The reason your receiver sets the crossover to 120Hz is probably due to the QS4s and in your room they probably can't output much content below that (fwi, the QS8s are rated to play down to 95Hz but in my room Audyssey detects the -3dB point being at 150Hz) and since you can't set individual crossovers, that's the setting kept by your receiver.
80Hz is usually a good starting point but I would follow Billy's advice, play with the crossover setting and leave it at what sounds the best to you. I would set it at the minimum frequency that you can hear a difference. For example if you can't hear a diff between 40 and 60, leave it at 60. If you can between 60 and 80, leave it at 60. This will prevent putting unnecessary stress on the speakers and receiver.
Also, having M80s and QS8s will not change anything regarding this crossover discussion, only having a receiver that allows for individual crossover settings will.
Last edited by bdpf; 03/18/11 02:01 PM.
