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The under appreciated impedance curve

One thing that a lot of audiophiles don't look at or don't know how to interpret is the impedance curve. I call it the honesty curve too.

Of course, most audiophiles know to look for high imepedance speakers for tubes, and that low impedance speakers are going to be more amplifier demanding.

I also look for:


  • A drop in impedance at 100 Hz at or below 3 Ohms - Indicates "amplifier sensitive"
  • A ragged magnitude instead of simple, clearly defined humps. If the impedance is ragged it indicates highly equalized components.


One speaker which breaks both of these rules was just reviewed at Stereophile, the Wilson Yvette.


https://www.stereophile.com/content/wilson-audio-specialties-yvette-loudspeaker-measurements



Like all things, there are no absolutes but these are the things I look for in a speaker. What do you look for in the impedance curve?
erik_squires

Showing 5 responses by erik_squires

erik_squires OP
16,592 posts
 
Prof,

It really only takes a little math to understand how it works.


An ideal amp:


[ input voltage x gain ] = Output Voltage


Gain is often around 20x (26 dB)


The reality :


[Input voltage x gain ] = Voltage lost in output stage + Voltage at Speaker terminals


Tube amps will loose more in the output stage. You can analyze it more or less like series resistors.

Vr1 = Vamp out x (   R1 / ( R1 + R2))


Where R1 = Amp output impedance  and R2 = Speaker impedance


Of course, R2 varies based on frequency.

For Solid State, R1 may be < 0.001 Ohms. For tube it is often in the range of 1-2


erik_squires OP
16,592 posts
 
that he could make it with any nominal impedance he chose.


This is true for all cones as well. Off the shelf components are often available at different impedance for exactly the same reasons. Lower impedance = more current = more force against the magnetic field.


However, I have in fact seen Focal create a crossover deliberately to burn power. It had 80 W worth of resistors that didn't need to be there.
erik_squires OP
16,592 posts
 
It isn't all a treatise on you, goerge.

I do think that the community at large does not appreciate how much we can learn.
That doesn't mean to be an accusation of anyone in particular.
erik_squires OP
16,592 posts
 
The quick answer: The weaker the amp, the more its output in the frequency domain will look like the impedance curve.


erik_squires OP
16,592 posts
 
ESL's are notorious, and I've seen down to 1/3 of an Ohm at the top of the frequency range. It's something hopefully purchasers learn about before they buy.

Of course, from the dealer's' perspective, they should jump on this as it gives them a reason to sell a bigger amp.
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