# 2 sub placement



## Guest (Jun 8, 2006)

Hi,

I've got 2 SVS PB12+s and am struggling to locate them. My original plan was to use two PB10s and locate them both in the front corners however in my wisdom I decided to get two PB12s and have been struggling to get a nice sound ever since :scratch: Because of their size I've had to site them at the back two corners but the sound is just too intrusive and it's so easy to locate them that I had to set my fronts to large to help the sound. 
I'm going to have to site them at the front corners but this will mean that I won't be able to have corner bass traps there which I was going to use to tame my room. 
I realise that it's a lot of trial and error but my fiance thinks I'm a complete maniac playing around with it all the time and never actually getting time to enjoy the music :blush: 
Anyway I do like a nice tight bass so is it best to site them close to the tri corner? Should I place some rockwool against the wall here or use the wall to strengthen the bass? Anyone had any experience with this configuation?

Cheers.


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## Sonnie (Apr 11, 2006)

Yup! ME!

These are not the mains I have now but you can get an idea... sames two subs you got...










I have them as close to the wall corner as I can get them and they were tuned to 16hz... been listening to them at 20hz for the last few shows.

I don't think corner bass traps are gonna effect these that much if you have them crossed over at 80hz.


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## JCD (Apr 20, 2006)

bobgenie said:


> Hi,
> 
> I've got 2 SVS PB12+s and am struggling to locate them. My original plan was to use two PB10s and locate them both in the front corners however in my wisdom I decided to get two PB12s and have been struggling to get a nice sound ever since :scratch: Because of their size I've had to site them at the back two corners but the sound is just too intrusive and it's so easy to locate them that I had to set my fronts to large to help the sound.
> I'm going to have to site them at the front corners but this will mean that I won't be able to have corner bass traps there which I was going to use to tame my room.
> ...


A few questions:

Have you calibrated them with a SPL meter?
Do you eq them with something like a BFD?
How big is your room?
Have you tried e-mailing Tom V at SVS? He's always been willing to help out in the past.

And yes, I think almost everyone here can sympathize with your 'struggles' with the 'other half'. My wife has NO IDEA why I care so much about this stuff. :huh: 

JCD


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## Guest (Jun 8, 2006)

I do have BFD and REW etc but just need to convince myself that siting them at the front will be worth all the trouble. I'd much rather leave them at the back but they just sound terrible. My problem is a lack of space. My room is only approx 5 metres by 4.5 metres and a fireplace to boot it's difficult to fit it all in. I'm going to move it all to the front at the weekend and see how it goes. At worst I'll have to leave the sofa in the dining room :R :R :R


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## JCD (Apr 20, 2006)

bobgenie said:


> I do have BFD and REW etc but just need to convince myself that siting them at the front will be worth all the trouble. I'd much rather leave them at the back but they just sound terrible. My problem is a lack of space. My room is only approx 5 metres by 4.5 metres and a fireplace to boot it's difficult to fit it all in. I'm going to move it all to the front at the weekend and see how it goes. At worst I'll have to leave the sofa in the dining room :R :R :R


 LOL..

Yeah, I've heard that there can be some issues with subs in the back -- not that I can remember or understand them mind you. In the end, I think you'll be much happier with them up from. 

I'm still surprised that you're having as many issues as you are. If everything is sound level calibrated and eq'd to the room, I would have expected huge  instead of  .

If moving it to the front doesn't work, I'd send an e-mail to Tom V (who pops in here every once in a while) and ask him for some advice. He's got more sub know how than I have.. well, anything. :hail: 

In any case, let us know how it goes moving the subs to the front.

JCD


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## Exocer (Apr 19, 2006)

Bob, I'd definitely try moving them to the front. Along my subwoofer locating journey I placed my subs behind me and hated it. The bass just felt disconnected from the mains and left a large gap. Even switching phases and subwoofer distance in the AVR didn't help. If possible I'd place the PB-12's in a front corner either side by side or on top of eachother for the 6db boost along with the advantage of being placed by two boundaries. That should surely knock your socks off :R


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## Guest (Jun 11, 2006)

As I am about to write, I got them in the front corners one each side. It looks a bit dodgy because I have to place my rack to one side and the fronts are left floating in no mans land. However, it sounds so much better :T Now all I have to do is get rid of the highs on my fronts as they're far too bright but that's another story :R


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## brucek (Apr 11, 2006)

> However, it sounds so much better


Have you carried out any sweeps with REW? Properly taming the response with that BFD will make quite a difference - especially with two monster subs in different corners (just ask sonnie). You never got back and posted any graphs for us in the BFD forum. Now's the time. 

brucek


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## Guest (Jun 11, 2006)

I have done some sweeps and the sub is a lot better with a couple of peaks which filters I have sent to BFD. My front speakers are very bright and I need to tame them with some room acoustics which will be another WIP. I have not yet posted any graphs as my head is still hurting :R but will soon :T


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## JimP (May 18, 2006)

Bob,

This might help take some of the brightness out of the mains.

If you have them aimed at the primary listening position, turn them so that they're shooting pass that position (to the outside). Tweeters are loudest when aimed at you, so by changing their aim, they shouldn't be as loud.


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## Guest (Jun 12, 2006)

Thanks Jim, yes I've already done that but it's still a little too bright. I've ordered some more cable and am going to move my rack out of the way which should enable me to position the speakers more favourably. Once it's all in place I will re-run the REW and post some graphs :T


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## Guest (Sep 15, 2006)

Disclaimer 1: I work mainly with PA systems, so I may have a different point of view about sub placement. 
Disclaimer 2: Home theater is usually in a much smaller space, so factors like room gain, etc. can render much of what I have learned useless in a small space.

On to my point: Spacing subs can introduce severe comb filtering (phase cancellation), especially on the upper end of the sub's range.

I will attempt to insert a couple of graphs run with EV RACE acoustic simulation program to illustrate.









This shows subs placed half a meter apart










This shows the subs at about 5 meters spacing.

Both charts are at 90 Hz. The problems become less pronounced as the frequency drops, but are still present. Lighter areas show louder positions.


BTW, the RACE program is free at the Electro-Voice site, ( http://www.electrovoice.com/index.php ). It is intended for pro audio, but is nice to try different sub set-ups in software before you put them in place. RACE only shows free-air response without room reflections, but it is helpful to me...

My sig image is a simulation of a large meeting space I have to run sound in at work. 4 speakers installed in the early 90's all working hard to cancel each other out. Looks great, sounds like crapola...


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## Guest (Oct 11, 2006)

As said, the simulated data is valid for open spaces, not in a small room where boundaries define the radiation. Corner location boosts the output and excites all room modes. For even response corners should be avoided. If you place the subs on the front wall at distance of 1/4 of the room width from both side walls you tame the first room modes directly. 

BR,

Ilpo


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## Josuah (Apr 26, 2006)

That's also what I was thinking. That by placing them in the corners you were getting boomy, uneven bass that was overwhelming you and thus localizable. I experienced a similar problem when I placed a sub in the corner, and it was very bad until I moved it out. REW will only show you frequency response but not decay.


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## brucek (Apr 11, 2006)

> REW will only show you frequency response but not decay


Not true.

REW calculates Response, Low frequency Spectral Decay, Low frequency Waterfall, Impulse Response.

brucek


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## Josuah (Apr 26, 2006)

Oh, I guess I didn't find that graph. Thanks.


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## Sir Terrence (Jun 8, 2006)

Ilpo said:


> As said, the simulated data is valid for open spaces, not in a small room where boundaries define the radiation. Corner location boosts the output and excites all room modes. For even response corners should be avoided. If you place the subs on the front wall at distance of 1/4 of the room width from both side walls you tame the first room modes directly.
> 
> BR,
> 
> Ilpo


You may tame the first room node, but you decrease low frequency support, something that you cannot afford to do unless you have a very large sub with a high powered amp and EQ. The best place for subs in a rectangular room (that is the only room that any research has been done on the subject) should be in the corners of the room, whether placed together in the same corner, or opposite corners. EQ should be used to even the frequency response. The corners provide the loudest and best LF support than any other position in the room.


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## norpus (Oct 11, 2006)

Bobgenie, I have found practically that 2 subs work well at centre front and centre rear - to tame room nodes and get a response not so sensitive to your listening position. Tested and proven first with 12" box subs. 4 subs is a little better reportedly but not by much
Here's the theory to back up the claim

http://www.harman.com/wp/pdf/multsubs.pdf

And ps, I am today knocking another permanent hole in my floor to truly _commit _to this theory - rear centre, 2nd IB infloor sub, 2x15".:devil:


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## jagman (Jul 8, 2006)

I also would like to see you follow the Harman white paper... at least try it out. It really is supposed to give a much nicer/cleaner sound. The fact that it should help with room nodes is really good for your HT, too. Better sound for everyone in the room, and less need for EQ. I haven't heard of anyone (besides Norpus) actually trying the center front / center rear alignment so I think a lot of people will be waiting for your opinion. Even if you intend to keep them in the corners, please try the this alternative.

BTW, even though having 4 subs at the 4 midwall locations gives a slightly more even in room response, if you look at the graphs in the Harman white paper, the ULF output is much less than if just 2 subs are used. I for one would rather have the ULFs... especially with the low end potential of dual IBs!!!

Norpus... please elaborate on what you heard with the 12" sub in the back supplementing the IB in the front.


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## norpus (Oct 11, 2006)

jagman said:


> Norpus... please elaborate on what you heard with the 12" sub in the back supplementing the IB in the front.


Jagman, unfortunately the little B&W 12" sub really couldn't keep up at all with the big front IB, so it sounded muddy in comparison. In another forum members room, this box sub was only good for circa 30Hz before a steep rolloff. (I was actually surprised it even got that low - room gain helped obviously)

With 2 subs, and one being substantially weaker than the other, you can make the sound worse - as you end up with less than 100% of the ELF if the 2nd sub cannot do them. Remember only one sub was capable of sub 30Hz material, and both subs were doing above 30Hz. 
I did not spend a lot of time and effort measuring the supplementation as that experiment was fundamentally flawed. It even convinced me to increase the driver size of the rear IB from 2x12 to 2x15" Tempests (a smaller hole would have helped WAF, but c'est la vie). The new IB will likely be flat to ~18Hz nearfield at a guess.

However, I do remember the better effect that the Harman alignment (1 centre front 12" box sub, 2nd 12" box sub centre back) gave me in an earlier incarnation of my room, so was happy to commit to a further more permanent Harmanising experiment.
So much so I this week now have a 550 x500mm hole in the back centre floor to match the 610x650mm hole in the centre front. A lazy 3 day diy project.

I gave the brand new rear IB its first fireup last night on movies (alone, without the front sub). My family seemed to think it was working OK and didn't really notice the location was only from the rear. 
On music, it was also good when crossed over at 44Hz, altho at my normal xover of 60Hz it was not quite as good as the front IB. More testing this week as time allows.....


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## Sir Terrence (Jun 8, 2006)

norpus said:


> Bobgenie, I have found practically that 2 subs work well at centre front and centre rear - to tame room nodes and get a response not so sensitive to your listening position. Tested and proven first with 12" box subs. 4 subs is a little better reportedly but not by much
> Here's the theory to back up the claim
> 
> http://www.harman.com/wp/pdf/multsubs.pdf
> ...


The problem with going this route is the loss of LF support, which places more strain on the sub and amp to reproduce X frequency at X amplitude. This will increase driver travel, and distortion as well as the loss of LF support. If you look at all of his positioning results, they all lack LF support. Midwall placements (unless you have a very large set of subs with gobs of power) usually experience a steep roll off below 40hz in my experience. 

Dr Toole's papers strongly recommend LF support by corner placement, and EQ to smooth out the modes that are excited by corner placement. 

This paper was not written by Dr. Toole, and doesn't really tell how to get the maximum performance from your subwoofer.


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## Ayreonaut (Apr 26, 2006)

I've tried it both ways and definately prefer the sub away from the corner. The 1/4 length and 1/4 width rule in a recatangular room has worked very well for me. I would definately try the opposite ends arrangement as recommended by the Harmon paper. My priorities for sub positioning: quality first, quantity second.


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## Sir Terrence (Jun 8, 2006)

Ayreonaut said:


> I've tried it both ways and definately prefer the sub away from the corner. The 1/4 length and 1/4 width rule in a recatangular room has worked very well for me. I would definately try the opposite ends arrangement as recommended by the Harmon paper. My priorities for sub positioning: quality first, quantity second.


Who says you cannot get quality performance from corner placement? I also did the 1/4 rule, and the amount of deep bass I lost was a non starter. I got better smoothness from EQ and corner placement with the added benefit of LF support and lower distortion. When you include the higher distortion into the mix, the smoothness of the output above 40hz is not even worth it.


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## norpus (Oct 11, 2006)

Sir Terrence said:


> Midwall placements (unless you have a very large set of subs with gobs of power) usually experience a steep roll off below 40hz in my experience.


Unusually then my flat response below 40Hz to 20Hz and below (without EQ boost in this area) using my mid front wall position must be a freak. I'm happy to accept that. (And yes I have a couple of large drivers but were not using much power or distortion at all to produce this result)


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## norpus (Oct 11, 2006)

Sir Terrence said:


> The problem with going this route is the loss of LF support, which places more strain on the sub and amp to reproduce X frequency at X amplitude. This will increase driver travel, and distortion as well as the loss of LF support. If you look at all of his positioning results, they all lack LF support. Midwall placements (unless you have a very large set of subs with gobs of power) usually experience a steep roll off below 40hz in my experience.
> 
> Dr Toole's papers strongly recommend LF support by corner placement, and EQ to smooth out the modes that are excited by corner placement.
> 
> This paper was not written by Dr. Toole, and doesn't really tell how to get the maximum performance from your subwoofer.


I agree, corner placement can get you more output
I guess my goals are not the same as those you mention. Like Ayreonaut, I am not chasing output as we have enough of that, including ELF. 
The way I read the Harman paper was the more subs, the less LF support - agreed. But, the things that I am chasing are a flat response to 20Hz (or below) and smoothing of room nodes in _multiple _listening positions, not just one sweet listening position.

I do not agree that 'EQ can smooth out the modes that are excited by corner placement' or placement at other places. The whole idea of the Harmanising process is to reduce the room nodes as much as possible, using the most practical number and position of subs. Then EQ can be applied to bandaid up the smaller problems and preferably they'll be not so sharp now. We'll see when I get the measurements done following my second IB sub commissioning

You can see by my original graph above that I had a couple of room node issues in my room at that microphone position where I often sit. With high levels of EQ around those nulls, they could appear to be tamed. But move the microphone 12" away and the EQ is then incorrect. This is what I believe the multiple subs can assist with, and hence my committment to the experimentation in this area


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## norpus (Oct 11, 2006)

Here's some more ideas on 2 sub placement

http://www.audioholics.com/techtips/setup/loudspeakers/SubwooferplacementP17.php


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## Sir Terrence (Jun 8, 2006)

norpus said:


> I agree, corner placement can get you more output
> I guess my goals are not the same as those you mention. Like Ayreonaut, I am not chasing output as we have enough of that, including ELF.
> The way I read the Harman paper was the more subs, the less LF support - agreed. But, the things that I am chasing are a flat response to 20Hz (or below) and smoothing of room nodes in _multiple _listening positions, not just one sweet listening position.


This is where spatial averaging plays a roll. Midwall placements do not avoid exciting room nodes, it just doesn't excite CERTAIN room nodes



> I do not agree that 'EQ can smooth out the modes that are excited by corner placement' or placement at other places. The whole idea of the Harmanising process is to reduce the room nodes as much as possible, using the most practical number and position of subs. Then EQ can be applied to bandaid up the smaller problems and preferably they'll be not so sharp now. We'll see when I get the measurements done following my second IB sub commissioning


You may not agree that EQ can smooth out modes, but Dr Toole's research proves that it does indeed. My experience also shows that EQ does exactly that. Subwoofer driver placement in a null located at or near "1/4" (or 3/4) of the distance between opposing walls can be used to reduce excitation of second-order front-wall-to-back-wall and second-order side-wall-to-side-wall axial room modes, assuming those room modes would otherwise cause a bass peak at your listening position. Everything really depends on where your ears are placed. You can place a sub in the corner and sit in a null position and possibly not hear a single mode. That is why I say your listening position might be as important as the sub placement itself. Lots of bass traps and/or parametric EQ are more effective in reducing bass peaks heard at the listening position, but subwoofer placement can help with a few of the five or six axial room modes under 80Hz. in the typical home listening room. The only way to avoid modes and nodes altogether is to place the sub in the center of the room, suspended halfway between the floor and the ceiling, and lay on it. 




> You can see by my original graph above that I had a couple of room node issues in my room at that microphone position where I often sit. With high levels of EQ around those nulls, they could appear to be tamed. But move the microphone 12" away and the EQ is then incorrect. This is what I believe the multiple subs can assist with, and hence my committment to the experimentation in this area


This is why one never should measure from one position. There is such a process called frequency averaging. This means taking measurement from several different positions (always recommended) and equalize the measurements averages. A second sub in a opposite corner helps smooth the frequency response in the front row in multiple seating arraingments, but is not as helpful as you move to the rear of the room. There are advantages to dual subs in none modal setups if you are not looking for LF support or lower distortion from your sub. 



> Unusually then my flat response below 40Hz to 20Hz and below (without EQ boost in this area) using my mid front wall position must be a freak. I'm happy to accept that. (And yes I have a couple of large drivers but were not using much power or distortion at all to produce this result)


Have you ever measured the distortion from your sub when played back you your loudest listening level? As my point stated, you can get away with this position with large drivers and a powerful amp, but you are not really avoiding room modes and nodes with this position.


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## Ayreonaut (Apr 26, 2006)

I did not get better results from EQ and corner placement, though they were arguably "smoother." Surely the merits of corner placement and alternative placements vary from room to room. 

Here is what happened in my room. (These are some old graphs generated from test tones played through my old B&W ASW600. I manually measured four listening locations and EQed for the average. :wits-end: It was a pain before I got my REQ sweeps figured out!)

Note: These were not generated at the same playback volume. :scratch:

Here is the result of CORNER loading the sub, and EQing for the "average."









Here is the result of locating at a QUARTER point, and EQing for the "average."









The corner loading did gain 3 or 4 dB and the seat-to-seat response was similar and smooth through parts of the spectrum, but there was a huge difference in the responses around 40 Hz. By contrast the quater point location yielded somewhat rougher responses, but without the very large differences at 40 Hz.

By inspection you could argue either way. But my conclusions are based on extended listening. I find the quarter point location to generate less reverberation and it simply sounds better to me in all of the listening positions. 

I would like to someday experiment with multiple subs, which was the original topic, come to think of it... :whistling:


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## norpus (Oct 11, 2006)

Sir Terrence said:


> This is where spatial averaging plays a roll. Midwall placements do not avoid exciting room nodes, it just doesn't excite CERTAIN room nodes


Thanks for your good reply
Agreed, placement to avoid overlapping of the ubiquitous room nodes is my aim. And yes every room may be different - which is why experimentation by ear and measurement is good first.


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## norpus (Oct 11, 2006)

Sir Terrence said:


> This is why one never should measure from one position. There is such a process called frequency averaging. This means taking measurement from several different positions (always recommended) and equalize the measurements averages. A second sub in a opposite corner helps smooth the frequency response in the front row in multiple seating arraingments, but is not as helpful as you move to the rear of the room. There are advantages to dual subs in none modal setups if you are not looking for LF support or lower distortion from your sub.


Agreed, the multiple listening positions will be tested with one sub and then two to see what the effect of the second is. Will report back findings when done (I have to wait for a mate to bring his measuring equipment over again)


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## norpus (Oct 11, 2006)

Sir Terrence said:


> Have you ever measured the distortion from your sub when played back you your loudest listening level?


No I have not measured it as I do not have equipment (apart from my ears). Have you and what did you use? 
My ears tell me at high volumes that the sub sound is still sweet - but (at 30dB down) the 75-80dB where I listen to 2ch I am sure distortion is negligible with the IB, as designed.

Edit: Oops, thought these 3 replies would layer on top into one like yours did ST - seems the board is a little different to somes others I visit. Tip from anyone please?


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