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# Sound Wave Amplitude and Loudness

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on 28 July 2013

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#### Transcript of Sound Wave Amplitude and Loudness

Sound Wave Amplitude and Loudness
Introduction
This presentation will try to explain the difference between amplitude and loudness for sound waves.

There is a sound test at the end where you can see if different frequencies appear to be louder than each other.
Loudness
Generally for a sound wave, as the amplitude becomes larger, the sound appears to be louder.

However, amplitude is something that is measurable by a computer and loudness is our perception of that.
Sound Waves
"Sound is a mechanical wave that is an oscillation of pressure transmitted through some medium (like air or water)"
Wikipedia

Sound can be represented as a transverse wave
Sound Waves
For sound, the amplitude is a measure of the extent that the air compresses and rarefies as the sound travels through the it.
Amplitude
Equal-Loudness Contours
Experiments have been conducted which tested our perception of loudness for different frequencies.

These are often called Fletcher-Munson Curves after the people who first created them.
An equal-loudness contour is a measure of sound pressure (dB SPL), over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones.
Sound Test
As a rough test of how we perceive loudness with different frequencies I created a sound file which includes 9 pure sine wave notes at 9 different frequencies. The amplitudes of the notes are the same.

The notes correspond to the notes C , C etc upto C .
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The frequencies (Hz) of the notes are -

C - 16.35
C - 32.70
C - 65.41
C - 130.81
C - 261.63
C - 523.25
C - 1046.50
C - 2093.00
C - 4186.01

Sound Test
Move to the next frame to play the notes
Did you perceive a difference in loudness?
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Full transcript