sound pressure, then we define the sound pressure level (SPL) Lp as

Lp = 20 log $\frac{P}{P_{ref}}$.

The (SPL) of audible sounds ranges from 0 dB to 120 dB. Sounds more than 120 dB may cause instant irreversible hearing loss, and will be quite painful.

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Decibel Level Chart

 Source Intensity Intensity Level Times greater than threshold Threshold of hearing 1 $\times$ 10-12 W/m2 0 dB 100 Sound of leaves 1 $\times$ 10-11 W/m2 10 dB 101 Whisper 1 $\times$ 10-10 W/m2 20 dB 102 Conversation 1 $\times$ 10-6 W/m2 60 dB 106 Heavy street traffic 1 $\times$ 10-5 W/m2 70 dB 107 Vacuum cleaner 1 $\times$ 10-4 W/m2 80 dB 108 Large Orchestra 6.3 $\times$ 10-3 W/m2 98 dB 109.8 Walkman at high level 1 $\times$ 10-2 W/m2 100 dB 1010 Front rows of music concert 1 $\times$ 10-1 W/m2 110 dB 1011 Pain threshold 1 $\times$ 101 W/m2 130 dB 1013 Jet take off 1 $\times$ 102 W/m2 140 dB 1014 Instant burst of eardrum 1 $\times$ 104 W/m2 160 dB 1015