Room Acoustics Forum by Rives Audio

You don't have to work them out for treatment…

121.222.135.172

In Reply to: RE: calculating nulls posted by Toology86@yahoo.com on June 25, 2008 at 23:05:04

Doesn't matter whether it's a null or a peak, the treatment is bass trapping in the corner. Do enough bass trapping and the nulls and peaks smooth out very nicely.

On the other hand, if you want to simply locate the listening position or speaker in a location other than a null it's a different matter. The nulls will occur at one quarter and three quarters of the wavelength from a wall.

First you need to work out whether the null is due to a standing wave between the front and back walls, the 2 side walls, or the floor and ceiling. Then you avoid locations spaced a quarter and three quarters of the null's wavelength from those surfaces.

The reason for the quarters is that there is a peak at the wall, and another peak half a wavelength away. The null is midway between the peaks.

There are also nulls associated with standing waves at half of each room axis, a quarter of the room axis, a third of the room axis and so on. Calculate how many times the relevant wavelength of the null fits into a room axis—eg 2 times for the wavelength that fits twice into the axis; multiply that number by 2—eg 2 x 4 = 8; then take the odd fractions of the room length so for that wavelength you'd take the first, third, fifth and seventh eighths of the room length.

Finally there's a null associated with the quarter wave reflection, ie it occurs at a frequency with a wavelength 4 times the distance of the speaker from a room surface. You can't eliminate that null unless you use absorption at the wall surface. All that moving the speaker does is to change the wavelength.

Hope that helps.

David Aiken

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