This discussion seems to keep coming back way too often.
I believe i do understand how the crossover works.
With most receivers, a setting of small puts the receiver crossover at 80Hz or so (brand dependant). This essentially means frequencies below 80Hz will be played primarily by the subwoofer and not the main speakers.
In theory, a sub cross higher than the receiver cross wouldn't do anything since the sub will still be 'limited' to playing sounds under 80Hz with frequencies above that being attenuated by the crossover. Yes i am aware of the 'cascading effect' but i have yet to hear of anyone having issues with it. Perhaps Alan or Ian can provide some more insight as to the unknown ugliness of cascading.
Again in theory if you had to keep the receiver and sub crossovers apart to avoid this phenomenon, then why not set the sub cross at 75 or 85Hz, a value still electronically above (or below) the receiver cross?
When the sub does play sounds above this receiver crossover value (or the mains play sounds below the value), then obviously you would have mixed frequencies from both your mains and the sub which is typically not desirable depending on their sound curves in relation to the crossover value. Hence lowering the sub cross from its maximum setting tends to increase the integration between the 2 speakers.
The suggestion is usually to start with the sub crossover set at the highest setting but then lower it until you hear a seamless integration of sub and sound (that nice point coming together where the main speaker sound curve begins to decrease approaching or passing the crossover value and the sub sound curve decreasing as it plays approaching or above the crossover value).
What i am saying is that most people find this 'integration' around the 80Hz range. You should be able to come to this integration level either above or below the receiver crossover depending on your listening preference. I don't believe it has to automatically be above.
link to crossover poll
So many users cannot all be wrong (77% of 23 polled use a crossover less than 85Hz), but even as the polls show, preferences can vary.
I myself am in a minority range of that poll. Personally i use the large setting for my M60 mains and turn down the sub crossover to the 50-60Hz range since i find it has a nicely integrated sound for music and plays those low notes solid for the HT application.
