Why does everyone assume this is going to work well, each time? It is not at all uncommon in even the low-pass section to smooth the response of the bass drivers around the crossover point, OR to provide Z-rise compensation. If that is built-in to the crossover - IE is not across the woofers' terminals - it will be absent when you remove the passive xover, and the sound will not be as OEM voiced! The slope may be a compound one - with a knee. There may even be a notch filter for the woofer's break-up region, above the xover point. Then we look at the high-pass crossover, where for domes you may have another trap for its Fs and response shaping I wonder if a standard active crossover that matches all that is going to be particularly easy to make, or at all cheap. And if the active crossover doesn't have those features - and MOST just don't - why do so many people convince themselves that going active bi-amping will be an improvement on passive bi-amping? So, you will need to get a bespoke active crossover made, after your find out what the actual examples of the low-pass& high-pass in each of your speakers actually does. Hmm take a speaker to crossover company so they can measure what it does. Better to take both, given driver production variances. The business that does this for you will need measuring gear. .... And this is going to be cheap? For high-pass duty? It is not my experience that typical off-the-shelf active crossovers are more transparent than passive spkr-level or line-level crossovers built with high quality components like film caps, air core coils, and low-l Rs. It's the other way around. My experience with passive bi-amping has been with spkrs with no low-pass but with Z-rise compensation across the terminals, which we kept. The high-pass uses a 3rd order slope, an FS notch-trap t-filter - tuned to each big dome tweeter - plus response shaping. Did I go and pay someone to replicate each channel that in an active box? No I did not. No low-pass did help in that decision, and I retained the z-rise compensation upgrade. We tried vertical bi-amping - it wasn't much better, and we had buzz and hum issues. What we did do was use one matching stereo amp for mid-bass but in pentode and upped its storage again*, and put the tweeter-only amp in triode mode. Big improvement on one stereo amp in UL, and that was with both amps *rebuilt with BIG PSUs already. There is a lot more headroom, bass is a lot better, everything's better, and no hum / buzz. Because one stereo amp and its PSU was doing just mid-bass, the treble amp's PSU was not working hard at all, ever. This is called horisontal bi-amping and IMO&E will be the best way to passively bi-amp with any gain-matched pair of stereo power amps. Our OP has used two large mono-block power amps for the bass job, so the advantage - given possibly audible PSU effects in the mid-treble - from heavy bass passages - is slightly better, again. IMO if you want to try bi-amping? ...... Unless you can - easily and certainly - match at line/active level what your existing passive crossovers do, you should still try passive horisontal bi-amping. Yes, you will need amps with matching voltage gain or a matched pair of the same circuit. IF the bass demands are serious a bigger amp but with matching voltage gain is a fine idea. OR a bigger PSU. Even where we assume that active HP/LP matching 4LR slopes for sub-woofer use is going to be best we still might be wrong. It might be simpler - and sound better - to allow the main speakers to roll off naturally. If the mains are sealed we could add a 2nd order passive line-level (PLL) input filter to that power amp's sockets -using high quality Rs and Cs. This will cascade with the 2nd order sealed roll-off giving a 4th slope acoustically. Likely to be more transparent than any active line-level HP crossover. Then gain-match with 4lR low-pass in the active crossover. If they are Rbs then a 2nd PLL would help kill cone bounce, but you do end up with a 6th order HP acoustic slope. Killing cone bounce is audibly a good thing. Stuffing the ports is cheaper! So, IMO&E there are quite good reasons for trying passive bi-amping if you can get a matching-gain bass amp or two matching amps. But go 'horizontal' if the PSUs are shared across both channels. Hi-fi systems are called systems because they are systems, so each one has its own dependencies. Eg. a complex OEM passive crossover in each speaker, possibly built for the individual drive unit's variances.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
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