The frequency of vibration can be heard if the frequency is in range of human hearing, that is 20 Hz – 20 kHz. If the frequency below 20 Hz, it is called infra sonic. Otherwise, if the frequency more than 20 kHz, it is called ultrasonic.
How can we hear the sound?
Sound can be heard because sound vibrates our eardrum. Source of sound which is vibration will create wave propagation in medium (such as air). Then it will vibrate eardrum. The propagation of sound has Intensity. Sound Intensity is defined as sound power in a surface area or in mathematic equation:
I = P/A.
Human hearing can hear sound if the Intensity of sound at least 10-12 W/m2.
How to calculate Sound intensity level?
Sound Intensity level is a logarithmic measure of sound intensity comparing with the reference Intensity. In this case, reference Intensity defined as the minimum intensity can be heard by human, that is 10-12 W/m2. Sound Intensity level can be calculated by:
Where I0 is reference Intensity. For example if the intensity of sound is 10-6 W/m2, then we can calculate sound Intensity level using that equation. That is L = 10 log (10-6/10-12) = 60 Decibel.
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