Axiom Home Page Forums General Discussion Home Theater Onkyo 875

Drew, the m80's have been driven in lab tests at 700 watts continuous for 2 weeks, 24hr/day, and peaks upto 1,000 watts. I think the problem, and you seem to ignore others above that have a wealth of audio/engineering experience, is that your limiting the current of your receiver. To little power is a lot worse on a speaker than to much.

i.e. Set the speaker impedance switch to 8 Ohms.

If you still hear distortion it more than likely means you've pushed the amps in the receiver too far and they are clipping--turn it down. The M80s can take peaks of 1000 Watts, they just don't like DC.

The one meter SPL test is interesting...I guess. But is your seating position at one meter? (I get the spec sheet comparison, but don't think you are using this info correctly.) Test the SPL at the seating position. My Denon 3300 begins to clip at 0.035 distortion at 84 watts (if I recall the test sheet right). My PSB towers are 4 ohms, and I can get clean sound at 105dB. Not at one meter, but at 12 ft. In short, your in depth tests are hard to compare to real world use.

The problem, if any, is not the M80s. There is far too much written on them, and users here, based on well over 150 watts (the real kind, not the advertised kind) in normal use to blame the M80 for the lack of output.

It's well known that M80s can be driven for long periods of time at 800+ watts, the limiting factor would be providing clean sustained power to them.

Ok, so can the 875/876 (876 since it's the same amp, I think) be added to the list of AVR's that can't effectively power M80's? If so, I need to know because if I go with an 876 and still will need my LPA-1 to power my M80's, I'm going to have to buy a whole new AV rack.

That clipping & distortion is exactly what my Pioneer Elite VSX-43TX does when I crank up my M80's (at about that same volume) and is the reason I bought my LPA-1 to power them.

I will readily admit that don't understand as much as some of this as others do about the relationship between the output db and wattage.... I am not an electrical engineer.

So if he flipped the switch to 4-ohms, where it's known that the 875/876 limits the wattage to ~55, but yet it produced the same amount of volume before the woofer cones started bouncing against the stops, then what difference would and extra 100, 500, or 1000 watts make? That does not sound right to me.

Is Onkyo lying about their output? That would be contrary to all of the glowing reviews that I've read. Please correct me, but if the cones are moving as far as they can, isn't that he limit as to how much volume the speakers can physically produce?

I would suppose that the frequency being produced would play a big role too. Asking M80's to produce a 25hz tone, for example, and getting a low db reading before distortion sets in, wouldn't really be an accurate test because M80's are not designed to produce that low of a frequency - right?

Peter, I'm not the expert you are hoping for, but I'm pretty sure you are confusing clipping/distortion with the speaker actually bottoming out due to the speakers ability to handle power. What is being described here - and I don't think we have this story cleared up - is the M80 producing the exact sound it is getting from the amp - distortion. Why the 876 would be distorting/clipping is a more difficult question, and I could not tell you don't worry about it. In Denon I trust. But the build up to this point - and I mean no disrespect to the original poster - does not lead me to believe you are getting great info here. We have a gumbo of current limiting, EQs, and many unknowns. Don't jump off the ledge yet.

Thanks Zimm.

I guess the problem is that I don't have a good understanding the relationship between the speakers, the wattage/power/signal produced by the amp, and the amount of distortion heard. At least, I don't understand it as well as I ought to.

In my case, I did some of this testing when I first got my LPA, and if I remember correctly:

From my couch, ~12ft away from my M80's, running with a 50hz cutoff (the only DSP), and my SVS sub switched *off*, 2-channel audio, my VSX43-TX could drive my M80's to about 97-98db (using the de-facto Rat Shack SPL meter) and then the sound would start to distort. Highs got weird, bass got flabby, just not pleasant. And pushed any harder and SQ went downhill very quickly without any increase in db. I didn't keep it there for more than a second because I know that can damage speakers. That's loud, but not loud enough for 'reference' material, IMHO.

With the LPA and the same test, I can get to 105-106db. At that point there was just a hint of strain from the system, but that may have been my hearing, as that was more than adequate for 'reference' tests. And therefore, I am happy with the LPA.

How do I equate those db figures with the actual wattage that the amps are producing?

No ledge yet!

I don't think you'll hear the M80s physically bottom out either. What happens is as you push into higher volume levels is you reach the soft limits of the woofers excursion and you get a compression-like effect, dynamics diminish, but no physical stoppage until you push much harder.

On the other hand, squaring off the tops of the waveform causes a very harsh sound.

Peter, that is the very question I have been begging for an answer to. Your experience is basically what I was trying to explain. With a real (or closer to real) 125 watts you system works cleanly because you get those watts without distortion. With BS watts, as on most AVRs, you only get a fraction of those watts cleanly, and you are capped at 90 db.

But how you read a spec sheet to know which amp section will give you clean watts, I can't get an answer to. Too many dismiss the question with "all modern well designed amps sound exactly the same." Yet, in Onkyo's line a mode increase by one add 10 watts, but doubles the high current capability from 36 to 72A. That tells me the amp section of the more expensive model has some gizmo (tech term) that allows it to fuel more of the 140 promised watts before distorting the sound.

But...I have been told that is not a key indicator, and that figure is damn hard to find on most amps, so it is of limited value. All this brings me back to the dirty place - I must put some faith in the professional reviews. Few of us have a Denon and a B&K and an Onkyo to A/B test. Hopefully they give us a grain of truth to work with.

Otherwise, I just have to trust Denon, because I have been impressed with every listen for 10 years, and I can't say that about any other product I own - well, the PS3 is damn impressive too, it does everything but prepare diner.

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