# dual box setup



## mike c (Apr 25, 2006)

if I were to get two PB12 Pluses for a dedicated HT ...

I plan to place one nearfield and the other upfront ...

can I set one of them in 16hz tune and the other in the standard 20hz tune (near field)

pros and cons?


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## Ed Mullen (Jul 28, 2006)

mike c said:


> if I were to get two PB12 Pluses for a dedicated HT ...
> 
> I plan to place one nearfield and the other upfront ...
> 
> ...


Unless you have an absolutely huge room, you'll have no shortage of output capability, and there is no compelling reason to split up the subs like this. 

If you can place both subwoofers together, you will get 6 dB of additional headroom and maximum acoustic coupling across the entire pass band.

Separating them and running them in different tunes will create cancellation issues at certain frequencies due to room acoustics and also because the two subwoofers will have a different in-room FR and phase response in the two different extension modes.

Front stage placement near the mains and center channel usually works best for a seamless blend and optimal phasing potential with the LCR speakers. Keep them within 4-5 feet and they will be considered colocated all the way up to 80 Hz (the typical XO frequency).


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## Sonnie (Apr 11, 2006)

Your best bet would be to experiment with the placements and run REW measurements, but since you will have two of them in such a small room, go ahead and tune them both to 16Hz, which is what I did.

I have one in the front and one in the rear, with the front crossed over at 80Hz and the rear at 60Hz. This ended up being the best locations for me to get a flat response without equalization. You really have to experiment with the x-over points and phase and do a lot of measuring, or at least I did. For instance, raising my rear sub x-over to 80Hz caused much more serious cancellations at around 65-70Hz. 

When you get a pair, I suggest as Ed does to start out co-locating them if possible or try to locate them symmetrically in the room if that is a possibility. If those do not provide smooth response, then start moving one or the other around... eventually you'll find the right mix. It took me a few dozen attempts... but I ended up with this unfiltered/unequalized response:


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## Ed Mullen (Jul 28, 2006)

Here is the FR of my dual Ultra/2 16 Hz tune with Rocket 850 Sigs included in the sweep. These are front stage placement flanking the center channel, to the inside of each 850. 

http://www.hometheatershack.com/photopost/showgallery.php/cat/501/ppuser/1779


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## mike c (Apr 25, 2006)

I forgot to post my reasons for wanting to separate them ... (or at least place one nearfield)

I agree that one subwoofer would suffice for "volume" ... BUT, my intention is the couch shaking, chest slam factors ... I have observed that increasing volume to a single or dual colocated subwoofer UPFRONT does not add chest slam/couch shaking before getting too loud overall. 

unlike when placing a subwoofer nearfield, volume doesn't have to be as loud, but I still get the couch shaking effect. believe me I want to colocate or have only one subwoofer, but the couch shaking effect is important to me.

perhaps if I place BOTH subwoofers nearfield?


oh and the room volume has to be about 3k-4k (no final measurements yet)


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## Sonnie (Apr 11, 2006)

Both nearfield...  you may need to wear a mouthpiece during some movies.


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## lienly (Sep 4, 2006)

what do you mean 'wear a mouthpiece [= mask, right?] in movies?:scratchhead: 



Sonnie said:


> Both nearfield...  you may need to wear a mouthpiece during some movies.


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## Blaser (Aug 28, 2006)

Ed Mullen said:


> Here is the FR of my dual Ultra/2 16 Hz tune with Rocket 850 Sigs included in the sweep. These are front stage placement flanking the center channel, to the inside of each 850.
> 
> http://www.hometheatershack.com/photopost/showgallery.php/cat/501/ppuser/1779


WOW!! Did you draw this room FR with a pen??:bigsmile: 

Do you use any equalization?

With symetrical placement on each side of the center channel and so I guess equidistant from listening position, do you obtain 6 db reinforcement from 16-80 Hz?

Blaser


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## lienly (Sep 4, 2006)

my problem is bit different from his.
I have 2 different SVSes, PB12-NSD2 and SB12+, so how to setup to make both work together well?:scratch: :huh: :dontknow: :wits-end: :scratchhead:


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## mike c (Apr 25, 2006)

lienly, using different subs in the same setup is a bit hard to do unless you co-locate them.
I have personally used two subwoofers, one with 18hz tuning and one with 23hz tuning at the same time ... not co-located ... and the total frequency response went the way of the 23hz tuning (the crappier sub), unless you have some way of measuring your response like REW or SMS-1 to confirm that they are helping each other instead of against each other ... I would stick to colocating them.

you should make a new thread asking Ed Mullen to help you out.


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## Guest (May 24, 2007)

Mike, I just hooked up dual 20-39 in a 20x12x9 dedicated and the result was "couch shaking, chest slam factors." The volume was not to loud either which impressed me even more because like you, I desire the feel as much, if not more than, the volume. Co-located, no plugs, with a 5-10 min calibration job (much more planned for this weekend.) Maybe these are an option for you. Hope this helps. I would also like to add that SVS was one of the best companies I've purchased anything from in relation to customer service...which I'm sure is news to all of you.:bigsmile: Ed's great.


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## Ed Mullen (Jul 28, 2006)

NickS said:


> Mike, I just hooked up dual 20-39 in a 20x12x9 dedicated and the result was "couch shaking, chest slam factors." The volume was not to loud either which impressed me even more because like you, I desire the feel as much, if not more than, the volume. Co-located, no plugs, with a 5-10 min calibration job (much more planned for this weekend.) Maybe these are an option for you. Hope this helps. I would also like to add that SVS was one of the best companies I've purchased anything from in relation to customer service...which I'm sure is news to all of you.:bigsmile: Ed's great.


Glad to hear you're pounding away, Nick - that dual PC+ B-stock was a great opportunity. :T 



lienly said:


> my problem is bit different from his. I have 2 different SVSes, PB12-NSD2 and SB12+, so how to setup to make both work together well?


The NSD/2 in the native tune (all ports open) and the SB12-Plus will have the closest FRs. If you want maximum output reinforcement from the pair, then run the NSD/2 with all ports open and the SB12-Plus nearby (on top of the NSD/2, even). 

Calibrate the NSD/2 about 6-8 dB louder than the SB12-Plus so they will reach their respective limits at about the same point. Experiment with this calibration differential, though, since it's unusual to mate-up these two subs. 

You could probably get away with tuning the NSD/2 to 20 Hz and benefit from the deeper extension and also still realize a bunch of headroom increase in the 32-80 Hz region by adding the SB12-Plus.


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## Guest (May 25, 2007)

Interesting suggestion Ed. For me I have a pb12+/2 in a 3200 ^ft room that is open resulting in a large 5300 ^ft or so. I've placed the sub nearfield to maximize the output after trying various locations. The sub is calibrated with a house curve using an ART351 EQ. It goes loud (max about 109 db uncorrected at 30 Hz) but not to reference levels. 

In my experience the power of the sub makes it possible to locate it in the room, specifically on my left side (HT use). Probably because of some pressurization. I was thinking in the future that adding a second sub in another location would fix that nicely, and an SMS-1 or upcoming SVS audyssey in that set up would help get better overall room response (than colocation).

Any thoughts?

kw...........


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## Ed Mullen (Jul 28, 2006)

kwtoxman said:


> Interesting suggestion Ed. For me I have a pb12+/2 in a 3200 ^ft room that is open resulting in a large 5300 ^ft or so. I've placed the sub nearfield to maximize the output after trying various locations. The sub is calibrated with a house curve using an ART351 EQ. It goes loud (max about 109 db uncorrected at 30 Hz) but not to reference levels.
> 
> In my experience the power of the sub makes it possible to locate it in the room, specifically on my left side (HT use). Probably because of some pressurization. I was thinking in the future that adding a second sub in another location would fix that nicely, and an SMS-1 or upcoming SVS audyssey in that set up would help get better overall room response (than colocation).
> 
> ...


While opinions vary, I rarely favor nearfield placement because of the increased potential for localization and difficulty in phasing the subwoofer with the front stage speakers over the crossover bandwidth. 

I prefer duals on the front stage, flanking the center channel and between the mains. You'll still get the benefit of colocation, they generally deal more effectively with room modes when configured this way, localization is a non-issue, and phasing over the XO bandwidth is much easier. 

Naturally a measurement system like REW and a PEQ like the FBQ 2496 can work wonders. 

BTW, 109 dB peaks (c-weighted fast) from a Plus/2 nearfield seems low; go through your processor and DVD player and make sure you don't have any limiters enabled or the LFE channel attenuated, etc.


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## Guest (May 25, 2007)

Ed Mullen said:


> While opinions vary, I rarely favor nearfield placement because of the increased potential for localization and difficulty in phasing the subwoofer with the front stage speakers over the crossover bandwidth.
> 
> I prefer duals on the front stage, flanking the center channel and between the mains. You'll still get the benefit of colocation, they generally deal more effectively with room modes when configured this way, localization is a non-issue, and phasing over the XO bandwidth is much easier.
> 
> ...


Thanks for the input. I checked my receiver over thoroughly when setting it up. Did it again and it seems fine.

I did check my receiver regarding the LFE bug that many have and it seems to do it right (boost it 10dB; it has the LFE 0dB and LFE -10dB option, set a zero as per recommendations). I run DD or DTS. 

Having played with it too much, test tones, movie passages, etc., the max I can (tried just now again) is about 108 dB max uncorrected (c weighted fast), 1 port plugged 20 Hz setting (12.3 drivers), sub 4 ft to the left of the seating position. I can push up the receiver SW level or gain on the SW, and it doesn't add to the output, and takes away from bass quality (compression I guess). What I really like about the +/2 is that I've never heard anyone who has bottomed it out (it doesn't appear probable in the 20 and 25 Hz tune). 

If I defeat the parametric EQ I can get another 6dB from room resonances , but it's too boomy for my tastes. :scratchhead:

Because most people under-sub for their room, I always recommend with caveats people get as much output as they can afford. A NSD12 isn't going to cut it in 4000^ft. Better to get the output over an incremental SQ improvement from an upgraded driver for HT. 

Sorry for going a bit OT.

kw.......


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