# Stereophile has started calculating EPDR.

#### MZKM

##### Major Contributor
Forum Donor
https://www.stereophile.com/content/goldenear-brx-bookshelf-reference-x-loudspeaker-measurements
And he is going back to previous reviews and adding this in.

EPDR (Equivalent Peak Dissipation Resistance) takes the impedance and phase data and computes a new impedance that shows what equivalent load the amplifier will see. This takes the guesswork out of knowing how an amplifier will handle a given speaker if we have measurements of that amp into low impedance.

For example, in the BRX link above, here is the raw impedance & phase:

The raw impedance never goes past 3ohm. However, at 135Hz where the impedance is ~5ohm and the phase around -45°, the EPDR is 1.53ohm, over 3x lower.

This is something that I believe would greatly benefit Amir’s reviews, we just need to know the calculation.

For those providing EQ adjustments to speakers measured here, it would also be interesting to see how they effect the EDPR.

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#### QMuse

##### Major Contributor
https://www.stereophile.com/content/goldenear-brx-bookshelf-reference-x-loudspeaker-measurements
And he is going back to previous reviews and adding this in.

EPDR (Equivalent Peak Dissipation Resistance) takes the impedance and phase data and computes a new impedance that shows what equivalent load the amplifier will see. This takes the guesswork out of knowing how an amplifier will handle a given speaker if we have measurements of that amp into low impedance.

For example, in the BRX link above, here is the raw impedance & phase:

The raw impedance never goes past 3ohm. However, at 135Hz where the impedance is ~5ohm and the phase around -45°, the EPDR is 1.53ohm, over 3x lower.

This is something that I believe would greatly benefit Amir’s reviews, we just need to know the calculation.

For those providing EQ adjustments to speakers measured here, it would also be interesting to see how they effect the EDPR.
REW calculates EPDR in Impedance & Phase graph since version 5.20 beta 46.

OP
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#### MZKM

##### Major Contributor
Forum Donor
REW calculates EPDR in Impedance & Phase graph since version 5.20 beta 46.
Is the formula available?
I want to include this in my speaker data files, and it’d be easier if I can just calculate it in the spreadsheet and not have to go into REW.

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#### QMuse

##### Major Contributor
Is the formula available?
I want to include this in my speaker data files, and it’d be easier if I can just calculate it in the spreadsheet and not have to go into REW.
Forumla how to calculate EPDR is published in AES paper "Audio Power Amplifiers for Loudspeaker Loads" written by Benjamin Eric (Dolby Labs).

#### Wes

##### Major Contributor
What is the EPDR for a Magneplanar 3.7i ??

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#### tjf

##### Member
If like most Maggies, very close to the impedance, as they have very low phase angles. Maggies are inefficient, but not current hungry.

https://www.stereophile.com/content/magnepan-magneplanar-mg36r-loudspeaker-measurements
And...there's the argument for 1st order (open baffle) and 2nd order (sealed box) bass driver/enclosure alignments....

With 3rd order (aperiodic/damped port) alignments coming in next....phase-angle-wise, that is....(3rd order alignment example in memory of Bud Fried and the transmission-line crowd...)

#### phoenixdogfan

##### Addicted to Fun and Learning
Peter Aczel used to do something called the "Power cube" which displayed the voltage output at varying level of impedance and phase angle.

An example.

http://www.biline.ca/audio_critic/audio_critic_web2.htm#ba

For the notorious Behringer A500 which as can be seen performs fairly well in this test.

I've always thought ASR's (or for that matter Stereophile's) amplifier reviews would be enhanced by this measure.

#### pozz

##### ЦАП
Forum Donor
Editor
Peter Aczel used to do something called the "Power cube" which displayed the voltage output at varying level of impedance and phase angle.

An example.

http://www.biline.ca/audio_critic/audio_critic_web2.htm#ba

For the notorious Behringer A500 which as can be seen performs fairly well in this test.

I've always thought ASR's (or for that matter Stereophile's) amplifier reviews would be enhanced by this measure.
A PowerCube is around \$20k, if I remember correctly.

https://www.audiograph.se/

##### Active Member
Forum Donor
the "Power cube" I've always thought ASR's (or for that matter Stereophile's) amplifier reviews would be enhanced by this measure.
https://www.audiograph.se Lars is a very cool guy, we had dinner with his wife in Vegas long ago. I got the humongoid audio claptraporation I worked for to buy a couple for amp testing. They are like \$10-20k or something like that.

Really a next-level test for amplifiers, sometimes showing truly ill behavior. I would have preferred probably 70 Hz but Lars said the physical parts to do that would get crazy big and expensive.

As for
...EPDR is published in AES paper "Audio Power Amplifiers for Loudspeaker Loads" written by Benjamin Eric (Dolby Labs).
- Here's a related link https://www.stereophile.com/reference/707heavy/index.html
- I think I have Eric's paper in my garage but it's too damn hot to look for it. Is that the one where he's using a oscilloscope to look at peak loads?
- And maybe the same question or maybe not: does it actually work? If you put in that frequency signal, is the current draw actually what it would be with the EPDR resistance? (Yes, theory says so, but speakers are funny beasts and it's nice to check reality)

#### amirm

Staff Member
CFO (Chief Fun Officer)
A PowerCube is around \$20k, if I remember correctly.
It is a bit cheaper. For a stereo, 1000 watt it is \$15,000 plus \$1000 for the travel case and shipping/customs clearance.

The cheapest is 1 channel, 500 watts for \$11K for the system itself.

Supported Test tone is only 1 kHz which is limiting.

##### Active Member
Forum Donor
Supported Test tone is only 1 kHz which is limiting.
I recall now Lars said he was working on making an "active load" which would get around the limitations of huge physical parts for low frequencies. Maybe an amp acting as a kind of load? I guess that never worked.

Hmm, to check ballpark values I randomly pulled up an impedance calculator which shows 1000 microfarads is like 2.2 ohms at 70 Hz.* And those don't seem crazy expensive...though for 400 watts at 8 ohms you need maybe 60 volts...well that's RMS so times 1.414 then times 2 so like 180 or call it 200 volts. Meanwhile a 10 mH inductor I get 4.4 ohms at 70 Hz. Those don't seem crazy expensive but I don't know about the current handling. Is the voltage/current why it would get expensive to make a hand load? Or am I calculating wrong?

I'm sure a large chunk of the Power Cube expense is the automation, and the multiple loads, and of course a large profit margin to support a small sales quantity.

*I randomly pulled 70 Hz out of my butt as a non-integer multiple of 50/60 Hz. If I was going to set up this testing I'd want to run FFT of the distortion spectrum at clipping, and so use some frequency and FFT setup such that 50/60 Hz mains bleed and the test signal would be in different FFT bins for at least the lower harmonics.

#### hardisj

##### Major Contributor
Anyone ever find the calculation for this? I would be happy to implement it in my reviews if it's useful. But I don't have time to hunt the equation down or the like.

#### Martin

##### Addicted to Fun and Learning
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Anyone ever find the calculation for this? I would be happy to implement it in my reviews if it's useful. But I don't have time to hunt the equation down or the like.

Martin

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Editor

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#### MZKM

##### Major Contributor
Forum Donor
Amir has not added this data (and I’m not going to use a digitizer on his plots every time). Also, he said he isn’t too keen on it as it makes high frequencies seem worse than in actuality (less energy up there so being difficult to drive isn’t an issue).

Oh, and I’m not paying for the formula, so unless someone already is able to access it, I would have to use REW every time to import/export the data, which would be annoying.

#### pozz

##### ЦАП
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Editor
Amir has not added this data (and I’m not going to use a digitizer on his plots every time). Also, he said he isn’t too keen on it as it makes high frequencies seem worse than in actuality (less energy up there so being difficult to drive isn’t an issue).
Ah well.

Would have been an interesting single-number figure to add to the dataset.