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Old 1st March 2014, 01:35 AM   #681
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Quote:
Originally Posted by Stan_R View Post
Thanks Patrick

There are a few changes I am going to make but your advice is right on. I have been trying to decide on a direction to take and your experience is invaluable.

I am going to sign off for the weekend.

Thanks again

Stan
Thanks! Art and Earl know more about these older boxes than I do though. I've only been at this for a bit over a decade.
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Old 1st March 2014, 01:55 AM   #682
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Stan,
That horn was not created to produce a diffraction effect, that was just the way that was chosen to load the driver at what looks like 50% of the cone area. It could be done with a circular opening but the way they designed the horn it was just simpler to just cut the cone area in half by a straight edge. I would think at high excursion that the surround would hit the back of that plywood area in front of the cone if there was not some sort of spacer in front of the bass speaker.
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Old 1st March 2014, 07:44 PM   #683
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Originally Posted by Kindhornman View Post
I would think at high excursion that the surround would hit the back of that plywood area in front of the cone if there was not some sort of spacer in front of the bass speaker.
The EV15BW and 15BWK used in the Centurion were designed for horn loading and fitted with a gasket deep enough for the expected excursion which was probably less than 3.3 mm, about 1/8" one way.

Other speakers may need an additional gasket.

I would agree with Patrick's suggestion regarding replacing the mid and HF with a coax, the original folded PA mid horn is more appropriate for carnival midway rides than home use, though the T-35 tweeters are not bad, if the diaphragm is properly shimmed and centered.

Those changes would require a crossover designed for the components, and delay of the mid/high to the LF horn path time of flight would be an improvement.
Attached Images
File Type: png Centurion Drivers.png (334.3 KB, 610 views)
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Old 1st March 2014, 08:00 PM   #684
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weltersys,
I brought up the spacer because I have had to do that on a large double 18" driven horn with high excursion JBL drivers. The spacer were substantial in that instance but they were for PA use and were driven by some high powered Crest class D amplifiers. Let's just say they made massive amounts of bass.
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Old 3rd March 2014, 04:56 PM   #685
Stan_R is offline Stan_R  United States
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Thanks everyone.

I didn't mean to hijack your thread but as I said, my Centurion is a mess in oh so many ways. Not only was it poorly constructed, (sorry dad) but as you guys have pointed out, there are some basic design flaws with the Centurion.

I started asking about running a coax through a folded horn but quickly realized just how bad an idea that was, but I am still not convinced that a 16" Paraline isn't a good way to couple a 16Ē driver to a horn. Looking at the picture in #673 I donít know where the throat of the horn is. Is it the whole semi-circular cut out or is it the rectangle formed by the straight edge as it is projected to the other side of the horn?

The reason I finally decided to jump into this thread in is it occurs to me that a Paraline will deliver 100% of the sonic energy efficiently to the throat of the horn, which is at the apex of the horn. In comparison, the semi-circular throat seems like it will deliver a mushy sound at best.

A little bit more about myself: I am an engineer by training and temperament. I am very good at visualizing things in 3D. I understand the physics behind optical systems and how lenses work. I usually donít plan out the things I build because I work out the plan in my head, although I do make sketches to work out dimensions. There was a decade long section of my career that I designed circuitry, test fixtures, tooling, and airplane parts in CAD.

Saying that is to support my contention that a Paraline is good method to couple my woofer to my horn. I am going to use a Great Plains Audio 515-8LF and I donít think I will need a spacer as they are designed for rear mount.

Patrick, you have said that you have been doing this for only ten years. Well, I have been thinking of doing this for only ten months, but I have so much confidence in what I see that I am going build a Paraline to couple my woofer to my horn.

The 515-8LF is an inch bigger in diameter than the Jensen that my dad used so I have to replace the plywood anyway, and while I am at it I will turn the LF horn into a properly shaped horn, not one with myriad sharp edges, constrictions, and contractions.

I realize I need my own thread for this rebuild but I am wondering if you guys are interested in seeing what I come up with. After all, out of the mouths of babes frequently comes wisdom, and if nothing else, I am certainly a newbie.

Stan
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Old 3rd March 2014, 05:00 PM   #686
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It won't work. Sorry.
Check out Art's comments and my comments.
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Old 3rd March 2014, 06:27 PM   #687
Stan_R is offline Stan_R  United States
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OK Thanks for your comments and time.
Stan
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Old 13th May 2014, 10:10 PM   #688
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Click the image to open in full size.

In Houston, there's a sculpture which acts a bit like the Paraline does. Here's how the sculpture works:

1) You sit down and say something
2) The sound from your voice radiates spherically
3) A segment of that sphere is collected and reflected by the marble parabolic reflector
4) The sound is radiated to a parabolic reflector about 20 feet away
5) The same process happens in reverse
6) And the person at the opposite sculpture can hear you as if you were standing right there.

It's a trippy effect; if you move your head two inches the effect goes away, but line it right up and it sounds like they're right in front of you.


Click the image to open in full size.

It occured to me that you could make a three dimensional curved array using a satellite dish. They're easy to find; on my local CL there's a few dozen for sale. As cheap as $10.

Might be an interesting project, particularly for situations where you don't want to bug people in the room, or your neighbors. For instance I work in front of a computer all day, and I like to listen to podcasts. Sometimes I won't listen to certain recordings because I don't want the kids to hear them. (cough cough 'the Opie and Anthony show'). A converging array will be loud at one point, and quiet everywhere else (due to comb filtering.)

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Old 8th July 2014, 09:11 AM   #689
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I have been thinking about the paraline for a bit, wondering if it would make it possible to somehow make a domestically friendly line array speaker without going floor-to-ceiling.

One thing that struck me is that although the path lengths for in the "standard" paraline that creates a flat wavefront are equal, the output along the line is not. Perhaps that is a good thing - perhaps not in all cases. But it seems to me that it would be interesting to have a device with equal output along the paraline along with a flat wavefront.

Here is a standard paraline (one quarter of it anyway), split into four 22.5 degree slices:

Click the image to open in full size.

You can see how when you fold the lines back, you get the same path lengths for each segment.

However, each slice of the pie gets a different horn profile. This is easier to see if we mirror the "folded back" sections:

Click the image to open in full size.

Different lengths of "expanding (conical?) and tube-like" expansions for each section.

I am wondering if this could be one of the reasons for the uneven response seen by people who have tried building these.

So I tried to draw a variant that would have equal expansion from the throat to the mouth. Through trial and error it seems like the only way to do this, is to make the mouth smaller, using only half of the area available radiating away from the driver. In the example below Iīm using three slices with 12% angle. You can see how the angle continues as that section is reflected back towards the line opening.

Click the image to open in full size.

Hereīs how the first two layers would look like:
Click the image to open in full size.

Third layer added:
Click the image to open in full size.

Fourth layer added:
Click the image to open in full size.

Final layer added:
Click the image to open in full size.

Now, I didnīt place any reflector or anything there yet, but this will have to do for illustration.

Anybody care to give critical but friendly feedback on these thoughts?
Attached Images
File Type: png paraline1.png (95.2 KB, 350 views)
File Type: png paraline2.png (94.5 KB, 343 views)
File Type: png paraline3.png (83.7 KB, 344 views)
File Type: png paraline4.png (117.4 KB, 345 views)
File Type: png paraline5.png (84.9 KB, 342 views)
File Type: png paraline6.png (107.7 KB, 341 views)
File Type: png paraline7.png (80.4 KB, 344 views)
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Old 8th July 2014, 09:46 AM   #690
Nissep is offline Nissep  Sweden
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Have you seen this movie?

https://m.youtube.com/watch?v=b8cX5Xs_vZg

It explains how to make the paraline have different waveshape in the opening.

If you have access to a 3d printer it should be an easy fabrication if you want to test your theories.
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