Originally Posted by kawie01
If I have towers for my fronts & backs, should I change the Audyssey from small to large/full?
Only if your main speakers are larger than you are and wall mounted or a healthy distance off the wall (4-5' is a nice start; otherwise the SBIR null is significant) or your sub-woofer sucks and you can't stand the sound of it.
When speaker companies (honestly) claim response to a given frequency they don't state at what SPL and in many cases you won't don't get usable output (or even audible) levels at those frequencies.
When crossing to a sub-woofer things get more complicated because the output from a port which unloads the active driver isn't usable since it's 180 degrees out of phase with the rest of the spectrum and will cause sub-woofer integration problems.
1. Reference level home theater takes up to 105dB peaks at the seats which can translate into 108-110dB+ at the speakers.
2. Output at the maximum linear excursion for various representative drivers at 3 feet is as follows at 80 and 20Hz. Many lower quality drivers have less excursion and lower output (one noted speaker designer commented that an $8000 MSRP allowed for an $80 mid-range driver). Subtract 3-5dB for living room dimensions and more for a larger space.
You can add 6dB for a floor mounted woofer (as in a 3-way) and 6dB if there are a pair of bass drivers. For a 2-way the numbers are what they are although in all cases you can add 6dB at the cross-over point when using an even order sub-woofer cross-over.
Size Driver Sd (cm^2) x xmax (mm) 80Hz 20Hz
5 1/4" Peerless 830873 88 x 3.5 88dB 64dB
6 1/4" Seas L16RN-SL 104 x 6 94dB 70dB
7" Seas W18EX001 126 x 5 95dB 71dB
8.5" Seas W22EX001 220 x 5 99dB 75dB
10" Peerless 830452 352 x 12.5 111dB 87dB
As you can see consumer 2-way speakers don't have enough for an 80Hz cross-over and floor standers with just a couple of 10" sub-woofers don't have enough for full-range use.