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?



I was just reading a review of the Rockport Orion speakers in The Absolute Sound by Robert Harley.

They weigh about 350lbs! Cost over $133,000 and it is still a 4-ohm speaker!


Nominal impedance means blah blah blah blah, meh...that said, Almarg was one of the reasons I bought a Pass XA-25. A cool guy who's missed around here. 

So, I guess I understand that now, nominal impedance is just a number. Highly questionable, I guess that is so with sensitivity ratings. Different frequencies produce different amounts of energy, so that could be all over the map in reality.

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.

And companies like Rockport, Wilson, etc. claim to make their own drivers, but they design them with lower ohms. Why?


Loosely translated into Layman's language it is the impedance at any given frequency. And of course Impedance is roughly  (improperly) equivalent to resistance. Most speakers , as the sound frequency approaches its resonant frequency, the impedance starts to spike. I have had many people ask why I use what is called a 'ZOBEL' network in my crossovers, and this is the reason. A Zobel network tries to compensate for that spike and lets the speaker operate more uniformly at lower frequencies. And be careful when Ozzy says it is just a number. It is but it is a very important number when designing a crossover.


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