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Impedance matching

Posted by sniffdog (My Page) on
Thu, Dec 2, 10 at 10:24

I am getting ready to order some components for my whole house audio system and wanted to double check on the requirement to keep the impdendance level on my amplifier within specifications. I am planning to use Onkyo M-282 2 channel amp that is rated for 6 and 8 ohm impedance loads.

I was planning to use a Niles HPS-6 speaker selector (without volume controls) that has an impedance load balancing circuit and individual wall volume contollers for each of the 6 pairs of speakers. If I use the Niles box, I see no need or benefit to also use wall volume controllers that also have impendance matching circuits which cost more.

Any comments?


Follow-Up Postings:

RE: Impedance matching

I looked up the specs on both the amplifier and the speaker selector. The amplifier requires a minimum 6 ohm load, the selector will appear as low as 4 ohms, so this is not a good match.

The speaker selector is not really impedance matching as much as it just keeps the minimum from dropping below 4 ohms. It is most likely a style that uses load resistors to maintain that impedance.

In switching the areas on/off the impedance will continually be changing, as well as the audio level. I'm not sure if you have a specific need for switching but usually a parallel block is used to feed impedance matching in-wall speaker level controls. This provides a fixed impedance and allows you to control the level in each area.

You would need to look at the specs for the controls to ensure you can set the jumpers for your configuration. The controls come with a little chart that you use to calculate the number of speakers, their impedance, the overall impedance and then the jumper setting.

I'm sure if you look on line at different controls, you can find the "manual" which will tell you if it will work. The minimum 6 ohms on the Onkyo may become an issue.

Oh, I have also found a certain level of unreliability on the slide type controls as opposed to the rotary.

RE: Impedance matching

yosemite - thanks very much for the reply. I am glad I checked with the forum first.

So it sounds like I either need to find an amp that can handle a 4 ohm impd load OR use the rotary volume controls and set the jumpers so that the selector and Onkyo see a 6 ohm load. Is that right?

I thought that at one time the older version of the M-282 did handle 4 ohms but was disappointed when I read the specs and saw 6 min.

Any ideas on a 2 channel amp (100 to 200 watts per channel) that handles 4 ohms?

Thanks again

RE: Impedance matching

It's hard to find good quality stereo power amplifiers without spending a lot of money. I searched a little and in this price range, I think the Onkyo is a good choice.

It's actually hard to find speaker level controls without impedance matching, usually you just set the jumper to X1 which gives you the same thing. I looked at the info on the On-Q/Legrand controls and they would work in the X4 position and actually give you around 10 ohms - that's OK.

I'm not sure if the Niles switcher does any kind of unusual series/parallel switching between multiple speakers, but as long as it doesn't, you could just leave the protection switch turned off.

Don't forget most amplifiers are not too happy about having external speaker switches turned on/off while powered up.

RE: Impedance matching


thanks very much - that sounds like a good plan. I like the Onkyo becuase it was at a nice price point and will do what I want. Its just a simple whole house aduio system that I don't want to spend a lot of money on.

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