"To OPTIMALLY separate the (low bass) subwoofer passband from the (mid-bass) main woofer passband, it’s necessary to use a full 4th order (24dB/octave) active Linkwitz-Riley crossover."
How do you know? Are you taking into account the rolloff inherent in the main speakers, and its accompanying phase shift? If so, what frequency and what slope is it? How much phase shift does it contribute? Well the answer is... IT DEPENDS!
The real world is far more complicated than your "one size fits all" claim implies.
I certainly do not agree with your claim that a 4th order LR crossover is "necessary".
And out in the real world, my second order highpass + the speaker’s inherent rolloff will usually (but not always) come closer to a 4th order acoustic slope than what you are suggesting (4th order highpass + the speaker’s inherent rolloff).
"A simple (generally passive) 2nd order (12dB/octave) crossover is simply not sufficient; the overlap is excessive."
If there does happen to be some overlap, you have more than enough adjustability in the amp’s lowpass filter section to deal with it: Phase, frequency, gain, and if necessary a parametric EQ. Low-frequency speaker systems in rooms are minimum-phase systems, which means that once you get the amplitude response right, the time-domain response is also right. And the amp has the tools needed to do that in the crossover region.
"Is a 12dB/octave crossover better than nothing? Well, probably; but why compromise unless there’s a cost-related cause."
Yes in the Swarm I’m trying to keep bang-for-the-buck fairly high. There is always some improvement that can be made for more money, so these sorts of things are judgment calls. I don’t think it would be a wise investment for me to have custom subwoofer amps made, but if I did, I’d look into parts quality in the highpass section before I opted for a steeper slope (or ideally, a variable slope).
Nobody is obligated to buy the subwoofer amp that I offer. Anyone can buy just the subs and provide their own amplifier and filtering.
Duke
