How the Room Equalizer Wizard Woke Up My Subwoofer

[geekwithfamily]

You’re not going to believe this, but dialing in the volume, crossover and phase on your subwoofer with a computer running Room Equalizer Wizard (REW) is totally fun. I walked a mile back and forth between my Hsu VTF-2 sub and MacBook Pro last night. I enjoyed every pace.
Here’s my formula for fun:

1. Carry our small, bar height kitchen table downstairs to the listening room without marking up the stairwell walls much (it’s a great height for my Mac Book Pro and it fits between the side of my listening couch and my component rack, so all the line in and line out cables can reach)
2. Set up my Radio Shack SPL meter on a tripod at ear height on my listening couch
3. Run RCA to mini-jack cables between the meter, the laptop and my Onkyo TX-DS989 AV Receiver
4. Start up Parallels (great Windows OS emulation on your Intel Mac) and run REW (I had to download the latest Java engine, I guess Windows XP SP2 doesn’t install it)
5. Load the RS Meter calibration file from the Home Theater Shack site for your meter model
6. Insert ear plugs to protect hearing from low and loud bass test tones
7. In REW Set the Measurement Level by setting the Radio Shack meter to 80 dB and increasing the volume on your amp until it reads -5 (75 dB)
8. Set the Input Volume (automatic audio input gain setting) and calibrate the dB SPL reading in REW with the RS meter’s reading
9. Fail at profiling the soundcard (I can’t defeat a feedback loop)
10. Select the Sub tab
11. Turn off the amp for the left and right front loudspeakers to measure the sub by itself
12. Set the Target Level for the sub
13. Take an Automatic Measurement sweeping up to 200 Hz
14. Click OK past the corrupt data error (YMMV, could be a Parallels problem)
15. After applying 1/3 octave smoothing look at the frequency trace and compare its ugly peaks and nulls with the flat target
16. Tweak the crossover, phase and volume on the sub again
17. Take another measurement
18. Repeat the last five or six steps until you like how your trace looks (you’ll never be satisfied) or need to go to bed because you’re keeping the rest of the family up with your short bursts of 75 dB pink noise and sine sweeps
19. Pack up.

So after over an hour of tweaking and measuring good times I had completely changed the settings on my sub to get the flattest response that blended with my front speakers. Before taking measurements my Hsu VTF-2 was set up with a ~80 Hz internal crossover, 180 degree phase and ~75 dB volume level. REW showed me that I got the flattest response by bypassing the internal crossover (I send the sub a full bandwidth signal so I guess I’m using the woofer natural roll-off). Eliminating the crossover killed a large peak at 120 Hz and raised a wide null I have between 140-180 Hz, all my peaks below 80 Hz were flattest without the crossover also. Weird.
I listened to Shellac’s At Action Park this morning before work and the bass was way more powerful than I am used to, but imaging was improved and shy bass lines and kick drums ruled the mix.
I think I’m going to try a few more crossover and level settings tonight, maybe seeing what happens when I set a low crossover and higher level. I may also remove the inline RCA 85 Hz high pass filters on the left and right loudspeakers, hopefully I have enough power in my amp for the extra low octave. It’s fun to experiment when you can see what the sound is doing visually.
I also measured the low frequency response with and without my new DIY bass traps. The bass traps definitely improved the low frequency decay times over most of the frequency range. A little empirical proof that I’m doing something right.
If you have a computer capable of running Windows (like my Mac Book Pro) and a Radio Shack SPL meter you should check out Home Theater Shack’s Room Equalizer Wizard ( I haven’t mentioned the whole other half of the fun with REW: its ability to build parametric equalizer filters for the under-$100 Behringer DSP1124P Feedback Destroyer Pro, when and if I get one I’ll tell you how that goes).
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