Stereo Subs - Do they need to be identical?

Thanks guys for all the responses - a lot to think about. I have a key, related question. My MBL monitors have a low pass filter that cuts the bass off at 49hz - that's the lower limit of the bass.

Were I to introduce two subs to the mix, where would you recommend I mark the upper crossover point for the subs? And, would it be worth introducing some external crossover to cross the MBLs even higher (not force them to go as low as 49hz). Finally, even then, would some room correction unit be a welcome addition (like the Copland DRC) - maybe I'm straying too off topic here, so would need a seperate thred, but I would like to resolve these questions together and they seem tightly related. Overall, I'm looking for absolute seamless integration for two channel music. I had thought of getting 12inch subs because I may move to an apartment in the near future and I want to make sure I don't overpower the room.

To answer one of the questions above - my MBLs are about 4 feet from the back wall and three feet from the sides - its a large open plan room. I hope to upload updated system photos later this weekend (after I tidy the room ;-) )

Thanks,
John.

i do not see a tv or projector. is this a 2channel music set up? if so skip the subs you really don't need them unless you are looking for an exagerated bottom end. subs very tuff to set up with out affecting the mids and upper end and not being an exagerated lower end. first class home theater system, yes(for action movies only), 2 channel music only NO! my thoughts anyway. could move that tt off the ground though.

Shadorne, I think it depends upon the distance from the rear wall and the construction of that wall. Frequencies below about 45 hz or so pass through typical sheetrock walls and so no cancellation takes place. Therefore speakers more than 6 feet or so from this wall will not be affected by 1/4 wavelength cancellations. If the wall is reinforced then it is still O.K. if the speakers are more than 8 feet or so away as the loss will be attenuated by typical " room gain" below 35 hz or so. If 6 or 8 feet is not practical then try pushing the speakers very close to the rear wall and use thick absorption behind them. ( thick enough to absorb 125 hz) If this is not practical then yes nonalignment is a good idea. My bias is that the same frequency (crossover region) coming from two different sources at two different distances always creates phase issues and its own cancellation issues as well as slurred imaging in frequencies high enough to be directional. A lower crossover of course limits the damage of the last issue but not the first two. Each case is unique and the only way to know for sure is to experiment which in my experience takes a lot of time and patience and in any given case can lead to unique solutions. JMHO - Jim

Funnily enough the link I gave above came from a manufacturer...

The link also shows up to a 20 DB SPL hole in the bass in some cases due to quarter wave cancellation and a succession of harmonically related cancellations further up in frequency (a comb filter)...

Furthermore one might wonder why studios often soffit mount large full range speakers ?

These same studios often leave small (less than full range) near fields out far into the room on the meter bridge.

Perhaps there is some logic ....perhaps is is all just aesthetics...

Here is another speaker designer's comments on the reasons for soffit mounting speakers.

Read and draw your own conclusions. Dismiss the science if you like...