I'm puzzled by this statement, since Stereophile does not mention D.C. resistance. And impedance is absolutely NOT lower than DCR-that was the genesis of Ottala's paper and then this thread.
So to twist that around and spit it back out, the nature of the usual dynamic transducer is such that the impedance rises around resonance counteract the phase angle to enough degree that the EPDR never dips below DCR?
Yes...but there was another one discussing the SOA (Safe Operating Area) of transistors, and how that could get violated by speaker impedance-thus harking forward to this thread-and showed some really ugly scope captures of protection misbehaviors. Can't remember for the life of me who/where. And I'd be curious to see that updated as applied to Class D (or G/H for that matter)
Not at all in my view. The way I think about EPDR is:
- Here is some impedance magnitude and phase angle at some certain frequency.
- At a given voltage from the amp, it will flow XX current
- That current is the same as a resistor of YY ohms would draw from the amp.
So it is an attempt to simplify things for non-technical folks who want to know stuff like "my receiver is 8 ohms but these speakers are 6 ohms, can I connect them or will it blow up the receiver?"
Like any attempt to distill something down to one number as a "figure of merit" it is of course an oversimplification. But a useful one, because even after years working with speakers and amps, if John Atkinsons writes in Stereophile that a speaker has an impedance magnitude of 5.82 ohms at 87 Hz with a phase angle of 72 or whatever, I have no idea how "bad" that is. EPDR is useful to compare that to 2/4/8/16 ohms.
It's seeming from this thread that designs with wacked crossovers can exhibit an EDPR "impedance" less than the D.C. Resistance. My question morphs into
Has anyone actually MEASURED to coinfirm the EPDR calculation really works???
I have no reason to doubt, and pardon if that was answered in the many pages I have yet to read. Science hypothesis should just be confirmed by observation.
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A drivers impedance has two form - the static DC resistance Re (and the inductance) plus the dynamic impedance caused by the back EMF. The total impedance can never lower than Re, which will occur if the back EMF is zero. Any back EMF will add to the drivers dynamic impedance, it can never subtract.
The reason that there is a resonance peak is because of the back EMF which is always greatest at resonance. Glue the voice coil or demagnetize it and all the dynamic portions will disappear.
PS. it is possible for a driver AND crossover to have an impedance lower than Re, but this is due to the crossover and not the driver.
Yes, but the universe will be dying a heat death, so I don't think that job can be finished in time...