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Need help with a unique subwoofer setup (expert discussion)

post #1 of 16
12/12/12 at 8:15pm
Thread Starter 
I have a set of BG RADIA in-wall subwoofers (4) which really are quite musical and do a great job on the higher end of the bass spectrum. 60-80hz in particular. Room is around 5000 cubic feet (pretty large)

I LOVE my mains (Avantgarde Duo Omega) and they have a powered lower end which also does a great job in the 80hz-300hz range in my room.

I put in Clark Synthesis Platinum bass shakers at a low level and used a crossover to only cover the 20-60hz range and this really improved the experience for home theater. You wouldn't know there were bass shakers in the couches unless you were told. This has little to no effect on music since most musical information is not in this range anyway.

Here are some problems I am facing however:

1. There is a serious null at my sitting position at around 50-60hz. (despite FOUR corner in-wall mounted subs).
2. The subs have ONE combined mono amp so you can't equalize them separately. I have an Audyssey 9.2 pre-pro (Integra 80.3) but I am not sure it independently equalizes the 2 subwoofers outputs anyway.
3. The BG Radia subwoofers don't really achieve reference levels at 20-50hz range (The part of the range that is not in a null).

Should I get new amps and try to equalize each sub separately to solve this null problem?

For more powerful bass in 20-50hz should I add yet another subwoofer (like a JL Fathom product)?

I have nowhere to put another super-powerful sub that won't end up being looking intrusive I think. Anyone know of something that would hide under a ottoman that is a balanced (opposing speaker) design that I could hide? maybe mount inside of my couch like the bass shaker?
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post #2 of 16
12/12/12 at 8:30pm
Just my take, but a good sub isn't a planar sub hidden in a wall or somthing that fits under or in an ottoman (what is that, a couch or a sofa or loveseat....large footstool?) etc. I look at the "spec" sheet for those BG things and there's no specs...what's up with that? Probably your biggest issue right there....they're not really subs. Gotta get that bass out in the room! Aesthetics be damned! JL's are overpriced but what is aesthetically going to float your boat? Submersives are very nice looking....Funky Waves can be custom made in gorgeous cabinets.... just my .02. smile.gif
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post #3 of 16
12/12/12 at 9:03pm
Quote:
Originally Posted by lovinthehd View Post

Probably your biggest issue right there....they're not really subs. Gotta get that bass out in the room! Aesthetics be damned! JL's are overpriced but what is aesthetically going to float your boat? Submersives are very nice looking....Funky Waves can be custom made in gorgeous cabinets.... just my .02. smile.gif

Agree. And I would add that just because your subs are in the 4 corners does not guarantee no nulls. My 4 are CLOSE to the corners but not in them. And having in room subs gives you a lot more flexibility for sub placement.

Now, on the other hand, if you want to build multiple IB subs, that could be a much different story !!!!!
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post #4 of 16
12/13/12 at 6:16am
Quote:
Originally Posted by blazar View Post

1. There is a serious null at my sitting position at around 50-60hz. (despite FOUR corner in-wall mounted subs).
That's a symmetrical placement. Symmetry and low frequencies don't mix; it's what causes severe room modes.
Quote:
2. The subs have ONE combined mono amp so you can't equalize them separately.
You don't want to. Room modes are fixed via placement, not EQ. EQ is used to fine tune the system after the room modes have been addressed.
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For more powerful bass in 20-50hz should I add yet another subwoofer (like a JL Fathom product)?
A good sub woofer doesn't need another subwoofer to extend its range. Subs that only go to 50Hz aren't subs.
Quote:
I have nowhere to put another super-powerful sub that won't end up being looking intrusive I think. Anyone know of something that would hide under a ottoman that is a balanced (opposing speaker) design that I could hide? maybe mount inside of my couch like the bass shaker?
If you want to go low and loud you have to go big. Would you rather it look good or sound good?
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post #5 of 16
12/13/12 at 2:53pm
Thread Starter 
Bill, I am certainly with you on all points you described... In some ways maybe I am just looking for magic methods that don't exist. I thought maybe if one sub speaker had a peak in the area that another has a null, that perhaps I could boost that particular speaker individually to compensate (this is the main reason for multiple subs in the first place right?)

I think there is no technical reason why one more sub might work out well. I have minimal outlets in the room however so I can't just plug it in wherever. There is in-concrete wiring under my main sittting position couches and wiring receptacles at also located at my main speakers.

One poster mentioned problems with "in-wall" vs "in-room" subs which I doubt is a serious problem.

The reason the BG radia in-walls are not "enough" is most likely due to the size of my room. They just don't pressurize enough. They don't reach effective volumes on the low end for the levels that I am trying to push them to.

Maybe I could go with the JL-Fathom in-wall solution perhaps? I could feasibly replace current subs with these without creating an aesthetic disaster.

Anyone with experience with these?
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post #6 of 16
1/10/13 at 1:20pm
What did you end up doing? (in the same situation with 4 subs and not quite enough output, although my room is 1/2 the size)

Did you try reversing the phase in the rear speakers? Helped in my case.

Jh
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post #7 of 16
1/10/13 at 1:50pm
Quote:
Originally Posted by blazar View Post

The reason the BG radia in-walls are not "enough" is most likely due to the size of my room.
I can't say, I don't see any real specs on their website, especially the all important SPL chart. But using fours for subs doesn't give me a warm and fuzzy, not even twelve per box. I use eight fours per box for my mains.
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Maybe I could go with the JL-Fathom in-wall solution perhaps? I could feasibly replace current subs with these without creating an aesthetic disaster.
IMO in walls are what you use if you don't care what it sounds like, only what it looks like. That's OK in an elevator or a restaurant, not in a real HT. I guess the JL looks OK, but $4500 for a sub is off the wall, pardon the pun, especially if you need two or more to smooth room modes.
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post #8 of 16
1/10/13 at 2:14pm
Having owned the BG-X system, both with 2 and 4 subs, and having owned other 18" and horn-loaded subs (in both the live audio context and in the home theater context), I will say the low frequency response is impressive for 4" drivers. With a system comprised entirely of BG speakers, I have had numerous people (with high quality systems themselves) rave about the quality of the sound. My issue, and it seems like the poster's issue, is the headroom - particularly during explosions, etc., on some of today's LFE intensive, highly dynamic movies. If I had another 2-4 db, I think I would be wholly satisfied with the 4 sub setup in my 17x13x9 room. With 5000 cubic feet, you may need 8 of those things!

While BG states that the woofer surface area of the 4 sub system is the same as two 18"s, the problem - in my opinion - is the lack of excursion in the 4" woofers as compared to larger drivers which can simply move more air. The speakers hit a hard clip, and when they do - the flub sound is very obvious and quite irritating during an intense passage.

I have considered adding a freestanding sub to augment the bass, but I think that may lead to additional issues in integrating the subs. Or I could sell them all and buy 2 very nice in-room subs and find room for them. The other solution is to add another 2 BG-X subs, but I'm not sure that will make enough difference.

As an aside, I get a fairly flat in room response down to about the mid 20 hz range, according to the ARC on my anthem receiver and REW. Not having any null issues at this point. We played with location prior to install.

Just food for thought.

Jh
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post #9 of 16
1/10/13 at 2:59pm
Quote:
Originally Posted by h20fam View Post


While BG states that the woofer surface area of the 4 sub system is the same as two 18"s, the problem - in my opinion - is the lack of excursion in the 4" woofers
The Sd (surface area) of an average four is 40 sq cm. That of an average eighteen is 1140 sq cm. So it will take 28 fours to equal the Sd of one eighteen. But that's only half the equation. An eighteen will have about 10mm xmax; I'm not aware of any fours with more than 5mm xmax. That puts us at 56 fours to equal the Vd (volume displacement) of one eighteen, or for that matter one long excursion fifteen. And then there's the matter of the driver Fs (free air resonance). Even twelves can have Fs values around 20Hz, which means that's roughly how low they'll go. 50Hz is the practical limit for fours. The definition of a sub-woofer is a speaker that plays below where a woofer plays. The classic definition of a woofer is a driver that will go down to the 41Hz low E of the double bass, so you really can't call a speaker loaded with fours a subwoofer.
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post #10 of 16
1/10/13 at 3:06pm
Thanks for the numbers.... makes sense to me.

The low bass from the BG-X speakers certainly measures lower than 50hz, though. I'm not sure of the distortion level, maximum spl, etc.

Right at the level of subsonic bass, my older 18" velodyne was much, much louder.

Would it make sense to use the existing 48 x 4" subs as a 50-100 hz solution and use a sealed sub for 50hz on down? I'd probably have to buy some external DSP to do that....at that point might as well start from square 1.
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post #11 of 16
1/10/13 at 3:18pm
Quote:
Originally Posted by h20fam View Post


Would it make sense to use the existing 48 x 4" subs as a 50-100 hz solution and use a sealed sub for 50hz on down? I'd probably have to buy some external DSP to do that...
You can, but as you noted there's added system complexity, and you're best off to have at least two for room mode smoothing. Sealed or vented doesn't matter, 20Hz is 20Hz, no matter what cab type produces it.
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post #12 of 16
1/10/13 at 3:22pm
I'm sure she'll love six subs! Great point on the mode smoothing.

Thanks.

Jh
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post #13 of 16
1/10/13 at 3:33pm
Quote:
Originally Posted by h20fam View Post

I'm sure she'll love six subs! Great point on the mode smoothing.

Thanks.

Jh
Just tell her subs are like shoes, you can never have too many. rolleyes.gif
At least subs don't get worn once and then thrown into a closet, never to be used again.
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post #14 of 16
1/10/13 at 5:57pm
Quote:
Originally Posted by Bill Fitzmaurice View Post

Just tell her subs are like shoes, you can never have too many. rolleyes.gif
At least subs don't get worn once and then thrown into a closet, never to be used again.

or purses...
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post #15 of 16
1/10/13 at 7:29pm
Quote:
Originally Posted by wlhungdude View Post

or purses...
Well, you can't very well expect for a girl to buy shoes without getting a purse to match, can you?
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post #16 of 16
1/10/13 at 7:32pm
I do suspect there might be a few here that may have a couple subs gathering dust in the basement....maybe not in the same league as the gals' handbag/purse counts, tho.
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