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Old 1st June 2010, 07:22 PM   #1
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Default PVC Alpair 6 Pensil

Hello,
I've a pair of Alpair 6 that I've used in OB with a H frame subwoofer.
Now I'm looking for a new house for this speakers.
I'm not able to use wood with good results and I'd like to make something different.
I'm thinking about a Pensil made with PVC pipe, I've seen many ideas on the net but I need some help for the right dimensions of the pipe.
Can you help me?
Thanks a lot.
Guglielmo
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Old 1st June 2010, 08:02 PM   #2
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Simple: you need to find one that has exactly the same cross sectional area as the Pencil 6, which you then cut so it has exactly the same length.
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Old 1st June 2010, 08:16 PM   #3
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I think is the right way for a good result.
And do you think about the tuned port?
Do you know the tune frequency?
I must calculate with the thichnes of the PVC and tune sperimentally (circular section) looking at the impedence curve?
Thanks for your help.
Guglielmo
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Old 1st June 2010, 09:23 PM   #4
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Quote:
And do you think about the tuned port?
Do you know the tune frequency?
I'd worry if I didn't, for the excellent reason I designed them.

Quote:
I must calculate with the thichnes of the PVC and tune sperimentally (circular section) looking at the impedence curve?
Well you could. Alternatively, you could use the designed vent CSA and length. If the PVC pipe is too thin, just add a lip around the inside of the vent hole you cut to get back to the requisite 3/4in length.
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Last edited by Scottmoose; 1st June 2010 at 09:28 PM.
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Old 2nd June 2010, 01:40 AM   #5
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Quote:
Originally Posted by Scottmoose View Post
Simple: you need to find one that has exactly the same cross sectional area as the Pencil 6...
6 1/2" diameter. 165mm.

dave
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Old 2nd June 2010, 08:10 AM   #6
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Hello,
I'll try in the next days and I'll post the results.
Thanks
Ciao
Guglielmo
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Old 26th June 2010, 07:02 PM   #7
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Default ABS Alpair 7

Bonjour diyAudio. This my first post...

I built two enclosures with black ABS pipes and fittings for the Alpair 7. ABS seems stronger and cheaper than PVC. Since these are my first diy speakers, I can't tell if the result is perfect, but I must admit that I'm very pleased. The sound is a bit aggressive in the mid range, but I guess I'm not used to full-range speakers. I plan to use DRC to equalize them, but I'm not in a rush. They're not finished; maybe I'll use passive filtering instead.
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Old 26th June 2010, 07:08 PM   #8
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Pictures?

dave
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Old 26th June 2010, 10:24 PM   #9
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Quote:
Originally Posted by planet10 View Post
Pictures?

dave
Bonjour Dave.

I first wanted to build a Pensil, but your design for the Alpair 7 was not ready, then I was intrigued by the "triffid", a bass reflex enclosure:

Mark Audio CHR-70 Application Thread

Rabbitz helped me a lot, his advice were priceless. My "triffidus" design is a bit different than the original "triffid", and as you can see it's not finished.

There's still no wooden base, and no binding posts (the cable goes out through the port)...

Only the top fittings are glued together; when the pipes are inserted into the fittings, it seems solid enough. They're easy to insert and remove after heating the fittings with a small paint stripper. Maybe I'll glue everything when I'm satisfied.

The second picture shows how the Alpair is attached to the ABS fitting. The diameter was almost perfect but I had to use a small file to cut little grooves. The screw holes are right between the fitting and the glued ring, and it's very solid. The whole interior is lined with 3/8" industrial felt (but only 1/4" around the basket).

The last picture shows how I listen to them; they stand behind a 32" HD monitor (a TV), spaced by 16" (from centre to centre) in a ambiopole configuration, driven by a T-amp and a Linux computer with cross-talk cancellation software.
Attached Images
File Type: jpg triffidus-01.jpg (73.6 KB, 265 views)
File Type: jpg triffidus-02.jpg (135.1 KB, 258 views)
File Type: jpg triffidus-03.jpg (96.6 KB, 251 views)
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Old 26th June 2010, 10:45 PM   #10
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The midrange issues are going to be from loading the drivers into too small a cross-section and having early sidewall reflections back thru the cone....

dave
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