Axiom Home Page Forums General Discussion Technical Questions Ohm rating, averages, and deceit in the industry?

I was going to post a followup to the M80-specific discussion but it felt a bit like hijacking. So!

People say that the M80's are "an easy 4 ohms" vs "a difficult 4 ohms", which would lead us to believe that their average impedance might have been rounded down to 4? (I'd say it's nicer to the consumer to round down, like Axiom did, than to round up). What's the 'actual' M80 impedance with standard testing material?

On avsforum I came across a post saying that many nominally 8 ohm speakers are closer to 4? I can see why manufacturers would like to do so, but whatever happened to truth in advertising? Are there any known tricksters in the industry?

Is this much like the receiver power output situation? Are there independent testers measuring real average impedances? It seems significant!

p.s. What brought this on was, I sold my Denon 1603 for a Yamaha RX-V1400 (and a HSU STF-2). Unfortunately the Denon left last Saturday, and the Yamaha doesn't come in until tomorrow-- I'm now having serious music withdrawl. (lesson learned, have some foresight regarding this stuff!) Anyway, with the Yamaha I'm wondering if I could drive M80s (with the load switch on 8 omhs, especially if they're a 'forgiving 4 ohm load') and have peace of mind.

Cheers,
Mike

I think the reason why people say they are an easy 4 ohm load is because they are very efficient. Imagine if you had a 4 ohm speaker with a sensitivity of 89db.

to get to a moderate volume level your really using some power there!

Raindance,

I have asked the same question, regarding appropriate receivers to use with the M80's, to both the Axiom technical line and Alan Loft (resident expert on the site for Axiom, I believe).

1) Alan only recommended the following receivers for the M80's:
Denon, Harmon Kardon, and new NAD because of their robust power supplies which will drive the 4 ohm load, despite the manufacturers warnings.
He said avoid Onkyo and Sony...they will shut down with any low impedances.
Yamaha very good with all but the 4 ohm load.
2) The Axiom techniacl department recommended Denon, Harmon Kardon and Outlaw 1050.

So I would say any of those four will be fine. I thought someone mentioned on the message board that they used the Yamaha RX-V1400 and the Axiom M80's with no problems, but as far as I can tell Axiom doesn't recommend it.

Rob

I have to correct RobR a bit here.
Axiom does not PROMOTE the use of a receiver they have not tested with the M80s and they should continue to do so. Obviously they cannot test every receiver out there with their speakers, they can only recommend the receivers they know for sure will drive the M80s, but that doesn't mean other receivers are incapable of doing so.

I own an Onkyo DS797 and it has driven 4 ohm speakers no problem.
Do not rule out receivers based solely on the suggestion of knowns from a single person. If you pose the question in forums and hear from ppl who own a combination of receiver and M80s you are interested in, then you should have your answer as to whether it will work or not.
More often you will see that the receiver companies will not quote their equipment as being able to run a heavier load so they can protect themselves from having alot of returned merchandise from over zealous customers pushing things too hard. Even some of the receivers Alan has mentioned have a listed 6 ohm max limit in their manuals, yet they still work with the 4 ohm speaker.
As long as you buy a quality unit and don't skimp on the $$ too much, you are more likely to have a unit that is capable of running the M80s.

As for the M80 impedance itself, see this graph for an idea of how much the speaker averages at the 4 ohm level.

Chesseroo,
Thanks for the reply. Guess I need to be more careful when wording replies, I don't want to get anyone in trouble.

Chesseroo is correct in saying that Axiom can not test every possible receiver on the market.
I should clarify that when I called the Axiom tech line they said the Denon, Harman Kardon and Outlaw 1050 would work with the M80 speakers. That does not mean that all other manufacturer's receivers will not work. These are just three manufacturers they have used, and are comfortable with. Also, by no means did I mean they were promoting these products...I just asked for some receivers that they knew would work.
Also I should say Alan Loft and/or his colleagues have used Denon, Harmon Kardon and the NEW NAD with the M80's, and have had satisfactory results.
So the above are four receivers Axiom and/or Alan have used, and have had good results with. This is not the only four that will work by any means, just ones that they had used and had satisfactory results. As, Chesseroo has stated he has had good luck with other manufacturers as well.

I am looking at buying a receiver and speakers myself. There are a large number of mfgr's available, and I was happy to narrow the search down to four. These are not the only four that will work, but for me I looked at it as....these are four that will work, so for me it's is a good place to start.

Rob

These are some of the speaker combinations I've used with my Yamaha RX-V2400:

Magnepan MG-12 - 4ohm, sensitivity=86(not an easy load, comparitively speaking)
Kef Q-95 center - 4ohm, sensitivity=91
Kef Q-75 mains - 6ohm, sensitivity=91
Kef Q-15 surrounds - 6ohm, sensitivity=91

The 2400 has performed flawlessly in my 15'X20'X14'(vaulted celing), well dampened room with no diminished dynamics, no clipping (at fairly high levels {as high as the pain threshold would allow}), no image smearing and the unit does not get any hotter than any other SS, receiver I've ever used. In fact, it has run considerably "cooler" than the Denon it replaced. BTW, the Denon with a power rating of 85 w/ch had no problems driving these speakers either.

Of course, your milage may vary but unless you have just a humongous, sonicly dead room, the Yamahas' should not pose any "matching" problems with most relativly effecient speakers of the 4ohm ilk. IMHO.

I also should have chosen a word better than "promote".
"Suggested" would have been more fitting i think.

Sushi was one of the first posters to put the myth of the Pioneer receivers to rest. They vehemently stated that their receivers were not for 4 ohm speakers but sushi (and others) proved them wrong.

So mwc, have you actually measured the max SPL just before distortion/clipping at a set distance with these speakers and receiver combos?
How about with the Axioms?

Could you also post some of the Yammy info ($, specs) along with a reply.
Thanks.

oh and while we're at it. i dont think alan has actually used the new NAD recievers. I just brought it up in a post that they will drive 4 ohm speakers, even says so on their website as they rate the continous power into 4 or 8 ohms.

Sorry chess, I did not take any SPL measurment regarding distortion/clipping. The level I was refering to was the one that I could comfortably listen at before my head exploded.

Oddly enough, while I have had my Axiom M22s in this system, I haven't pushed them to high volume levels and they were in the system only for a day. For the most part, the M22s have been hooked up to a vintage Sansui intergrated amp in a bedroom system.

As for the specs in the RX-V2400 was there something other than this or this
that you were asking for?

The Rotel receivers and or power amps are also solid. They powered my 4 ohm inefficent Maggies with no problems.

So what's the deal with the 2400 bass management that my 1300 doesn't do? I'm lost...as usual.

Jim, are you referring to the fact that the 1400 and 2400 have a wide choice of crossover frequencies between the speakers and sub, varying from 40Hz to 200Hz? The older Yamahas have a fixed 90Hz crossover, which is close to the most commonly suggested 80Hz. Someone using very small satellite speakers(e.g. Bose cubes)might have to use a crossover of 150Hz or higher because of their lack of bass response. Someone on the other hand using much larger speakers might(mistakenly in my view)want to set the crossover even lower than 80Hz for fear of "wasting" some of the bass that their speakers were capable of.

In reply to:

---

Someone on the other hand using much larger speakers might(mistakenly in my view)want to set the crossover even lower than 80Hz for fear of "wasting" some of the bass that their speakers were capable of.

---

John, you bring this up all the time but you have a "mistaken" view of people's perception. Granted some newbies have the question, "well why did i buy towers if i'm not going to use their bass drivers anyway?" and they should be given both reasons so they can decide for themselves.
Just to be clear now, there is no fear one is losing or wasting the bass of our towers. People, such as myself, may not like the overbearing sound of a sub playing notes in the higher bass area. I find it too boomy regardless of gain settings and if i lower the gain, i would have to turn it back up again for HT. Using the sub takes away the whole tightness of bass i was searching for in a speaker in the first place.

My personal reasoning for using a cross on the sub at 45Hz-50Hz and allowing my M60s to play as 'large' is to use the bass of the M60s for music while keeping the subwoofer for the truly low end musical bass notes (what the subwoofer is really designed for) and yet still having it add plenty of explosion oomph during HT.
As long as one mixes the crossover so the sound meshes together well, then it doesn't matter whether the THX suggestion of 80Hz or whether the cross is 50Hz, 40Hz, 120Hz, etc.
There is no 'mistake' in doing so.

As for the idea that Alan mentioned in regards to lessening the burden on one's amp/receiver, as long as the unit is robust enough, the difference is negligible if at all. I certainly have not heard any significant change in using the 80Hz vs. a 50Hz cross with my M60s. Certainly nothing that is so pleasing as to override the awful boom bass i also have to put up with in such a configuration.
If you try it out, it really does work nicely.

For those who have the M22s or another speaker with a far lesser bass extension or perhaps prefer a heavier low end sound than what the M60s can put out, then by all means, use the 80Hz or higher values. In this instance, the sub will provide more benefit than disadvantangeous boomyness.

Hi Raindance,

If you examine the M80's measured impedance curve (thanks to Chess for posting the link), it's quite smooth and "linear"; i.e, there are not dramatic peaks and dips in impedance. The M80s curve hovers around 4 ohms between 100 Hz and 500 Hz and is above 4 ohms over the rest of the audio range.

That is considered a relatively "easy" 4-ohm load, because it's smooth and linear, however, if a receiver does not have a robust power supply capable of supplying enough current into a 4-ohm load, then it isn't "easy" for that receiver. This is why previous Yamaha receivers have 4-ohm impedance switches that reduce the voltage drive in the 4-ohm position, thereby limiting power output and avoiding excessive current flow and heat build-up (and shut-down). By contrast, a "difficult" 4-ohm load might have fluctuations to 2 ohms or less followed by peaks in impedance.

Gene's tests of the new Yamahas on his Audioholics site are very thorough, and, as I suspected, the auto-EQ circuits are no panacea. An Axiom customer complained to us suggesting that his speaker had been wired with the polarity reversed. Not so. The Yamaha auto circuit mistakenly identified the speaker as being "out of phase" with the rest of the system, just as Gene DellaSala experienced in his tests of the Yamaha 2400.

It's true I've not used the new NAD receivers, however, a number of Axiom customers have reported that they easily drive M80s. Moreover, I checked with a very experienced engineer and amplifier designer who consults to AXiom (he has designed amplifiers, both solid state and tube, for Macintosh, Luxman, Harman/Kardon, and others, and is entirely familiar with the circuit design of the new NADs). He confimed that the NAD receivers do NOT impose current limiting (thereby reducing the power output) when set to drive a 4-ohm load.

Most other receivers that have rear-panel 4-ohm impedance selector switches do impose current limiting when set to the 4-ohm position. As to whether the new Yamahas will drive the M80s when left in the 8-ohm position, you'd have to try it at higher volume levels and see if the Yamaha's protection circuitry dectected the lower impedance and shut it down.

Regards,

That is in fact what I was referring to. Now I see why the different numbers are needed. Thank you.

Alan,

Thanks a lot for your comment. I feel that, with all the wonderfully smart people around, my audio education is in very good hands here.

As a sidenote on the Yahama RX-V1400, from my research I think a great deal of the innards have been overhauled for quality's sake compared to their earlier receivers:

To quote http://www.yamaha.com/yec/products/RECEIVER/RXV1400_lit.PDF (Basically a feature overview):

"Finest parts used throughout for high sound quality" (through deconstruction perhaps implying this was not always the case but is now)

"High Current Amplification Achieves Low Impedance/High Current Power from Input to Output" ...

"Yamaha receivers have always had fairly high current levels (ed: perhaps not), but with the RX-V1400, we have further improved this performance"

"Finest Parts Used Throughout ... Yamaha technicians completely re-evaluated all the parts used in previous receivers. As a result, many were replaced with more expensive or custom-designed units." (It goes on to detail the capacitors and transformer used)

Hopefully Yamaha is playing it straight and this is a new beast, much more capable of driving low-impedance speakers.

Best,
Mike

Well.... I tend to take marketing materials with just a little grain of salt. I mean, Bose has the best sound in the world from just a little radio, if you read their stuff. And KFC is health food.

True!

Hmm...

Perhaps the most convincing thing about the truthfulness of the yamaha RX-V series literature is that it makes the HTR series look bad (by comparisons in the literature).

Mike,
Where is there mention of the HTR series?
Doesn't sound good for me, since I was hoping to get a big discount at Best Buy...and they only cary HTR series of Yamaha.
Rob

Ah. It was implicit, not explicit.

Fair enough.
If there is no direct comparison shown on the site, could you at least direct me towards the HTR literature Yamaha has available on the site...I only see RX-Z and RX-V under receiver info.

http://www.yamaha.com/yec/products/RECEIVER/REC_main.htm

Thanks,
Rob

Robr - I found the link to the Yamaha FAQ on HTR vs. RX-V -- see this post (looks like I put it in the wrong Axiom thread) where you can find the link. Birdman

• Yamaha FAQ and other info

Thanks, found it already.
Just have to decide 1400 or 2400, local or online

Thanks for all the help everone
Rob