Originally Posted by millerwill
Has Mark made any recommendation of the x-over for Cat 8C's and a SubMersiveHP?
In choosing crossover frequencies the speaker and subwoofer really only set an allowable or potential crossover frequency range, not what is best for your system. As an example, the little M&K S150's were one time a very common home theater speaker, and they sound rather nice... above 80-120Hz. If you wanted any sort of dynamics and large scale sound, they needed to be crossed about 100Hz as the small sealed woofers were just not up to the task below there where the required high excursions would cloud the midrange and intelligibility. Cases such as the M&K's are one of the reasons I made sure the SubMersive was capable and smooth out to 200Hz to better enable good behavior with higher crossover frequencies.
The 8C's have a nice sealed roll off that is specified to 65Hz. In room, near a wall, that can easily extend a good bit lower, and a pair of 8" woofers with 500W motivating them give them quite a bit of capability. Of course capability is relative to the room and expectations. I intended the 8C's to be used with a crossover in the 60-100Hz range. In-room response dips at the listening position from the speaker or subwoofer can give cause to shift the crossover toward 100Hz or lower it to 60Hz, where I recommend most start at 80Hz. For those with the largest of rooms using multiple SubMersives or similar with the most ambitious dynamic/output expectations, stay above 70-80Hz with the crossover, although I hardly expect that will be a concern in your application.