designing a speaker driver

[korq7]

Hello all,

I'm designing a speaker driver for one of my engineering classes, and I had a few quick questions I was wondering if anyone had any thoughts on.
Quick introduction to the project, it gives us all a few basic parts, el cheapo magnets, wire of most any gauge of wire, and some bolts. We can buy additional things, with a rather small budget.
So the only thing I was going to buy was a nice Neodymium ring magnet (the ones they give us have a TINY hole, 1/4" or so, too small for any conceivable voice coil that I can build, and it seems inefficient to stack them outside the coil. The magnet I was thinking of was 1.5" diameter x 3/4" thick, 0.760" hole. That way I can just put a standard .5" steel rod as the center pole (aka 1st diagram on http://www.consult-g2.com/papers/paper8/paper.html). I was thinking that since there’s a stronger field with the neodymium the voice coil would have a larger force on it, and therefore get more sound with the same current. Is this correct, or is there some reason that this is inaccurate?
Also, I was wondering what a good diameter for the cone would be. I designed a basket for the front/rear plate with a 5” cone in mind. I was thinking “treated paper” for the cone would be pretty easy, though I’m not sure what they treat it with; cyanoacrylate (superglue) makes paper pretty stiff, though it might also make it kind of heavy. Or also, I was thinking I could get a stiff piece of polypropylene from a folder or something, and heat it with a heat gun, and trying to shape it over a mold. This seems hard though

Thanks for your suggestions!

Mike

 

[planet10]

I was thinking “treated paper” for the cone would be pretty easy, though I’m not sure what they treat it with;

PVA.

http://t-linespeakers.org/design/tweeks.html

And consider EnABLing them

dave

PS: you are not allowed to savage a dead driver for parts?

 

[AndrewT]

Stick with paper.
conical holds it's shape well, but does ring in bell mode. The surround might help suppress this.
Keep it light, very light. minimise any treatment, just gluing the parts together will add significant weight.
Tinsel leadouts will suffer fatigue if the cone movement allows them to bend at the junctions. Try to get them shaped so that they flex along most of their length.

 

[korq7]

Hey,

That mod podge looks like some interesting stuff, I'll order some and see what happens.
Heh we're not allowed to use any parts from existing speakers, that would make things too easy

Any ideas about the stong neodyimum ring magnet vs an array of crappy small ring magnets?

Thanks guys!

Mike

 

[tinitus]

Make the 5" with NO SURROUND and it will work as a tweeter cone could have a special zigzag shape to be flexible, a bit like the ringradiator tweeter

 

[korq7]

Hey,

For the surround I was planning on using thin craft foam, I ordered some 1mm thick stuff, it was really cheap so I'm not that commited to using it. I was thinking of using it for the spider as well, in a circle with flaps cut out, although thinking about it again I realize that the bottom of my magnet is going to be closed off by a steel plate with a .5" bolt in the center. I guess I could cut some holes around the bolt and stick toothpicks or something through. Or I could make the voice coil bobbin longer and have the suspension thing on top of the magnet. Man I don't know how the spider works in commercial speakers, it seems like the most difficult part (a very light spring in a tight space that has to maintain the V.C. in the tiny gap between the center pole and maget. All while oscillating.)

Mike

 

[tinitus]

You should make the back spider out of threads

First you align the voice coil former in the gap with paper strips from the front, before mounting the dustcap

Then arrange the spider threads so they just touch the voice coil former ... they should tightened equally
At the point where the threads touch the voice coil former you glue them with "fast glue"
You can have 4, 6 or 8 threads ... with this size driver 4 threads should be sufficient

Dustcap can be made from a table tennis ball ... but maybe too heavy fore this driver

A little reading

http://www.duelundaudio.com/downloads/Articles_Steen_Duelund/HJEM3.WPS.pdf from side 15

http://www.duelundaudio.com/Articles_by_Steen_Duelund.asp

 

[korq7]

Hey,
Wow that thread idea is fantastic, way better then the dumb kludge I was planning on, thanks. I think I know pretty well how I'm gonna build this thing now, though I'm still not sure if there are any issues with the really strong magnet I'm planning on.

Thanks for the advice!

Mike

 

[Ron E]

Re: Re: designing a speaker driver

And consider EnABLing them

Bet the engineering prof. will get a kick out of EnABL...


Depending on the type of speaker you are making, you may wish to download the driver design spreadsheet I threw together. You need to supply the gap flux, which requires a program like FEMM.

link:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=17936&highlight=

 

[Graham Maynard]

The dust cap could be the end cut off a hard boiled egg with a sub-miniature rotary cutter.

Cheers ......... Graham.

 

[KBK]

Stick with paper.
conical holds it's shape well, but does ring in bell mode. The surround might help suppress this.
Keep it light, very light. minimise any treatment, just gluing the parts together will add significant weight.
Tinsel leadouts will suffer fatigue if the cone movement allows them to bend at the junctions. Try to get them shaped so that they flex along most of their length.

Older design spiral wound stripped telephone wire makes a good tinsel lead for drivers.

The 'green' colored label Lepage's brand contact cement (for countertops) is PERFECT to be the glue for this endeavor. It is used for gluing foam surrounds onto cones, by many a repair shop. Find it at hardware stores. The basic point is that it is 'solvent free', which is necessary to bond plastics..and it remains flexible. It can be used in most constructional considerations of the driver, including spyder to basket and cone, cone to former, to support and anchor the flex leads, through the cone/lead perforation point, and the gluing on of dust caps/domes.