Impedance, 4 ohms vs. 8 ohms


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Aug 10, 2019
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Hi all,

If the spec for a amplifier says 2 x 50 rms, 4 ohms or 2 x 50 rms, 8 ohms, which one is the better? Is one of them more powerful with the sam set of speakers?

Is it required to have the same impedance on the speakers (most of the ones I have looked into is 8 ohm (minimun 4 or 5 ohm)). Does that mean that an amplifier with 4 ohm is no good gor these speakers. Are speakers with higher/lower impedance better?

Any explaination appreciated..



First off, ditch the word "better" here, the power of an amplifier is not, of itself, a decent measure of it's quality!

Second - 50 watts is 50 watts regardless of the load. But...

The amplifier that can do 50 watts into 8ohm is probably the more powerful, as if it can drive a 4 ohm load it will put out more than 50 watts - perfect class A behaviour would be 100watts, but most amps would manage 75 - 80.

Higher impedance speakers are "easier" for the amplifier to drive because they require less current, but ultimately it's the sensitivity and the consistency of the impedence for speaker across the frequency range that really matters. Speakers with less than 8 (certainly less than 4) ohms are generally aimed at higher end amplifiers and will often be harder to drive. Driving lower impedance speakers can tend to make smaller amplifiers overheat and shut down so caution is advised if in doubt, but if you keep the volume sensible and you don't try to drive an Apogee then you'll probably be okay. IMHO IANAL :)

For a stereo amplifier (assumed as you talk about 2x50) it wouldn't make much sense to have non-identical speakers regardless of the impedance. Why do you ask this as it seems an odd question?

Hope this helps


Thanks for the explaination!

What I meant was the same impedance on the speakers and the amp, not the two speakers..

concerning the capacity to drive a pair of 8 ohm speakers, will the 8
ohm amp will be able to drive speakers with slightly lower sensitivity?
Does that also mean that with 8 ohm speakers, the 4 ohm amp will
actually put out less than 50 watts?

The spec for the product i aim for is as follows:

Power output (stereo, 8 ohms within rated distorsion) 2 x 50 W
IHF dynamic power 8 ohms 2 x 70 W
IHF dynamic power 4 ohms 2 x 100 W


2 x 50 W, 4 ohms

So, if everything else (sound quality etc) is the same, is the first one better off driving speakers?



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