OK, I Get It But My Speakers Really Are LARGE!
For some, your main speakers may actually extend down to 30Hz or lower, especially if they include 10” or 12” side-firing low frequency drivers. The temptation will be to set these speakers to LARGE. The setting is there so there must be a place for its use, right? Actually, we usually recommend setting almost all speakers to SMALL, even if they are physically large floorstanding speakers. Here’s why: Even though those floorstanders have a low extension, they won’t necessarily go down to the lowest range of your subwoofer as linearly and free of compression (unless your main speakers have more piston area and box volume than your sub – but we won’t address that here) The problem with the LARGE setting is: the ultra low frequency information will not be heard if the speaker cannot reproduce it. Well if by some chance you were able to get your main speakers bass extension flat down to 20Hz, then adding the subwoofer on top of that would yield too much (up to 6dB) of bass output at the frequencies both are producing. Hence integration between the loudspeakers and subwoofer will be poor and the bass may be overpowering, sloppy and/or boomy.
As a practical example, my reference system has a pair of RBH Sound 1266-LSEs which extend down to 32Hz. I have them set to SMALL and I set my crossover frequency to 60Hz. Because of this, the subwoofer handles everything up to 60Hz that would otherwise go to my front speakers. The front speakers are now freed up to concentrate on only 60Hz and up. The result is no lost information, less distortion, more headroom and a better overall sound.
Alternatively, you can bi-amp your large tower speakers where the mid/tweet section gets connected to the receiver front main speaker level outputs which will be set to SMALL and you can connect the bass drivers to a separate powered amplifier to the sub output of your AV receiver. This will allow you to effectively treat them as powered subs which are now bass managed with your other powered subs in the system. However, this type of setup is more complex and you really need measurement tools and know-how to properly setup a multi-sub system to get the benefits that these type of systems offer.