I often read posts from people who seem to be under the impression that bass management is a "brick wall" filter. In other words, if the system is set up with "Small" speakers and the cross-over is set to 80Hz, they reckon that everything above 80Hz in the main channels is sent to the satellite speakers, and everything below 80Hz is sent to the subwoofer. This, of course, isn't true. Now, I've been working on some numbers for this, using my Bryston SP1.7 as an example; but I cannot believe that the figures I've got here are correct. Where am I going wrong...? The SP1.7's bass management's high-pass filter is "2nd order", which means 12dB per octave. In other words, for each octave below 80Hz that the signal is, the sound intensity is reduced by 12dB (correct?). Suppose we're playing a sound at reference level, 85 dB. Presumably this will be split evenly between the sub and satellite, so each will be producing 82dB for a total of 85. An 80Hz signal sent to one of the satellite channels will therefore play at 82dB through the satellite speaker. A 56.6Hz signal sent to one of the satellite channels will play at 76dB through the satellite speaker. A 40Hz signal sent to one of the satellite channels will play at 70dB. A 28Hz signal sent to one of the satellite channels will play at 64dB. A 20Hz signal sent to one of the satellite channels will play at 58dB. The low-pass filter on the SP1.7 is 4th order (24dB per octave). An 80Hz, 85dB signal sent to a satellite channel will play at 82dB through the subwoofer. A 113Hz satellite-channel signal will play at 70dB through the sub. A 160Hz satellite-channel signal will play at 58dB through the sub. A 226Hz satellite-channel signal will play at 46dB through the sub. A 320Hz satellite-channel signal will play at 34dB through the sub. Now, I can't believe that these figures are right! I might be able to swallow a subwoofer delivering 58dB at 160Hz. But what about dedicated satellite speakers? Can a speaker that is only rated down to 80Hz seriously be expected to produce a 70dB signal at 40Hz? Where am I going wrong? How do the 2nd-order high-pass, 4th-order low-pass filters of the SP1.7 compare to those of other processors? Even if other processors have 4th- or 5th-order high-pass filters, you're still going to end up pushing quite significant low frequency signals through satellite speakers. (4th order would be 70dB at 56.6Hz, or 58dB at 40Hz). Can dedicated satellite speakers really handle this kind of signal? Can subwoofers really cope with anything up to 66.5dB at 160Hz (assuming all 7 satellite channels are being driven at 80Hz, 85dB) on top of the LFE channel? And what are the implications for (for example) setting up a Behringer Feedback Destroyer to work with the subwoofer? Do we need to be doing frequency sweeps up to 300Hz or higher in order to fully control what the subwoofer is doing? And if so, can we actually get a room-curve reading at 300Hz without doing damage to the subwoofer in the process? And if the satellite speakers are only 6dB down at 56.6Hz, then surely they're going to be nearly as much of a problem as the subwoofer? (If your room imposes a +15dB peak at 56.6Hz, but this is "corrected" by a Behringer Feedback Destroyer, then your uncorrected satellites will be quite a few dB louder than your corrected subwoofer at that frequency!).