Impedance - The most ignored and useful measurement tool

@livinon2wheels  Got it. Easy to remember. Thank you.

Call me petty but I am still upset.   🤣🤣🤣

@lanx0003 Here is an easy way to remember what happens in an LC circuit: Remember the phrase ELI the ICE man. Voltage leads current in an inductive circuit and Current leads Voltage in a capacitive circuit. Helpful tool to remember. When you first apply current to an inductor the coiled wire resists current flow so voltage rises before current starts flowing. In a capacitive circuit, the current flows heavily at first and then slows as the voltage rises. ELI the ICE man...simple no?

I wonder how many of us try fixing something we hear as undesirable using other methods in/around the system and while not understanding the speaker impedance first.  

Re-tracing old steps, I ran into a situation last week about this, also realizing the different amplifiers I simply should have avoided trying prior.  

@erik_squires @ddlux @richardbrand  Thank you.  You're correct. The lower chart should represent the phase angle, which varies from -90° to +90°. I prefer Stereophile's presentation, as shown below, where the impedance and phase angle charts are superimposed on the same chart with the left axis ranging from 0 to 20 ohms for impedance and the right axis ranging from -90° to +90° for phase angle, making it easier to interpret.

On another note, Stereophile began reporting EPDR (Equivalent Peak Dissipation Resistance) around 2020. As you may know already, EPDR represents the lowest effective resistance, accounting for both impedance dips and reactive phase angles. The exact formulation used by Stereophile remains unknown to me, but thanks to Mr. Jack Oclee-Brown, his derivation appears accurate enough to reproduce the values reported by Stereophile.

As shown in the example below for the Wilson Alexia V, winner of Stereophile's 2023 Speaker of the Year award, the nominal impedance is approximately 2.9 ohms, which may seem manageable. However, when factoring in the phase angle, the corresponding effective impedance drops to just 1.15 ohms, indicating that the speaker is actually quite current-hungry at low frequencies.

@erik_squires 

I've been at this a long time and just today realized there was such a thing as negative impedance

Negative impedance must cause those pesky electrons to speed up.  Possibly a battery?

@lanx0003

If you look carefully at your graph, you will see a second vertical scale on the right hand side, calibrated in deg (degrees).  The bottom curve is indeed the phase angle, centred around zero, and swinging plus and minus about 35 degrees.

Ever wonder why VA is often used instead of Watts?  If the Voltage and Current in an AC circuit do not peak in unison, they have a time shift which can be measured as a phase angle.  Useful power in Watts is V A cos(phase) which is only equal to VA for resistive loads (the phase angle is zero).

The amplifier has to provide additional power to make up for capacitive and inductive losses.

I thought the dark green line is impedance as measured in ohms per the left hand scale; and the light green line is phase angle as measured in degrees per the right hand scale.

@lanx0003 

Well, you have taught me something new.  I've been at this a long time and just today realized there was such a thing as negative impedance.

No, it is clear the lower curve corresponds to all negative impedance at some positive and some negative phase angles.  But I do agree that negative impedance implies the voltage and the current are out of phase.  No idea what causes it though in practice.  Will reach out to other communities.  Thx.

@lanx0003 Suggest you hit up the very active REW forums! but I believe that's not negative impedance, it's phase angle.  Ask in DIYaudio for help with that, but it's related to how capacititive or inductive an impedance is.  These cause the current and voltage to be out of phase compared to a resistor.

Great post!  

Interesting to note negative resistance measure (shown in light green) in REW chart (from the link provided).  What does it mean, or how do you interpret it? Do you know?

Is there extra functionaity in the Dayton piece that makes it worth it

To be honest I have only used the DATS V2 and really love how well and easy it is to use, I’ve not tried the REW, but if I recall it requires you to use 2 audio channels at once?  I'm not sure.

It’s really a matter of convenience. Also, AFAIK DATS is Windows only, so if you are a MacOS only home REW is your only option.

There are other professional impedance measurement tools, BTW, these are just the two least expensive I know of.

All of Danny Richie's (GR Research) loudspeaker evaluations include impedance measurements.

Not sure enough people understand how impedance phase angle affects matching of amp to speakers, too many look at only sensitivity.

@sns Great point.

In both the case of Fritz's speakers and my others, Ascends, the builders (Fritz and Dave Fabrikant) wrote to me and explained about the kindness of the phase angles in their designs and how their speakers would work with a wide variety of amps without much trouble. On the other hand, when I was auditioning some other speakers, a couple years ago, @tvad helped me realize that the Focals were not sounding great because of a terrible, sharp dip down to 3ohms. I could not have understood it without the phase angle concept.

I was talking about this yesterday with @decooney -- the usefulness of knowing speakers' impedance loads. We were discussing how much class A power would be optimal for speakers.

YES @erik_squires !!!!!!! 
Been reading thru fathers electronics text books on impedance, and studying in regard to speakers, wire, input/output, etc.  Your post is perfectly timed and really well stated!!! 

Interesting! Kudos to you @erik_squires. Is there extra functionaity in the Dayton piece that makes it worth it. I already have REW but have not used it for this. In fact, I was not aware of this capability.

@sns 

+1 The first spec I look for in an amp: is it 2-ohm stable; second is wpc. I want it to be able to drive ANY reasonably priced speaker with difficult phase angles and deep dips in impedance.

Not sure enough people understand how impedance phase angle affects matching of amp to speakers, too many look at only sensitivity.

Great post @erik_squires.