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I have two massive resonances (more than 12db above the response curve elsewhere) with my bookshelf monitors placed on a desk in a large furnished, carpeted room. One is at about 110 Hz and another at about 250 Hz.

Are there any rules of thumb for determining whether response issues stem from the speakers themselves or from the room and/or placement besides common-sense "move the speakers to another location and re-measure?" Specifically, I'm looking for reasonable numbers I can expect for typical furnished rooms/placement effects.

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What kind of speakers, and especially, how big? – DarenW Dec 25 '12 at 9:25
@DarenW your question implies you have an answer. I think it might be more helpful to respond with a more universal answer that could help a wider audience than with guidance about my particular setup. – glenviewjeff Dec 25 '12 at 18:19

migrated from physics.stackexchange.com Dec 28 '12 at 19:35

4 Answers

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The 'rule of thumb' is to translate the resonance frequencies into resonance wavelengths. This is done by dividing the speed of sound by the frequency. For the 110 Hz resonance this yields a wavelength in air (speed of sound under normal circumstances close to 340 m/s) of 3.1 m, and for the 250 Hz resonance 1.4 m.

I am no audio/acoustics expert, but these wavelengths seem too long to 'fit within' a speaker. If the resonance is not caused by a standing wave due to air movement, but rather say due to a standing wave in wood, these wavelengths become an order of magnitude longer (the speed of sound in wood is about 10 times faster than that in air). These certainly don't 'fit within' your speakers.

This suggests that you have to seek the cause of the resonances in the environment in which the speakers are placed.

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For metric-haters and Americans, a rule of thumb is 1000Hz has a wavelength of about one foot. – DarenW Dec 25 '12 at 9:24
@DarenW So 2kHz is 2 feet? I don't think these kind of rules of thumb really help somebody... – Bernhard Dec 25 '12 at 10:34
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No, a 2 kHz wave would have a wavelength of about half a foot. Wavelength is inversely proportional to frequency. – Adam Strandberg Dec 25 '12 at 19:51
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@AdamStrandberg I thought Bernhard was being facetious implying that the rule of thumb doesn't give a direction. – glenviewjeff Dec 26 '12 at 4:19
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Could you place a sound absorber, like foam, in the room? If it makes no difference, then it's the speakers, not the room.

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Then I think it is easier and more reliable if you move the speaker set outside. But, I think he is looking for an answer where he doesn't have to do anything :) – Bernhard Dec 25 '12 at 9:14
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There is a standing wave calculator here. Not necessarily a one stop answer, but if your room's dimensions are indeed to blame, at least you can rule out the speakers :)

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My room's not rectangular. Besides, I'm looking for orders of magnitude of frequencies I can expect from a speaker vs. a room. – glenviewjeff Dec 26 '12 at 4:17
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You can check out if it is the nature/dimensions of your room that's causes the resonances.You can use this formula (f=n.343/2L) to check if you get the same frequency or not.If it is then it is the room which can be attenuated with absorbers.

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