Stereophile has started calculating EPDR.

[peng]

Once upon a time, Matti Ottala presented an Audio Engineering Society paper showing that an "8 ohm" speaker could eat up to "1 ohm" of current.* Later someone published a pushback, saying that Ottala's paper was based entirely on simulation and that an empirical study had shown no evidence for current draws greater than the D.C. resistance of the voice coil would indicate.
I don't know if there was ever further study made. I wanted to do that with some kind of simultaneous current and voltage readings into a data logger but have never gotten around to it. Another way would be a long term trace on a storage scope and looks at the trace slopes. Someday...

In theory, and on transient basis (not steady state), I can see that happens, and I guess it is understandable that to make his point, Ottala had to use simulation lol.. It is naturally hard for people, including many EES to understand the negative impedance effect, or "behavior".

*note this is different than EPDR, since no dissipation is factored in, it's just equivalent resistance.

That's very much my point, unfortunately is is very evidence on ASR that Stereophile and other experts in the field might have unintentionally misled many hobbyists who do not have sufficient understanding of the topic to believe "current/amperes capability" was the issue, when it is in fact not always current, but dissipation, that is just as important to consider but then how often would hobbyist, even amp designers look at transistors SOA? It's just much easier to push the hearsay that it's not power, but those speakers with low EPDR needs high current amps (mostly true anyway I guess..).

 

[Head_Unit]

those speakers with low EPDR needs high current amps (most true anyway I guess..).

Yes...though someone (I think here at ASR) posts that is nonsense and "you just need more power" (which supplies more current of course). They're probably correct, the beefiest 100W amp probably will clip sooner than a 400W amp unless the latter is super cheap ha ha. I started saying you need to get the most 4 ohm or even 2 ohm power if rated, since speakers have gotten lower and lower in impedance per Stereophile's testing.

 

[MaxBuck]

"One ohm of current?" WTF?

 

[peng]

Yes...though someone (I think here at ASR) posts that is nonsense and "you just need more power" (which supplies more current of course). They're probably correct, the beefiest 100W amp probably will clip sooner than a 400W amp unless the latter is super cheap ha ha. I started saying you need to get the most 4 ohm or even 2 ohm power if rated, since speakers have gotten lower and lower in impedance per Stereophile's testing.

When people said not power, but current, they usually meant to say don't just look at power, but current as well because a 200 W 8 ohm amp may not have enough current to meet the demand of many speakers in some use cases. Lots of misconception on the internet/forums, but lots of time it is also just the wording, emphasis etc...

So, I am all for using voltage and current specs. If an amp is rated say, 12 A, at 50 V, continuously for not less than 1 minute, 20 A for not longer than 1 second, then it is more informative than one that is rated 600 W 8 ohms.

 

[antcollinet]

When people said not power, but current, they usually meant to say don't just look at power, but current as well because a 200 W 8 ohm amp may not have enough current to meet the demand of many speakers in some use cases. Lots of misconception on the internet/forums, but lots of time it is also just the wording, emphasis etc...

So, I am all for using voltage and current specs. If an amp is rated say, 12 A, at 50 V, continuously for not less than 1 minute, 20 A for not longer than 1 second, then it is more informative than one that is rated 600 W 8 ohms.

But there is another factor that probably causes most of the confusion.

For any given voltage/current/impedance - which results in a certain current and resulting dissipation in the amp, with most of the V*A power going into the speaker there is also the phase of the speaker response. As that phase goes from 0 degrees towards 90 degrees (90 never actually reached), more of that power - which would normally be dissipated in the speaker now needs to be dissipated in the amp.

So even if the current is not getting bigger the heat in the amp can increase dramatically.

(Note this only applies to linear amp designs - class D designs don't operate in the linear region so don't dissipate this power - instead dumping it in and out of the PSU.)

So, not only current capacity is needed, but also cooling capacity. This of course is never specified.

 

[peng]

But there is another factor that probably causes most of the confusion.

For any given voltage/current/impedance - which results in a certain current and resulting dissipation in the amp, with most of the V*A power going into the speaker there is also the phase of the speaker response. As that phase goes from 0 degrees towards 90 degrees (90 never actually reached), more of that power - which would normally be dissipated in the speaker now needs to be dissipated in the amp.

So even if the current is not getting bigger the heat in the amp can increase dramatically.

(Note this only applies to linear amp designs - class D designs don't operate in the linear region so don't dissipate this power - instead dumping it in and out of the PSU.)

So, not only current capacity is needed, but also cooling capacity. This of course is never specified.

Agreed 100%!

 

[Head_Unit]

"One ohm of current?" WTF?

It's the new math!
Answer B: it's part of the updated FTC Amplifier Rule!