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Old 9th August 2012, 06:24 AM   #41
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Thanks HeatMiser, I understand this now.

But then, for Patrick, why does your prototype use a square hole instead of a circle?
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Old 9th August 2012, 06:47 AM   #42
smf is offline smf  United Kingdom
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Quote:
Originally Posted by Don Hills View Post
As described in the patents, the Paraline appears to be a way to generate a plane wavefront for applications requiring a "line source", rather than as an impedance matching device. It's what I would call a waveguide rather than a horn. Then I look at Patrick's Proof Of Concept, and I suspect it works differently. I assume his model has a radially expanding first part fed by the drivers, a circular (rather than eye shaped) slot, and a "circular" (sort of square) exit. I keep visualising it as a diverging conical horn capped with a converging conical horn, but this ignores the "two dimensional" nature.

Looking at the patent, Fig. 14, imagine a second "item 30" connected in place of "item 32".That's what Patrick's model looks like to me. I must be missing something basic. (I know it's not my marbles, every morning I look in my toybox and there they are.)
Help...

Edit:
I wonder... if you built a device like Patrick's, and used multiple HF drivers clustered closely together in the centre, would the output at the exit combine into a virtual point source? Would this be the basis for a "layered combiner"?
Don - It would be interesting to know how Patrick did his proof of concept. For the paraline to approximate a conical horn, the wavefront has to keep expanding radially even through the bends. The eye model seems to do this, and I assume that the area of the exit slot is again the next progression up in size from the surface area of the wavefront while still in the slot immediately prior to the exit. The little plug in the exit also seems to me to have a role to play, and of course that is missing from Patrick's model.

Ah, I've just been back through the thread and noticed that Patrick says that he was 'stacking a paraline on a paraline'. And he describes the phase plug in the Danley paraline as being to avoid phase issues between the different edges of the slit. I'm not sure I follow that given that the point of the design was to ensure that all parts of the wavefront hit the exit at the same time (or to allo wfor timing differences deliberately to control the wavefront shape).

Last edited by smf; 9th August 2012 at 06:56 AM. Reason: Additional comment
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Old 9th August 2012, 06:59 PM   #43
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Quote:
Originally Posted by smf View Post
Don - It would be interesting to know how Patrick did his proof of concept. For the paraline to approximate a conical horn, the wavefront has to keep expanding radially even through the bends. The eye model seems to do this, and I assume that the area of the exit slot is again the next progression up in size from the surface area of the wavefront while still in the slot immediately prior to the exit. The little plug in the exit also seems to me to have a role to play, and of course that is missing from Patrick's model.

Ah, I've just been back through the thread and noticed that Patrick says that he was 'stacking a paraline on a paraline'. And he describes the phase plug in the Danley paraline as being to avoid phase issues between the different edges of the slit. I'm not sure I follow that given that the point of the design was to ensure that all parts of the wavefront hit the exit at the same time (or to allo wfor timing differences deliberately to control the wavefront shape).
In hindsight, I think there are two problems with a square-exit Paraline:
  • A square exit is not ideal, unless the square is very small.

    There are five layers in a Paraline. It's like a sandwich and it goes like this:
    layer 1 - the bottom. Any thickness will do.
    layer 2 - This has the throat of the horn, in the center. Sound radiates radially in here.
    layer 3 - the middle layer 'slices' the horn in half. Due to this, the shape of the middle layer is critical. In my square exit Paraline, I had a middle layer that includes a measure of error, but I basically ignored it because it was close enough. Total proof of concept really.
    layer 4 - this layer is the second half of the conical horn. It connects to the mouth of the horn.
    layer 5 - this is the mouth of the horn. One problem with a square mouth is that high frequency energy from one edge can interfere with high frequency energy from the other edge. For instance, my square Paraline has a mouth of 2.25" square. So high frequency energy could see comb filtering as low as 1500hz. If you download the measurements of the Paraline from VTC's website, you'll notice some comb filtering, but it's way way higher in frequency than that, likely due to the phase plug at the entrance and the exit.
  • Layer 3 of my square Paraline could use a better shape. On page 1 'Nissep' posted a way to make the shape better, and I recommend trying it yourself if you'd like to build one of these. It works. Here's his comment: Square Pegs

The layered combiner in the Jericho horns appears to have a square exit; but I have a hunch that it's not designed to run full-range, like the ones that I'm building are.

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Old 9th August 2012, 07:33 PM   #44
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I really need to get some work done today - so I'll keep this brief.

But last night I stumbled across the solution to a problem which has been vexing me for literally two decades!

Very exciting stuff.

Click the image to open in full size.
The thing that got me into horns, way back in the 90s, was an interview with Richard Clark in Car Audio and Electronics. In that article, Clark talked about how the ideal loudspeaker is a point source that covers 20hz to 20khz. While Clark's car was not perfect, he *did* manage to squeeze about 300hz to 20khz out of a pair of horns with Altec Lansing drivers.

My whole journey down the rabbit hole started back then, and I'm not exaggerating when I say that I've been searching 20 years for something that will get close to that goal of 20hz to 20khz off of one driver.


As I see it, the Synergy horns are about as close as we can get right now. While there are nine drivers in the horn, it 'looks' like one driver due to the way the wavefront expands in the horn.

Second best to a Synergy horn is a plain ol' fullrange, but the problem with a fullrange is that it can't do 20hz to 20khz with any real authority. (IE it don't get loud.)

Coaxials have intrigued me also, but I *really* like it loud, and I've never heard a coaxial tweeter that can do real SPL.

Last night I came up with something new:

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
What you're looking at is a Paraline, but with a 'Smiley' shaped exit. I actually invented this to solve a completely different problem, and then it occured to me that the 'Smiley' exit allows you to stack the woofer and the tweeter face to face!

This puts the woofer and the tweeter within [b]one quarter wavelength[b] at the crossover frequency, a level of coupling that's nearly impossible to do without buying a coaxial.

If you're into Unity or Synergy horns, this solves a whole pile o' problems for those of us that want Synergy horns in the home or car:
  • The Unity and Synergy horns use about nine drivers to get the job done. That's great if you have the space for a speaker that's the size of refrigerator, but I'm really sick of big boxes. The 'Smiley' Paraline has just two drivers.
  • The on-axis SPL of a horn is related to it's directivity index. To put it simply, narrow directivity horns are louder on axis than wide directivity horns. And the Paraline is a VERY narrow directivity horn. Therefore, my 'Smiley' Paraline gets exceptionally loud.
  • Clamping the drivers together makes a surprising reduction in distortion.
  • The 'Smiley' Paraline enables the use of a lot more midranges. For instance, I think it should be possible to go up to an 8" midrange, or perhaps even a 10" midrange. This wasn't possible in a Unity or Synergy horn, as the use of large midranges would drive the xover point down to 500hz or so, due to the very specific spacing requirements of the crossover filters. (The VTC Paraline gets away with the use of 8" and 10" drivers by using a digital delay.)
  • If you peruse the main Unity horn thread on this forum, you'll see that people have literally spent *years* trying to find a suitable midrange that will meet up with the tweeter. Basically there are only a handful of drivers that will play high enough. If you don't get everything perfect, you get a gap between the midrange and the tweeter, right in a frequency band where problems are very noticeable - about 1500hz. My 'smiley' shaped Paraline gets the midrange and the tweeter very very very close together. I believe that part of the reason that there is a gap in a conventional Unity horn is due to the spacing from side-to-side of the midranges. The 'Smiley' Paraline solves that.

The last advantage of the 'Smiley' Paraline is the whole reason I built it in the first place. You can bend the wavefront.

Click the image to open in full size.
In the Danley Paraline that's used in the Genesis horn, Danley bends the wavefront via a delay inside of the Paraline. But it occurred to me that you could also bend the wavefront by bending the whole device! (Picture how plywood is bent like the pic above.)

So my original goal with bending the Paraline was simply to get a curved wavefront, but then it occurred to me that I could stack the drivers.

Click the image to open in full size.
My Smiley Paraline will be mated with a conical horn, a la the Image Dynamics HLCDs.

Smiley - YouTube

Here's a video of the Smiley Paraline. It's pretty rough - there's just one cap on the compression driver. But you get the general idea - full range sound off of a 15cm long (566hz) conical horn folded into a Paraline.

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Old 10th August 2012, 04:02 AM   #45
smf is offline smf  United Kingdom
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Patrick - thanks for sharing that. Interesting! How did you make sure that the wave fronts from the tweeter and midrange both hit the smiley slot at the same time, or is the delay between them part of your desire to bend the wavefront (although I'd assumed that that was what the smile was for)? I've thought of a couple of other ways to do the same thing - I'll try to draw them up.
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Old 10th August 2012, 04:50 AM   #46
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I think I see what Patrick's done - the smiley mouth isn't to make the wavefront curved, it's so that he can mount a second driver where the slot would have otherwise been. Remember the "piece of string" video? Patrick has pulled the drivers "off centre". This would result in unequal path lengths in the horn, but he has also pulled the slot "off centre" to equalise the path lengths again. Imagine the horn with a lot of strings tied between the driver opening and the corresponding parts of the slot - if you pull the driver one way, the slot must move the other way to keep all the strings the same length.

(I assume that the tweeter extends through the "top" plate so that the sound from the driver enters the horn in the "rear" chamber directly opposite the midrange.)
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Old 10th August 2012, 05:42 AM   #47
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Quote:
Originally Posted by Don Hills View Post
I think I see what Patrick's done - the smiley mouth isn't to make the wavefront curved, it's so that he can mount a second driver where the slot would have otherwise been. Remember the "piece of string" video? Patrick has pulled the drivers "off centre". This would result in unequal path lengths in the horn, but he has also pulled the slot "off centre" to equalise the path lengths again. Imagine the horn with a lot of strings tied between the driver opening and the corresponding parts of the slot - if you pull the driver one way, the slot must move the other way to keep all the strings the same length.

(I assume that the tweeter extends through the "top" plate so that the sound from the driver enters the horn in the "rear" chamber directly opposite the midrange.)
That's correct.

Here's what you do:

1. Take the eye-shaped configuration that's in the Paraline patent
2. Move the ENTRANCE off center by one inch
3. Move the EXIT off center by one inch
4. As long as the the change is balanced, path lengths stay equal. For instance, move the horn exit to the left by 1" and the horn entrance to the right by 1". Path length is same.
5. As Don noted, the tweeter fires THROUGH the center plate.

Click the image to open in full size.
The eye shape ends up looking a little droopy, bcuz the widest point of the Paraline (aka A1) moves along with the entrance.
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Old 10th August 2012, 12:37 PM   #48
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To anyone trying this: Remember to keep the space at the junction of the driver(s) with the horn as small as possible. If the space is significantly larger than the width of the eye cavity, it will form a throat chamber which will act as a low pass filter. The ideal configuration for a tweeter/midrange pair would be a "naked" dome tweeter / compression driver with the dome protruding into the cavity formed by the cone of the midrange driver.

I do worry a little about possible interaction between the two drivers placed so close together, with the horn load increasing the interaction.
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Old 10th August 2012, 03:08 PM   #49
smf is offline smf  United Kingdom
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Ah! My response was lost. Never mind. Don/Patrick - thanks. The offset wasn't troubling me, but you've cleared up that the tweeter was protruding through into the back layer. I should have realised.

Patrick - out of interest, this is for your car?

NB: I'm more interested in using the paraline as a way to make horns shorter (in order to use compression drivers not cones). I live in Hong Kong and don't have much space in my sitting room (and my wife won't allow the speakers too far into the room anyway ...) I actually took a day off work today to go to the HK Hifi show. So, many of the rooms had 'big' speakers out in the middle of the rooms - it made you wonder whether they've actually been to any of the typical listening spaces that we have to live in here. I can't say that there was a huge amount that I was interested in, although I did buy quite a few records and a small tube amp ...
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Old 10th August 2012, 07:12 PM   #50
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I think the correct descriptor for this device is simple- it's a method for making phaseplugs with various wavefronts.

Pretty slick stuff but no getting around the challenges of that 180 degree turn in the real world. It could be mitigated by softening the transition and using some damping a la geddes, but then you're getting into a more complex construction and deeper assembly. But 2" of depth added to allow this transition to happen in a smooth fashion may be a very worthwhile tradeoff for sound quality apps.
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