8 ohm speakers (including center) and Onkyo TX-SR573 Receiver [Archive] - Audio & Video Forums


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02-19-2006, 09:26 PM
I've spent the day reading about the Onyko TX-SR573 and I just looked at my speakers and they are rated at 8 ohms, while the receiver is rated for 4 & 6 ohm speakers.

Looking at the features page (http://www.onkyousa.com/model.cfm?m=TX-SR573&p=f&class=Receiver) you'll see that it does support 8 ohm speakers but with the use of *Dynamic Power*. Has anyone been in this situation before? If so, what did you do?

02-20-2006, 06:33 AM
I wouldn't worry much about this.

First, the ohm ratings on speakers given by manufacturers are almost useless. There's no real "standardized" scheme for determining the ratings. The impedance of a speaker changes as the frequency the speaker is producing changes. It doesn't always stay at 8 ohms. In a typical 8 ohm speaker, the range of impedance can be anywhere from 3 to 30 ohms. You could think of 8 ohms as an "average" for rating purposes, but even then that'd be generous. I think it's just a habbit in the industry now. To keep things simple.

We worry about the low number of the impedance profile mostly. If the low number (3 ohms for example) only exists for a short band of frequencies, and the overall "average" impedance is 8 ohms or so, then a company will call it an 8 ohm speaker. Sometimes a 6 ohm speaker just to be safe and let you know it might be demanding a lot of current. Now a speaker rated at 4 ohms might have a low dip down to 2 ohms or below at some frequencies. That means the amp will be sending a lot of current when playing those frequencies.

At 3 ohms, the speaker isn't resisting current very much at all (less impedance, more current getting through), so the power supply unit of the amplifier is delivering a lot of juice. If it's not rated to handle 4 ohm speakers, it could be damaged (but probably not at low to moderate volumes).

If your receiver claims it can play 4 and 6 ohm speakers (which are more dangerous to an amp than 8 ohm speakers), you should have no problems at all.