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?




So, what number(s) are meaningful when it comes to speaker specs?

Is this what you mean by a Zobel Network?

RLC network to prevent unstable amplifiers from oscillating, to reduce distortion, and to act as an RF filter


But if 8 ohms is optimum then why are there so many 4-ohm speakers? I put together a DIY speaker a while back and I was able to use all 8-ohm speakers. So, the drivers are out there.

impedance of a speaker is one of many design parameters that speaker designers trade off in very complicated ways

think of speaker impedance very roughly as how much work an amp needs to do.... you can put in a few simple drivers and a minimal crossover in an undamped box, and the amp will have a super easy time doing the work, but how will it sound? (if this were so easy, we would all have speakers like this...) - but easy to drive, simple lightweight drivers will distort when pushed and don’t have broad, controlled, flat frequency response (they shout, they ring, they break up...)

so the designer uses more robust drivers, and more of them, then this complicates the crossover and cabinet design, all of which makes for more work for the amp... more stuff to grip, to stop and start, to deliver current into (how the amp does the work...)

so the designer says, well, mister speaker owner, you want better super clean sound, full range response, plenty of power handling to play loud AND clean... so i have had to do all this to my speaker design -- include all these well damped drivers, put in a well tuned box, match them all, filter them all superbly with a complicated crossover -- to give you the performance you want... but hey now, you gotta use a strong amp to do the work to get that sound...

whenever i see 3 way tower speakers with 3-4-5-6 drivers, multiple woofers, think of an amp needing to grip it all (think big focals, magico, thiels)... there is alot of work to do (compared to say a single driver speaker) so you can bet the impedance will be lower... not to mention the efficiency



Lower impedance = higher current = more output.  Since most solid state amplifiers can drive 4 Ohms without issue as a speaker designer I might chose a lower impedance driver to give me more output. Especially in matching say a woofer to tweeter, when tweeters usually have more output for the same voltage. 

AFAIK there's no actual standard for rating your speakers, and some like modern KEF speakers, are so optimistic in rating their speakers that you can't use them to pick matching amps at all. 

jjss49, erik_squires,

Thanks for that very good information. It’s interesting and confusing at the same time.


At Townshend Audio we match the average nominal speaker impedance (around 8oHms) with the impedance of the amplifier using Isolda 'impedance matched' Speaker Cable. Here we explore the reasoning behind our cable products: https://townshendcable.com/ 

Our Analysis uses a test set-up to prove how mismatched speaker cables will cause audible differences between a range of cables.

Thanks for your time.

Harriet Townshend

Yes Ozzy, this is the micro-site for the Townshend F1 and Isolda Speaker cables. Max tried to understand the clear differences he heard when hearing matched impedance cables Vs unmatched impedance cable.

Dedicated to understanding the phenomenon and spending a large chunk of his last years researching and testing.

His videos on You Tube called 'Geometry Matters' charts his reasoning.



Harriet, thank you for that info.

I must say the Townshend F1 speaker cable is the best I have ever tried/owned, and I have tried alot, perhaps it is because of the impedance network built into the cable?


So, does a 4-ohm speaker play louder than an 8-ohm speaker with the same amplifier and volume setting?

It's entirely dependent on speaker's sensitivity and output level, which is usually measured at 1 m.

On the other hand, an amplifier will output more power with lower impedance.

Here's the output of Hypex NC400:
580 watts at 2 ohms
400 watts at 4 ohms

200 watts at 8 ohms

If you were to measure a speaker with DC you'd get a resistance. If you were to measure it with AC at various frequencies, you'd get impedance.