Adding a sub - what will I loose?

Wow! Lots of great info here...except for SoundsReal and his $10K sub. LOL

Doak - you bring up a good point. I'll have to check with the speaker manufacturer.

My plan is to use two small 8" subs. Found a good deal on Sunfire HRS-8 that's within my budget. My listening room is 12x16 with 13' ceilings.

I'll report back.
TG

12-02-11: Tghooper
My plan is to use two small 8" subs. Found a good deal on Sunfire HRS-8 that's within my budget. My listening room is 12x16 with 13' ceilings.

I use a pair of Mirage MM8's, which are 8" drivers and passive radiators in a 9" cube. However, they really don't add much below 35 Hz. Still, they're a good match for my system at this point. And I got them for less than $280 each.

If 14" cubes aren't too big and you want strong performance down into the 20's, you might want to consider these. They're sealed and tight, and the price is right for what they do. I have a local audiobuddy who uses them with his Magnepan 1.7's.

"Doesn't that imply that the main amp is superior to the amp in the sub, even within the limited frequency domain of the sub."

No. The sub driver is always driven by the sub's amp. The speaker-level inputs use a relatively high input impedance to reduce the main amp's output to just a couple of volts, and uses the low-voltage signal to drive the sub's internal amp. More likely there's some sort of frequency response difference caused by the interaction of the amp's output stage and the sub that is fortuitous.

Lots of cool stuff.

If you have a low efficiency speaker and listen at low volume you might lose some of the bottom end. You can always adjust the volume on the sub to compensate.

I say go for it. IMO it's tough to find a speaker with a really good midrange and 20hz bass at a reasonable price.