January 24, 2007

Sealed Sonotube Subwoofer Graphs

I've been using a program called Room EQ Wizard to perform subwoofer equalization, level matching, and crossover/phase measurements. It's a very useful multi-platform program that's also available for free although donations are welcomed. Since building my sealed sonotube subwoofers required measurements below 10Hz, I managed to get a beta copy of REW 4.0 that would measure that low. I haven't posted the following graphs until now because the program was still in beta, but now that it's officially released I can post my measurements.

These measurements were done with a Behringer ECM8000 microphone, and REW was loaded with a microphone calibration file made available at the Home Theater Shack. The ECM8000 isn't super high grade so the calibration file of someone else's mic is probably good enough. I extrapolated below 10Hz since the calibration file was only down to 10Hz, based on a converstaion with the person who performed the microphone calibration, and also my subjective listening.

I used a M-Audio MobilePre USB preamp to supply phantom power to the mic and serve as an outboard input and output audio interface to a laptop. The MobilePre doesn't perform super well in the very low frequencies, with a measured drop off by REW, but at least it can be perfectly measured and compensated for by REW.

Here is the measured room response for the subwoofers in conjunction with the mains, crossed over at 70Hz after equalization and boost was applied. There are about 16 filters being applied to boost below 20Hz and flatten the response with the lowest center frequency at 20Hz.

Posted by josuah at January 24, 2007 6:14 AM UTC+00:00

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