Thinkly, it looks like you may already have some of the answers I tried to post yesterday (did anyone else have problems?)

Reference the main question in your original posting (bass levels), the Avia disc subwoofer test compares the levels of a "high freq" signal from your (left) main speaker to a "low freq" signal from the sub. BUT (as Larry and Matt pointed out) if your main is set to Large it is also getting the "low freq" test tone. So you're definitely getting way too much low freq test tone! If you temporarily set the main speakers to Normal/THX the left main should only get the higher test tone and the subwoofer should only get the lower tone. After balancing, you can go back to the Large setting on your mains if you wish (but see below).

Reference the second question in your original post (85db vs. "match to the mains"), the Avia disc recommends that you balance ALL (non-sub) speaker levels to 85db if -- and this is a very big if -- you want to calibrate at the THX studio reference level. The disc then goes on to caveat this by stating in multiple places that you may find this level too loud. It also mentions that "most" of its test tones are designed to balance at 75db. Confusing, huh? But... I don't know what formula they used to generate the subwoofer comparison tones, and I haven't tested it myself (I'm not using a dedicated subwoofer at the moment). My theory is that Avia has taken the "extra"
10db into consideration when devising the subwoofer test tones. Therefore if you follow their directions of first setting your main levels -- to whatever level you want to listen at, perhaps 75db? -- and then balancing your subwoofer by using the special sub tone and ONLY adjusting the sub's level, the Avia people have set it to be in the proper balance. I'd be interested in knowing whether the "high freq" test tone is the same level as the tone they use to initially balance the main speaker levels. (Guess I'll be digging out the SPL meter tonight :) This seems to be borne out by your observation that after you calibrated your mains to 75db, the low freq subwoofer test tone came out at 85db.

Moving along to why your left and right main channel show a different SPL at 72Hz: (BTW, your post says that both the 95db and 80db are your "left" channel :) The difference is almost certainly due to the room's acoustics rather than the speakers. Perhaps one speaker is losing part of its output into an upholstered piece of furniture, or the other is bouncing off a glass-framed picture, etc. The simplest way to fix this is with an equalizer. IMHO, equalizers are absolutely essential in any setup where you want to get a balanced output from multiple speakers.

Reference your later posting about whether your subwoofer is "useless:" In theory, with your current system settings you still need your subwoofer. When your sub is connected to the LFE channel and the receiver knows it's there (is set to "Subwoofer ON"), it should be the only speaker getting the signals for that channel. Setting your other speakers to Large or Normal/THX should not impact on this at all: That setting should only determine whether or not the bass information on those channels is sent to the subwoofer IN ADDITION to the LFE information it's already getting! (LFE should only be directed to Large speakers when the reciever has been told there is no subwoofer, which is not the case with your configuration). Notice I use the word "should" a lot. Larry, jump in here if I'm wrong. So with your current settings, your subwoofer is the only speaker receiving not only the LFE, but any bass from your center and surrounds. Definitely not useless IMHO.

My recommendations: First, set your mains to Normal/THX, and see if you can then successfully use the Avia subwoofer test tone to balance the sub. Keep Larry's comment in mind: If the max reduction (-10db) setting on the sub is still too loud, you may have room from your initial balancing to raise your other speakers' level settings to meet it. Second, assuming the above works, play your favorite movie scenes with the following three settings and pick the one that you enjoy listening to the most!
1) All speakers "Normal/THX" and "Subwoofer ON."
2) Mains "Large," others "Normal/THX," "Subwoofer ON."
3) Mains "Large," others "Normal/THX," "Subwoofer OFF."
Switching back and forth between options two and three should tell you pretty quickly whether your sub is making a worthwhile contribution.

One last possible consideration, if you still can't get the sub's level low enough. Your subwoofer's placement may be allowing it to take unfair advantage of the listening room's acoustic resonance factors, making it too loud. Try moving it to a different location and see if that makes it quieter. A good article on placement advice can be found at [Link: sonicdesign.se]

Remember, the test tones are only the starting point. What really matters is whether your subjective ears enjoy the sound!

-Bruce

This message was edited by Bruce Burson on 12/19/01 10:06.26.