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Old 18th April 2013, 03:59 PM   #431
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Quote:
Originally Posted by coctostan View Post
Here is the thread about Paul's new center channel that is a sort of mini-array: A new center channel for the Octagon

Pic: Click the image to open in full size.

I'm thinking a home version of a Danley J2 or J3. It seems those aim to achieve a similar goal.
Danley Jericho has wide directivity; it wouldn't offer the narrow directivity that Paul is looking for.

Danley's designs put phase coherency at a high priority.
And though I'm a big cheerleader for the Paraline technology, they simply cannot be phase coherent at high frequencies. This is because of the distance from the top of the Paraline exit to the bottom of the Paraline exit.

For instance:

Click the image to open in full size.
Let's say you have a Paraline with an exit that's 25cm tall by 1cm wide. And let's say you are seated 300cm from the Paraline. [b]With a Paraline that size, the top of the Paraline will be 1.03cm 'out of sync' with the bottom of the Paraline. If we want to keep all our wavelengths within one quarter of each other, then this Paraline will not be phase-coherent above 8252hz.

Does that make sense?

Basically, the ideal radiator is a point, and as our radiator becomes more and more astigmatic, it's ability to be phase coherent gets lower and lower in frequency.

In the example above, our 'cutoff' where it can no longer be phase coherent will drop every time you add a Paraline. So one Paraline is phase coherent to 8252hz and four Paralines are potentially phase coherent below 2063hz.


And of course I said "potentially", because you have to satisfy a bunch of other requirements first

But, basically you can't get phase coherent with a Paraline above a certain frequency, and that frequency depends on the shape of the Paraline exit.



If you start looking at the maths, you'll notice that this is also a reason that the VTC is curved
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Old 18th April 2013, 04:40 PM   #432
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Oh, if it wasn't clear from my last post, "A" is the height of the radiator, "b" is the distance to the listener on axis, and "c" is the distance to the listener from the top of the device. With a sphere we have the potential to be phase coherent, but the flat radiator can't be phase coherent at all frequencies. (it CAN be phase coherent BELOW a specific frequency.)

Click the image to open in full size.
While a sphere is optimum, it's possible to get phase coherent with a flat diaphragm. The old Quads do that, and IMHO it's one of the reasons they sound so much different (and better) than conventional planars and ribbons. The Quad radiates from a series of rings, as shown above.
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Old 18th April 2013, 04:59 PM   #433
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by Patrick Bateman View Post
Oh, if it wasn't clear from my last post, "A" is the height of the radiator, "b" is the distance to the listener on axis, and "c" is the distance to the listener from the top of the device. With a sphere we have the potential to be phase coherent, but the flat radiator can't be phase coherent at all frequencies. (it CAN be phase coherent BELOW a specific frequency.)

Click the image to open in full size.
While a sphere is optimum, it's possible to get phase coherent with a flat diaphragm. The old Quads do that, and IMHO it's one of the reasons they sound so much different (and better) than conventional planars and ribbons. The Quad radiates from a series of rings, as shown above.
That's what Keele does with his CBT, bent backwards and shaded volume so it performs like part of a sphere.
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Old 18th April 2013, 05:28 PM   #434
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Originally Posted by wesayso View Post
That's what Keele does with his CBT, bent backwards and shaded volume so it performs like part of a sphere.
If anyone reading this thread wants to learn about how the Paraline works, read the CBT papers. As wesayso noted, there's a lot of common ground. (Don Keele is a horn guy going waaaaaaay back, of course, and the CBT is a technology that competes directly with the VTC boxes in the prosound world.)
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Old 18th April 2013, 06:05 PM   #435
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I understand that, but a paraline that is 12.5cm tall should allow for coherent phase below 16khz. I'm not suggesting 4 long paralines.

I guess I've just been trying to find a good creative use for HiFi paralines.

How about reversing the paraline to take a line source and converge it to a point source. Something like a tall, narrow AMT converged to a circular point source exit. I'm trying to visualize what the wavefront would look like. I think it would be inverted spherical but like Danley said you can manipulate the wavefront with different exits. The advantage to putting a paraline in front of a rectangular AMT is that you would get the benefits of the large surface area AMT without the downside of its height and beaming above 8khz. maybe I'm not thinking of it in the right way.
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Old 18th April 2013, 06:18 PM   #436
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Originally Posted by coctostan View Post
I understand that, but a paraline that is 12.5cm tall should allow for coherent phase below 16khz. I'm not suggesting 4 long paralines.
Agreed. I just pointed out the phase problems with the Paraline because I think some people might be wondering why Danley doesn't use them in anything but the Genesis horns. I can't speak for him, but I'm guessing it's because the Layered Combiner can be phase coherent in three dimensions, while the Paraline can only be phase coherent in two. (Because the LC can generate a spherical wavefront, while the Paraline can only generate a flat or curved wavefront.)

Quote:
Originally Posted by coctostan View Post
I guess I've just been trying to find a good creative use for HiFi paralines.

How about reversing the paraline to take a line source and converge it to a point source. Something like a tall, narrow AMT converged to a circular point source exit. I'm trying to visualize what the wavefront would look like. I think it would be inverted spherical but like Danley said you can manipulate the wavefront with different exits. The advantage to putting a paraline in front of a rectangular AMT is that you would get the benefits of the large surface area AMT without the downside of its height and beaming above 8khz. maybe I'm not thinking of it in the right way.
Click the image to open in full size.

I hate to be a downer, but the optimum shape at the entrance is a ring or a point. There really isn't a lot of room for error; if you diverge from the optimum shape by even one inch, you're going to see comb filtering.

Check out the Peavey paper on the 'Quadratic Throat Waveguide'; in the Peavey paper they showed that even something as basic as shaving a fraction of an inch off of the throat reduces distortion.

Again, I don't want to discourage anyone from experimentation

Just suggesting that based on my understanding how the device works, you want a point or a ring at the throat. Even the flat disc-shaped radiation of a conventional compression driver is sub-par, and that's the reason that Danley gets good results with a ring radiator.

It took me a few years before I could comprehend how getting the right shape at the throat of a horn makes a huge difference; it's kind of brain-crushing really. Using the CLF file viewer with the data from danleysoundlabs.com makes a huuuuuge difference in helping me visualize what the wavefronts are doing
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Old 18th April 2013, 06:22 PM   #437
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by Patrick Bateman View Post
Agreed. I just pointed out the phase problems with the Paraline because I think some people might be wondering why Danley doesn't use them in anything but the Genesis horns. I can't speak for him, but I'm guessing it's because the Layered Combiner can be phase coherent in three dimensions, while the Paraline can only be phase coherent in two. (Because the LC can generate a spherical wavefront, while the Paraline can only generate a flat or curved wavefront.)



Click the image to open in full size.

I hate to be a downer, but the optimum shape at the entrance is a ring or a point. There really isn't a lot of room for error; if you diverge from the optimum shape by even one inch, you're going to see comb filtering.

Check out the Peavey paper on the 'Quadratic Throat Waveguide'; in the Peavey paper they showed that even something as basic as shaving a fraction of an inch off of the throat reduces distortion.

Again, I don't want to discourage anyone from experimentation

Just suggesting that based on my understanding how the device works, you want a point or a ring at the throat. Even the flat disc-shaped radiation of a conventional compression driver is sub-par, and that's the reason that Danley gets good results with a ring radiator.

It took me a few years before I could comprehend how getting the right shape at the throat of a horn makes a huge difference; it's kind of brain-crushing really. Using the CLF file viewer with the data from danleysoundlabs.com makes a huuuuuge difference in helping me visualize what the wavefronts are doing
Did you catch the part where he said he wanted to reverse the paraline? The amt would go for the rectangular part and exit at the round shape time aligned.
Reverse horn in that way but fun to think about.

Last edited by wesayso; 18th April 2013 at 06:27 PM.
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Old 18th April 2013, 06:29 PM   #438
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Originally Posted by wesayso View Post
Did you catch the part where he wanted to reverse the paraline? The amt would go for the rectangular part and exit at the round shape time aligned.
Reverse horn in that way but fun to think about.
ahhh, interesting!

When he said that he wanted to reverse a Paraline, I thought that he mean that he wanted a *divergent* Paraline.

And a divergent Paraline still needs a point or a ring at the throat.

But, yeah, the idea of doing a Paraline IN REVERSE is intriguing. Basically start with a rectangular wavefront and compress it into a square throat, and then have that square throat feed a square waveguide.
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Old 18th April 2013, 06:38 PM   #439
wesayso is offline wesayso  Netherlands
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Originally Posted by Patrick Bateman View Post
ahhh, interesting!

When he said that he wanted to reverse a Paraline, I thought that he mean that he wanted a *divergent* Paraline.

And a divergent Paraline still needs a point or a ring at the throat.

But, yeah, the idea of doing a Paraline IN REVERSE is intriguing. Basically start with a rectangular wavefront and compress it into a square throat, and then have that square throat feed a square waveguide.
And use that as the base of a synergy horn?
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Old 18th April 2013, 07:10 PM   #440
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Originally Posted by wesayso View Post
And use that as the base of a synergy horn?
well, again, I feel like I'm being a wet blanket here...

But if you were to do this, you'd want that shape 'feeding' the horn to be curved.

Click the image to open in full size.

I took this picture of a compression driver cut in half about ten years back, and you can see the curvature of the diaphragm and the phase plug.

Click the image to open in full size.

It's like radians of a circle, you want all of those pie slices to be equidistant from the focal point*



Good news though!

If you sit down and think about this for a bit, you'll notice that it MIGHT be possible to use flat wavefront in a 'reverse paraline'. Basically you would distort the shape of the Paraline so that it takes a flat wavefront and produces a flat exit. This MIGHT be possible, by going the same route that a normal Paraline does to CURVE the wavefront.

Very interesting stuff!

I'm not 100% sure it's possible, but very interesting! You might be able to scale this up for subs or midranges too.
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