Thanks for these great technical explanations. I'm still greatly enjoying my AHB2 amps you sold me in 2017
I am curious how many ms of bass delay you'd expect to see between an AHB2 and an amp such as the aforementioned Accuphase (given the AHB2's best in class bandwidth)?
My room is actively tri-amped and well treated. Output is fed from my RME soundcard digitally into Xilica XD4080 speaker processors, and I'm using RME's totalmix for volume control. I'm using FIR filters for the three way speakers and a low order bessel filter for the woofers crossing to 5 subs. Even crossed to multiple subs to eliminate room issues and using a lot of bass traps I could never get a perfectly flat group delay curve. I suspect my small room is the only remaining limiting factor. It is interesting how Dirac improves group delay though.
10 AHB2 amps tri-amping 5 speakers and crossed to 5 JBL Fathom subs:
Same room and system, Dirac versus no EQ:
In a different room, I briefly drove my front woofers with an Emotiva XPR-2 amplifier prior to going all out and ordering another 8 AHB2's to fully tri-amp my surround system. I remember noticing a drastic difference in driver control when eliminating the front speaker crossovers and going full-active even with my old Emotiva amps, and an even bigger improvement in clarity when I switch to using all AHB2 amps in my system. I attributed the difference I was hearing between the AHB2 and the XPR amps to be mainly from the lower distortion, although my setup is drastically different from Coach Kaarlo's.
I wonder if or how well Dirac or similar correction software could correct the phase issues you point out that are due to an amplifier's short comings? I don't think Dirac is going to improve an amplifier's distortion, but it would seem that correcting time delay differences and small SPL errors like +/- 1dB are definitely possible and would make for an interesting double blind test.
Regardless, from experience, even with Dirac on my old amps, I'm definitely not giving up my AHB2's! I still haven't heard a system that sounds better, and that's comparing several 6 figure systems I've heard in much bigger rooms to mine.
With the Accuphase, the combination of late delivery and less damping will emphasize the bass on some recordings. You seem to have found one recording where this added emphasis was desirable in your room with your speakers, but it is quite likely that the bass in a different recording would sound uncontrolled.
0.56 dB may not sound like a lot, but keep in mind that it has been shown that A/B and A/B/X tests should be level matched to +/- 0.1 dB.
But there are more issues:
At the crossover frequencies, the speaker impedance can change very rapidly. If the amplifier output impedance is too high this variation in the load impedance can impact that phase alignment between the two drivers at the crossover point. This change in phase alignment can have a big impact on the amplitude response at the crossover frequency.