What is an octave?

eryn shannon

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If a subwoofer plays 2 octaves below your main speakers what does this mean? Is 1 octave a specific number of Hz?
 

Craig Chase

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An Octave is the doubling of frequency... for example, 300 Hz is one octave above 150 Hz... and the 150 to 300 Hz range of tones represent one octave.

We also have the human hearing scale...

20 - 40 - 80 - 160 - 320 - 640 - 1280 - 2560 - 5120 - 10240 - 20480 Hz...

We have a hearing range of about ten octaves...as shown above...and if your main speaker can play to, for example, 80 Hz, and a subwoofer adds 2 octaves, it would play to 20 Hz...
 

Wayne Ernst

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Craig,

Very good job of explaining the octives in "laymans terms."
 

Chu Gai

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And you may have also heard of things like 1/3 octave as in 1/3 octave equalizers. One might think that is nothing more than divvying into numerically equal thirds the spaces between two octaves. However it doesn't work like that.

While in a 1/3 octave equalizer, the spacings are three to an octave, they are spaced by the cube root of 2 = 1.2599. An example of frequencies spaced by 1/3 octave would be: 20hz, 25.2, 31.7, 40, 50.4, 63.5, 80 and so forth. Note how every third number (20, 40, 80) is another octave (doubling).

20 * 1.2599 = 25.2
25.2 * 1.2599 = 31.7
31.7 * 1.2599 = 40

Make sense?
 

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