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In Reply to: RE: Ping tomservo regarding US patent US4845759A posted by Rafaro on January 10, 2023 at 09:32:58
Hi
Well a source that radiates from a single point has a wavefront that is curved on a radius while a line source has no curvature (technically one could say that is what you have infinitely far away from the point source).
One can do what you ask, IF what one makes is an astigmatic point source, a point source that has two different focal lengths (just like with ones eyes they can have that issue as well), one in the horizontal and an other in the vertical.
With the wavelength at 20KHz being about 5/8 inch, there is no simple way to put sources that close together to form a single radiation (1/4 wl or less apart), at least i couldn't think of a way and i tried hard.
What i did figure out is that if one formed curved the curved wavefront of a single source like longer horn would have, that you could make that with segments IF they were close enough together edge to edge so that they did form one big wavefront (and so have the vertical directivity of a horn that tall with that horn wall angle).
To curve the wavefront i used an acoustic lens I called a Paraline, the job was to take the radiation from individual drivers and make segments with a new radius one could add right up edge to edge.
Fast forward through a bunch of dull R&D;
Doug Jones (the guy behind the LEDR hearing test recordings) made a video for us that shows the idea behind that lens.
https://www.youtube.com/watch?v=b8cX5Xs_vZg
This fellow from another forum came to shop to hear some other speakers and saw one of those standing there in the warehouse and asked to hear it. He was playing something on his phone showing there are no seams, it sounds like a single source.
https://www.youtube.com/watch?v=8HxWGzelwNE
So it is in one place in time, like a single driver
Keep in mind that one has 8 coax drivers in it and most of our stuff, nearly all is for large scale listening, hifi and DIY is my hobby and my goal sound wise for our big stuff...
Best
Tom Danley
Follow Ups:
That made my day along with seeing the great Mr. Danley posting again.
What is the lowest useable frequency for this topology? Can you build a larger one to say 300hz then stack a smaller one on top for a two way?What could the high frequency bandwidth be with inexpensive drivers?
Since you're using coax what shape do you use to attach the coax drive to the Paraline lense?
Edits: 01/13/23
Hi
Well the speaker in the 2nd video is good to 80Hz all by itself using 8 coax drivers (cone and normal compression driver).
For a paraline, the main limit to HF is how large the passageway is where the sound changes direction.
Sound can act like a fluid, go around corners (like inside a compression driver at the dome) but it does this elegantly only when the dimensions are small compared to the wavelength.
It's not to hard to make a 1 way paraline work but the larger it is, like any two radiating systems, the harder it is to make a seamless crossover.
The same thing applies to the last question, in that speaker, the mid energy is added into the hf horn where the dimension is about 3 inches in diameter and so at crossover, they can combine (less than 1/4wl across) into one single radiation.
That (radiating as a single point in time and space) and horns has been the thing that makes our company go, in a live sound world in love with hanging speaker bananas.
If you were ever at "Rivers of light", all the audience speakers are those SBH10's, the far away speakers are some of our bigger stuff.
Tom
"hanging speaker banana"
Great new terminology, Tom!!! I'm adding to my official Audio Vocabulary.
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