I thought I understood what this crossover-malarky was all about, until today when I started playing various test frequencies on my Denon 1804. I had assumed that if I set the amp crosover to, say, 100 Mhz, then everything below 100 Mhz would be sent to the sub, and everything over would be sent to the speakers (set to small on the amp). This made sense. However, I played a 80 hz test tone with a 100 Mhz crossover, and the sub turned off, and I heard sound from the main speakers. I then played 120 Mhz tone with the amp on, but speakers switched off, and heard a tone from the sub. Admittedly, the sounds were a lot quieter when coming from the 'wrong' speaker, but I hadn't expected to hear anything! So, is the crossover frequency just the centre-point of a crossover-slant, or is it supposed to be all or nothing as I had supposed? Or could it be that my 'pure' test tones actually have some other frequencies in them too (generated use a PC-based tone generator and then burnt to CD)? Can anyone explain as I'm a bit confused? Thanks, Balders.