Try a sub a third in the back

I’ll share something I stumbled upon in the off chance it transforms your listening experience as it did mine. I purchased a rel s/510 while they were on sale to replace a lesser sub. First, the sub is remarkable. I thought it would just add bass extension. I had no idea it would improve the sound stage so much. But now I had 3 subs with absolutely no space in the front of the room to place the third. I planned to sell it. If you like to tinker like me with your system, you probably would have had the same thought I finally did: connect the third sub for the hell of it. In part, the idea was inspired by the long and very good article someone on here linked to about subs: that talks about putting a sub at the back of the room for HT. The lower the frequency, the more non directional the sound. So, having a sub behind me should be okay in a two-speaker setup. The worst that might happen, I thought was that I might shake my house off it’s foundation. But what happened was absolutely unexpected. The sound in the room became amazingly three dimensional. This is not hyperbole. I have a good system and especially with the new Rel sub, there was good width, height, and depth to the sound. But the effect of adding the third sub was to double or triple the depth into the room. I didn’t believe it so I turned the rear sub on and off, repeating the songs. I’ve done this for a week because sometimes new experiences don’t hold up over time—a product of wishful thinking. This one has lasted. I will describe the change this way. Without the rear sub, the vocals were centered, other instruments were placed around the front of the room—some further away than others. Adding the rear sub stretched the centered voice in front of me from 2d to 3D, like someone was in the room, or better, I was in the vocalist’s room. Imagine taking a photo of the singer and stretching it into a 3-dimensional figure in front of you. It’s like that. Although my previous system had good depth before, with the third sub it sounded like I was swimming in the music. there was an exceptional separation of the instruments around and over me not just in front of me. I won’t go on because results will vary. But if you like to tinker and you have a third sub in the house, give it a go. I hope it turns out as holographically for you as it did for me. (Details: I connected the Rel using the line in from my power amp and two RCA outs on my Dac (it also has XLR outs that I use) to connect the other subs.)


My bad. My understanding was that the advice from REL was that the subs had to be at the front. I misunderstood.

Why so funny?...a stack is exactly what rel told me to do...doesn't matter where it is located...I asked them about 3 subs one in the back which is totally different 

I haven't measured it exactly. I know the subs are in phase with the mains but I haven't actually done the fine adjustment of phase listening from the sweet spot. So, you're right, there is likely a spread of the bass as a result.  Coincidentally, REL just sent out an email with a link to a video, "What does a $100k system sound like?" The guy has a swarm of 6 stacked REL speakers but guess where they are? Behind him! LOL. So funny, given the advice someone received from REL above. 


I’m curious how close these third sub placements are? If closer than mains, could it be improved group delay effects?

It’s great to hear everyone’s experiences with 3+ subs. Part of the joy I get from this pursuit of audio hallucination (as an agon contributor called it) is learning and tinkering. Thank you for sharing your experiences. I will tinker again in the ways you suggest.



Glad to hear they liked 3 subs. I have 4 and could not be happier.

I believe the secret is asymetricality (is that is even a word?).

A lot of us audiophiles suffer from OCD and the urge is to place the subs in a balanced formation, similar to our main speakers. Typically, two subs in front placed behind the main speakers and two in the rear corners.

This is a less than ideal configuration, as it only exacerbates any bass issues by doubling up the reflection points.

I use three RELs in my 2 channel setup to great effect. Ears and RTA show very even bass throughout the room (and house, for that matter).

I have a REL Carbon Special in the front right corner playing both channels and two REL S/5s on either side of the listening position playing the right and left channel bass frequencies.

All are crossed over very low ( my main speakers go fairly low) and set at relatively low volumes in order to have them stay in a linear range.  They are completely aurally invisible, but provide outstanding bass weight.

I love this setup...



Just want to thank you for posting about your discovery.  I sure appreciate it.  

Earl Geddes and Floyd Toole both contend that three asymmetrically located subs will provide the best bass response.

Glad to hear you've agreed.

I believe that a minimum of three subs works best in many HT systems, especially if there is an open floor-plan in the mix. MY main HT system is in the living room, with a 5-foot opening at the right-side rear into the dining area/kitchen. An L-shaped hallway branches off of the front right-side of the room and no two opposing walls are the same dimension as a result. I think all of that actually works to my benefit, making it easier to tune the subs for the best (even) bass response. There are two 15-inch subs at the front and two 12s at the rear, with the rears slightly offset from each other on opposing walls. The plane-crash scene from Cast Away is a gut wrenching thing to experience and is a good test to see how your system can handle that cacophony of mixed sounds.

Funny about the advice from Rel. I respect them, love their products, and suspect they were not just trying to upsell you to a swarm. Most of us here don’t have the luxury of trying things out for free. So, we read articles, ask for advice here and when enough evidence piles up we spend thousands for things we may have not heard. So, I entirely understand the comments about consulting Rel or looking at graphs… trying to understand in the abstract because many of us can’t easily/cheaply audition components in our homes. If I could invite you to my house I would so you could hear. I can’t so my opening entry in this thread is another piece of abstract advice: some guy you don’t know claims he had a transformative experience— a person who has little credibility compared to folks at Rel. I get it. And I can’t promise that any 3 subs plus any 2 mains will yield the same result. I can only say it happened in my system and might In yours if you try. Would I spend thousands to buy a new sub in the hope of achieving a holographic sound? No. The results are too system dependent. But if you have a third sub, try it out because you know for a fact that for one person something special happened.

Fun/long article about subs sited by another agon member:

After reading this post and thinking huuuum, sounds like I might try this as I'm running 2 Rels in stereo up  front ..I picked up the phone and called Rel service technical support....I read him the post etc and asked if they knew of this or heard of doing this for 2 channel systems...I got a bad idea,a very bad idea along with 10 minutes of why and that stacking upfront is really the only way I should approach this.On the positive side for me ,I save money not buying a 3rd sub,lol

Im using a single velodyne hgs-10 sub directly behind me, 180 degrees out of phase.  My speakers are magenpan lrs running full range of a Kinki Studio.  It sounds fantastic!  

The way I connected 3 subs was by taking advantage of the Rel being connected to the speaker outs on my power amp and the other subs being connected to the rca outs on my dac. My dac also has XLR outs that I run to my power amp. I did run both speaker channels to my rel. I’m not sure that matters. I used to run 2 subs in the front. Perhaps if I’d moved one to the back I would have had a similar 3D experience with just 2 subs. I haven’t tried that. Logically, adding a third sub would seem to just make the bass louder and smooth the bass. I can guess why the third created the holographic effect but it would be a guess. Definitely the Rel dramatically the imaging with just 2 subs. My previous subs mostly added bass extension. The high level inputs on the Rel dramatically improved the separation of the instruments in front of me. But a/b testing with the third sub in the back proved to me in my system that the 3D effect is real. Might there be an even better configuration? Probably. Might the effect be component dependent? Probably. I just thought I’d share what I stumbled upon in case you like to tinker. Bottom line, try one of your subs behind you to see if you achieve a 3D effect. I hope you do.

Post removed 


I actually have the subs about 2 feet from each corner. The F-113 have a master/slave output for additional subs.



Someone was asking how to connect a third sub.

I was giving an example of one of the ways to do it using a splitter in a dual mono configuration.

Yes a third sub in the back does help, but try moving them around until you find the sweetspot. Ozzy - Have you tried moving your subs out of the corners of the room? I've found I like the sound better when they are not in corners. 

FWIW, I'm  aware of different ways to do it. I was wondering how OP had done it.


I did go from a Rel Storm III  to two sealed Rythmiks with servo and was a very significant improvement. Learnt to measure the room, identified key issues, treated the (living) room, and have a 4-way active system with advanced DSP. I've ran subs mono and stereo and haven't come to a preference, at least with 2 of them. I was on my way to adding two additional sealed subs, but detoured on dipole speakers (DIY) and now pondering adding 2 sealed vs 2 OB subs, but surely adding a MiniDSP to allow implementing time delays per Toole, and use of Multitude Optimizer. 


Anyway, I was interested in OP's implementation to tie his results to the approach.

I use a pair of Whirlwind Split 6 (XLR) out of my DAC. One Split 6 connected to Left Channel, other to Right Channel. I don’t run my Subs in Stereo, instead, I run them in Dual Mono. Out of Split 6 (left channel), one cable to Amp, one cable to Sub on right side of room (5’ out of corner facing opposite wall), one cable to Sub on Left side of room (behind couch) facing opposite wall. Do the same for the Right Channel, connecting the cable to the Right Channel input on both subs and amp.

I tried adding a 3rd sub, and it didn’t make any difference in my measurements (couldn’t hear any difference either).


I would also like to know how to hook up a 3rd sub.


1. You can split the left or right low level signal out.

2. You can split the low level sub out.

3. You can come off the main speakers or amps speaker terminals with certain plate amps. REL is one.

4. Certain sub plate amps have a RCA/XLR out to daisy chain.

5. Install a 1 in, 4 out, not switched, split and fixed, low level out.

6. Install an active crossover. 2 in 6 out. DCX 2496. Will add everything up to 12 db of gain for any bass contour through a PEQ and or GEQ

7. Wireless

8. Passive. 1 large power amp running 2-4 passive sub enclosures. Debra, or Swarm.

I ran 4 Tallboys on 1 Mcintosh MC2500. They would crumble a house with a single MC2500 power amp. You could fry eggs on that amp, and it just sounded better and better and better. 220/240 vac power supply. It cost 25% more to run it at 120 VAC vs 220 VAC. Heavy piece of $hit. Hated moving that amp (s).

How's that? There is a few way. If you give me a while I can come up with some more.



I love seeing the excitement people get from adding a second sub. Also surprised though… as DBA is approx. 25 years old.

Seems some still think of it as folklore or a tall tale.

IME if you’ve got a troublesome room from 150Hz & down (like most) going from one to two subs (obviously distributed not co-located) can make a huge improvement.  
If you’re room is a disaster at bass frequencies (mine was) then four subs should  certainly do the trick. My most distant sub was best served 180 out of phase…





How did you connect the 3rd sub?

Understand the 1st & 2nd are in stereo, but how is #3 connected?

Earl Geddes distributed bass array has subs played in mono, up to 80Hz, adjusting each to achieve an even bass response across various spots in the room.. 


On the other hand some folks run stereo sub arrays and place one sub very close to the listener so to minimize the room interaction at the listening seat.


Glad you are liking it!

Not sure if the OP was more championing 3 subs or the 3D effect that placing a sub behind the listening position creates. My system has 2 subs but because I live in a small house I don’t have a lot of choice on placement. The recent addition of the 2nd sub behind the primary listening position was totally transformative to my system in all the ways the OP states. My soundstage became amazingly 3D at all frequencies - not just in the lower octaves. My mains have now completely disappeared and there is much more space between all instruments. One of the best additions I have made to my system as it is now much more involving. 


I took the advise from the REL tech and added my second T/9i on the back wall on the opposite diagonal corner. Dialed in the settings for volume and crossover frequency based on the room dimensions and WOW! Ask for help from REL, they know what they are doing. 

@oldhvymec That .  .  .  sub . . . what  . . . planet? . . . back to kindergarten for me.


And from the link above:


Moving from one subwoofer to two makes a very noticeable difference in the performance of the system. Going from two to four was always an improvement, sometimes for certain seating positions more than others. Often the improvement was so subtle, that it would probably not be worth doubling your budget for subwoofers.


Third test:

We added a second subwoofer in the same position behind us. The least effect was in the chair in the center of the room, but the bass was considerably cleaned up in that position, and to a greater degree in all other positions. Front to back frequency balance was much smoother.

Fourth test:

We had two subwoofers in the two front corners. All the front to back ringing came back with a vengeance. Side to side was consistent, but consistently bad. Very noticeable excitation of the front to back room resonance.


“For the best imaging when you have more than two subwoofers, the other subs should be placed so the listeners are equal or greater distance from the mains and at a somewhat lower sound pressure level. In my experience, a 30-50 millisecond delay works well to keep the image up front. Also, having all the extra subwoofers combined, play slightly lower in sound level than the main/front subs alone was the best for music.”

I agree with you pennpencil,

I am using (4) JL Audio F-113 subs in the corners of the room. Each sub can be calibrated based on its location and my sitting position. I also have the JL Audio Electronic crossover the CR-1 which blends the whole thing together.

Once the bass is dialed in everything else locks into place.


oldhvymec, thanks for taking the time to share your explanation, I did not know that. Peppercorn putty balls, all right!

Adding an extra low frequency system seems to be a great deal of trial and error regardless. It's nice to hear when someone like the OP has improved their personal satisfaction with their own low frequency system.


LOL at the guy who has his subs in the worst position possible...


Haven’t seen any naysayers reply on here yet. Sure, 3 or 4 subs work best, but how much better are they than 2 subs? Measurements, and proper sub positioning are required to know what the number should be, not just throwing subs in the room and saying OMG. Just look at the measurements in the link Hilde45 posted earlier on. Would you add a 3rd sub for a 3dB change in a couple of frequencies, that you wouldn’t be able to hear the difference anyway?


OP should try turning off 1 of the subs, at the front and than the other at front of the room to try and hear the difference. Better yet, be blindfolded have someone turn 1 sub off (or none) and see if he can guess how many subs are on (assuming the sub in the rear is always on).

@pennpencil   Don't let the naysayers detract from what you hear pennpencil.  That's the only thing that matters.  Glad that the third sub has worked out so well for you.

Apologies for the title, which should have been, "Try a third sub in the back of the room." 1 AM might not be my best time to write titles. 


621 posts

They are tuned to the room through, Putty Pinching. Perfect integration without digital correction.. Pretty cool actually. 50-100 sand bags worked the best. The slot glued to the floor so to speak.. Ceiling will work too. :-)

oldhvymec, this seems an interesting technique which I know nothing about. Is it possible to explain a bit further or provide a reference or a link to this method? 


There are two approaches to passive radiators. One is a standard cone with a suspension added and conventional butyl rubber surrounds. Then there is a lighter mass version. The cone is lighter and so is the suspension. Normally the surround is foam too. There is a reason.

With a light moving mass the key is to add enough fixed weight to match the port frequency's lowest point with the space and active drivers used. Now to go below that point we add non hardening putty, (Mortite putty is the best) to the point of BOOM in the room.

Now comes the tricky part. You remove mass (putty) the size of a peppercorn at a time until the boom goes away. Your single sub unit has been added and blended to the perfect (Q)uality, with your amp, your mains, you cables and your room. NO electrical correction of any kind, digital or analog. Purely mechanical, just like me.

Now correct your room mechanically. Passive materials. You absorb the bass, you let the bass escape, you control the bass with (Q)uality control. Now you can add just slight correction, vs full blown DSP room killing correction.. I hate it.

Direct coupled subs that use active crossovers and (Q)uality control are pretty amazing. Very close to a DBA servo sub system, SQ wise. 

One of my bass system uses 10-20 drivers, there is a lot of cubic inches of cone material, but perfectly controlled and tuned to any gear, cables or room. GRs servo subs and my SAT Bass columns direct coupled. No crossovers.. There is a small set on my Virtual page..

It's my ways, they work very well. I like the VMPS columns. I wish someone would make them again. I need 20 acres, a wearhouse, and a mule..


Google Tom Welti white paper.

Conclusion from his testing:

Four subwoofers are enough to get the best results of any configuration the best results of any configuration tried. Two subwoofers is very nearly tried. Two subwoofers is very nearly as good and has very good low as good and has very good low frequency support as well.


Problem is, some members are advocating 4 or more subs is the only way to go. It just isn’t true, as well as a complete waste of money - let alone telling everyone that corner placement is essential, which also isn’t true.

@golfnutz I’ll take a look. That article was just a primer I ran across; it’s not my bible or anything. The testimony I’ve seen here by some experienced folks has convinced me that it’s helpful, and my own measurements have, too. But my sense is that one need not spend a lot to get the benefits of additional subs; assuming the room is in need of them, even inexpensive (but not cheaply made) subs can help with room modes.

I'd note that what you've said is self-verifying. You said, "the DBA is a complete waist of money on extra subs if they're not needed, or do very little in the difference they make."

Of course a DBA is a waste of money if it's not needed or does little. Same thing is true of literally anything. But if it IS needed or does a lot, well, there you go.

There is a lot of hype about DBA but some good discussion, e.g. here:



Please look at the graphs for 2 subs, and 3 subs in the link you provided for Distributed Bass Array. Why on earth would anyone spend in excess of $500 - $4000 by adding a third or fourth sub  based on those measurements. I know in your case you bought a pair of Rythmic subs and already had the REL, but still, IMO the DBA is a complete waist of money on extra subs if they're not needed, or do very little in the difference they make (measurements required). Also, search, and check out Tom Welti, to see what his recommendations are for subwoofer placement in a rectangular room.

For years I used a single REL  a few feet BEHIND the listening position, along a long wall, near a corner(speakers are projecting from the short wall).  Much more convincing than the traditional corner behind one of the front speakers.  YMMV.

I imagine DSP would provide even "better" integration. I just go by ear. 

Still have the REL in the back, but with a 2nd opposite side. One of these years I will spring for the other 2 for a proper DBA. 

Rear placement sounds more realistic in my particular living space arrangement. Also less obnoxious. I have 2 old made in England B3's. Big bulky boxes, compared to modern REL's. 

They are tuned to the room through, Putty Pinching. Perfect integration without digital correction.. Pretty cool actually. 50-100 sand bags worked the best. The slot glued to the floor so to speak.. Ceiling will work too. :-)

oldhvymec, this seems an interesting technique which I know nothing about. Is it possible to explain a bit further or provide a reference or a link to this method? 


@dbphd  Bass management is the best way to add subwoofers by a long shot. People should understand that you do not have to buy a theater processor to get it. There are several stereo processors that have complete bass management systems from companies like Anthem, Trinnov, DEQX and MiniDSP. There are many more digital sources now than there are analog and the capabilities of digital preamps far exceeds that of analog ones. Conversion to digital at high rates is “invisible.” A turntable sounds just like it always sounds except you get the benefits of bass management, room control and EQ.



2-4 of these work better.. Very Rare.. 1000 watts all night 5000 watt burst. Very low distortion too. Under 5% <15hz - 150hz optional 250hz.

@oldhvymec Thanks for the suggestion. I'm saving this into my "subwoofer" file. Until I move into a new room (it's built but kids are still in it with their game stuff) I won't be adding a fourth sub or make other sub changes.

hilde45 if you really like the REL subs another sub that will really reach deep is a VMPS, Tallboy < 16hz. They were/are used in the NASA simulation lab. I used 4 in the 80/90s. They would and could crumble your house.

They run a 12 and 15" active and are tuned with a second passive 15" They were set up with a HP filter to. They are tuned to the room through, Putty Pinching. Perfect integration without digital correction.. Pretty cool actually. 50-100 sand bags worked the best. The slot glued to the floor so to speak.. Ceiling will work too. :-)

I have sub columns that have sound pressure coming from 4 (X2) of the 6 surfaces. They are made to go a against the wall in the middle of room, either side of the seated position. You only need 2. With 4 columns people would start having  nose bleeds and then concussions. They are 20cf 60" tall 400 lbs cabinets. Direct coupled to 12,000 watt pro amps. Best cone control I've ever seen at 8 ohms medium price super refined reference drivers. With no ports 15 hz. With ports < 10hz.

Plates will fall and screws will unscrew though.. LOL

I have a REL R328 and bought two matching Rythmiks to put at the front. I figured I'd try the REL behind the listening chair and then go ahead and sell it. No way! I'm keeping it for exactly the effects you described, plus it helps smooth out the bass response. This is really just 3/4 or 3/5 of the way toward a distributed bass array, but it's working well and I'm not selling the REL.

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I use a pair of Velodyne HGS-15s with bass management to augment KEF Reference 1s.  The subs sit close behind the mains.  A third HGS-15 is in the rear of the room, and receives LFE from a Bryston SP3 processor.  The SP3 has a provision that enables* the three subs for full range front LR plus rear LFE.  It gives new meaning to the sense of surround.  I have never before used LFE, and was surprised how often it is invoked for emphasis in TV programs and commercials.

*The preamp sends an output for the front subs through the bass manager; for surround, the SP3 sends full range front LR to the preamp by-pass and LFE to the rear sub.