Axiom Home Page Forums General Discussion Technical Questions 6ohms or 8ohms?

Hi everyone, I am glad to be a newcomer in the great Axiom family. I've just purchased a set of speakers 1 months ago(M22, VP150 and QS8) and by the way there are amazing speakers :-)

now I've decided to get myself a new receiver worthy of my speakers. so I finally pulled the plug on a Yamaha RX-V2500(I got a great deal from Mark at AudioShop by the way).

now here is my problem:

the Receiver give me the option to be set in 6 or 8 ohms mode.

but my speakers are a mix of both :
M22 are 8ohms
VP150 and QS8 are 6ohms(8ohms compatible)

so my logic choice was to put the receiver in 8ohms, but now I wonder if it is really the best choice? anyone got any input on this matter?

thanks!

Leave the receiver in the 8 ohm position... unless you have problems with the receiver shutting down (really that should only be a problem if you run A & B speaker sets together)

Bren R.

"8 is Enough"

Oh, and for reasoning... usually the manufacturer will drop voltage to the power rails in the lower impedance position... like making sure you don't overheat your car by intentionally shutting down half the cylinders.

Bren R.

I have the RX-V2600 which is a newer model for RX-V2500. You should set the reciever for 6 ohm. This is the basic rule i read somewhere. The tech support from Yamaha will tell the same thing i said.

Enjoy!

Han

thanks for all your input!

while waiting for an answer, I've search a bit on AVSforum and it seem in fact like the general opinion seem to favor the 8 ohms setting stating that in fact a 6 ohms(or 4 ohms on some receiver) setting might reduce the power output.

As Bren and Randy already suggested use it in the 8 ohm mode. Here is an article from Audioholics that pertains to these switches.

Han, the tech support guy can't say "oh, yeah, the switch is pretty much just a dummy thing that Underwriter's Labs makes us put on it" because on the off-off-off chance you damage a transistor, then they'd be liable.

Bren R.

Hi, Rick:

I talked to tech support in Axiom and Yamaha. They both suggest me set it to 6 ohm for my HT: M60tis, VP150. I will switch back to 8 ohm after i read the link.

Thanks,

Han

Odd, do you remember who you talked to at Axiom?

Bren R.

I can see the person at Yamaha saying this but it seems odd that a person from Axiom would.

Han, as other replies have indicated, you should only use a lower than 8 ohm setting as a last resort in the highly unlikely circumstance that your receiver would shut down at the 8 ohm setting. Otherwise you'd simply be voluntarily limiting the maximum voltage(and therefore power, which the voltage controls because of Ohm's law)which the receiver could supply. Disregard any advice to the contrary, which may possibly be motivated for legal rather than real technological reasons.

I agree Bren, I've never heard any of the Axiom main techs like Alan, Tom, or even Ian suggest the 6 ohm position. I'm guessing they misunderstood Han's question.

I know at least 3 of my friends with Yammy's that were told by Yammy tech support they could use the lower settings when lower ohm rated speakers were in the loop, not a good thing when the other speakers aren't rated for this resistance.

Hi, BrenR:

I don't remember whom I talked to at that time. I did talk to the Axiom person before I was about to buy the Yamaha RX-V2600 .

Thank you guys. I just reset my Yamaha reciever to 8 ohm. It is always a pleasure to communicate with you guys.

Good night,

Han

Hi Thanwu,

Odd indeed. No-one at Axiom should be telling you to set your Yamaha at a 6-ohm setting. I'll have to do some internal detective work!

This has been a continuing issue with various brands of AV receivers for years because of the 4-ohm M80ti towers, which many brands will not drive without overheating, current limiting or protection-circuitry shut-down. As Bren pointed out, the presence of an impedance-selector switch suggests that the AV receiver has limiting circuitry that will severely limit the power output to lower impedances to avoid liability and overheating issues. Leave the switch at the 8-ohm setting to maximize the receiver's potential output into 6-ohm and 8-ohm loads.

Axiom has been advising this for years now.

Regards,

Hi, Alan:

It is possible I misunderstood when I talked to the Axiom tech support. No need to do your detective work. I am very happy with the service you company provided to customer. One more question. In terms of my setup: M60tis and VP150, do you have a rouge guide how much ajustment I need to make manually for my center speaker because the 8ohm setting?

Thanks,

Han

Hi,

The impedance rating of the speaker and the setting of your Yamaha do not relate directly to the level settings for each channel.

Just go through the normal calibration for each channel. Use a Radio Shack SPL meter and a setup DVD and do a manual adjustment of each channel's level from your seating area.

Other than just leaving your Yamaha at the 8-ohm setting, there are no special adjustments required for using a group of speakers of different impedances. Each speaker or channel is driven by a separate amplifier in your receiver, so the impedances do not interact with each other.

Regards,

That raises an interesting question. When Axiom (and others) publish sensitivity ratings (typically SPL at 1 watt, 1 meter from the speaker) is that really 1 watt (measuring voltage and current) or is that "the voltage which corresponds to 1 watt into an 8 ohm resistive load" ?

In other words, does it take into account the fact that a 4 or 6 ohm speaker will draw slightly more power at the same volume control setting ?

Hmm... now THERE's some internal detective work

I would think the resistance is taken into to account when measuring for specs, one watt at one meter @ four or six ohm.

In a perfect world yes.... but last time I looked it wasn't perfect.

John, yes that is interesting and the handling of it doesn't appear to be consistent. My view would be that since 1 watt is a specific amount of power and 2.83 volts a specific voltage, that when Axiom uses 1 watt in its specs rather than 2.83 volts, it means exactly that. Therefore the spec would be an efficiency(rather than sensitivity) rating, e.g. the M80s would put out an SPL of 91dB at 1 meter with 1 watt of input. Since 1 acoustic watt at 1 meter is equivalent to about 112dB, 91dB at that distance would be an efficiency of just under 1%.

Since power equals volts(squared)divided by resistance, the two measurements would give the same dB number at 8ohms, i.e. 2.83 volts(squared)divided by 8ohms equals 1 watt. But 2.83 volts into 4ohms would give 2 watts. So, yes, if the spec is to be taken literally, the measurement into 4ohms is taken by turning the voltage down to 2 volts rather than 2.83, so that 1 watt of power is used.

In reply to:

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In a perfect world yes.... but last time I looked it wasn't perfect.

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It's not?

So that would mean into a 6 ohm load the voltage required to deliver one watt would be cut down to 2.45 vs the 2.83 for the 8 ohm load.