I recently did a little searching on the internet for devices that could be used to control the dispersion of HF devices, other than highly engineered horns. I came across acoustic lenses that JBL developed back in the late fifties, early sixties. They looked like louvers mounted in front of the horns. They look funny, but once I figured out how they worked, they struck me as very elegant solutions to the targeted problem. By providing ever longer pathways for sound sound emanating further away from the centerline of the horn, thus delaying its launch from the device to varying degrees, it diffracts the sound much like a glass lens diffracts light. But they only control horizontal dispersion given their 2-dimensional form.
I was blown away by this.
Seems like metal foam with open cells of the right size could be used to create acoustic lenses that could control both vertical AND horizontal dispersion. Since you use a foam plug in your horn designs, I was wondering if this approach ever occured to you and if so, what you thought about it.
I was blown away by this.
Seems like metal foam with open cells of the right size could be used to create acoustic lenses that could control both vertical AND horizontal dispersion. Since you use a foam plug in your horn designs, I was wondering if this approach ever occured to you and if so, what you thought about it.
Those JBL lenses are a very outdated concept. There's a reason why they haven't been used for so long. They sucked. 
I remember Geddes responding to this exact topic here in the past. I don't remember his exact words, except that they didn't work very well.
edit:
http://www.diyaudio.com/forums/showthread.php?postid=1541195#post1541195
I remember Geddes responding to this exact topic here in the past. I don't remember his exact words, except that they didn't work very well.
edit:
http://www.diyaudio.com/forums/showthread.php?postid=1541195#post1541195
graaf said:
gedlee said:
Hmm,
I'm looking at these. I checked with a guy who built the Wall of Sound who might know, and he thought these sounded great. It seems that they might sound better than the horrible constant directivity stuff popular today. You may be able to simulate that low cost injection molded computer designed horns are better than expensive to build hand assembled from many unique component lenses, but the proof is in the pudding. Modern PA sound systems suck.
I'm looking at these. I checked with a guy who built the Wall of Sound who might know, and he thought these sounded great. It seems that they might sound better than the horrible constant directivity stuff popular today. You may be able to simulate that low cost injection molded computer designed horns are better than expensive to build hand assembled from many unique component lenses, but the proof is in the pudding. Modern PA sound systems suck.
Acoustic Lens Notes
The concept of an acoustic lens is not outdated, but the implementations you refer to are. It is not the lens, but rather, artifacts of outdated horn designs that you were hearing at the time you made the negative assessment. The reasons acoustic lenses are not used today are due primarily to cost, fragility, the lack of research, and the notion that they present a too-narrow bandwidth according to Earl Geddes who promotes use of Freehafer's horn under the moniker "Waveguide". He fills the horn with foam to primarly to supress HOM's.
Regards,
WHG
See this thread for additional information:
http://www.diyaudio.com/forums/multi-way/202243-acoustic-lens.html
Those JBL lenses are a very outdated concept. There's a reason why they haven't been used for so long. They sucked.
I remember Geddes responding to this exact topic here in the past. I don't remember his exact words, except that they didn't work very well.
edit:
Geddes on Waveguides - Page 78 - diyAudio
The concept of an acoustic lens is not outdated, but the implementations you refer to are. It is not the lens, but rather, artifacts of outdated horn designs that you were hearing at the time you made the negative assessment. The reasons acoustic lenses are not used today are due primarily to cost, fragility, the lack of research, and the notion that they present a too-narrow bandwidth according to Earl Geddes who promotes use of Freehafer's horn under the moniker "Waveguide". He fills the horn with foam to primarly to supress HOM's.
Regards,
WHG
See this thread for additional information:
http://www.diyaudio.com/forums/multi-way/202243-acoustic-lens.html
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This is very interesting. Are there loudspeakers that do exactly that? Would you let us know some examples?