Why is voice coil former material important?
What exactly is it changing or trying to achieve? For example, some use something like titanium, but others use aluminum, why?
What exactly is it changing or trying to achieve? For example, some use something like titanium, but others use aluminum, why?
What material choice will change and influence:
Weight (mms)
Thermal mass (peak power)
Thermal conductivity (long term power)
Thermal stability (power)
Electric conductivity (eddy currents, thus efficiency and possibly Le)
Stiffness (durability)
There is probably much more ...
Weight (mms)
Thermal mass (peak power)
Thermal conductivity (long term power)
Thermal stability (power)
Electric conductivity (eddy currents, thus efficiency and possibly Le)
Stiffness (durability)
There is probably much more ...
Aluminum is popular in aftermarket cois becuse it´s cheap, strong, stands hi temp and dissioates heat away, problem is that being conductive eddy currents brake it, kill resonance, waste energy (you are wasting cherished mechanical energy just to heat up the vice coil former, go figure).
Paper is light and responsive, "sounds good" but has low power handling.
Kapton is strong, stands 400C , is non conductive so no eddy currents, is the best jack of all trades so it´s most used today.
Paper is light and responsive, "sounds good" but has low power handling.
Kapton is strong, stands 400C , is non conductive so no eddy currents, is the best jack of all trades so it´s most used today.
It is a polyimid. We use it in superconducting magnets because it is hugely radiation resistant and is the only plastic we use that is still flexible at 4.5 Kelvin. They used to use it for military aircraft wiring insulation, but eventually found out that it was not self extinguishing so would cause fires. Now it is banned for that use.
With polyimide insulated magnet wire, and polyimide glue cured properly on a kapton former, the VC assembly can go into the 250 to almost 300 C range without falling apart. The primary difficulty being the copper will expand so much that the structure will hit the front plate ID surface before the insulation fails. Or, the gap to the plate needs to be larger, kinda in the wrong direction magnetically.
But for when I lend my system to my son, just what the doctor ordered....
jn.
If you wanted the perfect hypothetical material for the voicecoil former, you'd probably want to use diamond. Very high melting point (the coil would melt first) with a very low thermal expansion coefficient, so the former dimensions won't change much in varied temperature conditions. One of the highest specific stiffness of any materials so a small amount of diamond can be used to achieve the same mechanical properties required, which also allows a tiny mass. Since it is incredibly stiff the loss coefficient would be next to nothing, as all compression/extension is elastic and not viscoelastic allowing for less mechanical damping artifacts in the output. Diamond has a low magnetic susceptibility and is an insulator so no inductive effects or eddy currents could occur allowing for lower motor distortion due to Le. Diamond also has an extremely high thermal conductivity, but I think its one downfall may be the lowish specific heat capacity, so the extreme peak power requirements may not be satisfied. Otherwise if it could be made cheaply it probably would be best.
Yes, I use it to roll my own.
1 detail: being very stable and non porous, it´s harder than usual for adhesives to stick to it, now and then you will see copper wire separating from kapton formers.
I suggest you lightly sand the area where actual winding will be, and degrease it very well.
There is a chemical bath which etches Kapton surface leaving it slightly porous but I avoid it, it contains nasty stuff.
Definitely not California approved.
1 detail: being very stable and non porous, it´s harder than usual for adhesives to stick to it, now and then you will see copper wire separating from kapton formers.
I suggest you lightly sand the area where actual winding will be, and degrease it very well.
There is a chemical bath which etches Kapton surface leaving it slightly porous but I avoid it, it contains nasty stuff.
Definitely not California approved.
Would it be possible to use the voicecoil itself as the former rather than a layer of CCAW and then a separate former material?
The EV T35 and similar low power, low excursion horn tweeter's voice coils use no former to save weight, the glued voice coil directly attached to the outer portion of the diaphragm.
A former extending beyond the coil connecting to the cone allows excursion beyond the the length of the coil, required for a subwoofer- extending an unused portion of a coil would be a weight penalty compared to the former weight.
What is "CCAW"?
A former extending beyond the coil connecting to the cone allows excursion beyond the the length of the coil, required for a subwoofer- extending an unused portion of a coil would be a weight penalty compared to the former weight.
What is "CCAW"?
Copper Coated Aluminium wire, It works as a composite to find a balance of conductivity, density and possibly thermal dissipation.
Yeah I suppose the direct bond to the diaphragm limits mechanical excursion limits, though if applied so that the coil was under the former which connected to the cone of a speaker, the mechanical limitations may be overcome.
