That's right!
I had the pleasure of having Earl on my podcast.
Please watch, like and subscribe!
Waveguides, Acoustics and Speaker Design with Dr. Earl Geddes - YouTube
A lot more content coming too. 😀
Podcast | The Intellectual People Podcast
I had the pleasure of having Earl on my podcast.
Please watch, like and subscribe!
Waveguides, Acoustics and Speaker Design with Dr. Earl Geddes - YouTube
A lot more content coming too. 😀
Podcast | The Intellectual People Podcast
That was a great interview with Earl, thanks for sharing. It was interesting to me to hear about the NA12 and NS15. I hadn't been aware that the NS12 used the larger 15" waveguide and the NS15 used an 18". I got to hear Earl's Summas a couple of times over the years at listening sessions at his home organized through a local audio club. While I never bought one of Earl's speakers, I was tempted and ended up with some SEOS 12's to experiment with.
Dan
Dan
Thanks for the podcast. I've never had the pleasure to meet Geddes or audition his speakers. I think him for contributing here. He is that rarity, like Tom Danley, a commercial designer who supports DIY.
Earl Geddes had to suffer through about ten hours of my questions at the RMAF, back in 2005. That was really fun, I wish I took more pictures. I also had the opportunity to talk shop with him and Lynn Olson.
To me, the thing that a lot of people don't realize about Earl is that he's got a great sense of humor. Very dry, British sense of humor. It's hard to pick it up online, because Internet forums aren't a great medium for subtle humor.
But once you meet him in person, you realize that a lot of the things that he say are provocative and playful.
For instance, if you posted a bunch of quotes from Jim Carey on diyaudio he'd sound like a jerk, but in person, you realize he's pushing your buttons. When I was in college, all my best teachers were like this. Part of the educational process was to take the student and make them justify their engineering. One way to evaluate that teacher is to say that they're being a jerk, another way to evaluate the teacher is to say that they're pushing you to justify your engineering decisions.
To me, the thing that a lot of people don't realize about Earl is that he's got a great sense of humor. Very dry, British sense of humor. It's hard to pick it up online, because Internet forums aren't a great medium for subtle humor.
But once you meet him in person, you realize that a lot of the things that he say are provocative and playful.
For instance, if you posted a bunch of quotes from Jim Carey on diyaudio he'd sound like a jerk, but in person, you realize he's pushing your buttons. When I was in college, all my best teachers were like this. Part of the educational process was to take the student and make them justify their engineering. One way to evaluate that teacher is to say that they're being a jerk, another way to evaluate the teacher is to say that they're pushing you to justify your engineering decisions.
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I disagree with some things that Earl Geddes said on the podcast.
In the podcast, he stated that the foam plug makes an "incremental improvement in the waveguide."
I believe this ignores the fact that the worse your waveguide is, the more the foam makes a difference.
For instance, when I used the Summas as my reference, the foam plug made a VERY subtle difference.
But when I put foam in horns that had bends or diffraction slots in them, the difference was SUBSTANTIAL. Basically the foam plug makes a bigger difference in bad horns than good waveguides. The Summa has a good waveguide. So the improvement in the Summa is subtle.
An example of this phenomenon is here: The HOMster! (or How I Learned How to Fix a Horn)
The reason that the foam has a much more substantial effect on a horn with reflections or diffraction, is because the way that the foam works is that it absorbs Higher Order Modes.
For instance, if you have an absolutely PERFECT waveguide, the wavefront that's generated by the driver will radiate to the listener with zero diffraction or reflection. One way to reduce or eliminate diffraction is to place the driver on a flat baffle. If you put a one inch tweeter on a flat baffle, the wavelengths below 13500Hz will not suffer from diffraction or reflections because there's nothing in the way of the wavefront that's radiated from the tweeter.
Once you put a waveguide or horn in front of the driver, you're going to have to deal with reflection and diffraction.
If the waveguide or horn has a diffraction slot or a reflector, there's a very good chance that the diffraction slot or reflector will generate higher order modes. (My thread named "Square Pegs" digs deep into this.)
The foam that Geddes uses can reduce these higher order modes. Basically the reflected or diffracted waves have to radiate through the foam three times or more (because Reflections) and this means that the incident waves are attenuated less than the reflected waves.
In the podcast, he stated that the foam plug makes an "incremental improvement in the waveguide."
I believe this ignores the fact that the worse your waveguide is, the more the foam makes a difference.
For instance, when I used the Summas as my reference, the foam plug made a VERY subtle difference.
But when I put foam in horns that had bends or diffraction slots in them, the difference was SUBSTANTIAL. Basically the foam plug makes a bigger difference in bad horns than good waveguides. The Summa has a good waveguide. So the improvement in the Summa is subtle.
An example of this phenomenon is here: The HOMster! (or How I Learned How to Fix a Horn)
The reason that the foam has a much more substantial effect on a horn with reflections or diffraction, is because the way that the foam works is that it absorbs Higher Order Modes.
For instance, if you have an absolutely PERFECT waveguide, the wavefront that's generated by the driver will radiate to the listener with zero diffraction or reflection. One way to reduce or eliminate diffraction is to place the driver on a flat baffle. If you put a one inch tweeter on a flat baffle, the wavelengths below 13500Hz will not suffer from diffraction or reflections because there's nothing in the way of the wavefront that's radiated from the tweeter.
Once you put a waveguide or horn in front of the driver, you're going to have to deal with reflection and diffraction.
If the waveguide or horn has a diffraction slot or a reflector, there's a very good chance that the diffraction slot or reflector will generate higher order modes. (My thread named "Square Pegs" digs deep into this.)
The foam that Geddes uses can reduce these higher order modes. Basically the reflected or diffracted waves have to radiate through the foam three times or more (because Reflections) and this means that the incident waves are attenuated less than the reflected waves.
I have wondered about the foam. Your last sentence makes it very clear how it operates. Thanks!
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No problem!
It's the reason that so many people are like "I don't hear much of a difference."*
You wont - unless the horn or waveguide is particularly bad.
I've never seen a case where it didn't improve the performance.
It's the reason that so many people are like "I don't hear much of a difference."*
You wont - unless the horn or waveguide is particularly bad.
I've never seen a case where it didn't improve the performance.
Maybe Earl was talking in the context of a specific waveguide?
It's clear that he understands that only the wanted sound takes the shortest path through the foam. It's only one step from there to imagine what happens in a troublesome waveguide.
I get the impression that Earl has never been into putting lipstick on a pig, whereas I do a lot of work in car audio, where we're often using waveguides that are wildly axisymmetric, and a lot have reflectors in them!
Ironically, I eventually realize that putting lipstick on a pig is a bad idea. I reached a point where instead of using wildly axisymmetric waveguides, I just started using mostly symmetrical waveguides that were smaller.
Old school car audio waveguides looked like this:
Ironically, I eventually realize that putting lipstick on a pig is a bad idea. I reached a point where instead of using wildly axisymmetric waveguides, I just started using mostly symmetrical waveguides that were smaller.
Old school car audio waveguides looked like this:
Attachments
I just watched your interview with Earl Geddes and it was outstanding. One of the best audio related pieces on the Internet.
There are a lot of so called "audiophiles" posting their videos and most of them are garbage. It's great to find something that is intelligently done and has real worthwhile content.
I learned some important things from this one. Please keep it up. Thanks.
There are a lot of so called "audiophiles" posting their videos and most of them are garbage. It's great to find something that is intelligently done and has real worthwhile content.
I learned some important things from this one. Please keep it up. Thanks.
It's a loss that Geddes's ideas haven't had mass-market success. "Patrick," your wild projects too would be great. If I had Elon Musk money, I would hire you at a salary that would make you rich beyond your wildest dreams of avarice, to be a full-time designer with the proviso you made available copies of your projects to other DIYers.
The Geddes foam plug likely also reduces the mouth reflection "reverb" problem of a poorly terminated horn, which is the standard type of waveguide 🙂 I use the towel cowel mod, explained well in this classic thread:
http://www.audioheritage.org/vbulle...ic-Quality-of-Mid-amp-HF-Horns-amp-Waveguides
The Geddes foam plug likely also reduces the mouth reflection "reverb" problem of a poorly terminated horn, which is the standard type of waveguide 🙂 I use the towel cowel mod, explained well in this classic thread:
http://www.audioheritage.org/vbulle...ic-Quality-of-Mid-amp-HF-Horns-amp-Waveguides
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