I see speaker impedance curves that are interesting in their humps, going to 20 ohms or more. How does this affect the frequency response?

If it doesn't, why wouldn't it? If a constant signal voltage is applied at all the frequencies, the power output would or should vary with the impedance, no?



Hello Charles,

Yes, at first glance, it appears that would be the case. But it isn't.

I quizzed our chief electronics engineer, Tom Cumberland, on this subject and here is his reply:

Due to the way speakers work, as the impedance rises, the speaker is more efficient. This makes the speaker flat with respect to the output changes in the amplifier power. This is why sweeping them in an anechoic chamber is so important. Determining this from charts or a guess of the output from data sheets is not very meaningful. Knowing the rise and fall of the impedance is only useful in determining the lowest impedance that the amplifier sees. If it drops too low, the amp may go into current limiting and shut down. Triad has this problem with their newest 'high-end' speaker systems and some amplifiers. The speakers that have the crossover designed to flatten the impedance curve is also a poor way to design a loudspeaker in that it adds components that affect the overall efficiency and output of the speaker.

It's a complex subject.

Alan Lofft,
Axiom Resident Expert (Retired)