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djkimmz
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receiver to speaker impedance matching

Hi to everyone! Im a newbie in this world of hifi systems, and im very interested in having a nice set-up and needs your help! I have an onkyo av receiver tx-ds777,2 infinity primus 150, 2 polk audio r30, 2 bose 401 and an infinity bu2 sub. As far as i know the av receiver is designed for 6 ohms spkrs only, the infinity and the polk audios are I thinks 8 ohms. while the bose 401s are 4 ohms...would I be able to hook up these speakers to my receiver without damaging it? coz i heard that if u use a 4 ohms speaker into a 6 0r 8 ohms receiver, it would toast the receiver! Is this true? and Is it safe to hook my 8 ohms spkrs into my onkyo av receiver which drives 6 ohms only as it says at the back of it? Pls help! Thanks!!!

jackfish
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Re: receiver to speaker impedance matching
cyclebrain
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Re: receiver to speaker impedance matching

O.K. This will be simplified so you experts out there, be quiet.
Amplifiers are limited in their amount of output current.
Being a voltage source an amplifiers output current is determined by the value of the load (speaker).
As the impedance (ohms) of the speaker decreases the current demand from the amplifier increases.
As long as the load doesn't cuase a current value greater than the amplifier can supply you are O.K.
That may mean using a reduced max volume level when driving low impedance speakers.

The next issue is that a specified speaker impedance doesn't much. A speakers impedance varies with frequency.
Sometimes very little, sometimes a lot. At what point do you choose it's impedance?

Jan Vigne
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Re: receiver to speaker impedance matching


Quote:
The next issue is that a specified speaker impedance doesn't much. A speakers impedance varies with frequency.
Sometimes very little, sometimes a lot. At what point do you choose it's impedance?

As we've discussed, there is no point knowing the impedance without also knowing the electrical phase angle at the same frequency. To an extent, it doesn't matter what the impedance is (assuming a reasonably decent power supply in the amplifier) if the capacitive or inductive load of the speaker/crossover is minimal at the same frequency. However, in the case of most home theater receivers, the power supply is probably not going to take kindly to low impedance loads no matter the phase angle. I would recommend against running four Ohm "nominal" impedance speakers on an Onkyo receiver.

cyclebrain
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Re: receiver to speaker impedance matching

As I said, I was keeping it simple. No phase info even though important.
The power supply in most surround receivers are seriously lacking in ability to drive all channels together no matter what their impedance.
Most high volume A/V receivers will let you know if you are exceeding their ability.

Monty
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Re: receiver to speaker impedance matching

Most modern receivers have protection circuits that will shut the unit down if it begins to struggle. You can usually let her cool down for a few minutes, turn it off and back on and be good to go.

If it were me, I wouldn't hesitate to try the speakers. If the unit is getting plenty of air circulation and trips the protection circuit at the levels I like to listen to then I would have my answer. More likely, the unit will give you problems at louder volume levels during multi channel movies when all speakers are being driven.

It really boils down to how bummed you would be if the unit did tank.

cyclebrain
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Re: receiver to speaker impedance matching

After rereading your question, using an 8 ohm speaker on an amplifier rated for a 6 ohm load should be no problem. Going to a speaker with a lower value could be.

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