Originally Posted by feisty
Interesting comment. How could you damage your speakers by setting the crossover too low? Does not the receiver drive the mains and the subwoofer amp drive the subwoofer? My concern stems from setting my mains to "large" even with the subwoofer (due to midbass problems). It would seem I run a risk based upon your comment. If you could expand upon your comment I would appreciate it. Thanks.
I think you are confusing amp power with frequency response and crossover points. You are correct the receiver's amps do drive the 5,6,or 7 main speakers while the sub's amp powers the sub. This is amp power, but where talking about damage do to sending frequencies to your speakers that they are not capable of handling. By properly setting the crossover you send only the frequencies to a speaker that it can handle and let the sub handle the lower frequencies that the other speakers can't.
If you set your receiver to "LARGE" then your speakers will get the full DD or DTS signal recorded for those channels, lets say front L&R channels also known as your main speakers. If a movie like War of the Worlds for instance has bass recodred as low as 20Hz in the front L&R channels(I'm not talking LFE just regular bass) then you front L&R speakers will get a 20Hz signal. Now if you front L&R speakers only extend down to 40Hz then your risking your speakers. At very low volumes this won't be a problem, but at any normal movie volume you're in for trouble.
Now let's take the same situation as above and apply it to setting your speakers to "SMALL" and running the crossover at 30Hz. When you set your speakers to LARGE they get the full signal recodred in a channel, but when you set them to SMALL they only receive the signal "above" the crossover everything below the crossover goes to the sub. So if you set them to small and set th ecrossover to 30Hz, but the speakers only extend to 40Hz then you are allowing at the minimum 10Hz more extension than your speakers can handle and this is bad.
Now for the kicker. Even if you set the crossover to 30Hz the crossver has a slope and doesn't just stop the frequency at 30Hz like a brick wall. It acually allows the signal to reduce in volume starting at 30Hz and depending on the slope it will gradually drop off the volume over a number of Hz. This is why you should set your crossover 1 octave above the speakers lower extention. Some people just set the crossover 20Hz higher than the speakers extension and that gives enough room for the slope and eliminate damaging the speakers.