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Old 30th December 2008, 04:50 PM   #1
sergiof is offline sergiof  Portugal
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Default fiberglass TL

Good evening!

I hope I'm not repeating some old topic about the subject, but I couldn't find any, so I decided to ask (also consider that I'm a newb in here, so any stupidity of mine "should" be taken with a smile )

After building some TL loudspeakers in wood, I became a little bit more ambitious and started to plan building a spiral pipe around a pole, that would work as the QWTL tube for the L22 Seas Woofer, in a 3 way loudspeaker (the other 2 being, most likely, Seas W15CY and Vifa XT25). That said, a lot of ideas on how to make this pipe came into mind, notably building a structure in fiberglass (or any other fiber that suits this). The bigger problem is the mould for that.

I thought in 2 possibilities, both needing to be explored (and eventually abandoned if not suitable). One of them would be doing a pipe structure using wicker, this one rolling around the pole. This "wicker pipe" would be later covered by fiberglass (being some kind of endoskeleton). The other one would be using a regular PVC pipe, again covered by fiberglass, and removed (have no idea how) when the fiberglass is firm.

Can you please help me with this?
(here's a very ugly sketch)
Click the image to open in full size.

Thank you very much!

(and since I'm on the season, Happy New Year to all of you!)
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Old 30th December 2008, 07:19 PM   #2
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Hi and Welcome.

When I saw your design sketch I couldn't help but think of this:

http://www.t-linespeakers.org/projec...uke/index.html

It's not fiberglass but it looks so much like yours I thought you might get some ideas from it. You won't need to make molds but it looks like a good bit of work nonetheless.

The rest of the site might help too, if you haven't seen it.
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Old 30th December 2008, 07:44 PM   #3
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Based on your sketch looks like your line may be too small a cross-section ... what driver did you plan?

dave
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Old 30th December 2008, 08:12 PM   #4
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He said the L22 Seas Woofer.
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Old 30th December 2008, 09:20 PM   #5
Brewboy is offline Brewboy  United States
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I really like your design idea.

If I were to make this out of fiberglass, I would start out with a block of extruded polystyrene and carve the shape out of this block. You have probably seen this product used as insulation sheets mostly colored pink or light blue. This product is easy to cut, carve, plane, sand and can be easily shaped to whatever. This is sometimes the method used for making surfboards. I would not use expanded polystyrene, the structure of this (little balls) makes it hard to shape, Nor would I use Polyisocyanurate as it is to brittle, unless you can get high density stuff.

After I had the pattern shaped I would make a mold of the pattern, with the simplicity of this shape a 2 piece mold would most likely work.
Then after the mold is made it is just a matter of making your 2 pieces ( DON'T FORGET TO USE MOLD RELEASE )and fiberglassing them together.

You could purchase sheets of expanded polystyrene and glue them together to get your thickness or you could try to find a block of the product. Often they use blocks of this as flotation under docks and floating homes, I would suggest locating a dock builder or small shipyard.

Usually I would suggest that epoxy resin be used instead of polyester resin, however for this project polyester resin is fine and the beauty of it, it's cheap. Polyester resin will melt the foam however, so you might want to make the mold out of epoxy or wrap the mold in a "saran" type wrap and be prepared to do some sanding.

Good luck.
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Old 30th December 2008, 10:17 PM   #6
sergiof is offline sergiof  Portugal
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wow!

i never expected help to come this quickly! thank you!

about the seraphim, i already knew it, but once i did a loudspeaker made out of pipe and the sound of it was not very pleasing (sounded to much like a pipe ) anyway, thank you!

about the sketch, please don't take the proportions seriosly. the dimensions and the exact shape of the tube has still to be worked out.

brewboy, what a great idea! what you're sugesting is that i carve the counter-mould in EP, than make a mould out of it (2 pieces), and then work the fiberglass on it, from the "inside to the outside", correct? can you please direct me to any link where they explain the epoxy technic you mentioned? thanks a lot!
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Old 30th December 2008, 11:25 PM   #7
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Quote:
Originally posted by sdclc126
He said the L22 Seas Woofer.
Duh.. smack me in the head... using MJKs rule of thumb, you'd start with 30 cm diameter, but i'd guess from the Vas that it may need to be bigger. With a dramatic taper 6-7' long (seat of the pants guess)

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Old 30th December 2008, 11:45 PM   #8
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When I saw your sketch first off it reminded me of an eeltrap.
You could do it in woven flexible reeds, then cover it in chopped strand mat and resin it up.
Although I believe that the reeds are now quite expensive in Western Europe, perhaps you could substitute something else.
I imagint the central pipe would need to be substantial too.
Regards
Ted
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Old 30th December 2008, 11:58 PM   #9
Brewboy is offline Brewboy  United States
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There is a 2 part video on u-tube showing a guy making a mold out of a auto sub box


http://www.youtube.com/watch?v=gzng9...eature=related


Some of the things that he does, I would not, however it is a good example of how to make a mold. Working with epoxy is basically the same as polyester resin except the epoxy will not melt the EP. Several coats of paint or pva sealer might seal the foam enough to make the mold or like I said wrap the EP in saran wrap, but then you would have wrinkles that would have to be sanded out.
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Old 1st January 2009, 07:20 PM   #10
sergiof is offline sergiof  Portugal
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interesting...

in this case, since the pipe is simmetrical to it's axis, i suppose the best thing i should do is to divide the continuous pipe in sections, knowing that for each one i would make a mould (for the 2 halves of the pipe, since it's simmetrical), and in the end connect all the sections. do i loose structural rigidity with this?

another thing, i presume that all TLs must be tappered (correct me if I'm wrong), which means that for using the same mould for the outside on all the pipe (regular curves, repeated as a pattern), i could simple thick the wall (thus lowering the effective diammeter) as long as i would progress down on it, right?

another thing, slightly out of topic: even knowing that i'm thinking on the drivers said before (both L22 and W15CY from Seas, plus Vifa XT25), i keep some doubts about the tweeter. thinking on its really low distortion and terribly cheap cost (at least compared to the other 2) makes it tempting, but maybe i'm missing a better integration (Troels, for example, uses ribbon tweeters in this kind of setup).

last but not the least, what do you recommend me? active/passive(is this possible?) crossover before the amps, or passive crossover after the amp?

once again, sorry for all the newb questions! (and thanks a lot for all the patience and enlightening)
happy new year for all of you!
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