Well, this is driving me crazy. In the year or so that I've been lurking on this forum, I've often seen it said that in order to get reference level bass with all speakers set to small, a subwoofer needs to deliver an SPL of 121 dB at the seats. SVS says the same thing on their web site. So where does this "121 dB" number come from? My understanding is that in a 5.1 system, the LFE channel by itself can generate a maximum of 115 dB. But, with bass management sending the bass from the other five channels to the sub, the sub needs to be able to deliver MORE that 115 dB. But how much more? Is it really 6 dB more? I think the number is more like 1.8 dB. That is, 116.8 at the seats is all that's required for reference level. I'm sure I must be wrong, but I can't figure out why. Would someone please check my assumptions and my math and tell me where I've gone wrong? Here are my assumptions: The left, right, center, left surround and right surround channels (the "5.0 channels") can EACH generate a maximum of 105 dB of bass. The LFE channel (the ".1 channel") can generate 115 dB of bass. A 3dB increase in SPL is a doubling of SPL. A 4.8 dB increase in SPL is a tripling of SPL. A 6 dB increase in SPL is a quadrupling of SPL. A 7 db increase in SPL is a quintupling of SPL. How am I doing so far? Okay, so if we have the 5.0 channels that can each generate 105 dB of bass, altogether they'll generate 112 dB. (112 dB is a quintupling of 105 dB.) Since the LFE channel can generate 115 dB of bass, it can generate double the bass of the five other channels combined. (115 dB is 3 dB more than 112 dB, so it's double.) Thus the maximum SPLs generated by all 5.1 channels is triple the SPLs generated by just the 5.0 channels. Since the 5.0 channels can generate 112 dB, then triple 112 dB is 116.8 dB. Not 121 dB. This is really driving me nuts. Please help me figure out the right way to get to the 121 number! Thanks!