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Old 3rd May 2008, 01:18 AM   #1
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Default Anyone try building a driver?

Has anyone given this a try? I'm mostly interested in building one as a learning experience. Surely I can't be the only one interested, but all I find are sites with speaker box plans and lists of compatible drivers. It's a difficult search I guess. I do know about diy electrostatics, etc.

Anyways, I have a lathe, a huge collection of speaker magnets, some very large, and a pretty good selection of tools to work with.

As a first attempt I think I'll shoot for just reproducing sound. I'm not sure how to build a spider, I have a couple ideas involving pressing a loose weave fabric impregnated with a resin or glue between a pair of dies shaped like a speaker spider. I'll probably just buy a foam surround repair kit from dayton for the surround.

I'm all set up to wind the voice coil, just have to modify the rig I used for a tesla coil I built.

As stated I have a large selection of magnets and might use one. I had some success separating the back plate from the magnet using heat to soften the glue. This might not be necessary, but all my magnets have crud in the coil gap so they need to be cleaned. This also gives me the chance to machine the center pole of the magnet to allow for a larger gap if I have trouble making a voice coil thin enough.

Another option that is actually more appealing is using an electromagnet, I guess that would make it a field coil speaker. I like the idea because it allows me to make a larger percentage of the components.

I've been reading up on the theory. I'm confident I could throw something together that would work, but I want to make a real attempt at producing a driver with some predictability.

Any websites out there with ideas? Anyone with some experience that wants to share?

Oh, I already know I'm crazy.

Eric
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Old 3rd May 2008, 01:22 AM   #2
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I did find this, not really helpful, but interesting.

http://www.youtube.com/watch?v=VN0tmyyC0ak
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Old 3rd May 2008, 03:09 AM   #3
jkeny is offline jkeny  Ireland
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Don't know if this will help but I am attempting to rebuild a pair of KEF drivers - details here: Rogers LS3/5a speakers just blown

Tricky business!
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Old 3rd May 2008, 03:45 AM   #4
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I'm too busy/lazy to try it, but like you I've got a lathe and have had the exact same thoughts about doing an electromagnet design. That opens up another variable for tuning. If you look at antique radio speakers, there are various spider designs that can just be cut out of some thin stiff material. Or, the die method should work. IMO, it's not fully diy unless you figure out some way to make a decent surround. Old speakers used the same folded resin coated fabric method as the spider, or I've been thinking about using a 2-part RTV (or 1-part liquid rubber in a tube) and coating some sort of form. A die is possible so it could be cast, but it would be a big pita to machine, and the size would be limited. Winding a voice coil should be pretty easy, but the electromagnetic math behind the whole design is daunting, at least to me. In my case it would be strictly seat-of-the-pants and trial and error. Lots of error.
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Old 3rd May 2008, 07:45 AM   #5
el`Ol is offline el`Ol  Germany
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Hello Eric!

I am trying to build a magnetostatic driver, like many others here have done, just with a new type of diaphragm. Originally I intended to use a FAL-type linear dynamic drive.
http://www.sibatech.co.jp
A flat diaphragm is always easier to manufacture, and the magnetic circuit can be built with neodymium magnets from Ebay and drawn 1020 steel profiles. But finding suitable flexible tubes for the suspension might be difficult. I would use bars to fill the holes at the corners (with narrow gaps, as FAL should have done, since avoiding the suspension being torn there is tricky). An other type of flat diaphragm driver (bending wave transducer) can be seen here:
http://v3.espacenet.com/textdraw?DB=...N=US2007064972
But I doubt it will be more than mid-fi.
The diaphragm of a conventional dynamic driver isnīt easy to manufacture. "chinese" here in the forum did it with concentric stripes, and there are old Zeiss-Ikon drivers made of radial stripes. The "chinese" design is a bending wave transducer without any suspension. If you intend to use a suspension, a cantilever suspension like the old phenolic spiders will be easier to manufacture than a folded cloth spider. A second suspension in front of the cone like the Goodmans Axiom 80 and the Fertin Model 7 have, reduces the requirements for the surround.

Regards,
Oliver
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Old 3rd May 2008, 09:45 AM   #6
Pano is offline Pano  United States
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Haven't I seen string spiders somewhere? Might be worth a try.

For an easy cone one might be able to use a good quality water color paper. It's good stuff and very stiff. Wouldn't be seemless, but so what?

I think the electomagnet ideas is cool. =)
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Old 3rd May 2008, 10:03 AM   #7
AndrewT is offline AndrewT  Scotland
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there are a couple of websites with pics showing homespun cone manufacture.
At least one guy has given a lot of detail on making his electromagnet for VC gap flux.
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Old 3rd May 2008, 10:09 AM   #8
Vikash is offline Vikash  United Kingdom
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Default Re: Anyone try building a driver?

Quote:
Originally posted by etcetera
Any websites out there with ideas? Anyone with some experience that wants to share?

Oh, I already know I'm crazy.

Eric
http://www.vikash.info/audio/transducer_design/

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Old 3rd May 2008, 11:42 AM   #9
el`Ol is offline el`Ol  Germany
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Just had an idea for the FAL suspension: thin-walled carbon tubes filled with soft foam for damping.
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Old 3rd May 2008, 04:11 PM   #10
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Thanks for all the replies, some good ideas. The spider and surround problems are the toughest to crack.


Vikash, your website is very helpful. Many good ideas. Thanks. I like the idea of an electromagnet spider, but I think it might be difficult to make it work unless the speaker is facing up.

I'm going to do a search on string spiders. Perhaps strings to center the cone and an electromagnet circuit to adjust the compliance. Or just using the length and tension of the strings to adjust compliance.

I do have a friend who is a special effects makeup artist. He uses many different forms of foam rubber to make masks and stuff like that. I'll have to swing by his place and take a careful look at some of the stuff he has available. I'm envisioning making a mold using 2 different diameter tubes cut in half and positioned inside each other. Another possibility is a treated cloth surround, or maybe just paper.

I've got some crazy ideas for basket and magnet design that are difficult to describe. I've been playing around with some cad software in an attempt to show what I'm thinking. For the basket, the support pieces will be perpendicular to the cone. This should minimize reflections and make it easy to build.

As for the magnet, I'll have to try to find a diagram showing the insides of a field coil speaker. I have a couple ideas but it's somewhat time consuming to try them. Not to mention the cost of wire.

Time for more research.

Eric
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