[schw06]

Since the purpose of multiple subs is to have a smoother frequency response, is it better to run both subs as summed left and right bass rather than 1 dedicated to the left channel and 1 dedicated to the right channel???

[neekomax]

Good question, I'm interested.

If I had to guess - and, this being the Internet, I DO have to guess - I'd say for the response, doesn't super matter, BUT, depending on your crossover point, you might negatively affect your stereo image running them summed.
 

[GT Audio Works]

Since the purpose of multiple subs is to have a smoother frequency response, is it better to run both subs as summed left and right bass rather than 1 dedicated to the left channel and 1 dedicated to the right channel???

Assuming the main speakers go low enough..I would run them mono as not to interfere with the response of the main speakers low frequency output.
Just my opinion but I use this setup on mine..Greg

[sts9fan]

Mono!!!!!!

[medium jim]

It all depends on how low you x/o and such.  I'm going to go against the grain and say stereo so to keep the proper soundstage.

Jim

[Donald]

I would try it both ways and see which way you prefer in your particular setting.

[rockadanny]

Yo D!
IMO, it depends on your crossover value. My mains are rated -3db at 55Hz, so in  my system, with the crossover set relatively high (around 45-50Hz), I prefer the subs wired in stereo. Even wired in stereo I still get smoothing benefit, though perhaps not as much as I would were they wired mono. Were my mains rated into the 30's or lower I'd probably go mono.
BTW, we need to , if you know what I mean.

[neekomax]

Yo D!
IMO, it depends on your crossover value. My mains are rated -3db at 55Hz, so in  my system, with the crossover set relatively high (around 45-50Hz), I prefer the subs wired in stereo. Even wired in stereo I still get smoothing benefit, though perhaps not as much as I would were they wired mono. Were my mains rated into the 30's or lower I'd probably go mono.
BTW, we need to , if you know what I mean.

Yeah dude! Can I come? 

[GT Audio Works]

I would try it both ways and see which way you prefer in your particular setting.

Always what it comes down to for me !!

[Russtafarian]

I say the first priority is to get the subs placed in the room for optimum output and smooth response in mono.  If the placement puts them in close enough alignment with the L & R speakers to run stereo, then try try it.

BTW, stereo subs placed either side of my listening couch has always worked well in my listening room.

Russ

[JRace]

Here is a paper by Tom Nousaine:
http://www.nousaine.com/pdfs/Stereo%20Bass.pdf

My conclusion is that your should run multiple subwoofers L&R mono when possible because stereo bass may degrade performance of non-optimal, non-corner placed subwoofers

In other words, unless your room works best with two subs mounted in the corners directly behind the main speakers run the in mono.

In my experience anything less than >60Hz is not going to be perceived by the brain in stereo du to the way our brain processes low frequency info.

[Haoleb]

When I used to have a dual sub setup, I ran it as a true stereo configuration. I used the DCX24/96 as a crossover and eq correction and from there fed my two monoblock amps for the main speakers and then two sub amps also running in monoblock configuration. Each sub sat next to the main speaker in the room. It was the best sound I have ever had. But.. play with it and see which works best for you.

The only best option is what works and sounds best to you   

[*Scotty*]

Since you have already have two full range speakers in the ZU Definition Mk.IV with a low frequency response of 14Hz., you don't need sub-woofers beside your main speakers at the front of the room. The primary problem which causes uneven bass response in your room is the reflection of bass energy from the wall behind you which collides with the bass radiated from the front speakers causing standing waves.
 With the addition of two subs to the full range loudspeakers you already have you are in an idea position to implement a four sub system. By placing the two additional subs you have at the back of the room behind you and operating them out of phase with your main speakers you have a chance to cancel out the bass energy from the front speakers before it can impact on the rear wall and reflect back towards the front of the room and interfere with the bass emitted by the front speakers.
See image below

Here is a link to the complete paper the the above image was sourced from.
http://vbn.aau.dk/files/12831869/AC-phd.pdf
All you will need to try this out is some inexpensive ICs long enough to reach the subs in the back of the room. Don't place the subs in the corners back there, rather space them at one third the distance from corners of the room along the wall or roughly the same distance apart as your front mains. Your problems with standing waves in the room are going to start at about 125Hz,depending on the subs crossover slope you may want set it between 60Hz and 80Hz, my subs have a 12dB/oct slope and I run mine at about 60Hz. 
Have fun, you may also notice a substantial improvement in the imaging the system has when you reduce the amount of standing waves in room.
Run the subs in stereo, left channel to left rear  sub, right channel to right rear sub.
Scotty

[MaxCast]

Scotty, if the mains are full range and you add two subs would you not be adding to the output below the subs xo?
Would you not have to lower the mains output (below sub xo) to match the added output from the subs?

[schw06]

I apologize for not updating my system profile but I am not using the Zu speakers any longer. I have had to downsize to a pair of monitors (Pioneer S-2EX).
David

[WC]

Full range speakers should be full range without a crossover.  Not that the OP has full range speakers.

[*Scotty*]

David, the same basic advice applies, try putting one sub in mono in the front between the satellites and one in the rear on the back wall out of phase. Match the crossover points on the subs on the front and the rear. No guarantees that you will like the setup but you should have considerably flatter response in the room than you might have with the two subs in the front augmenting the output of the front mains.
Scotty

[*Scotty*]

Maxcast, you may or may not see an increase in total bass energy in the room. There is usually room gain adding to the bass output of the full range speakers below the room's Schroeder frequency, the out of phase bass energy from the subs in the rear helps to counter act the room gain to a degree.
 The key thing to remember is that you are not running the rear subs at the same level as the front mains. What you are trying to do is cancel out the energy that remains that could be reflected by the rear wall after losses due to transmission through the rooms walls and any absorption that might have taken place.
 Typically you can't tell the rear sub is even operating unless you are right next to it if the levels are set correctly. When everything works right the bass gradually diminishes as you approach the rear of the room until it is virtually gone. However at the listening position you have the full bass energy required by the source material for proper reproduction.
Scotty

[medium jim]

David, the same basic advice applies, try putting one sub in mono in the front between the satellites and one in the rear on the back wall out of phase. Match the crossover points on the subs on the front and the rear. No guarantees that you will like the setup but you should have considerably flatter response in the room than you might have with the two subs in the front augmenting the output of the front mains.
Scotty

But which sound live and which doesn't?

Jim

[*Scotty*]

Quote from medium jim

But which sound live and which doesn't?

That would be determined by the listener.
Scotty