Compression Driver Adapter Phase plug position - diyAudio
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Old 30th September 2012, 01:46 AM   #1
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Default Compression Driver Adapter Phase plug position

I want to make a adapter to couple an inexpensive compression driver to the dayton JBL waveguide clone/Selenium ADM25-25 Horn Adapter combo. The bullet shape phase plug on the CD is quite long. Since I will build the adapter on the lathe I need to select its width. The width will determine how far the phase plug goes into the ADM25/HORN throat. What is best, 1 or 2? or something in between? ? Also the exit of the CD is aprox 3/4 inch while the throat of the horn is 1 inch. Should I taper the adapter from 3/4 to 1 inch or do a fixed 1 inch diameter adapter throat to match the horn's? The drawings are not to scale.
Attached Images
File Type: jpg H6512.jpg (45.8 KB, 123 views)
File Type: jpg ADM25.jpg (41.0 KB, 119 views)
File Type: jpg IMAGE_E9835D1A-83C0-42B3-9A7A-82BA98C14E63.JPG (73.3 KB, 123 views)
File Type: jpg IMAGE_DE5A2622-69E1-44CB-96E4-E3A07A2663C5.JPG (42.2 KB, 121 views)
File Type: jpg horn adapter 1.jpg (41.5 KB, 121 views)
File Type: jpg horn adapter2.jpg (41.6 KB, 36 views)
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Old 30th September 2012, 03:06 PM   #2
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Old 30th September 2012, 04:31 PM   #3
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Default SWAG: Option #2

Quote:
Originally Posted by avincenty View Post
I want to make a adapter to couple an inexpensive compression driver to the dayton JBL waveguide clone/Selenium ADM25-25 Horn Adapter combo. The bullet shape phase plug on the CD is quite long. Since I will build the adapter on the lathe I need to select its width. The width will determine how far the phase plug goes into the ADM25/HORN throat. What is best, 1 or 2? or something in between? ? Also the exit of the CD is aprox 3/4 inch while the throat of the horn is 1 inch. Should I taper the adapter from 3/4 to 1 inch or do a fixed 1 inch diameter adapter throat to match the horn's? The drawings are not to scale.
Notes:

[1] The ADM25 has a reverse conical bore and 1-3/8"-18 external thread for horn connection.

[2] The bullet tip should not extend materially beyond [1]

[3] The bore for the new adapter plate, as well as that of [1] should be machined together to avoid discontinuities in the throat wall and to open up the adapter [1] exit I/D as much as possible.

Regards,

WHG
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Old 1st October 2012, 01:18 AM   #4
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Thanks WHG,

I think I can get away with building the two adapters and test their performance. I figured that I could mount the original plastic horn on the chuck and turn it. By doing this I was able to quickly build an adapter that goes inside the JBL clone with a pretty decent matching of the horns throat's end, better than the matching of the ADM25 (but the phase plug is like in picture #2 of initial post). Next is to build a simple MDF sub plate so I can do the testing with the ADM25 and the phase plug and have it like in picture #1 and like you suggested. My concern with picture #1 is that it makes for a very long throat, almost 2.5 inches. I have a hunch that it may honk a bit.
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Old 1st October 2012, 04:06 PM   #5
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Join Date: May 2004
Location: Pensacola, Florida
Default SWAG: Bird in Hand

Quote:
Originally Posted by avincenty View Post
Thanks WHG,

I think I can get away with building the two adapters and test their performance. I figured that I could mount the original plastic horn on the chuck and turn it. By doing this I was able to quickly build an adapter that goes inside the JBL clone with a pretty decent matching of the horns throat's end, better than the matching of the ADM25 (but the phase plug is like in picture #2 of initial post). Next is to build a simple MDF sub plate so I can do the testing with the ADM25 and the phase plug and have it like in picture #1 and like you suggested. My concern with picture #1 is that it makes for a very long throat, almost 2.5 inches. I have a hunch that it may honk a bit.
What you have at the moment is about as good as it will get. Test what you have, then focus on expanding, filleting and smoothing the exit into the horn. As you do this, diffraction edge reduction, expect a trade between a decline in HF dispersion for a decline in response ripple.

Regards,

WHG
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Old 2nd October 2012, 01:07 AM   #6
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I ran some quick FR's today, no fancy setup. In addition to the JBL Clone I also tested the Dayton 12 Round waveguide. Also included is the CD as purchased with its plastic horn. Lastly I ran the FR without the phase plug and without a horn, the HF is more extended this way. With the horns they are very similar. I wonder if the phase plug is too long and affecting the HF.

Also noticeable in the Dayton 12 is a dip centered a little over 3K. I believe this is what others complain about round waveguides. The dip gets smaller off axis.

BTW the CD is from APEX JR at less than 10 dollars. The CD was used in some Fender Bassman units. On sale the Horns from PE were 6.95 each. So the combo is less that 17 each. I am planning to do some super econowave speakers and see how they come out. I am already running the econowave deluxe in my listening room and I like it a lot. My deluxe setup is with the DE250, QSC waveguide and JBL2204H mounted on 2.8cf vented boxes, Horn on top.
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File Type: jpg cheapo cd in jbl clone and dayton 12 round.jpg (141.1 KB, 20 views)
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