I have just been reading parts of this fantastic thread: https://www.diyaudio.com/community/threads/geddes-on-waveguides.103872
Quick summary: In horns a part of waves is reflected back towards the source due to diffraction and thus takes a longer time to finally reach the listerners ear. This time delay leads to degraded sound quality and increased distortion as of my understanding. Please correct me if i'm wrong! HOM = Higher order modes
A few questions came up:
What happened in the the 15years after this thread? Why is nobody using foam plugs to absorb HOM?
I tested it in 18sound XT1086 with NSDA1095N from the same company and the effect is way more pronounced than it should be. So why is nobody doing it, has there been a better fix for the problem like improved horn design? Which were the major improvements to waveguide theory since 2007 and how to incorporate them?
What happened to Geddes company AI? Apparently their products didnt really hit the market as hoped and large companies like JBL started doing basicaly the same as he did - except foam plugs.
I think i have more questions i can not remember right now but i want to get this topic started!
Best
Martin
Quick summary: In horns a part of waves is reflected back towards the source due to diffraction and thus takes a longer time to finally reach the listerners ear. This time delay leads to degraded sound quality and increased distortion as of my understanding. Please correct me if i'm wrong! HOM = Higher order modes
A few questions came up:
What happened in the the 15years after this thread? Why is nobody using foam plugs to absorb HOM?
I tested it in 18sound XT1086 with NSDA1095N from the same company and the effect is way more pronounced than it should be. So why is nobody doing it, has there been a better fix for the problem like improved horn design? Which were the major improvements to waveguide theory since 2007 and how to incorporate them?
What happened to Geddes company AI? Apparently their products didnt really hit the market as hoped and large companies like JBL started doing basicaly the same as he did - except foam plugs.
I think i have more questions i can not remember right now but i want to get this topic started!
Best
Martin
Earl filed a patent on this, that's probably why.
https://patents.google.com/patent/US7708112B2/enThough it seems it has expired...
There may be also feasibility and long-term durability concerns.
Did you apply frequency response and level matching in your comparision?
https://patents.google.com/patent/US7708112B2/enThough it seems it has expired...
There may be also feasibility and long-term durability concerns.
Did you apply frequency response and level matching in your comparision?
Horn design is pushing forward, right here on DIYAudio!
https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/
/Anders
https://www.diyaudio.com/community/threads/acoustic-horn-design-the-easy-way-ath4.338806/
/Anders
Several of us here use (or at least experimented) the Geddes foam plug idea. I salute Dr. Geddes for his contribution and his speakers, although I never had the privilege to hear them. A related mod is the "towel trick". You can find old threads on both the foam plug and the towel mod. I've used both in my horns (stripped down Yorkville Unity U15) for years. I can't honestly say I hear a difference, but many people claim great improvements. Intuitively, the towel mod is most easily explained (and verified) as it both reduces diffraction, which is usually a good thing, and also reduces cavity resonance. A full foam plug would help with both, but perhaps not diffraction on a sharp edge at mouth. The HOM is more elusive. I think of it as unpredictable ricochets along the horn's surface, the sound wave getting bounced off into another direction.
I'm surprised that more don't try it/or sell it as a commercial product, since neither idea is on-patent any more, to my understanding. This tweak is one that falls into the category of being generally inexpensive, easily reversible and at worst robs a few dB from the top registers.
I'm surprised that more don't try it/or sell it as a commercial product, since neither idea is on-patent any more, to my understanding. This tweak is one that falls into the category of being generally inexpensive, easily reversible and at worst robs a few dB from the top registers.
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