Dagogo interview of Earl Geddes

[MediumRare]

Here's an article Keith Howard wrote, it's over my head but probably not over yours:

http://www.gedlee.com/Papers/THD_.pdf

Excellent, thanks. So in layman’s terms, it weights the type of harmonic distortion based on the number of the harmonic and its relationship to amplitude, all to better correlate to our understanding of psychoacoustics. (Did I get that right?)

So, can one of you math whizzes (@MZKM ?) take an FFT provided by @amirm and generate the metric for some speakers already tested?

 

[Duke]

Excellent, thanks. So in layman’s terms, it weights the type of harmonic distortion based on the number of the harmonic and its relationship to amplitude, all to better correlate to our understanding of psychoacoustics. (Did I get that right?)

So, can one of you math whizzes (@MZKM ?) take an FFT provided by @amirm and generate the metric for some speakers already tested?

My understanding is that the GedLee Metric is concerned with nonlinear distortion, which is generally not an issue for loudspeakers unless they are pushed beyond their linear limits. In other words, it's not applicable to speakers.

 

[MediumRare]

My understanding is that the GedLee Metric is concerned with nonlinear distortion, which is generally not an issue for loudspeakers unless they are pushed beyond their linear limits. In other words, it's not applicable to speakers.

Let's find out. Amir has mentioned dissatisfaction with some scores not matching his subjective impressions.

Or let's examine amplifiers - tubes v SS for example. In other words, let's see if we can measure things the subjectivists have been saying for years but have not been captured in THD/IMD.

 

[Lbstyling]

Excellent, thanks. So in layman’s terms, it weights the type of harmonic distortion based on the number of the harmonic and its relationship to amplitude, all to better correlate to our understanding of psychoacoustics. (Did I get that right?)

So, can one of you math whizzes (@MZKM ?) take an FFT provided by @amirm and generate the metric for some speakers already tested?

Oh your just outright dangerous arnt you!

In all fairness, we know that:

-Harman group products are science and fact focused.
-Revel and JBL (for instance) are designing for very low distortion.
-It's not easy or cheap to do.
- in many designs (More JBL) they will drastically cost save on things that are not strongly audible (such as cabinet thickness)
-yet they spend considerable money on copper Faraday rings etc on their drivers.

They clearly take great efforts to lower distortion.

The higher distortion IL10 measured extremely well, yet amir (and myself in this case) rate the speaker as lacking detail.

I have subjective experiences that I would happily add, but that's enough for me to come to the conclusion that although as toole says pattern control accounts for 70% of preference (or so) that's Vs speakers with poor pattern control.

Against many modern designs with excellent control, distortion likely correlates with preference.

The more I read geddes papers, the more I think he is under appreciated (but perhaps a bit blunt)

'Geddes is a blunt Toole'
Lol.

 

[Duke]

Amir has mentioned dissatisfaction with some scores not matching his subjective impressions.

Very interesting! Do you happen to know which speakers those were, off the top of your head? I'd like to read what he had to say. If not that's okay, I'll dig through and find out.

Or let's examine amplifiers - tubes v SS for example. In other words, let's see if we can measure things the subjectivists have been saying for years but have not been captured in THD/IMD.

Well I'll pass along this anecdote: After he had analyzed the data for his distortion perception papers, Earl said to me: "Now I understand why you and your friends like tube amps."

Just to be clear, Earl is NOT a tube amp guy. Actually he used (and may still use) a Pioneer receiver which scored exceptionally well by the GedLee Metric. The engineer in Earl doesn't believe in paying a premium for what he considers to be a small improvement.

 

[MediumRare]

Very interesting! Do you happen to know which speakers those were, off the top of your head? I'd like to read what he had to say. If not that's okay, I'll dig through and find out.

@amirm will answer better, but here's one https://www.audiosciencereview.com/...aph-audio-za5-2-diy-kit-speaker-review.12086/ and another https://www.audiosciencereview.com/forum/index.php?threads/kef-q350-speaker-review.13484/ and here's a bad score that sounded good: https://www.audiosciencereview.com/forum/index.php?threads/jbl-xpl90-speaker-review.13449/

 

[Duke]

@amirm will answer better, but here's one https://www.audiosciencereview.com/...aph-audio-za5-2-diy-kit-speaker-review.12086/ and another https://www.audiosciencereview.com/forum/index.php?threads/kef-q350-speaker-review.13484/ and here's a bad score that sounded good: https://www.audiosciencereview.com/forum/index.php?threads/jbl-xpl90-speaker-review.13449/

Thank you VERY MUCH!!

 

[Lbstyling]

Duke:

The infinity IL10 was the most notable.

 

[Duke]

Duke:

The infinity IL10 was the most notable.

Very interesting that there's a lack of clarity/grunginess which doesn't show up in the measurements. I presume there is a measurement which would reveal it, but measuring everything is not practical and may not be possible.

 

[dped90]

Earl published the Oblate Spheroid without patenting it. I use a wooden Oblate Spheroid waveguide in one of my models, though without his patented open-cell foam plug.

I also use SEOS waveguides and have used the Pyle/JBL waveguide which Zilch used in the original Econowave.

While possibly off topic, as you didn't and perhaps still don't use any such foam to damp out HOMs (?), I presume you leave driver bug screens intact? Art and Earl were going at it a bit on the page before this https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/page-1022 And it raised my concerns, now that I will be going with Earl's recommended A460D/DE250 combo.

 

[Duke]

While possibly off topic, as you didn't and perhaps still don't use any such foam to damp out HOMs (?), I presume you leave driver bug screens intact? Art and Earl were going at it a bit on the page before this https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/page-1022 And it raised my concerns, now that I will be going with Earl's recommended A460D/DE250 combo.

I never used Earl's reticulated foam insert. I don't doubt that it reduced HOMs but it was visually undesirable to too many potential customers. If YOU don't mind it, the one thing to be aware of is that it reduces the level of the high frequencies somewhat. Maybe 3-4 dB? Earl will know. If you will have an active system and can easily equalize, that's not a problem. But if you will be using a passive crossover, I'm not sure you'll have enough top-octave energy coming through to "keep up" with your high-efficiency Altecs.

At first I carefully cut out the bugscreens with an exacto knife and filled the gap/smoothed over the junction with a black high-end polymer modelling clay. But then I had two customers complain about the bugscreens being missing so I replaced their drivers with ones that still had the bugscreens. After the second one I quit removing the bugscreens. I didn't notice a difference, but that doesn't mean there was none.

If you're making speakers just for yourself, with no risk of actual bugs or whatever entering the compression driver, then imo you might as well remove the bugscreens.

 

[dped90]

But if you will be using a passive crossover, I'm not sure you'll have enough top-octave energy coming through to "keep up" with your high-efficiency Altecs.

Though I do find the foam plug aesthetically clunky if the color came close to matching the black painted A460D horns then I might be okay with it. And it is an elegant solution as it reduces HOMs and serves as bug screen.

Is this the 30ppi open cell foam that Earl used? https://www.thefoamfactory.com/opencellfoam/filter.html

Which foam thickness to fill the mouth? https://cults3d.com/en/3d-model/various/ath-a460d-stl-kit

But will the foam and/or the glue deteriorate over time?

Yes, passive crossovers but since a Windows server supplies music sources could a DAW based EQ plugin or even the EQ utility in JRiver be used to restore the lost HF level? If not, then removing the bug screen would seem unwise.

 

[dped90]

Here’s Marcel’s take on it. https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-8268470

Apparently, he finds no advantage using foam plugs with his waveguides, but advocates removing the bug screens though not without adding a “small piece of foam”.
Presumably, this would be small enough not to attenuate HF response level.

 

[Duke]

Though I do find the foam plug aesthetically clunky if the color came close to matching the black painted A460D horns then I might be okay with it. And it is an elegant solution as it reduces HOMs and serves as bug screen.

Is this the 30ppi open cell foam that Earl used? https://www.thefoamfactory.com/opencellfoam/filter.html

I don't think "The Foam Factory" was in existence back then. Or maybe it went by another name. But I don't see why that foam wouldn't work.

Which foam thickness to fill the mouth? https://cults3d.com/en/3d-model/various/ath-a460d-stl-kit

I would guesstimate it was about eight inches thick.

But will the foam and/or the glue deteriorate over time?

Probably. There may be some types of foam that last longer than others. I think Earl used something like 3M Type 77 spray-on glue.

Yes, passive crossovers but since a Windows server supplies music sources could a DAW based EQ plugin or even the EQ utility in JRiver be used to restore the lost HF level?

Probably, but I don't really know because that's not something I have experience with.

 

[dped90]

Probably, but I don't really know because that's not something I have experience with.

Okay.

On another matter, have you had any experience with both the B&C DE250 https://www.bcspeakers.com/en/products/hf-driver/1/8/DE250
and BMS 4554? https://bmsspeakers.com/fileadmin/b...te/bms_4554_2011-04_hf_compression_driver.pdf

Why would which be your choice for use with the A460D horn?

How would you assess Marcel's findings? https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-8162164

Acoustic Horn Design – The Easy Way (Ath4)

How louder is twice the displacement (either the excursion or Sd)? Is it +6dB SPL? The extended throat adds more than 10dB SPL around 600 Hz with less excursion than before. For some reason that's beyond me this is still completely ignored in the above posts.

www.diyaudio.com

And how much might the DE250's Polyimide and the BMS 4554's Polyester diaphragms have the drivers sounding somewhat similar?

 

[Duke]

On another matter, have you had any experience with both the B&C DE250 https://www.bcspeakers.com/en/products/hf-driver/1/8/DE250
and BMS 4554? https://bmsspeakers.com/fileadmin/b...te/bms_4554_2011-04_hf_compression_driver.pdf

Why would which be your choice for use with the A460D horn?

I have some experience with the forerunner of the DE250, which was the DE25. No experience with the BMS driver nor anything similar from BMS.

How would you assess Marcel's findings? https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-8162164

Acoustic Horn Design – The Easy Way (Ath4)

How louder is twice the displacement (either the excursion or Sd)? Is it +6dB SPL? The extended throat adds more than 10dB SPL around 600 Hz with less excursion than before. For some reason that's beyond me this is still completely ignored in the above posts.

www.diyaudio.com

I assume he's talking about using a 3D printed insert that fits into the driver itself and gives you an effective throat diameter of 16 mm? If so, imo that would tip the scales in favor of the BMS driver.

And how much might the DE250's Polyimide and the BMS 4554's Polyester diaphragms have the drivers sounding somewhat similar?

Well personally I'd tend to choose a polymer diaphragm over a titanium one, so I think they are both good choices. I don't have any opinion between Polyimide and Polyester.