Measurement of Sound
• A sound source is transferring energy into a medium in the
form of sound waves (acoustical energy)
• Sound volume related to pressure amplitude:
- sound pressure level (SPL)
• SPL is measured in decibels based on ratios and logarithms
because of the extremely wide range of sound pressure that
is audible to humans (from one trillionth=10-12 of an acoustic
watt to one acoustic watt).
– SPL = 10 log (pressure/reference) decibels (dB)
– where reference is 2*10-4 dyne/cm2
– 0 dB SPL - no sound heard (hearing threshold)
– 35 dB SPL - quiet home
– 70 dB SPL - noisy street
–110 dB SPL - thunder
–120 dB SPL - discomfort (threshold of pain)