Voice Coil Material

Jayden

Im making my own sub-woofer just for fun, messing around with different ideas, and I was just wondering this; What is the best material to use for a voice coil? Now all the speakers/sub woofers I've ever dealt with are copper coils, isn't that kind of a standard for material that carries electricity? Isn't there a better material to use? Just wondering. Thanks

zingo

There are many quick answers, but this is a deep study in material science and physics. There any many voice coil materials that could be used including copper, aluminum, silver, but what are you looking for in power handling? Do you want the most conductive material? When you apply a signal to the voice coil, how magnetic are you expecting the response to be? How large are you going to wind the voice coil and why? What material are you going to be using as a voice coil former and why? What magnetic material will you be using for the magnets on the basket? How magnetic are you expecting them to be, and how will that interact with the voice coil? How large of a gap will you run between the voice coil and the magnets? What are you going to make the woofer basket out of? If it's a ferrous material, have you accounted for the interaction between the magnets and the basket?

These are just a few of the questions you need to have answers for while designing your own subwoofer, and most of those only relate to the voice coil....

In my opinion, a $100 subwoofer is starting to look pretty good.

mhardy6647

actually - and I don't know why - brass was often used in the old days for voice coils in woofers and extended range drivers. Aluminum was also common, probably because on a per dollar as well as on a a per gram of mass basis, its conductivity is very high.

Copper's a good default, though.

Face

Accuton uses titanium in some models.

mhardy6647

Interesting - let's look up the conductivity (or, inversely, the resistivity) of titanium vs. the "good" conductors (Marky scurries off to Wiki-land...)

all righty:
some selected resistivity data from http://www.engineeringtoolbox.com/resistivity-conductivity-d_418.html

silver: 1.59 x 10^-8 ohm-m
copper: 1.724 x 10^-8 ohm-m
gold: 2.24 x 10^-8 ohm-m
aluminium: 2.65 x 10^-8 ohm-m
tungsten: 5.69 x 10-8 ohm-m (this is the stuff used for light bulb and vacuum tube filaments)
brass: 5.9 (to 7.1) x 10^-8 ohm-cm (depending on copper content)
osmium: 9 x 10^-8 ohm-m
vanadium: 25 x 10^-8 ohm-m
titanium: 43 x 10^-8 ohm-m
NiChrome: 100 (to 150) x 10^-8 (this is the stuff used in electric space heaters)

I mean, titanium is fairly light and strong, but it is hard to work, it is (if memory serves) stiff and brittle and it's not a great conductor compared to the ever-popular favorites... seems like a non-obvious VC choice to me, but needless to say I am not a materials scientist nor a speaker engineer.

Wonder if, perhaps, they use an alloy?

newbie308

mhardy6647 wrote: »

Interesting - let's look up the conductivity (or, inversely, the resistivity) of titanium vs. the "good" conductors (Marky scurries off to Wiki-land...)

all righty:
some selected resistivity data from http://www.engineeringtoolbox.com/resistivity-conductivity-d_418.html

silver: 1.59 x 10^-8 ohm-m
copper: 1.724 x 10^-8 ohm-m
gold: 2.24 x 10^-8 ohm-m
aluminium: 2.65 x 10^-8 ohm-m
tungsten: 5.69 x 10-8 ohm-m (this is the stuff used for light bulb and vacuum tube filaments)
brass: 5.9 (to 7.1) x 10^-8 ohm-cm (depending on copper content)
osmium: 9 x 10^-8 ohm-m
vanadium: 25 x 10^-8 ohm-m
titanium: 43 x 10^-8 ohm-m
NiChrome: 100 (to 150) x 10^-8 (this is the stuff used in electric space heaters)

I mean, titanium is fairly light and strong, but it is hard to work, it is (if memory serves) stiff and brittle and it's not a great conductor compared to the ever-popular favorites... seems like a non-obvious VC choice to me, but needless to say I am not a materials scientist nor a speaker engineer.

Wonder if, perhaps, they use an alloy?

I had no idea that silver was a better conductor than gold or even copper for that matter! Aluminum would be interesting due to it's light weight. Seems to me that the lighter the moving mass, the more control you will have over the acceleration and deceleration of the cone and voice coil assembly. Therefore you need a weightless superconductor! Just order some Unobtanium from Pandora!

mhardy6647

Folks that espouse certain... shall we say... esoteric... hifi products and./or technologies would, IMNSHO, do well to check basic science/technology before shelling out the shekels :-)

nooshinjohn

Why was there no unobtanium on the list?

mhardy6647

didn't see it ;-)

pitdogg2

maybe this is why they would use Ti in a VC

http://en.wikipedia.org/wiki/Paramagnetism

thanks to Mhardy I learned a little today......

mhardy6647

Sure, maybe so!
I don't doubt there is a good reason that they'd use it (and I am not a physicist, I'm a biochemist, so I am a l'il outta my depth on this subject)

I am having deja vu, paramagnetism came up elsewhere this week but I cannot remember the context.

pitdogg2

mhardy6647 wrote: »

I am having deja vu, paramagnetism came up elsewhere this week but I cannot remember the context.

Yea I have that all the time drives me nuts sometimes

Face

Ah, it appears I made a mistake. After visiting their page, it appears the voice coil former is made of Ti(piece VC is wrapped around), not the coil itself. This is probably done to keep the moving assembly's mass down and strength up. They use Cu for the actual coil. http://www.accuton.de/drivers/detail.php?driver=11&matID=4&appID=2

mhardy6647

That makes some sense - although I wonder whether there can be any magnetic eddies induced into the titanium from the VC...?