Sub driver surface area vs wattage.

I have two infinity reference 1040w subs brand new that I just got.  I originally intened to install just one sub and install it bridged on the rear channel of my infinty 7540a amp.  The store I got them from was doing a  buy one get one so now I have two.  My question is how do I hook them up and should I use just the one or both?

Now the amp puts out 111w rms @4ohm per channel, so 222W for both rears.  It will put out 278W @4ohm when bridged.  It's not 2 ohm stable bridged.  The subs I have are 4 ohm svc.  So my options are pretty much one sub on the amp bridged at 4ohm for 278W or one sub on each channel driven at 111W @4ohm.

WIll I get better results driving the one sub at higher wattage or two subs at half the power?  or does it come out the same in the end?  I'm going sealed inclosure.  I'm looking for a clean tight bass, not boomy.  I'm also aiming for just some low end fill.  SPL is not the goal, just clean bass to round out the music.  Country mostly, some jazz/soft rock occasional so you have an idea of what my goals are.

First, of course, is that you have to take into consideration the amount of space you have that you can dedicate to the subwoofers.  And there is the factor of weight.  Your's is a particularly different situation because you have a "free" subwoofer that can be used...all you have to do is give up the weight, room and box expense.  So...when you have decided through all of that...

Adding the second woofer will give you an increase of about 3 db just for the doubling of cone area alone.  The two subs wired at 8 ohms will indeed receive the same power that one sub at 4 ohms would receive...but the added 3 db will make it louder.  (yes, I am saying to series-wire the subs instead of putting one on each channel.)  The amp will work less hard at an 8 ohm bridged load than it will at 4, so that is a benefit to the amp.  And, you can make this less loud if you wish when you finalize the setup of the system.  That is, having too much sub bass is normally not a problem because you can easily minimize it, usually using just the deck controls.  Lowering the amp gain a bit from the set position will accomplish the same thing, resulting in less output.

One thing to consider when you are deciding whether to use both subs is this:  you may, one day, decide to use that amp for the cabin speakers and get a mono amp for the subs.  If you already have an enclosure built for two, you would be able to rewire them to 2 ohms and then you would be talking about some more serious sub bass.  Maybe too much for the music you listen to, but as I said above...

Thank you for input.  So instead of one sub at 278W run two subs at 139 W total?  I'm not sure how that would increase sound output.    The amp puts out 278W when bridged at 4 ohms.  Bumping that up to 8 ohms would reduced the power to approx 139W on the channel.  Then you'd have to split that between the subs, so 68W to each sub?  I might be missing something here but i'm not sure what.

As far as room, there is plenty in the trunk for it.  Due to the odd shape of the trunk and my need for symmetry in these types of things, two subs would actually take less room than one.  (I'd have to put the one sub in the center of the rear trunk wall,  if two, then one in each rear corner.   The corners are set back a little bit so there is extra room there.)

The Infinity 7540 is a 4-channel class A/B amp.  This is not the best choice for subwoofers, although you could certainly use it.  If you bridge two channels or any amplifier into an 8-ohm load, that is the same as operating in 4-ohm stereo (`111 watts per channel or 222 watts total in your amp's case.)  The advantage that stevedart was trying to point out is that you will be ensured the subs produce the same signal if wired in series, as opposed to operating them in stereo with the possible cancellation issues that allows.  You cannot wire them in parallel and bridge this amplifier.

OKay I think I understand the reasoning behind the 8 ohm.  So there is one finally question.  

It's seems that bridged is the only way to go, so bridge it with one sub or two?  In suit with the simplicity of the previous post

Okay, feed the same power to the subs and the two will produce +3db more, but what about when you double the power to the single?

one woofer @278 vs 2 woofer @111each?  Do you need to know that the subs are 250W rms 1000w peak?  Does that make difference?

Damn, for a min i thought you had DVC, cause then you could wire them to get 8 ohms a speaker, then turn it into 4 ohms together.  But since is a single voice coil. i would suggest getting a new amp.  Either use one sub, or get a new amp.  It wont put out enough power for the woofers to be very loud, and if it does, it will be very strained. 

When i was real short on cash, i ran 2 10in Kicker Comps off an amp with the same power ratings as yours for about a month.  It would heat up so much that it would shut off after 10-15min, until it cooled down enough to work.  This shows that it was being strained way too much.  Ide be carefull!

Ok, I see the mistake I made in my post.  The output would not be the same as I said it would be, but it will be closer than you thought at first.  It looks like you got what was said in response but I will clarify this again anyway. 

DYohn pointed out that when you bridge an amp with an 8 ohm load you should look at the stereo 4 ohm output to find the result...instead of looking at the 2 ohm (4 ohm bridged) output and deducing the result from that (for various reasons, like amplifier limitations, that we won't thoroughtly disect right now).  So instead of halving the amp's 278 watt  @ 4 ohm bridged rating, you should double (actually, add together) the 4 ohm per channel rating.  So, the comparison looks like this:

278 watts into one sub, or

222 watts into two subs

It at first appears that the 278 watts is the winner here, but when you take the doubled cone area's +3 db into consideration the clear winner goes to the two-sub combination.  Remember that it also takes a doubling of power to achieve +3 db.

]Do yo wrote:

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need to know that the subs are 250W rms 1000w peak?  Does that make difference?

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Feeding a 250 watt RMS sub 100 watts or thereabouts is perfectly acceptable.  This is, in fact, more standard than you might think in SQ systems.  You just might want to tend toward the large side when designing the sub enclosure, or stuff it with polyfil.  The larger air space (with polyfil it's an equivalency) results in less of a need for power.

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