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Old 14th March 2013, 09:41 PM   #1
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Default DIY Voice Coil with Cone

Hello forum members,

Are there any online calculators or is there a mathematical formula that can be used to calculate the target impedance of the voice coil based on the gauge of the wiring, the number of winds etc?

For example, if my initial target is an 8 ohm voice coil and I am using 38AWG wiring, what would the optimal method be for determining the number of winds to get to an 8 ohm voice coil? I have a standard LCR meter and a high precision LCR meter as well, I had thought about periodically melting the wire during the winding process to measure the inductance/capacitance/resistance of the coil on the jig to derive a formula for the length of wiring/number of winds needed, but that's probably not the right approach nor do I think it would work based on the wire still being attached to the spool feeding the winding jig.

I am also curious about how the number of winds affects the magnetic field collapse. I am sure these are basic electronics 101 questions but I can't find any direct answers from the research I've done so far.

Thanks in advance for any input!

Last edited by argh; 15th March 2013 at 05:08 AM.
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Old 16th March 2013, 03:33 AM   #2
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I don't know what you are doing, this might interest you. Yes?!
Boxal s.r.l. VOICE COIL MANUFACTURERS
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Old 16th March 2013, 03:36 AM   #3
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No, that's the point of the project. I am building a subwoofer from scratch, and by scratch I mean building a winding jig, winding the voice coil, sourcing parts for the speaker cones etc.
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Old 16th March 2013, 09:40 PM   #4
Zero D is offline Zero D  United Kingdom
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Hi, it sounds like an interesting, but daunting project !

These links might be useful to you

Quote:
Coil Physical Properties Calculator

Coil Physical Properties Calculator
Keep us posted as to how you're progressing, hopefully with pics

All the best with it
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Old 16th March 2013, 10:02 PM   #5
JMFahey is offline JMFahey  Argentina
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So simple you just use pen and paper, and work interactively ... which you must do anyway because wire does not come in "any" size but there's a predetermined size table.

So you start by VC diameter, winding length and amount of layers (usually 2) and start with some value, say: 0.20mm .
You go to a wire table which gives you actual diameter (because it's enamelled).
Then you calculate amount of turns with that wire size.
Simple geometry tells you turn length, multiply this by amount of turns and you have the total VC wire length.
Check ohms per meter from the wire table and you get DCR.
For an 8 ohms nominal VC you try to have around 6 to 6.5 ohms.
If you got too much or too little, select a new wire diameter and start again.
A couple minutes per calculation, not worth writing an Excel table for this, although it's not a bad idea if you do it often.
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Old 17th March 2013, 01:41 AM   #6
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Interesting subject,

I've been playing with the thought of making a subwoofer myself.

I suppose you have some idea of the gap depth you're going to use? How do you plan to get/ make the pole plate and might there be a specific steel that's optimised for this use?
Once you know the gap depth and have a target Xmax, you know the winding depth, which is where JMFahey started.

Or are you going for the winding only and an excisting motor structure?

PA drivers often use inside and outside winding on the voice coil former to optimise heat transfer (say 2 layers on the inside plus 2 layers on the outside)

If you have a target BL (flux times length), it will tell you the ratio of magnet field strength to wire length, which would result in an estimated wire length and thus thickness.
Most PA manufacturers advertise a magnetic flux around 1 Tesla for subwoofers but 0.35 T throughout the gap would be a good start.

You might find this interesting. It's an older project that looks stranded but Vikashy is also an moderator on here. I for one would be interested to know what happened to it.

Best regards Johan
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Last edited by Rademakers; 17th March 2013 at 01:43 AM.
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Old 17th March 2013, 03:10 AM   #7
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If you know the gauge of the wire and the type of wire material you should be able to calculate DC resistance for a given length, or conversely the length of wire needed to obtain Re= N ohms. An 8 ohm "nominal" speaker will have Re around 5-6 Ohms.

How you wind the VC is another topic alltogether.
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