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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
Post removed 
soix
9,597 posts
 
I can't for the life of me understand why manufacturers aren't required to state minimum impedance, and would be nice to know what frequency it occurs at as well.  That's not a hard ask, is it?  Nominal impedance is a near USELESS spec to me.  

One example, my buddy's Martin Logans dip to 2 Ohms, but it occurs at 2Khz so not as tough a load as it would be at 200Hz.  This is such critical information to know when purchasing a speaker, I almost can't believe they don't make it more transparent. 
erik_squires OP
16,144 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.
atmasphere's avatar
atmasphere
11,844 posts
 
Anytime I get asked about the suitability of a speaker with our gear I always look for the impedance curve. All amplifiers make more distortion into lower impedances so I look for that sort of thing- it can be pretty detrimental in the bass where a lot of energy can be needed. The reason its so detrimental is distortion components can extend to some very high frequencies- and we might be talking about some very high orders- not just 7th but well above the 20th and the like. The ear finds this irritating!

You can reduce the amplitude of the harmonics by simply presenting the amp with an easier load. This has the effect of smoother sound with greater detail, regardless of the amp.

Tubes in general like to drive higher impedances solely due to a higher output impedance. Our smaller amps are the most popular, so I impedance curves are very helpful. I'm not a fan of Stereophile but their measurements of speakers have been very helpful in the past.
beetlemania
834 posts
 
What do you look for in the impedance curve?
The minimum value and the frequency at that value. Also, whether the curve is flattish over multiple octaves and, if so, the average impedance over that range.
That said, the map is not the territory. This is even more true for amp measurements. No way to know how amp+speaker will sound until you actually listen to the combo.

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