All there is to know about dB :
The sound intensity level B (beta) is given by (10dB) x log I / Io
Io is a refernece intensity chosen to be 10E-12 Watts per metre square, the
approximate threshold of human hearing at 1000Hz.
If the intensity of a sound wave equals Io, its sound intensity is said to
be 0dB. An intensity of 1 watt per metre square is equivalent to 120dB.
However, the ear is not equally sensitive to all frequencies in the audible
range, and this gives rise to the dBA scale. This scale de-emphasizes the
low and very high frequencies and uses the midrange frequencies to give a
better indication of the sound level you are hearing.
Back to ordinary dB - an intensity increase of a factor of two leads to a
3dB increase in sound intensity level. This change is barely perceptible to
the human ear, and most people usually equate an increase of 8 to 10dB in
sound intensity level to a doubling of loudness.
So there is a point in doing a degree in Electronic Engineering! Hooray!
Ian (going to put his in-car MD player in to his new car :-) )
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