In a theater, a bigger speaker is generally not better. The subwoofer already handles the lower sounds. A bigger speaker is slower to react to mid-range sounds than a smaller one. That’s why we recommend 6 ½” speakers. These work best for home theater in-wall and in-ceiling speakers. A 6 1/2″ speaker will produce sounds from 80-100 hertz on up (mid-range type sounds like snare drums, gun shots, and snaps and higher).
You’re already going to use a powered sub-woofer for your theater room and that will take care of the low, bass sounds. Subwoofers handle frequencies from about 120 hertz and lower (the low, boom sounds).
Some people we have talked to wanted to use 8″ speakers for their home theater because they figured bigger is better. An 8″ speaker is made a little larger so it can reproduce lower sounds better. But in a home theater application, those sound ranges are already being handled by the subwoofer, and it would only be redundant.
If you use the 8″ speaker in your home theater realm, it will be slower to react to those mid-range noises than the 6 1/2″ speaker because of its larger mass. Just like a sports car will be quicker off the line than a big truck.
Does it matter how big your room is? Not in terms of the speaker sizes themselves but the number of speakers for coverage. Check this out: How many speakers should I use for theater set up?
Does it matter how big your room is?
Not the size of the speakers themselves but the number of speakers for coverage. This this FAQ about How many speakers should I use for theater set up?