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Old 10th September 2012, 03:00 AM   #301
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Not a problem, thank-you for the bit of information. You do certainly make logical sense.

Mitch
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Old 10th September 2012, 03:25 AM   #302
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Mitch,
Ask me about a normal exponential or hyperbolic and I can answer with authority, but here I am treading in another realm. Not really that different but slightly is the real answer. These paraline and horn combinations are following more of a constant directivity model, only the initial section is unusual. The concept is a way to combine different devices on a single waveguide with all devices have equivalent dispersion down to the mouth cutoff frequency.
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Old 10th September 2012, 05:42 AM   #303
WT is offline WT
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Last weekend, I build a Paraline with 20 centimeter height and 4.34 cm wide (30 degree vertical) with 3mm thick acrylic and put B&C DE500 as tweeter.
Since, I don't understand how to calculate the wide of the opening slot, so I made some experiment. Here is the result. Opening slot is 20 centimeter long with 6mm wide and 10 mm wide. Seem to result in the same shape except 10 mm lost some dB.

Measure with REW, indoor, gate 8ms
Attached Images
File Type: jpg paraline 20cm 6mm & 10mm wide.jpg (81.3 KB, 656 views)

Last edited by WT; 10th September 2012 at 05:47 AM.
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Old 10th September 2012, 05:45 AM   #304
WT is offline WT
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Measure of 10 mm wide opening. Horizontal and vertical measurement. I also compare it with Dayton 12 inch waveguide.
Attached Images
File Type: jpg paraline 20cm horizontal .jpg (84.0 KB, 649 views)
File Type: jpg paraline 20cm vertical.jpg (83.6 KB, 629 views)
File Type: jpg paraline vs dayton 12%22 wageguide.jpg (70.4 KB, 620 views)
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Old 10th September 2012, 09:12 AM   #305
SunRa is offline SunRa  Romania
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Getting a good HF response seems to be the real difficulty with the Paraline. You mentioned using 3mm thick acrylic. That means the height of each chamber/channel in the paraline is 3mm in your build?

Also, did you used any deflectors at the entry & exit slots?
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Old 10th September 2012, 09:43 AM   #306
WT is offline WT
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Sunra,

Yes, the height of each chamber is 3mm. But I cut it by hand so very crude.

I didnot use any deflectors because I don't know how to calculate the size and shape. My compression driver, B&C DE500, has grill at the opening so I can not use deflector at the entry point.

Can anyone guide me on the size and shape of the delector at the exit slot, please.
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Old 10th September 2012, 02:44 PM   #307
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Quote:
Originally Posted by Don Hills View Post
You'll need to do some trigonometry.
This post shows how it looks for a "standard" Paraline:

Square Pegs

You'll need to move the focus closer to the vertex (same as making the curve shallower) to get your desired vertical dispersion.
Don,

Thanks for referring to my post. By moving the focus closer to the vertex, you no longer have reflections that are all vertical in the graph (or horizontal on a real paraline), if I am thinking correctly. In order to increase vertical directivity, we need a shape that will have all reflections in the same direction like the graph, but with a 'spherical' delay.

A hyperbola has the reflecive property that if a source is at one focus, the reflection will be as if the rays are coming off the other focus. But this means that in a paraline, the reflections will not all be perpendicular to the output slot. Not sure if it really matters for small dispersion angles, but for large ones, you can have some strange things happen.

Here's a diagram for the hyperbolic case:

Click the image to open in full size.

When sound comes from F1 and strikes the left part of the hyperbola, its reflection behaves as if it were coming from point source F2.

What we need is a shape that will have the property of the parabolic reflection with necessary delay to approximate a point source with some degree of programmable dispersion. I have this coming week off, but I have many projects to complete, so I will see if I can crank up the old calculus engine in my brain to help get a solution to the shape of the curve for a proper diverging paraline.

JSS
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Old 10th September 2012, 09:31 PM   #308
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Quote:
Originally Posted by maxmercy View Post
By moving the focus closer to the vertex, you no longer have reflections that are all vertical in the graph (or horizontal on a real paraline), if I am thinking correctly. In order to increase vertical directivity, we need a shape that will have all reflections in the same direction like the graph, but with a 'spherical' delay.
Thank you. I see what you're getting at. It's not quite the same situation as with light, though. The wavelengths relative to the reflector size are too different. The angles of incidence and reflection are less important than the distance from the source to the mouth. ... But as you pointed out earlier, in the case of a focussed parabolic reflector, all path lengths are equal. My head hurts... I think I've forgotten more trig than I ever learned.

I suspect that, although Nate asked to increase vertical directivity, he really wanted to decrease vertical directivity. That is, increase vertical dispersion.

That leads to another thought... To increase vertical dispersion, the wavefront that develops at the mouth of the line has to be curved. The wave has to leave the centre of the mouth earlier than it leaves the ends. This may make the straight line mouth shape less than optimum to generate a curved wave. Maybe the mouth should project outwards in a curve, looking like a section of the original radial horn, giving a shape like "pursed lips".
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Old 10th September 2012, 09:53 PM   #309
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Quote:
Originally Posted by Don Hills View Post
I suspect that, although Nate asked to increase vertical directivity, he really wanted to decrease vertical directivity. That is, increase vertical dispersion.
Doh! That's what I meant to say
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Old 10th September 2012, 09:54 PM   #310
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Don, now we are starting to talk about other shapes that I would think would conflict with the premise of the Paraline in that it is a flat construction using diffraction effects from the the slit to the matching waveguide. I was thinking what you are now talking about here and what if the shape of the internal intermediate shape was not flat but more like a football shape and giving a radial wavefront at the slot. The surrounding shape would have to also follow the let's just call it for now an elliptical form with a thin outer shell that would keep with the thin cross sectional rules of the Paraline. Things are getting much more difficult for the amateur to produce this type of device, but if we are only talking hypothetical's here I can see many improvements on the original concept. If you were going to this complexity then I also don't see any reason that the cross sectional dimensions could not follow an exponential expansion rate in this section before joining the conic waveguide which is being used to blend multiple devices.
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