Subwoofer EQ

A friend and I thoroughly and painstakingly auditioned various Emotiva multi-channel amps several years ago for our Orions. My reason for selecting the combination we ended up with was that the bass had a cleaner and more discrete character than with any other amp I’d had on the woofers. Textures and subtle amplitude envelopes are heard riding on the fundamentals of many bass instruments that otherwise weren’t heard before.

I’ve been speculating that this particular amp has lower harmonic distortion at the bottom end than other amps, leaving the harmonics on low bass notes relatively unmolested. This is unproven.

I read about Room EQ Wizard (REW) again yesterday, something I hadn’t looked at in several years. I have a Behringer DSP1124, the BFD “feedback destroyer”, which is a very cheap digital parametric stereo EQ with 12 bands that is popular with the home theater enthusiasts for equalizing subwoofers. I hooked up my modern laptop with a modern OS and a stable EMU 0404 USB soundcard to a cheap measurement mic and my Benchmark DAC. After installing REW, I was measuring away in just a few minutes. REW output signals went from the laptop to the Benchmark, through the system and out the speakers. The input from the mic went through the EMU and back into the laptop. This was really nice experience, unlike the old days of endless hassles with incompatible drivers and software and electronics.

After EQ’ing the sub conservatively, it sounds like there is a little less bass. There are four bands of equalization, a 1/2 octave band at 20Hz boosting about 4db, and three 1/6 octave bands cutting 3-4db at 35Hz and in the crossover region above 50Hz. The cut at 35Hz is probably responsible for the sense of less bass, as this is where “rumble” and “thump” is. (See the bottom right corner of this wonderful interactive chart.)

The subwoofer sounded fine with the EQ, but it lost a good degree of impact on good drum recordings and that discrete character that was so hard won by amp selection was gone. Maybe something good will come to light with further listening but for now it seems that the quality is better without EQ.

Perhaps the problem is group delay introduced by the equalizer, and not harmonic distortion after all. The BFD is not a very transparent unit, but one wouldn’t expect much grunge added to the deep bass from opamp noise and artifacts from the roundtrip A/D and D/A conversions it does.

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