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Old 4th September 2012, 11:54 AM   #211
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Quote:
Originally Posted by bwaslo View Post
Maybe someone can clarify things for me a little here? Just what does this paraline-like thing... **do**??

I've read Tom's patent, and interpreted it as providing a way to take one or more plane wave sources and transform them into a line source. But in PB's post (#203), it appears a planewave source or a dome drives a small opening, the pressure expands out... then compresses again to an area about the same size as it entered, then exits??

What is the goal here?
I'm with you, as of this point, I think it's a very innovative way to convert a point source to a line source.
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Old 4th September 2012, 05:40 PM   #212
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It took way longer than I'd like to admit, but I made an 'evolution' of the Paraline. This 'evolution' allows the device to be mounted ninety degrees off-axis.

Click the image to open in full size.

In particular, it's good for cars. You can have it fire UP into the dash, then bend the wave ninety degrees the other way, so it ends up firing forward.

If you look at the Danley Paraline, it might seem like one could simply fire the Paraline straight up, but this won't work. The wavefront from one side of the Paraline would lag the other side of the Paraline by about 2-4 centimeters. That may not sound like a big difference, but it would basically nuke all output above 10khz.

My 'evolution' of the Paraline adjusts the pathlengths, so that the output at the mouth is still in phase, even though the Paraline is on it's side.

Besides being useful in cars, there are some other uses:

#1 - you could velcro this right onto something flat. For instance, place it UNDER a flat screen tv. The flat surface will extend the horn mouth.

#2 - In a car, you could not only put these under the dash, you could put them right ON the glass. The surface is perfectly flat, so the entire windshield of the car could extend the horn curve. Personally, I'm really curious how this would sound because the idea of having a horn that's the size of an entire car windshield sounds pretty exciting Also, glass is an excellent material for a horn, because it's stiff and it's strong.

details here:

DIYMA Car Audio Forum - View Single Post - Biggs^H^H Poppa


construction pics coming soon.
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Old 4th September 2012, 05:42 PM   #213
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forgot to mention - the weird purple and yellow checkerboard is just there to measure the pathlength. The reason that the thing took so long is that I had to adjust the entrance, exit, and horn mouth centimeter by centimeter until everything lined up. The pathlengths are identical from compression driver exit all the way to the mouth.
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Old 4th September 2012, 07:30 PM   #214
SunRa is offline SunRa  Romania
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This looks great you already got two novel foldings for this stuff!

Sorry for insisting, but I can't wrap my head around what's the relation between the length of the paraline path and the cutoff frequency. I mean, suppose if I have a midrange in a paraline capable of output down to 400hz, how do I calculate the paraline to achieve this output?

I've looked in Danley's patent, but that's focused on getting a line-source.

Thanks!
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Old 4th September 2012, 07:50 PM   #215
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Quote:
Originally Posted by SunRa View Post
This looks great you already got two novel foldings for this stuff!

Sorry for insisting, but I can't wrap my head around what's the relation between the length of the paraline path and the cutoff frequency. I mean, suppose if I have a midrange in a paraline capable of output down to 400hz, how do I calculate the paraline to achieve this output?

I've looked in Danley's patent, but that's focused on getting a line-source.

Thanks!
Danley elaborates on this question in the eighth post on this thread:

Mid cone driver slots and holes

A lightbulb went off over my head when I read his comments, as I'd messed around with bending waves for years. Over the years I'd invested gobs of time building some gorgeous oblate spheroidal waveguides that I'd bent around a ninety degree curve. But they didn't work at all. (That's the reason I haven't posted them - my attempts at bending sound didn't work.)

The reason that my 'bent' waveguides didn't work is very simple. The pathlengths weren't equal.

Click the image to open in full size.

For instance, a lot of people have made transmission lines using PVC. And these gorgeous, gentle gradual bends look great. But they don't work. The reason they don't work is that the pathlength on the outside of the curve is longer than the pathlength on the inside of the curve.

Click the image to open in full size.
That's why the Paraline needs these ultra-abrupt bends. If you look at the device, it looks like it would work horribly. In audio we're simply not accustomed to devices which bend waves so violently. But these ultra-short bends actually work better, because they keep the pathlengths equal. Well, technically, the inside and the outside of the bend is different in length, but the difference is much much less than you'd get with a conventional bend. Basically if you want to bend sound you want the inside and outside of the curve to be as close as humanly possible. The shortest distance between two points is a straight line, which is why we use reflectors in the Paraline bends, not curves.

Bruce Edgar figured this out thirty years ago, and there's a Speaker Builder article on Volvotreter's page which covers the same subject. (Thanks to Jason Winslow for the tip)




To give you an idea of just how tight our tolerances are, our margin of error is just 0.85cm at 10khz. Once the pathlength differences start to exceed 0.85cm, we start to get comb filtering. At 20khz, the margin of error is 0.425cm.

Click the image to open in full size.
Click the image to open in full size.
So PVC pipe is wildly inappropriate, but a flat disc works very nicely. And a Paraline is simply a disc-shaped horn that's been folded. A bit like a Smith horn, but a full 360 degrees instead of 135, and much shorter in height.

Last edited by Patrick Bateman; 4th September 2012 at 07:54 PM.
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Old 4th September 2012, 07:55 PM   #216
JLH is offline JLH  United States
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Quote:
Originally Posted by SunRa View Post
This looks great you already got two novel foldings for this stuff!

Sorry for insisting, but I can't wrap my head around what's the relation between the length of the paraline path and the cutoff frequency. I mean, suppose if I have a midrange in a paraline capable of output down to 400hz, how do I calculate the paraline to achieve this output?

I've looked in Danley's patent, but that's focused on getting a line-source.

Thanks!
The cutoff frequency is determined the same as it is for all horns. Its area change across a defined distance. The effective flare rate is from the tap in point over the length it takes to double in area. This is covered in the Synergy patent. Let's say the mids tap into a point on the paraline that has an area of 30cm^2. Next find the length it takes for it to expand out to 60cm^2. Fire up Horn Response and plug in 30 for S1, 60 for S2 and whatever your length was to get out to 60cm^2. Have Horn Response calculate what the effective exponential flare rate is and you’re done.
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Old 4th September 2012, 08:02 PM   #217
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haha, I've been so focused on extending the upper frequency response, I totally mis-read SunRa's question. Thanks to John for answering it properly
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Old 4th September 2012, 08:02 PM   #218
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Quote:
Originally Posted by Patrick Bateman View Post
forgot to mention - the weird purple and yellow checkerboard is just there to measure the pathlength. The reason that the thing took so long is that I had to adjust the entrance, exit, and horn mouth centimeter by centimeter until everything lined up. The pathlengths are identical from compression driver exit all the way to the mouth.
Patrick,

Using a mirror left and right (up and down in your picture) set of drivers, adding a rear set of drivers, and delaying the front drivers to the rear, one could achieve a density of sixty four BMS 4552 drivers in about a four foot vertical horn mouth slot.
The mouth slot would be 1.75" wide using 1/4" slots and material, which would limit HF horizontal dispersion to less than 90 degrees, OK for a stadium device requiring that type of driver density to combat HF air attenuation.
That said, a deflector in the center of the slot or slight path length adjustment could probably increase the horizontal dispersion to 90 degree or wider if desired.

I don't know if this arrangement is similar to the "layered combiner" Tom Danley mentioned that uses 64 HF devices, but it looks to be a viable concept.

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Old 4th September 2012, 11:11 PM   #219
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Quote:
Originally Posted by Patrick Bateman View Post
...
For instance, a lot of people have made transmission lines using PVC. And these gorgeous, gentle gradual bends look great. But they don't work. The reason they don't work is that the pathlength on the outside of the curve is longer than the pathlength on the inside of the curve. ...
I don't think that's quite right. The difference between the inside and outside path lengths is similar regardless of whether the bend is abrupt (right angled) or curved. I think the real reason they didn't work is that they failed to keep the difference in path lengths small enough relative to the wavelength. (Duct not narrow enough for the wavelength.) The difference in path length for a "right angled" (sharp cornered) 90 degree bend is twice the width / diameter. For a curved 90 degree bend, somewhat less. For a Paraline with a 1/4" wide duct, that's 1/2". The Paraline patent recommends keeping the path length difference for each 90 degrees of bend to less than 1/3 of a wavelength. That implies a wavelength no shorter than 1.5 inches (frequency no greater than 9 KHz).
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Old 4th September 2012, 11:17 PM   #220
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Don Hills,
I think that you have nailed the problem that I see with the paraline design in general. Trying to use a to wide bandwidth with a single device such as a compression driver. Just as in any other horn design we have a limitation in the upper frequency output and the cutoff frequency of the device. If the paraline is designed to match the expansion rate for a low cutoff frequency we are going to be band limiting the upper frequencies. It will become a band pass filter at the higher frequencies, no matter the way it is folded, curved corners or not.
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