4 corner subs and Audyssey XT32 - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 11-08-2019, 09:33 AM - Thread Starter
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4 corner subs and Audyssey XT32

I am planning on going from 2 subs to 4 smaller subs. I am currently running 2 UM18 in the front corners of a 23’x13x7.5’ theater. The goal will be better frequency response as there is a lot of variation seat to seat and some nulls I would like to deal with at the main listening positions. Not sure what subs yet, but they will all be the same. Receiver is a Denon X8500 with 2 sub outs.
My question, however is if my two front and back subs are positioned in the corners, and I split the front subs of of sub out 1, and the back subs off of sub out 2, will audyssey do an adequate job, or will it be necessary to use something like a minidsp hd? My hope would be since the front/back subs are symmetrical Audyssey would be able to handle it. Thanks.
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post #2 of 9 Old 11-08-2019, 09:58 AM
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My recommendation is to try your plan with splitters to see if you like it given the subs in corners are likely equidistant from MLP. If equidistant, the Audyssey delays should be set correctly and Audysey will equalize Sub 1 and Sub 2 as though it's a single sub.

If you enjoy digging in, you will definitely get better results with the MiniDSP HD particularly if you use MSO (Multi Sub Optimizer) freeware to improve seat to seat performance / variations.

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post #3 of 9 Old 11-08-2019, 10:14 AM - Thread Starter
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Originally Posted by zorax2 View Post
My recommendation is to try your plan with splitters to see if you like it given the subs in corners are likely equidistant from MLP. If equidistant, the Audyssey delays should be set correctly and Audysey will equalize Sub 1 and Sub 2 as though it's a single sub.

If you enjoy digging in, you will definitely get better results with the MiniDSP HD particularly if you use MSO (Multi Sub Optimizer) freeware to improve seat to seat performance / variations.
That is what I was thinking of doing. Will I need to adjust the phase of the rear subs?
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post #4 of 9 Old 11-08-2019, 10:57 AM
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Try it two different ways: run front subs and rear subs using both subwoofer outputs versus running all 4 subs from one subwoofer output. Don't be surprised if the latter gives better results, but the only way to know for sure is to try them both.
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post #5 of 9 Old 11-08-2019, 12:27 PM - Thread Starter
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Originally Posted by sdurani View Post
Try it two different ways: run front subs and rear subs using both subwoofer outputs versus running all 4 subs from one subwoofer output. Don't be surprised if the latter gives better results, but the only way to know for sure is to try them both.
Thanks. I wouldn’t have thought of even trying that. Another question in running 4 subs, how essential is it that they are identical. For example if I keep the two sealed UM18’s in the front 2 corners, and added something like the Rythmik L12 or similar to the back two corners...
1-Could this still work ok if my main goal is to reduce room modes above 20hz?
I just don’t have the space to put 2 more UM18 sealed subs in the back corners but do have space to put something like a pair of L12’s in the back corners. Pluses/Minuses of something like this?
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post #6 of 9 Old 11-08-2019, 12:36 PM
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Quote:
Originally Posted by dj7675 View Post
Thanks. I wouldn’t have thought of even trying that. Another question in running 4 subs, how essential is it that they are identical. For example if I keep the two sealed UM18’s in the front 2 corners, and added something like the Rythmik L12 or similar to the back two corners...
1-Could this still work ok if my main goal is to reduce room modes above 20hz?
I just don’t have the space to put 2 more UM18 sealed subs in the back corners but do have space to put something like a pair of L12’s in the back corners. Pluses/Minuses of something like this?
Ideally they would be identical, but as long as their capabilities are similar, you should be OK. I suggest having 1 of each on each of the 2 channels in order to achieve balance between the channels.

The only thing a DSP would get you is proper delay on each channel. And maybe some eq'ing, but the eq'ing by the receiver is set with all subs playing at once, so unless the receiver does a bad job, you wouldn't need the DSP to eq. Getting the distance exactly right on subs isn't nearly as important as the other speakers sine the sub wavelengths are very long.

I would leave the phase alone. You'll likely make a mess of things if you play with it. Better to have the receiver make adjustments.
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post #7 of 9 Old 11-08-2019, 02:08 PM
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Quote:
Originally Posted by dj7675 View Post
Thanks. I wouldn’t have thought of even trying that. Another question in running 4 subs, how essential is it that they are identical. For example if I keep the two sealed UM18’s in the front 2 corners, and added something like the Rythmik L12 or similar to the back two corners...
1-Could this still work ok if my main goal is to reduce room modes above 20hz?
I just don’t have the space to put 2 more UM18 sealed subs in the back corners but do have space to put something like a pair of L12’s in the back corners. Pluses/Minuses of something like this?
You always want to use similar subs (sealed or vented) with your specific goals. Better yet is to have all matching subs for best results.

Dr. Floyd Toole's book references using different size subs to accomplish better seat to seat variances as different locations have different power needs for the subs. Section 8.2.8 starting on page 244 "Sound Field Management" describes the process. You can use MSO and his instructions to do this properly and make it work. The book is available on Amazon and is a great life long resource if you love AV.

My own thinking (not paraphrasing from Dr. Toole's work or ideas) is that you'll be getting a lot of gain from two UM18s in front corners and there will be a huge output disparity. IIRC, you'll want to gain match the subs so they run out of headroom at the same time. However, I don't know if the frequency response would remain consistent with volume changes between the two different pairs. People do integrate subs as MBMs and behind their seats that aren't as powerful as their main subs so I think it would work.

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post #8 of 9 Old 11-08-2019, 03:13 PM - Thread Starter
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Quote:
Originally Posted by zorax2 View Post
You always want to use similar subs (sealed or vented) with your specific goals. Better yet is to have all matching subs for best results.

Dr. Floyd Toole's book references using different size subs to accomplish better seat to seat variances as different locations have different power needs for the subs. Section 8.2.8 starting on page 244 "Sound Field Management" describes the process. You can use MSO and his instructions to do this properly and make it work. The book is available on Amazon and is a great life long resource if you love AV.

My own thinking (not paraphrasing from Dr. Toole's work or ideas) is that you'll be getting a lot of gain from two UM18s in front corners and there will be a huge output disparity. IIRC, you'll want to gain match the subs so they run out of headroom at the same time. However, I don't know if the frequency response would remain consistent with volume changes between the two different pairs. People do integrate subs as MBMs and behind their seats that aren't as powerful as their main subs so I think it would work.
Appreciate the detailed response. I think will pick up a couple of 12 inch sealed subs to put in the back corners. First, will try different combinations of just using Audissey and measure to see how it does. If I want better, will get a minidsp to get it eq’d the best I can before Audissey calibration. I have always wanted to pick up a copy of Dr. Toole’s book so now looks like a good time for a little education Thanks again.
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post #9 of 9 Old 11-08-2019, 04:44 PM
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A few ideas for you:

1. Equalize once - after everything is configured (Dr. Toole's recommendation). I know people on AVS occasionally advocate for pre-tweaking before or after Audyssey but Dr. Toole recommends not doing that.

2. If you have a calibrated microphone, take your existing sub and measure it in REW from each possible location in combination with each possible seat. Then, run those measurements in MSO and it will give you are very, very good idea of how things will work for you even before you purchase other subs. I've done this for my own theater to test the impact of adding a 3rd and/or 4th sub. MSO did a great job in helping me evaluate how those would work without having to purchase subs to try it out.

3. Definitely buy Dr. Toole's book - given what we all spend on audio, it's well worth the price. The section I previously referenced will clearly go over everything you are trying to do.

7.2.4 with Denon X4300W, ATI 2005 & 1807 Amps, Kef Reference 203 Mains, 202c Ctr, 201 Surr, Ci200RR-THX Top Rears, Q300 Frt Hts, E301 Rear Surr, Power Sound Audio PSA dual S3600i Subs,
GIK & DIY Acoustics, JVC X790/RS540 Projector, Stewart Neve 100" Screen, Panasonic Blu-Ray DMP-UB900, Xbox One X, Crowson Transducers, INSTEON, UDI ISY994i, Amazon Echo
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