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Old 9th July 2007, 07:20 AM   #121
Hennie is offline Hennie  South Africa
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Quote:
Originally posted by lovechild


I found the 18Sound XT1086 'Constant Coverage HF Horn' mentioned here and there, and the measurements look great, but how does it perform in reality...

Many posts on the net refer to the XT1086 horn as a Geddes type waveguide, but in reality it still has a diffraction slot.
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Old 9th July 2007, 09:33 AM   #122
Giarsun is offline Giarsun  France
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Quote:
Originally posted by Hennie


Many posts on the net refer to the XT1086 horn as a Geddes type waveguide, but in reality it still has a diffraction slot.
This is not obvious from the drawings on the PDF file.

Where is the diffraction slot located ?
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Old 9th July 2007, 10:31 AM   #123
gedlee is offline gedlee  United States
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Quote:
Originally posted by lovechild
Hi,

I'm wondering if there is any waveguide/horn available (for diy), that would come close to the Gedlee OS waveguide.

I found the 18Sound XT1086 'Constant Coverage HF Horn' mentioned here and there, and the measurements look great, but how does it perform in reality...

These measurements do look great - a bit too good perhaps. I can never seem to get things quite that good myself - makes me wonder. In the past I have found 18-Sound to be a bit optimistic in their data sheets compared to actually measurments of their stuff.

Bottom line here is that I didn't design this waveguide, and I didn't take the measurements so I can't really say if they got it right or not. I can say that an elliptical waveguide is not as easy to do as an axisymmetric one and how its done is a big factor. I've done these kinds of designs in the past, but I have never told anyone HOW I do it, so it remains to be seen if this waveguide works as well as claimed.

I will say that it looks like it would work a lot better than about 90% of what I've seen out there.

The throat is obscured, so its hard to tell exactly whats going on there.
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Old 9th July 2007, 12:23 PM   #124
Hennie is offline Hennie  South Africa
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Quote:
Originally posted by Giarsun


This is not obvious from the drawings on the PDF file.

Where is the diffraction slot located ?
It is elliptical in shape and closer to the compression driver mounting interface than usual. Yes, it is not apparent from drawings or most photos.

I have not seen the horn personally, but someone whose judgement I trust has inspected it at the local 18S distributor.

I have seen an image on the net which does show up the diffraction device (for lack of a better term since it is elliptical), but that specific image does not show up in a Google image search.

Here is a thread with some discussion:

http://www.htguide.com/forum/showthread.php4?t=20386
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Old 9th July 2007, 12:37 PM   #125
Giarsun is offline Giarsun  France
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Thank for this interesting link on Eighteen Sound horns.

Maybe this is the XT 1086 pic you saw ?

http://lscon.tripod.com/xt1086/index.album/horn?i=1
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Old 9th July 2007, 12:38 PM   #126
-CGL- is offline -CGL-  Finland
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http://lscon.tripod.com/xt1086/

Those measurements aren´t "tuned". There´s a picture of the "diffraction-slot" too.
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Old 9th July 2007, 12:55 PM   #127
Hennie is offline Hennie  South Africa
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Quote:
Originally posted by Giarsun


Maybe this is the XT 1086 pic you saw ?

http://lscon.tripod.com/xt1086/index.album/horn?i=1
Yes, that's it. Still a bit difficult to interpret exactly what is going on there, but somebody who has more experience with diffraction horns saw it in the flesh and judged it to be a diffraction horn, however with a smooth profile from the diffraction aperture onwards.
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Old 9th July 2007, 05:47 PM   #128
Jazr is offline Jazr  United States
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Default Earl's Waveguides

Earl,
I'm interested in your 1" waveguides. Are they designed for a specific driver like the B&C? You mentioned before that the throat angle must match the exit angle of the driver which was 6.5 degrees on the B&C. I have some interest in BMS, Radian or TAD drivers. Do you know of any other drivers that are an exact match to your waveguide? Do you have available any polar plots, csd or response for these guides mated with your choice of driver?
Thanks,
Randy
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Old 9th July 2007, 07:04 PM   #129
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The XT1086 employs a diffraction device at the throat, full stop. It is a weird elyptical device and potentially a lot cleaner in execution than something like a manta-ray but I felt a little let down when I drove 80kM in traffic one day to investigate after all the hype.

As to how benign the diffraction would be (they apply liberal "FEA" to their marketing literature, much akin to JBL) I have no Idea, but I decided to CNC-turn an OS waveguide and didn't really miss the XT (is cheaper though and excellent for the money compared to many competing products).
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Old 9th July 2007, 07:56 PM   #130
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Quote:
Originally posted by lovechild
Hi,

I'm wondering if there is any waveguide/horn available (for diy), that would come close to the Gedlee OS waveguide.

I found the 18Sound XT1086 'Constant Coverage HF Horn' mentioned here and there, and the measurements look great, but how does it perform in reality...

Also the Monacor Wg-300 it supposed to work quite well with several dome tweeters, but it is rather small so it only works above 2kHz.

best,
LC

I've been wondering the same thing myself for some time. What I've ended up using for my application (mated to a 12) is this: http://www.partsexpress.com/pe/showd...number=270-312 In order to use mine with a bolt on B&C DE200 I've cut off the screw on part and attached a couple rings of 1/4" masonite on the back to mount the driver on. The driver exit butts right up to the entrance of the horn, but the entrance is a little big. Here are some pics of the back:

Click the image to open in full size.

Click the image to open in full size.

and the entrance:

Click the image to open in full size.

Click the image to open in full size.

I've taken some measurements and it does show some odd behavior above 12k not present with the same driver on other horns, but I don't know the exact origins of this- I'll be experimenting in the next few weeks to see if I can narrow down the source. Also, I lopped off 1.5 inches from one edge to cut that much off of the center to center spacing with the 12:

Click the image to open in full size.

As far as I can see, this waveguide seems to be about the best option for a DIYer who can't fork out $500 for a pair of OS waveguides or who doesn't have the machinery or skills to make one. And at the current price of $8.88, one can afford to get a few spares to mess around with!

I don't have access to my previous measurements right now, but I'll be taking more soon and I'll try to get them up here everyone. What I can tell you now is that below 10k, the polar behavior is as such: at about 1.5k it has a 90 deg BW, below that it loses control. From 2-3k there is the typical slight dip in the BW to about 60 deg, at 3k it is back to about 90 degrees and from there up to 10k it is smoothly decreasing to about 60 degrees. It really does look similar to the OS waveguide, except that the directivity generally increases slightly as you go up in frequency, meaning the system off-axis responses are a straight downward slope instead of a downward slope that levels off above 1.5k. The FR in general below 10k doesn't have any nasty stuff- I've been able to get where I want to go with about 4 bands of EQ. I don't think you'd want to try that passively though.


Dr. Geddes, do you have any comments on this particular horn?

Also, I'm curious what you have to say about two (not including side of the box) potential sources of diffraction shown in my pictures: the slight mismatch from the exit of the drive to the entrance of the horn and where the bottom of the horn is cutoff resulting in a slight bump at the top of the 12. Either way, when I start taking measurements in the near future I'll be putting clay in to these places to see if it makes any difference.

Another question- if enough people are interested, is there any way to get the OS waveguides produced cheaper? Perhaps something along the lines of making one mold for them and using it to produce many fiberglass replicas? I've tried to do something like this myself by stacking progressively smaller circles of wood on top of each other and then using bondo to smooth it out and a template to try to get the contour right but I don't have the skills or tools to make it symmetric enough.
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