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Help EQing subwoofer w/ REW (graphs included)

3066 Views 6 Replies 5 Participants Last post by  HifiZine
Hi all, I needed some help getting my EQ set up for my DIY Shiva-X subwoofer. I tried to include all the needed details below. Thanks in advance for the help!

My DIY subwoofer is built around a Shiva X driver (note: the original, not the X-2), and the design is a 6.5 cu ft. box, with two 4" ports tuned to about 19hz (design here). My current configuration of everything while doing my REW measurements is:

  • UMIK-1 calibrated by Cross Spectrum Labs, and REW (5.01 Beta 17) set up for ASIO, which all appears to work great
  • Pioneer SC-05 receiver with subwoofer channel level set to 0.0 (i.e. no gain or attenuation, dead middle)
  • ART Cleanbox PRO set to +5db boost (I tried raising it to +10, the max., and REW showed absolutely no difference, so I backed it off to +5db)
  • iNuke 3000 DSP running in Dual Mono (i.e. not bridged), with Channel A level set to 75% of maximum, and all filters disabled (note: I probably need a highpass filter since my box is ported...but not sure how to set lower than 20hz w/ the iNuke).

I did some initial testing/measuring by moving my subwoofer around the room and checking for major differences in the measurements. I settled on the position indicated in the following diagram of my room, which also details the size and any doorways/openings.

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From this position and with the settings I described above, I ended up with the following measurement from REW:

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I know I need to do some EQ, and I've played around with the Auto-EQ functionality in REW, but am not totally clear on the settings to use to obtain a good set of filters from REW. So I used the following settings to then generate the new curve & filters shown below. Further down I also show an EQ I created with some adjustments to what REW had originally done; this seemed to be a bit smoother and eliminates one filter (from my reading it seemed less EQ was better).

Auto-EQ Settings in REW: I'm not sure if these should be adjusted to give "better" results from REW
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Auto-EQ Results:
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Auto-EQ Filters:
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My own adjustment of the REW EQ...this seemed to be a little better and use one less filter...

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Can you show the target curve? It's hard to guess where your target is. From what I've read here, don't worry as much about valleys as you do peaks, as the absence of sub is less audible than excessive gains. I noticed you have a few filters over 10db gain. My sub took issue with that, and had some audible warble like sounds when going over 10db while playing music. During the sweeps it wasn't noticeable though. You may suffer the same issues as I did. I decided to go the opposite route however and lower things around it instead without worrying about the drop outs. In the settings you can set the maximum filter gain. Perhaps set that at 10db and rerun it?

With my setup I had two sizable drop outs. Placement took care of one of them and using a feedback destroyer lowered everything around it helped minimize the other valley by half. It sounded a lot smoother afterwards and the warble issues went away.
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Unfortunately you can't set an HPF below 20Hz on the inuke and there isn't a work around I'm aware of aside from disabling it and using something else in the signal chain for an HPF.

What's your crossover point? If it's near 90Hz, everything is looking good and your FR looks very flat. How's the waterfall look?

You mentioned trying a few different positions, since you have a regular looking rectangular room the current beta release of REW has a room simulator that could help you find another layout to try. If nothing else you should be able to identify the sources of your peaks and nulls so you know where to apply room treatments.

As I understand, this is a predicted curve – there’s no EQ actually in the signal chain?

For starters, the 70.5 Hz filter is probably useless – it’s too close to the crossover frequency and will probably be blown out by overlap from the main channel speakers.

The 53 Hz issue is probably a null; they’re easily identified as being deep and narrow. If that’s the case, you can’t do any equalization to correct it. So scratch that one, too. You might have the same problem at 70 Hz as well.

58 Hz? I don’t see a problem there that requires equalization!

You probably won’t like the sound of a flat EQ curve. The REW auto-EQ curve will probably sound better, except that there are too many filters doing virtually nothing – take out #1, 3, 4, 5, and 7.

I’m surprised you have extension as good as you do with the sub located on the center of a wall. That usually gets dismal response. Still, I’d suggest taking a baseline reading with the sub in a corner. That may well eliminate those nulls you have.

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Thanks for everyones help. To clarify a few things based on the responses:

  • No EQ is actually applied - the EQ shown is the "predicted" EQ from REW. I didn't want to go applying EQ until I had some feedback.
  • My crossover is set to 80hz right now, but this was just randomly set. My mains and center are Monitor Audio RX-6's (and the RX centre).

Based on the advice from many to try some positioning, and specifically Wayne's on trying a corner, I tried placing the subwoofer in a corner (see picture below) and running some measurements. What does everyone think of the difference? It seems less smooth below 30 Hz, but drops off much more smoothly above 80 Hz.

I think once the position is settled then I can go apply the EQ suggested by Wayne and be pretty much set.

Red Line is the original position, Blue line is the alternate / corner position

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Room layout with alternate sub position (sub driver facing left, towards the TV in each)

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Hmm, not hugely better. Is the front right corner an alternative? Or perhaps directly to the left of the right front speaker?

On the settings side, try reducing your max boost settings to say 3 dB, and also lower the target level. That should prevent those high-Q boosts from coming in, which as Wayne says you don't really want.

And/or post your mdat file here and we can all play with it :)

Another idea: do a measurement with the sub crossver turned off and then try the eq generation with the "full range" setting, range say 20 to 150. I prefer doing it this way as then I can adjust the sub crossover to get the best bend with the mains.
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