Wavelength vs. Frequency


Member Sponsor & WBF Technical Expert
Jun 23, 2010
Monument, CO
Nothing special in this one, just a simple plot. When discussing distances, whether related to room interaction, comb filter effects, room treatment or whatever, there is often the assumption that bass frequencies are "everywhere" while higher frequencies can be "directed" or are "more directional". The reason for this argument has to do with wavelength -- the length of the total sonic wave at a given frequency. Like waves in the ocean, there is a certain distance from peak to peak of audio signals, and that is their wavelength. It is related to frequency; higher frequencies have shorter wavelengths. The actual equation is w = vp / f where w is the wavelength (e.g. feet), vp the propagation velocity (about 1130 ft/s for sound in dry air at sea level), and f the frequency (Hz). Room modes or comb filter effects happen when sound waves bounce off walls or interact with other surfaces, or even arrive from two different sources (like, two speakers) at the same time. at the listening spot. The sound waves recombine, either adding (constructively) or canceling (destructively). This changes the frequency response.

There are many discussions about the effect of reflections and recombination of sound waves from various sources (speakers, walls, ceiling, tables, whatever) but all I am going to do here is show wavelengths for various frequencies. This will hopefully provide a little insight into what distances matter in your room. Note that room modes tend to happen around w/2*x (x = room dimension), and w/4 can lead to sound cancelling or doubling as well.

HTH - Don


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