It is a pity this was not a better design. It is interesting that they chose a passive crossover because of noise issue.
I have now have quite a bit of experience with active speakers now.
There is an S/N issue that I have mentioned before. The best amps produce some noise. Most bass/mids have cone break up at some point and the aim is to cross before cone break up and the resulting peaks. So at the break up point the driver has an increase in sensitivity. This can and often does make amp noise audible, that would otherwise be filtered out by the passive crossover. So if you direct connect and amp to a driver with significant cone break up peaks, you will hear noise that you would not have heard with a passive design. So my practice is to place a notch filter between amp and driver, tuned to the break up peak. I can assure that does the trick perfectly and filters out noise that is easily audible without the notch filter.
I find it really hard that people fail to understand that this is often an essential part of active speaker design.
Quad 909s are very quiet amps. However direct connected to bass drivers, the hiss reproduced by the break up peaks is audible at the listening position. After installing notch filters between the amps and their connected drivers, there is absolute silence.
This should not be difficult to understand, nor its solution.
