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Multiple Subwoofers....what I didn't know


Rudy81

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I recently completed my build of four Full sized Marty ported subs using 18" Dayton Audio RSS460HO reference drivers.  The subs turned out great and put out a tremendous amount of bass.  I originally placed them in front of my HT, next to my mains, and removed the two RSW-15's and two SPUD clones I had been using.  This is what the original setup looked like.

 

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My experience with the new setup was really good, actually too good, in that the bass was simply overwhelming and I ended up continually turning down my amps to make the bass tolerable.  I also experienced the usual problems with room modes that were greatly magnified with all the bass output. 

 

That led me to doing quite a bit of research on subwoofer placement and the current theories on bass management.  After reading some articles from acousticfields.com I dove deeper into the subject.  Acoustic fields recommended spreading out the subs around the room and also raising the subs off the floor.  Frankly, it did not make sense that it would improve the perceived sub performance.  It seemed like a crazy way to set up 4 subs around a room.  But, I figured I didn't have much to lose and had a way of actually measuring the results. 

 

I also found that Room EQ Wizard, REW, has a new feature which simulates moving as many as 4 subs around a room and displays the resulting room modes and frequency response.  I modeled my room in REQ and this is what it predicted:

 

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I then used REW and my calibrated mic to measure the actual room response.  I should note that my room is heavily treated for mid to high frequencies and some low frequencies.  Of course, the room also has carpeting, furniture etc. Much to my surprise, I found the actual room response to be similar enough to the prediction to convince me that there is something to this theory. Here is the actual room response, unsmoothed, raw data for the 4 subs.

 

5a84d77d96640_OriginalMartySetupSweep.jpg.b0a449b3295580c6199c0183f5b208b9.jpg

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I then decided that it would be worth my time to move all the subs around and place them in whatever 'optimal' positions I could find around the room.  I used the REW simulator to locate the placement since it is rather difficult to move the subs with ease.  I played around with may configurations, including some default corner and mid-wall positions.  After hours of playing with this, I came up with an optimal room response if I placed one sub along the left wall, two along the right wall and one along the back wall.  The other issue was that the optimum simulation required the subs to be raised off the floor approximately 4 feet.  Turns out that was easy to do since I built the subs with the drivers at the end of the 4 foot cabinet.  In some instances the sub needed to be raised a bit more and I used some stands I had laying around.  This is what the room looks like now.

 

FrontSideWallSM.jpg.a65c5fb473d52473bbc8b10a844d1e47.jpg

 

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The REW simulation indicated this:

 

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The simulation certainly indicated a much smoother response within the room. After setting up the subs I then ran REW again.  Here is the new response in the room, unsmoothed and raw.

 

5a84d9cea64f0_4Martysphasealigned.jpg.6fa5b6dcdb5443d4f98ec37243eba2be.jpg

 

The above graph shows the first run in red with no other adjustment done to the subs.  Frankly, I found that to be amazing!  The black line is the result after phase aligning all 4 subs and optimizing the response by using time delay so that the 4 subs reach the listening position simultaneously.  I am thrilled to have found all this information. After many years of working with my room and various subs, this is simply amazing!  Subs have always caused major problems in optimizing my room response.  I decided to post this thread in case it might help other sub fanatics with their setup. 

 

BTW, I did bring back my two RSW-15s and they are now integrated with my mains and the 4 Marty's.  I just finished all the work today, so will be doing some critical listening in the next few days. 

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44 minutes ago, RoboKlipsch said:

fantastic effort for a huge payout.

 

i want to see a sweep starting at 5hz....those martys arent looking tired at 20 😀

 

The subs have huge performance I will probably never push.  I have two Behringer EP4000 amps powering the 4 subs.  In order to get Audissey Pro to even accept the readings, the amp gains are only half way up.  The nice thing is the bass is amazingly even throughout the 7 listening positions in the room.  Of course the main listening position is darn near perfect.  

 

I am really surprised that such an unconventional setup actually works and improves greatly upon what I had normally considered a good setup.  All 4 Marty's are pointing at the ceiling and I am getting really nice, clean, in your chest bass.  I hope to do some more listening tomorrow, but thus far I am glad I took the time to learn the theory and implement the idea. 

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45 minutes ago, CECAA850 said:

Great summation and pictures Rudy.  Many wouldn't go to the effort to do things right.   As you can tell it really pays off.  Your bass needs should be satisfied for the immediate future lol.

 

Yes, more than enough bass.  Audyssey Pro also noted the change in room/subwoofer interaction as well.  My original setup had a nasty bass cancellation that Audyssey could not fix. That problem was no longer evident with the new setup.  So far I am thrilled with the results.  My future plans call for making some minor tweaks to the room in terms of absorption and diffusion. 

 

The acousticfields.com site has some interesting ideas on bass absorption and diffusion which I hope to build at some time.

 

These are the original and new final Audyssey Pro plots.

 

5a8502d0f38e0_AudysseOriginal.thumb.jpg.ed3b54a16de32b7f3801c346a9b291f3.jpg

 

5a8502e996000_AudysseyOptimized.thumb.jpg.e6ecf909147b420346cc9f9d5fcbd912.jpg

 

A rather noticeable difference in the raw readings and the Audyssey EQ'd results.  I really like that flat line at the bottom right with the new setup. 

 

BTW, if I didn't mention it before, for the mains, I am using my old RSW-15's from 20-80Hz.  REW recommended placing one sub mid-wall front and one mid-wall back of the room.  Worked out great.  The integration with the mains was really good.  I ended up needing to invert the polarity on the RSW and Marty's to get everything to work in phase and sum vs. creating response dips.  So far....so good!

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More subs is more consistency, and placement as you found is by far the most important part.  The modeler helps a lot but testing is really the way to do it.

 

The extra amp power could be used but you dont need it, that is the point. I almost never hit the 3rd light on my inukes simply because i have that much headroom and my gains are similar.  More subs also reduces how much each has to contribute.  

 

I kept tweaking for days and hours until no change made it better.  Kind of a quest for perfect. The only real benefit of that last 20% was to know i cant make it better.  Yours is pretty darn good.

 

The only thing that comes to mind is facing the drivers up may lose some tactile feel vs facing the lps, but with full martys it may not much matter.  Kudos for shuffling around those monsters.

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I could be wrong but i think -12 on the sub trim is maxed out...its still too high.  Audyssey cant lower it enough to perfectly balance with the other speakers.  You may want to try rerunning it after lowering gain a few clicks on the knobs.  

 

Anything higher than -12 will show it is in range from what i recall.

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Thanks.  I am aware of the -12 trim issue.  Right now the gains on the amps are half way down.  For a while I plan on doing some critical listening and then I can re-run Audyssey if need be.  I have found that I tend to like a little more bass than Audyssey would have me set.  The beauty of my active system is that I have plenty of flexibility in adjusting gain.

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48 minutes ago, Rudy81 said:

I have found that I tend to like a little more bass than Audyssey would have me set.

Audyssey should have an optional Fletcher Munson curve setting.  Anytime I calibrate anything, I set everything flat then bump the sub by about 6dB.  Flat sounds way too thin for me.

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54 minutes ago, CECAA850 said:

Audyssey should have an optional Fletcher Munson curve setting.  Anytime I calibrate anything, I set everything flat then bump the sub by about 6dB.  Flat sounds way too thin for me.

 

That's exactly what I do.  Yesterday I ran Audyssey Pro and then had a short listening session.  As usual, I found the bass to be a little thin and using the ability to modify the resultant curves I boosted the region below 80H by 3db.  So far, it is sounding good.

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2 hours ago, RoboKlipsch said:

just wanted to mention it.  many people calibrate then use the full gain, just wanted to point it out.  u know what youre doing👍

Ha!  The full gain blows me out of the room!  This afternoon I took the LFE channel from -12 to -10 based on some Blu Ray concerts I have.  So far, so good.  Plenty of nice clean bass with lots of punch!

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8 hours ago, Khornukopia said:

Your bass response graph is impressive.

 

I agree.  Certainly the flattest and least response needing correction I have ever gotten with any of my subwoofer projects. Just a crazy concept if you ask me.  Funny think is I built 4 subs on the advise of an AVS forum member who suggested 4 in order to properly fill the volume in my room.  He was right.  My two RSW-15's also provided a nice curve positioned along opposite mid-wall locations.

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I had 1 and its fine for 1 seat only.  Then 2 and it got 3 seats good but not matching.  I maxed out what could do in an l shaped room.  4 is the sweet spot.  Its enough to provide ample headroom and lots of nulls and peaks nicely cancelled. Beyond 4 gets even better but is more a matter of slam and punch bonus ime.    I still request a sweep from 5 and up.  You bettet not be high passing at 20! 😈

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On ‎2‎/‎14‎/‎2018 at 5:56 PM, Rudy81 said:

The other issue was that the optimum simulation required the subs to be raised off the floor approximately 4 feet.

 

So placing my subwoofers on top of some Cornwalls or similar size stands, at the middle of the four walls is the recommended positioning?

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1 hour ago, Khornukopia said:

 

So placing my subwoofers on top of some Cornwalls or similar size stands, at the middle of the four walls is the recommended positioning?

 

If you are really interested in examining the options, download and install REW.  Then use the room sim to model your room.  Add the number and type of subs you have and then move them around the room as much as you wish while you observe the expected room response.  The sim, AFAIK, is only for rectangular rooms.  You can change the locations and vertical placement of the subs in the simulation.

 

My experience and graphs prove there is something to this 'multiple subwoofer' theory.

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