Demystifying speaker impedance--what audio shoppers need to know

Speaker impedance is a confusing subject and based on the letters we get here at CNET (see below), I thought I should try shed a little light on the subject. This letter sums up the typical quandary:

"I have a bit of a dilemma that I hope you can help me solve. I have an entry level Yamaha HTIB system that I purchased a few years back and I would like to upgrade it with better speakers. I've done a lot of research and found that owning a 6 ohm receiver limits the selection of brands that I could look at in store or online."

Rotel's 100 watt RSX-1067 A/V receiver can drive any speaker I know.

(Credit: Rotel)

I'm all for the speaker upgrade, but he went off track with the concern about his "6 ohm" receiver. The writer mistakenly thinks he's limited to buying 6 ohm rated speakers. Wrong! Any 8-ohm rated speakers would work just as well, and since the vast majority of speakers are 8 ohm rated, his choice of speakers is wide open.

Back to the question at hand: speaker impedance. It's never a fixed number, a 6 ohm speaker may be, on average 6 ohms, but its actual impedance varies with the frequency the speaker is reproducing at any given instant. For example, it may be 4 ohms at 50 Hertz, shooting up to 21 ohms at 100 Hz, dropping back to 7 ohms at 1,000 Hz, and up again to 9 ohms at 10,000 Hz. So in other words, it's impossible to "match" a speaker to a receiver. Impedance is a moving target.

The real world impedance concern comes when using 4 ohm speakers with low power A/V receivers, but even then ONLY when the buyer expects to play the system at high volume. You see, low impedance, 4 ohm or less rated speakers, demand more power than 8 ohm speakers when playing LOUDLY, and that's when the receiver's power might come up short. In a typical "mismatch" scenario the receiver's protection circuit would trip, and shut the receiver off.

Which bring us to the hard cold fact that not all 100 watt receivers are not even close to being equally powerful, but I covered that in my "What's up with watts" blog from a few weeks ago.

[Brolix]

Great Topic

I'm glad that you cleared up this impedance issue. It was something i have been curious about since i first got into home theater a few years back.

[marvin long]

pioneer VSX-1017TXV-k A/V receiver

I am a very happy C-net member user in houston, Tx. What are the honest power ratings on the above receivcer? What is the difference between this and the 1016. Thanks for the help.. marvin long. [e-mail]

[Iboughtbeta]

Speaker Impedance

Mr. Guttenberg. I just found your article. Will the Rotel drive my Quad 63s? Could you talk somebody at CNET into reviewing the current Rotel stuff. I have an old 1080 model Rotel DVD Player. I have a Mitsubishi Projection TV that is HD ready and displays 1080i via my FIOS cable. What reciever(s) can you suggest to link my Rotel DVD to the TV. The TV ony has one set of YPR inputs and I use those for the cable via the DVR directly. I currently have an old Pioneer Elite reciever that I purchased with the TV 7 years ago, going through that I only get 480i with my Rotel DVD. Rotel has a new reciever the 1058. I have also been looking at the Pioneer vsx92txh, and the Denon AVR-2808ci. They seem to have the Faroudja upconversion process. I used to shop at a stereo store where a heart surgeon bought his stereo gear. He said, "there is no substitute for money". Alas I have limited funds so I have to double think these moves. There seems to be a lack of demonstration where these products are sold. They have them and there is no A/B comparison available like there was when audiophile stores existed. The current equipment just throws noise at you from all angles. Sensory overload seems to be the result. I'm a Stereo guy caught in a 7.1 world. Thanks for your time.
ap