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Old 6th September 2012, 02:03 AM   #271
winslow is offline winslow  United States
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Bill, it doesn't have to be. As long as the path lengths to the exit are all the same, you could make it any other shape. Which, geometrically speaking there aren't too many other shapes that could do this...the eye or a couple of circles.
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Old 6th September 2012, 02:55 AM   #272
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The shape of each half of the eye is a parabola with focus at the driver center. It's the only shape I know of that can take a spherical wave and make it a planar wave, all in phase, with a single specular reflection.

This now makes PERFECT sense.

Here is a diagram:

Click the image to open in full size.

All the line segments that coincide are equal in pathlength.

The paraline exit is a line horiontal through the focus, and the focus is where the driver inserts. Very elegant.

JSS
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Old 6th September 2012, 03:01 AM   #273
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Does the path length always have to be the same? If we're looking to build arrayable modules like the VTC stuff I could see keeping a super narrow vertical window, but for home use I want a bit more directivity than that. There was talk earlier in the thread about "pinching" the center of the eye in effect creating a time delay and increasing the vertical dispersion. Conversely you could widen the center and get a pattern that actually narrows. I think I can "see" how this works in my head, but can't really explain it. Or am I just making stuff up.....I built my 'lines based on Bateman's spreadsheet for 40deg vertical dispersion. I'll see if I can't get it rigged up on my rotary table and get some polars.
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Old 6th September 2012, 01:05 PM   #274
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Yes.

If you make the sides of the eye a hyperbola with one focus being the driver position, the reflection from the eye will be a 'circular' wave with curvature equal to how far away the other hyperbolic focus is.

If you make the sides of the eye elliptical, with the long side of the eye the minor axis through a focus, and the driver at the focus, the reflection off of the eye will converge in phase (circular wavefront) to the other focus of the ellipse, making a converging wavefront.

With a few equations, you can customize one of these things to focus, spread, or project straight away.

The pretty cool part of the diverging/converging wavefront would be that it is already power tapered, so it will act like a CBT, and not have any vertical lobing.

The coolest thing about this device is the fact that it constrains the sound within such a small chamber that it can be treated almost optically/specularly, and use simple conic sections to do what you need.

The problems with this are driver size/driver opening size. You can have pathlength differences significant enough to cause cancellation if your driver opening starts to get large compared to the max wavelength possible constrained by the plate thicknesses. I would suggest using smaller driver openings if possible to avoid this, provided it doesn't cause other problems. Of course a point source and paper-thin plates would be ideal, but not possible.


JSS

Last edited by maxmercy; 6th September 2012 at 01:10 PM.
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Old 6th September 2012, 03:59 PM   #275
stinems is offline stinems  United States
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Busted out the rusty geometry skills and made the attached spreadsheet. Not sure if it's right but here is my line of reasoning:

Let "theta" be the angle between the reference axis (the paraline "slit") and the rays like A1, B1, C1 etc. Lets use the variable "H" for the length of rays like A1, B1, C1 etc coming immediately out of the compression driver. Lets use the variable "X" for the length of the lines returning to the centerline after bending around the eye (A2, B2, C2 etc). Finally, lets call L half the width of the narrow dimension of the eye (you pick it to be whatever size you want).

First of all, we want to set H+X=2L because we want the wavefront to arive at the front slit all at the same time or distance.

We also know that Hsin (theta)=X or after some algebra, H=X/sin(theta). This is because, with driver at the origin, the wave propagates radially (the H ray, or hypotenuse), bends around the eye, and heads towards, and normal to, the center slit (the X path). This creates a sort of "right triangle" geometry.

Substituting the latter into the first and manipulating algebraically yields X(1+1/sin(theta))=2L.

Finally, after some more manipulation, X=2L/(1+(1/sin(theta))), where X is the distance from the curve normal to the reference axis (like A2, B2, C2 etc).

To get the corresponding cartesian coordinate, take X/tan(theta)=Y.

There is probably a way to do it totally in a cartesian system without messing with the polar calcs (ie, no trig functions), but I'll leave that to someone else. And you might find that it is really a hyperbola, but I just constrained the curve to what we know & want.

All of this assumes the "vanilla" version of the eye with a 2:1 aspect ratio. No phasing/focusing as a few of you have discussed. For that you're on your own.

By all means, correct me if my math is wrong.

Cheers,
Sam
Attached Files
File Type: zip paraline.zip (9.6 KB, 85 views)

Last edited by stinems; 6th September 2012 at 04:18 PM.
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Old 6th September 2012, 05:56 PM   #276
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Quote:
Originally Posted by maxmercy View Post
The problems with this are driver size/driver opening size. You can have pathlength differences significant enough to cause cancellation if your driver opening starts to get large compared to the max wavelength possible constrained by the plate thicknesses. I would suggest using smaller driver openings if possible to avoid this, provided it doesn't cause other problems. Of course a point source and paper-thin plates would be ideal, but not possible.

JSS
B&C sells compression drivers with 0.5" and 0.7" exits.

hmmm...


Here's a review from Voice Coil : http://read.uberflip.com/i/34611/13#

Jason Winslow has some of these I believe

Last edited by Patrick Bateman; 6th September 2012 at 05:59 PM.
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Old 6th September 2012, 06:22 PM   #277
winslow is offline winslow  United States
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I do have a single DE5. I wanted a DE7, but they were not avaible in the US at the time.

I have offered to let a few people borrow it for some Paraline experiements.

Nice little driver.
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Old 6th September 2012, 10:19 PM   #278
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Default Use a Paraline instead of a 2" driver

First of all I want to thank Tom Danley for his generousity with the DIY crowd. Thanks a lot to you other guys explaining (and using ages to produce drawings) to help us understand the inner workings of yet another clever device from TD.

Before I plunge into a full Synergy project, I would like to play with the Paraline device. And looking in my basement I could not miss two huge horns looking for a decent driver. My JBL 2360 horn consists of two parts. The throatpiece has a 2" entry. The main horn has an entry of 18x252 mm and the mouth is 80x80 cm with 90x50 coverage. What if I substituted the throatpiece for a Paraline?

Having looked around for a 2" driver, my main candidates has been JBL 2452/2446/Radian 950 with Truextent or a BMS coax. But with some patience, a lot of tinkering, measuring and listening, maybe I could end up with a Paraline that has both a more extended low and high frequency than my 2" options.

With any 2" I would need a supertweeter wich are difficult to integrate. With a Paraline there are lots of options. I really liked Patrick Batemans design with a mid/midwoofer behind the tweeter.
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Old 6th September 2012, 10:48 PM   #279
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Quote:
Originally Posted by maxmercy View Post
The problems with this are driver size/driver opening size. You can have pathlength differences significant enough to cause cancellation if your driver opening starts to get large compared to the max wavelength possible constrained by the plate thicknesses. I would suggest using smaller driver openings if possible to avoid this, provided it doesn't cause other problems. Of course a point source and paper-thin plates would be ideal, but not possible.


JSS
I guess some of this is covered in the Synergy threads, regarding getting the midrange holes small enough. I understand this is helped by using frustums. Because its the midrange holes that present the biggest hypothetical problem?

FLH has loads of hands-on experience with this and his Paraline build uses a curved opening for the midrange that at least looks a bit wide for the wavelengths involved. So I guess you could get away with it. Have to try it myself.

Patrick Batemans idea of using a mid/midwoofer behind the tweeter in post
Square Pegs looks really clever. Having the mid symmetrically around the tweeter, is it possible to use several smaller openings to get the desired area?
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Old 6th September 2012, 11:28 PM   #280
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Patrick or anyone else do you have the information on the .7" and .5" exit B&C drivers? I am not registered on the Voicecoil website and will look to do that later.

Steven
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