# Subwoofer Crawl Test: What is the acoustical explanation?



## AudiocRaver (Jun 6, 2012)

HOW does the subwoofer crawl test work, in physical and acoustical terms? I know how to go about it, placing the sub at the prime Listening Position (LP), right up on the couch or the Lazy Boy, and then playing music through it, or LF sine sweeps if you really trust your judgment, and crawling around the room to find the location where the bass sounds best, nice and strong and even throughout its range, and that is supposed to be a good location for the Subwoofer Position (SP). What I would like to hear is the explanation for WHY and HOW this method is effective? Can anyone explain it in terms of room modes, coupling efficiency, etc..... in real acoustical terms?

Edit: Beg pardon, did not realize I had accidentally posted an early "not ready for prime time" version of the question. I deleted it in favor of this version.


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## hjones4841 (Jan 21, 2009)

I am sure someone else will give you a more eloquent discussion, but my understanding is that the room modes are "interchangeable" between the main listening position and the sub location. If the sub excites at the MLP, then the same modes will be present wherever you crawl to as they would be with you at the MLP and the sub at each place you crawl to. 

Each "tone" has a particular wavelength. In a room, there will be a resonance for each major dimension (some say also for diagonals.) Also resonances at the harmonics of the "tone" 30, 60, 90 Hz, etc. So, the best location is the one that provides the smoothest freq response - no overlapping of peaks and nulls of modes.

Having measuring equipment is superior to using your ears. In that case, put the sub at the MLP and move the mic around instead of yourself.

The problem with all this is that a foot or two can significantly change the freq response at any given point in the room. Audyssey, as well as other room compensation algorithms, compensate that by adjusting EQ and timing for an average of seats by moving the mic around.

So, again, I am sure you will get more info from others but that is what came to my mind when I read your post.


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## asere (Dec 7, 2011)

hjones4841 said:


> I am sure someone else will give you a more eloquent discussion, but my understanding is that the room modes are "interchangeable" between the main listening position and the sub location. If the sub excites at the MLP, then the same modes will be present wherever you crawl to as they would be with you at the MLP and the sub at each place you crawl to.
> 
> Each "tone" has a particular wavelength. In a room, there will be a resonance for each major dimension (some say also for diagonals.) Also resonances at the harmonics of the "tone" 30, 60, 90 Hz, etc. So, the best location is the one that provides the smoothest freq response - no overlapping of peaks and nulls of modes.
> 
> ...


Other than an spl meter what equipment can you use for the crawl?


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## hjones4841 (Jan 21, 2009)

asere said:


> Other than an spl meter what equipment can you use for the crawl?


There is always REW, which requires a computer, a microphone (preferably calibrated). REW is available free here at HTS:

http://www.hometheatershack.com/forums/rew-forum/

A calibrated mic is available here:

http://www.cross-spectrum.com/

The mic requires a phantom voltage source; many of our members use an inexpensive mixer, like this Behringer:

http://www.amazon.com/Behringer-Pre...d=1362221780&sr=1-12&keywords=behringer+mixer

(I think there is one with fewer inputs for less money.)

With this you can go far beyond finding the best spot for your sub(s). It can help you design and place room acoustic treatments.


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## The Yeti (Jan 23, 2013)

And don't forget, you can get a USB mic that doesn't require a phantom power source.

http://cross-spectrum.com/measurement/calibrated_umm6.html


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