Axiom Home Page Forums General Discussion Technical Questions ARGH!!! Impedance question....

My first post.
First thing, I bought a pair of M50ti's a couple months back, and simply love them more than anything right now!
Axiom, you are the best sounding speakers I have personally ever heard in my 33 years on this earth!!!

Ok, now to the question.

I have a brand new Harmon Kardon AVR-330 Home Theater amplifier.
I have the Axiom M50Ti's as my front left and right speakers.
Now, I want to get the VP150 and QS8's for my center and surrounds respectively...but... the AVR330 is rated for only 8ohms...
I emailed Harmon Kardon and explained that I would be using 6ohm rated speakers from Axiom.
They responded with:
"The AVR330 us rated for 8 ohm speaker operation only. It is not recommended to use speakers with an impedance lower than 8 ohms. It is possible that you may be able to use the Axiom speakers but I cannot guarantee that the receiver will be able to handle this without protecting itself."

So what should I do now???
Should I now go with a Pre/Post amp setup before getting the speakers??

I would appreciate any information on this...

Thank you for your help!

-seven

I'm running 6 ohm speakers on my H/K 525 right now, and I've had no problems. I don't tend to listen to them extremely loud (I think -20 to -15 is the highest I've gotten them), but I've never hit the temperature protection or had the fan turn on.

Thanks for the reply kcarlile,

I read of others using lower than 8ohm rated speakers on their H/K recievers without any problems.
I also only go up to -20 on my volume. I dont really need to go any higher as I live in an apartment.
I was hoping that when I emailed H/K they would give me a little more information to go with... rather than the one they emailed me.

Anyhow, thank you for the information.

-seven

Hi seven,

In a general way, any A/V receiver designed for operation with 8-ohm speakers will always drive 6-ohm loads without any trouble. It is 4-ohm loads with the big increase in current flow that cause many receivers to go into protection mode or impose current-limiting circuits, which severely limit the output power of the receivers.

All manufacturers of receivers will be very conservative on this issue, as they don't want consumers driving pairs of speakers in parallel or very difficult impedances that might cause overheating and/or shutdown, although I'm surprised that H/K suggested caution with a 6-ohm load.

My experience with H/K (the AVR 525) is the same as kcarlile's. Despite the warning on the back panel (Use 8-ohm speakers), the 525 and other current H/K models will drive lower impedances--even 4-ohm loads--without overheating problems or protection-circuits kicking in.

The 525 will even drive the 4-ohm M80s with no problems, albeit in a modest-size living room (19 x 13 x 9 ft). On the basis of my own tests and those of several colleagues, H/K and Denon are the only brands of A/V receivers I currently recommend for the Axiom M80s. An engineer friend also tells me that the new NAD A/V receivers will drive a 4-ohm load without current-limiting or problems, though I don't have direct experience with those units.

Regards,

In reply to:

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the new NAD A/V receivers will drive a 4-ohm load without current-limiting or problems, though I don't have direct experience with those units.

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Are you kidding me? you can arc weld with them! lol. But really, i beieve on the recievers that they deliver whatever the rated power is, into 8 or 4 ohms. At least thats the way it is with their other amps (370,270 etc) and they have the rated clipping power in 8,4, and 2 ohms.

Alan,

Thank you very much for the information and clearing up my confusion on the issue.
I was also suprised that H/K warned me about using 6ohm strength speakers as well.

Again, thank you. I am excited to finally get rid of my Bose system and move to an all Axiom setup.

-Seven

Wow, a lot of people switching from Bose these days.

I sense we are entering a new period of enlightenment...

Such a relief after reading in a sales blurb that "some reviewers even thought [the sound from the Bose Wave Radio tm r c etc.] was live!"

Of course, when recordings were introduced in the early 20th century, people thought those were live, too. We all know what those sounded like...

Haoleb,

Not to disagree with you, but the NAD models you mention are 2-channel stereo amps. The NAD stereo models have always been good into lower impedances. It's 5-channel and 7-channel receivers where amplifier cooling becomes a huge issue with lower impedances.

And it's the continuous power output with five channels driven that separates well-designed power supplies in receivers from cheaply engineered units. "Clipping" power can be measured in a short-term instantaneous burst (and the manufacturer will make those claims, sometimes calling it "dyamic peak power" into loads as low as 2 ohms) but after a few seconds, the receiver will go into current limiting or shut down. (Naturally, that is never mentioned in specifications!)

By the way, lots of old stereo amplifiers and receivers had no problem driving lower impedances.

Regards,