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?



@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...


@ozzy Wrote:

Wonder why companies just don’t make speakers that are 8+ ohm and with high sensitivity? But it seems to be just the opposite, that is; many of the big-name speaker manufacturers produce speakers that are 4-ohm and low sensitivity.

Wonder why that is?


Maybe Hofmann's iron law is one of the reason. Article



Probably, but many large speaker cabinet types still have low impedance and sensitivity requiring monster amps to drive them.