I know this will remind you of an old joke line, but you simply label the terminals as the last step. That way you will never miss the target.
B.
hi all, not quite sure where to ask this so I'll tack onto this thread.
I have a mid-range voice coil that is a nominal 1 and 1/4 inch diameter coil. The Gap I have to work within is 1 mm. Or .04 inches. My question is what would be a reasonable overall thickness for my coil.
If I did something like assuming I need .01 in clearance on either side of the coil which would allow me a combined thickness of .02 in, would that make sense? Or do I need more forgiveness on either side of the coil?
I have a mid-range voice coil that is a nominal 1 and 1/4 inch diameter coil. The Gap I have to work within is 1 mm. Or .04 inches. My question is what would be a reasonable overall thickness for my coil.
If I did something like assuming I need .01 in clearance on either side of the coil which would allow me a combined thickness of .02 in, would that make sense? Or do I need more forgiveness on either side of the coil?
Thanks For All The Fish
this should be a wiki entry! I am certainly glad to have found it so early in my research. I'm much closer to just doing it. This thread and your response answered questions I didn't know to ask. all of your replies gives me confidence to go forward. Now I'm off to find theory so I can sort out my actual requirements.
I have a nice Mitsubishi 12 inch frame with unknown specs to experiment on , one of two Navy battle announcement horns to rewind after I abused them very very badly
and next thing you know ill be creating the next fad exotic. 
One more excuse to buy a new fancy pants scope with memory.
Great Information,1) you must make a core so you wind around it.
Nominally 51mm, but the final check is that it slides in/out of the coil you are cloning with a little friction.
Length to suit, anything from 25 to 50mm is fine.
Surface must be polished.
Chrome plating it is best, second best is using brass, for lowest cost just to try the idea you *may* use aluminum, but finished coil may stick to it.
A former employee who learnt from me, nowadays repairs "any speaker", specially weird car speakers with odd sized coils, and he makes his own cores out of some hardwood, but I don't recommend it for any serious work.
He does it for cost, of course, plus most are never seen again (and car speakers have terrible tolerances).
You need a center hole in the core to mount it to some kind of hand crank.
An externally hosted image should be here but it was not working when we last tested it.
2) winding:
look at this video which shows it reasonably well:
[How It's Made] Building a Speaker - YouTube
Start at: 2:24
a) the core is mounted on the winding machine.
Manual is the same (or better), only problem is speed.
Since actual hand winding takes 1 or 2 minutes, no big deal.
b) you must pre-cut the strip which will be your VC form.
Then degrease it very well with some kind of solvent and never ever again touch its surface.
Best sounding and easiest to wind and glue is paper, only problem is that it does not handle much power.
In the video they use Kapton.
What they do not show is that being non porous adhesives don't stick very well to the raw surface, it needs some treatment , chemical or mechanical.
You can "scratch " it with fine emery paper, until it's uniformly dull.
Same for aluminum.
c) you momentarily stick your form strip around the core.
4) modern factories use advanced coated wires, with adhesive enamel pre-applied, which is made "sticky" by brushing it with a solvent.
Final curing is in an oven, or with an infrared lamp or heat gun.
I suggest you use what I do: Industrial Epoxy (forget Home/Hobby type "5 minutes"), the kind that hardens overnight at 25ºC , stays usable for around 1 hour , and if in a hurry, can be heated for faster curing.
Apply it with a small brush, wind the first layer, apply a little more, wind the second, heat the coil a little with a heat gun so it becomes "more liquid" so it "wets" the former and the wire for better adhesion and set it aside for curing.
5) momentarily you hold the still free start and end wires with a small piece of tape.
Tomorrow you pull the tape, put wire ends where they belong, apply a little epoxy to them, temporarily hold the unglued long ends (which will later be connected to tinsel wires) with some extra tape, if you wish you can add a "neck" of paper, also glued with epoxy,which later will help adhesion to cone.
If this is a midrange or tweeter VC, you need no "neck" (as shown in the video) and you will save weight.
6) when the epoxy is cured, you slide the VC out of the core.
7) if you do not need a lot of power handling, (as in a midrange), you can wind the first layer "dry", apply some good Cyano acrylate (Crazy glue) which will spread evenly thanks to capillarity, and in a couple minutes wind the second layer, also "dry" and repeat cyano glueing.
Personally I don't use it because mine are routinely abused guitar/bass speakers, so I use Epoxy, but maybe you should explore cyanos.
Loctite or Hernon have a whole range specific for speakers.
NOTE: be very careful to avoid adhesives going where they should not.
If the VC sticks to the core, you'll have to destroy it and maybe damage the core in the process.
Keep some acetone close by, worst case wet VC and core with it so you can pull it away (destroying it in the process).
That's why a polished chrome plated core is best.
Good luck.
this should be a wiki entry! I am certainly glad to have found it so early in my research. I'm much closer to just doing it. This thread and your response answered questions I didn't know to ask. all of your replies gives me confidence to go forward. Now I'm off to find theory so I can sort out my actual requirements. I have a nice Mitsubishi 12 inch frame with unknown specs to experiment on , one of two Navy battle announcement horns to rewind after I abused them very very badly
and next thing you know ill be creating the next fad exotic. One more excuse to buy a new fancy pants scope with memory.
The coil former itself is a strip of paper/Nomex/kapton/aluminum wound around a core.
Which is custom lathe turned, and surface must be polished to allow removal of finished voice coil.
Voice coil must be slightly larger than speaker pole piece so it moves without touching it.
If polepiece is, say, 50mm, winding core (which sets voice coil former inner diameter) must be turned to 50mm + "2 shim thicknesses plus a little more"
When you assemble the speaker voice coil former is centered and held in place by puttin thin plstic sheet strips or "shims" between polepiece and voice coil and yhey must friction fit but easily removable.
Typical shim material is used X-ray film which is actually very high quality polyester .
or you buy a Mylar sheet and cut it into strips, popular thickness is 0.1mm (about printer paper thickness) or 0.125mm
Which is custom lathe turned, and surface must be polished to allow removal of finished voice coil.
Voice coil must be slightly larger than speaker pole piece so it moves without touching it.
If polepiece is, say, 50mm, winding core (which sets voice coil former inner diameter) must be turned to 50mm + "2 shim thicknesses plus a little more"
When you assemble the speaker voice coil former is centered and held in place by puttin thin plstic sheet strips or "shims" between polepiece and voice coil and yhey must friction fit but easily removable.
Typical shim material is used X-ray film which is actually very high quality polyester .
or you buy a Mylar sheet and cut it into strips, popular thickness is 0.1mm (about printer paper thickness) or 0.125mm
There's also a waxy material called Mold Release Compound, used by boat shops and other folks that do hand fiberglass lay-up. It was available where I bought the epoxy coatings, though that was 45 years ago .. don't remember the brand name.
Used to be able to get mylar at just about any blueprint shop, but I haven't seen one of those in (seems like) almost as long.
Cheers
Used to be able to get mylar at just about any blueprint shop, but I haven't seen one of those in (seems like) almost as long.
Cheers
Attention fans of motional feedback:
A good way to get a feedback signal is to have a separate purpose-built VC winding. Ordinary dual voice coil winding (like 8 plus 8 Ohms) don't make much voltage. But many more turns of very fine wire might work.
A few manufacturers have tried this (I only know about Sony) but Sony used a separate magnet fitted to the far end of the driver. Not sure why, maybe it could be made longer than VC depth or to avoid too big a VC gap for the driving VC.
Not perfect, but don't know any MFB sensor that is.
B.
A good way to get a feedback signal is to have a separate purpose-built VC winding. Ordinary dual voice coil winding (like 8 plus 8 Ohms) don't make much voltage. But many more turns of very fine wire might work.
A few manufacturers have tried this (I only know about Sony) but Sony used a separate magnet fitted to the far end of the driver. Not sure why, maybe it could be made longer than VC depth or to avoid too big a VC gap for the driving VC.
Not perfect, but don't know any MFB sensor that is.
B.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.