I want to drive a resistive load with a commercial 50W audio amp. What resistance do I need to use to prevent damage to the amp if itreplaces an 8 ohm speaker.I understand the 8 ohm represents inductance. The actual speaker coilresistance is much lower.Thanks for any advice.Robert Moore

Robert,An 8 ohm resistor is safe. The "8 Ohm" speaker rating is a nominalimpedance. The actual value varies with frequency. It consists of theDC resistance plus another resistance component that results fromacoustic loading, plus reactive componenents that may be positive(Inductive) or negative (capacitive). At frequencies below theresonance of the speaker/enclosure combination, the impedance becomesquite low, and approaches the DC resistance value. By using an 8 Ohmresistor, you are guaranteeing a constant resistance load, andtherefore a load that is less severe thatn a real speaker load.However, the 8 ohm resistor is not a good simulation of an actualspeaker load.

Sub resist load for speaker?

Oct 04, 2005 41 Replies

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John Woodgate 20 years ago

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Sub resist load for speaker?', on Fri, 7 Oct 2005:

You go on thinking that until you find it isn't true.

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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John Woodgate 20 years ago

I read in sci.electronics.design that GregS wrote (in ) about 'Sub resist load for speaker?', on Fri, 7 Oct 2005:

Yes, but efficiency is (energy out) divided by (energy in), and that is not only embarrassingly low and extremely difficult to measure but also of little practical use (oh, there are cases....). Sensitivity, on the other hand, is extremely practical and useful. Stick to it and forget 'efficiency'.

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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