Hi Peter,
I'd point out that in past years, I've generally avoided recommending Pioneer and Onkyo AV receivers to drive the 4-ohm M80s because of current-limiting/shut-down experiences reported by Axiom customers. It seems the Onkyo's some years ago had overly touch protection circuitry, and Dan Kumin's bench tests confirmed that. At that time, and even now, we have not had any problems of current limiting or shut-down driving the M80s with Denon or Sherwood Newcastle AV receivers.
It is encouraging that the newer ONkyo's--the 875, 876--seem to have more robust amplifiers. On the other hand, I'd point out that Dan Kumin's bench tests of power output are at a single fixed frequency--1 kHz--and you cannot extrapolate from that to music signals, which represent a very complex load across the audible bandwidth of 20 Hz to 20 kHz. Moreover, there are other factors going on that are not easily predictable. When loudspeaker voice coils have wide excursions at higher power levels, they actually generate current and send a spurious signal back to the amplifier. It's called back EMF (electro-motive force) and that will increase the complexity of the load that the amplifier "sees".
I tend to be the cautious sort and recommend the brands of AV receivers that I know--from testing at Axiom--and from customer feedback, will not have problems of early current limiting or shut-down when driven within their output limits. Obviously, if you are in a big room and/or listen at extremely loud SPL levels (quite common among many of my Axiom colleagues), then all AV receivers will run out of power and clip, which is why we recommend an auxiliary power amplifier (Axiom's A1400) to achieve clean, ultra-loud SPL levels, which the M80s will do. It is also why Axiom developed the A1400. Ian was weary of his five Denon mono-blocks shutting down, and those put out 350 watts into 4 ohms. At parties, typically two or three of them would shut down. I, of course, would retreat to the deck outside or wear earplugs!
Personally, I find peak playback levels of greater than 103 to 105 dB SPL insane, because it's louder than any real-life music save for some rock concerts. And those that I've attended I made certain I was far enough away to avoid deafening levels or damaging my ears.
All this is to try and point out that AV receiver and amplifier power output levels are very complex. In times past, amplifier power output was always measured over the full audio bandwidth, 20 Hz to 20 kHz, because it more closely echoed a real-world music signal. Single frequency power output tests at 1 kHz were reserved for the car audio business and were mostly ridiculed by those of us into home audio, because those measurements misrepresented what the amplifier would likely do with broadband music signals and gave abnormally high power output specs that car audio makers could trumpet in their ads.
I do hope current Onkyo receivers have more robust power output into lower impedances than in the past, because I'd like to be able to unequivocally recommend them, as I do with Denon, Sherwood Newcastle, H/K, Rotel and a few others.
But right now, I'm still cautious.
Regards,
Alan
