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Monteverdi 7th November 2017 09:11 PM

How to optimize a voice coil
I am building my own voice coils for my bending wave driver (for mid and highs) project. Initially I used titanium foil to make my formers but then I tried some fiberglass and found that I can measure less distortion with the fiberglass formers. I am using relative thin S-glass fabric (2 layers) and using heat resistant and curable epoxy. I am designing my drivers that the entire voice coil former is only 12mm high in order to reduce flex of the former but that means that the magnetic motor structure is closer to the speaker membrane which could be a cause for distortion by back reflection. As my drivers are bending wave the actual movement is minimum. So what is the more important parameter?

As voice coil wire I am using single layer of 35awg enameled copper wire (Cardas) and end up with 6Ω. I am bonding the copper coil with Loctite EA9017 epoxy (which has reasonable heat resistance) to the former . Is there any better adhesive for that task available? Are there any adhesive pre coated voice coil wire available (heat cure) for diy and would they be an improvement?
Would be it worth to try 2 or more wire layers and should they be in series or parallel?

Joshcpct 7th November 2017 09:47 PM

Hi. I don’t have experience with the materials.
Interesting that titanium distorts more. It was just recently found by an engineer to be superior.

Maybe inside outside winding could help having equal distance to the inner and outer pole pieces ?

lowmass 8th November 2017 01:30 PM

The "12mm" high VC former may actually flex more than a longer one.

The more important parameter is the one that offends your ear the most. Ha I know thats a loose statement BUT Ive done a fair amount of development and often reguardless of the "information" out there it comes down to doing the hard work and hearing whats what with various different designs.

I suspect you will want to do as much work as you can on making the magnet structure ether far from the cone OR as smooth a structure as possible or both. Diffraction/compression may be a bigger issue than VC flex.

Im curious about your find " Initially I used titanium foil to make my formers but then I tried some fiberglass and found that I can measure less distortion with the fiberglass formers."

How much distortion did you measure and how much difference was there between the two. Also was the Ti VC former a conductive ring or did you leave a slit?

Monteverdi 8th November 2017 04:33 PM

The Ti VC former I made was not a complete conductive ring but the foil was overlapping about 3mm and bonded with epoxy. I don't know if the ends touched directly to conduct circular eddy currents. With the Ti former I got several distortion peaks above 1kHz (highest around 1.5%) which were not present with the GF former (identical dimensions etc.).
Maybe I try a Ti former with a wider gap and local GF reinforcement.
Also a dual (inside/outside of former) VC sounds interesting but making it is quite more challenging.

Joshcpct 9th November 2017 10:24 AM

dont you just wind on a temporary carrier of smaller diameter first, from start to end.
then wrap the final former on top, and wind from end to start back?

gibber 11th November 2017 07:09 AM

A metal will be prone to eddy currents even if a slit is left to avoid the "single turn coil" effect. But metal doesn't need to be bad at all unless lowest Rms is on your agenda, as it was for many in the '00-years, justified or not i'm still not sure.
As lowmass said, you will probably fare best by listening to the combination of coil and to-be-dribven structure in conjunction with the chosen magnet design


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