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 know this is a complicated subject & not as simple as this but the primary way to get decent, extended, deep bass that can play relatively loudly from smaller woofers ( less than 8” or so) is to have 2 or more of them usually wired in parallel which lowers the effective impedance ( the reciprocal of the sum of the reciprocals). 

The taller, narrow baffle designs popular now for the sake of theoretically better imaging lends itself to smaller woofers if the cabinet cost is to remain reasonable & not “sculpted” in some way. many new speakers today have pretty low impedance & thus their actual effective sensitivity is lower than stated. 

@ozzy it is rare that a large cabinet speaker is also not sensitive. The reason for the large cabinet is to increase its efficiency and thereby sensitivity. Small speakers are typically more difficult to drive and require greater power to overcome their lack of sensitivity and low impedance curves. Ohm’s law explains these electrical properties but I suspect it will be a little over your head unless you intend to do a deep dive into the subject. 

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

I have the Thiel 3.6's. From Stereophile:


Impedance is a combination of linear R (resistance) and non-linear X (reactance)

A Reactance is a combination of Inductive and capacitive components. In the world of complex algebra the impedance Z is represented by = R + jX. In case of the DC, X component is null so the Impedance in this case is linear resistance R.

Inductive component impedance is known as wL where w is frequency and L is Inductance. 

Capacitive component impedance is known as 1/wC where C is capacitance

Overall Z = R + j(1/wC + wL) where j is directional vector

Notably, with increase of frequency Inductive component increases while capacitive component decreases. that means that on DC capacitor will have an infinite impedance and Inductor will act like short circuit.