An Improved Paraline.
I've built a bunch of Paralines*, but I wasn't satisfied with the sound. A lot of dips in the response, and a character that was generally harsh.
I believe the problem is that the sound radiated from the diaphragm hits the bends in the Paraline and is reflected back to the throat. The reflected wave is a higher order mode. HOMs make a horn sound harsh.
I wanted to use some of the same tricks that we use with waveguides to reduce higher order modes. I wanted to use gentle curves to reduce reflections back into the throat.
The first thing I do is draw that familiar 'eye' shape. The point of this shape is to take a spherical wavefront and flatten it into a ribbon shaped wavefront...
* For more info on how Paralines work, read my threads here:
and here: http://www.diyaudio.com/forums/multi...uare-pegs.html
and here: http://www.diyaudio.com/forums/multi...-stargate.html
Those are in chronological order, but the real 'eureka' moment was the second thread. Danley has comments in all three, which are valuable insight into the devices.
The L'Acoustic VDOSC was patented in the 80s iirc; you can see it's shape in the top left. Geometrically, it's perfect, but I wonder if those abrupt transitions will create higher order modes.
Danley Paralines are similar, but with some new tricks thrown in, such as the ability to generate various wavefront shapes, not just 'ribbon' shapes.
My device is using a diffraction reducing curve, similar to what JBL and Genelec use. Basically the way that this curve works is that the exit angle is 90 degrees, but it slooooooooowly expands to 180 degrees at the mouth. The Geddes speakers work in a somewhat similar fashion, but the curve on the Geddes speakers changes more abruptly; the Genelec in particular is verrrrrrry slow.
Here's a pic of the Genelec waveguide, you can see the curve is the same as what I've drawn.
Have you gotten around to 3D printing a paraline yet?
I took some liberties with the Paraline idea here.
In a Danley Paraline, the waveguide is an 'eye' shape, and that eye shape is a very specific shape. The distance from the center of the eye to the top of the eye is EXACTLY half the distance from the center of the eye to the left of the eye.
Here's one of the illustrations from the Danley patent.
Why did I use a rectangular shape?
I did this for a few reasons:
1) A plain ol' rectangle satisfies the requirement that the distance from the throat of the waveguide to the top of the waveguide is half of the distance from the throat to the left of the waveguide.
2) While it's true that the distance is too long on the obliques, I don't really care about the obliques. I'm just trying to get the correct horizontal coverage. I don't care about oblique coverage.
3) By far the main reason that I did it is because the area of a rectangle is about 27% higher than the area of an 'eye' shaped Paraline. I believe that additional 27% should smooth out the overall response. (It is my belief that the very small volume of a Paraline is one of the reasons that the response is ragged. You can model this in Hornresp; very small horns have a lot of ripple. An additional 27% of volume should smooth out the ripple.)
4) The last reason that I used a rectangular shape is because I intend to curve the wavefront so that the listening axis is 30 degrees off the center. IE, if you're in front of this waveguide, you're 30 degrees off axis to the listening axis. And if you're 30 degrees off axis, you're on the listening axis of this waveguide. Hope that makes sense. The idea here is that you could put this speaker in front of you and it will 'throw' the sound to a spot that's NEXT to you.
At the time, I wasn't aware that 3D prints are porous.
So all of my early 3D prints are basically worthless, because they don't work until you seal them up. That's why you'll notice all my new ones are slathered in glue, I do that to seal them.
In these pics, I've added the center piece. This center piece is functionally equivalent to the center piece in a paraline. But a Paraline is two dimension and this is three dimensional. The V-DOSC is also three dimensional.
Here's a pic of the center piece with the waveguide that surrounds it hidden from view. Tolerances here are insanely tight; that gap is just five millimeters(!) Here's where the 3D printer comes in handy...
Here's an illustration of a sideview of a Paraline that I drew up for the 'Square Pegs' thread a few years back. What I'm doing today is the same idea, but it's three dimensional, so that the bends here are no longer 180 degrees, they're just ninety. Slower transitions means less diffraction.
One 'funky' thing I'm doing with this waveguide is that it's designed to bend the wavefront. If you're immediately in front of it, the sound is 'thrown' fifteen degrees off axis. I'm doing this by tweaking the pathlengths in the waveguide, to create a curved wavefront. So the device itself has a flat face, but the wavefront that comes out of it is shifted fifteen degrees off axis.
The pics above show the 'normal' curve on the left, and the 'tweaked' curve on the right.
We're pretty close to finished here. I wanted to obliterate any rough edges, I wanted the waveguide to look like a bar of soap. I *think* those 180 degree bends in the Paraline and the sharp edges of the VDOSC are creating diffraction.
Here's another pic of the VDOSC for comparison
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While unintentional, it's starting to look like the speakers from Funktion One
I hope you have a ppa on this because this is brand new groung I think.
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