Q: Kapton vs Aluminum VC-former and different wire

[Ultima Thule]

Hi,

I have tried to find some informtion regarding the use of different voicecoil former materials, as the the subject states: Aluminum VS* Kapton... but I would also like to know about other VC-fomer materials as well and what's the advanatge and disadvantage with respective.

I hvae understod so far that VC fomer of a conducting material is acting as a brake in the magnetfield as the magnetic filed developes a cuurent in the VC fomer, but because the VC fomer is a conducting material it will shortcut the current developed by the magnetic field.

Now I have read that some manufacturer actually use a combination of both Aluminum and Kapton for VC fomers, but that is another storry where they just want to "linearise" the VC ecursion in the magnetic field.
Ok, I give an example: Some have a copper ring at both ends, and when the VC is making large excursion the copper ring will act as brakes at the end excursion when they enter the magnet field in the magnet gap in an attempt to controll cone movement, especially in subwoofers.

But let us now concentrate at the material choice alone for VC fomers.

I wonder also how the VC fomer of a conducting material affect the magnetic field, does it give rises in eddy currents and modulating magnetic field when a conducting VC fomer moves in the magnetic field?

VC wire: are there different types of materials and alloys used as VC wires besides pure Copper and Aluminum wires?

And what is the objective/subjective sound qualities among the different material choices in VC fomers and wires?

Regards Michael

* VC = voice coil

 

[Ultima Thule]

After a week without any new answers in this thread I bump it up!

 

[gary f]

about voice coil wire, some manufacturer use silver wire (seas excel tweeter 001 for example). The conductivity is higher but mass is also higher. Alu is lighter than copper. Don't know what are the consequences of different materials, but a light voice coil and cone assembly is a good thing for sensitivity.

There is also different kinds of wire. Flat wire, round wire.

And you can have many layers of wire. More layer means more motor strenght but more VC inductance.

F

 

[rjb]

In bass drivers an al former damps the bass resonance and so alters the Q of the driver

 

[AndrewT]

Hi,
square and rectangular wire is used edge wound.
The idea being to minimise resistance by maximising conductor without making the gap wider.
Hexagonal wire is also available.
A stiff former is required to take the motor drive forces out to the cone without any flex.
Aluminium is often used in treble units to lower weight.

 

[Joules]

Metal voice coil formers are machanicaly much more ridged and compress less under large impulse loads. This means they should provide a more detailed and dynamic sound. How ever because of metals conductivity it does have damping issues that can get in the way. There is a metal that is more ridged and slightly heaver than aluminum however it is very resistive for a metal and has graetley reduced damping effects. This material is Titanium!

 

[AndrewT]

Hi,
does a slot in the coil former get over the shorted turn problem?
Or is the shorted turn even a problem?
Titanium is stiffer than Aluminium but how much? Compare an aluminium alloy (maybe L72 or select another high stiffness alloy) with titanium and then divide the stiffness by the S.G and get stiffness per unit weight. I suspect there will be little difference.
Do you have access to the figures?
Titanium has a superb fatigue life but I don't think this could make up for the additional cost involved.

When speakers use 1, 2 or 4 layers, are all the layers wound on the outside of the former?

If there is only one layer how does the return wire get back to the start end through the gap without making the gap wider?

Would it be better to wind a 4 layer coil with the 2 layers on either side of the former?

 

[Ultima Thule]

Hi all!


Joules:

About Titanium, yes i have heard about it very little, do you know who use Titanium for their VC's?
Pitty it's a such expensive material, I guess just the coilformer would cost something like 100$ or so...


AndrewT:

Slots in the coilformer may help a bit, but at the same time the structure rigidity will be also weaker, and the roundness of the VC may suffer is my doubts.


In general:

Yes, different coil wire materials have their advantage/disadvanatge, weight is one thing.
BTW, does anybody know any Aluminium, Copper or any other metall which is an alloy and have such a property that the resistance doesn't increase too much with temperature?
I have read somewhere about one Copper alloy yet patented.


Regards Michael

 

[DanWiggins]

Hi,
does a slot in the coil former get over the shorted turn problem?
Or is the shorted turn even a problem?
Titanium is stiffer than Aluminium but how much? Compare an aluminium alloy (maybe L72 or select another high stiffness alloy) with titanium and then divide the stiffness by the S.G and get stiffness per unit weight. I suspect there will be little difference.
Do you have access to the figures?
Titanium has a superb fatigue life but I don't think this could make up for the additional cost involved.

When speakers use 1, 2 or 4 layers, are all the layers wound on the outside of the former?

If there is only one layer how does the return wire get back to the start end through the gap without making the gap wider?

Would it be better to wind a 4 layer coil with the 2 layers on either side of the former?

The slot in the former helps immensely in eliminating the "shorted turn" effect. Without the slot, you get a massive shorted turn, and very little motion. With the slot, things dramatically decrease in terms of counter-force from a shorted turn.

Titanium is stiffer than aluminum, but considerably heavier. And since it's really in compression/tension along the former (not across the former) the extra strength from titanium isn't needed. Just a lot of extra mass for really no more usable strength.

Typically all voice coil layers are wound on the outside; winding them on the inside is occasionally done, but can lead to buckling of the windings as they thermally expand.

For the other question... Yes, there are some metals with nearly zero temperature coefficients (DCR doesn't change with temperature); however, they tend to have very high bulk resistivity to start with, meaning you begin with a very high DCR.

For example, phosphor bronze. About 1/5th the tempco of copper, but about 7 times higher in bulk resistivity. So you end up with more thermal stability, but 7 times the DCR of the copper voice coil.

Dan Wiggins
Adire Audio®

 

[pajazo]

Hi all!


Joules:

About Titanium, yes i have heard about it very little, do you know who use Titanium for their VC's?
Pitty it's a such expensive material, I guess just the coilformer would cost something like 100$ or so...

Is titanium really that expensive? I did a quick google search and this is the first result:

http://minerals.usgs.gov/minerals/pubs/commodity/titanium/670798.pdf

According to it titanium costs only a few dollars per pound (~0,5 kg).

 

[Joules]

Any time a conductor moves through a perpendicular magnetic field, eddy currents will circulate around the field line, absorbing energy. The higher the resistivity of the conductor the smaller the circulating currents and less energy absorbed. Titanium has both stiffness and low conductivity with a small increase in mass (approx 1.6 X that of Alum). Titanium is approx 1.5 x stiffer than alum. and if done right could be made abit thinner to help compensate for it's higher dencity.

 

[Ultima Thule]

Thanks all..


Dan:

Are there any acceptable constant tempco wire with low enough resitance used for voice coils?(except that, as I mentioned earlier, someone have a patent for some alloy for VC wire, just don't find the source when looking right now, have to come back later, if my memory serves me at all..)
Do you use any kind of alloy wire for your products or just the common Copper and Aluminium?


Pajazo:

thats not the kind of source to look for, Titanium foils are very expensive, try goodfellow.com for yourself...

But if anyone knows a cheap source for Titanium foils I would really like to take part of that information!


Regards Michael

 

[DanWiggins]

Ultima,

There are two alloys that I know of, one patented by JBL and the other by Dr. Earl Geddes. Using either for voice coils would violate their patent.

We use plain copper for 99% of all drivers; aluminum only when mass must be kept to an absolute minimum (it is less conductive than aluminum, meaning for a given DCR you get less BL with aluminum as compared to copper).

Dan Wiggins
Adire Audio®

 

[rjb]

Titanium

By the way, Jordan used titanium in one of his 4 inch designs, marketed by Audio and Design in 1966/67. Cost even then did not seem an issue, but it was rather difficult for him to shape. An article in November 1966 Wireless World covers this. He claims better HF and transient response using this material, but I have not seen any listener reviews. I suspect different cone shaping gave him similar results with aluminium.

 

[Ultima Thule]

Dan:

Yes, Geddes was the guy I had in mind, I did btw a search at USPTO with Geddes as inventor and came up with 153 hits, non of them talking about Low Thermal Compression Voice Coil, yet I found several other patents by the Earl G.
Would be curious to know what the patent says as Copper Nickel alloy is nothing new, but maybe the "use" of it...


RJB:

I note your point regarding the cost, good question, was Titanium so much cheaper before, however I do admit I dont know the cheapest source.
Or perhaps it was fake "Titanium", eg. heat treated Aluminium is also greyish.


Regards Michael

 

[David Gatti]

The Scanspeak 26w8861 10" woofer, which I use in my Delta, also uses a titanium former.

 

[Pan]

I think most of the new revelator woofers from SS uses titanium formers. Accuton also use Ti in several new drivers.

A very good Swedish speaker manufacturer (Ino Audio) also uses Ti in some designs.

/Peter

 

[hunter audio]

hi

Ultima - I think you need the Loudspeaker Industry Sourcebook

the least - as it seems from your queries you are gearing up for production - all the best

suranjan