What does Nominal Impedance mean?

What does Nominal Impedance mean?

I’m trying to decide on some new speakers (Clarisys Minute). They are rated at 86-88 sensitivity and a nominal impedance of 3.5 flat. Although graphs show it about 6 ohms from 20hz-500hz and at 2Khz and above about 3 ohms.

My present speakers, Focal Sopra 2 are rated as 91 sensitivity and 8-ohm nominal impedance, but minimum is 3 ohms.

So, I am presently using Bob Carver 350 amps (rated as 350 Amps/channel 8 ohm and 400 watts /channel 4 ohm) which are tube mono blocks. and I like to crank it up at times!

Can someone explain about Nominal Impedance and if my amp(s) will have a problem driving the Clarisys Minute speakers?



Nominal means "in name only" and has little to do with the actual impedance of the speaker. That’s why it’s confusing. The speaker impedance is measured across the frequency band and someone at the speaker company looks at it and says hmmm... that looks like about 6 ohmsish on average so we’ll call these 6-ohm speakers.

This is one area where published specs are important. I look at the impedance curve of my speakers and they are a flat 2.5 to 3 ohms from 100hz to 10kHz which tells me I need a hefty solid state amplifier for the low impedance but a tube amp with a 3 ohm output tap would work great also since the impedance is flat.

Nominal impedance in electrical engineeringand audio engineering refers to the approximate designed impedance of an electrical circuit or device.”

@gs5556     How right you are!

'Nominal impedence' is generally concocted by a speaker manufacturer to hide elements of his speaker's impedence curve that he would rather hide.  It has no basis whatsoever in physics.  Responsible manufacturers show the full curve for impedence vs. frequency and the phase angle at audio frequencies, because bad combinations of impedence and phase angle can often occur making a speaker tougher to drive than could be apprehended from the impedance curve alone.

Incidentally I have never seen a speaker whose impedence measures a flat 2.5-3 ohms over 100-10k Hz.  Have you?

This poor manufacturer behaviour is mirrored by not quoting a dB range when specifying low frequency extension, and by over-stating sensitivity, which occurs very often.

(Proper) measurements matter.


Yes, I think so. Though it will be a long wait to get them, and I will probably have to rob a bank...