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 windings on a voice coil

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Jake Jesty
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PostSubject: windings on a voice coil   Sun Nov 25, 2012 2:19 am

Does windings on a voice coil matter. Like is thicker the better. Or thinner and more windings better. Is 22 gauge better than 16 gauge and why please let me know.
Thanks
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muriloalvares
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PostSubject: Re: windings on a voice coil   Mon Nov 26, 2012 5:21 pm

Depends,

smaller gauge allows for more turns (more length) increasing the L on BL (force factor of the speaker). Smaller gauge also increases the Re thus the impedance. Trade offs, trade offs...
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chrisbaldelli
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PostSubject: Re: windings on a voice coil   Tue Nov 27, 2012 4:46 pm

As Murilo said, current carrying capacity (ampacity) is directly related to wire cross section and thus the awg.

The magnetic field is relatively set, as is the size of the gap (length and width). To maximize force (BL), you want to maximize the number of windings. Smaller cross section allows for more layers and tighter winding. Flat winding helps slightly.

With smaller wire and the same power... you'll generate more heat. Woofers can fail mechanically, thermally, or electrically. Mechanical failure can be from the suspension extending too far or the force being too high on glue joints. Thermal failure is usually due to exceeding temperature ratings for the coil, tinsels, former, etc. Electrical failure is typically a short due to mechanical or thermal.

So if you want more power handling, the wire gauge should be bigger, spiders should be softer, better motor venting, and a long throw setup. If you can't change the motor, stiffer spiders, a smaller box, and looser clearance between the coil and gap will help. The decreased resistance and better cooling will help to cope with the added power... but the efficiency will drop off due to lower BL.

If you want better efficiency, the wire gauge should be smaller, spiders should be softer, better motor venting, and a long throw setup. If you can't change the motor, make sure the voice coil to gap clearance is tight, keep the motion relatively linear, make sure the coil is cool. Maximum the BL without coil rub or bottoming. Box design should minimally affect the woofer's behavior (no impedance rise).

Just my 2 cents.
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Alan
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PostSubject: Re: windings on a voice coil   Tue Nov 27, 2012 6:05 pm

So jake. At the end of the day. My 16guage 4 layers i told ya about are pretty badass Very Happy
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Jake Jesty
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PostSubject: Re: windings on a voice coil   Wed Nov 28, 2012 1:21 am

Man Alan u told me urs is 22 gauge
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Alan
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PostSubject: Re: windings on a voice coil   Wed Nov 28, 2012 11:40 am

Nope. Told ya mine was 16guage 4 layer vs others we spoke about 22 guage 8 layer that like to hold heat and burn up from the inside out
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PostSubject: Re: windings on a voice coil   Wed Nov 28, 2012 11:59 am

Smaller cross section, more windings... call the fire department. Confirmed by the man himself.

Alan, which materials have you identified as the most successful for high power applications? Wire (cu, al, ccaw), wire coatings (not a clue what ceramics are used), and formers (kapton, stainless, aluminum)
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chrisfish
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PostSubject: Re: windings on a voice coil   Wed Nov 28, 2012 1:02 pm

8 layer flat wound aluminum Smile
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PostSubject: Re: windings on a voice coil   Wed Nov 28, 2012 5:37 pm

That's what I've always heard. Aluminum is the voice coil material of choice.

This paper by GE outlines it quite well:
LINK

Basic story is that aluminum is 40% less conductive, 40% less strength, 50% lighter, and expands 50% more when hot. Once the material is sized appropriately, the conductivity-to-weight ratio is equivalent.

To us... it means that you should size the top plate appropriately, but otherwise it doesn't make much difference.

As Jacob @ Sundown suggested in this thread:
LINK
Acoustic power is generated when the cone gives momentum to the surrounding air.

Acceleration = Force / Mass

The force is motor force from B*L. The mass is the moving soft parts. B is relatively fixed. L is approximately:
L = pi * voice coil diameter * # of turns
L = pi * D * (# of layers * gap height / wire diameter)

From this you can see that small diameter and lots of layers is best... but the cooling capacity will determine how small you can go. These will produce more resistance, which is why alot of people use BL/Re or BL^2/Re to measure the relative beefiness of a woofer. Given how "hand waving" the arguments get, and how confounding the variables are, it's a decent metric.

I think the best solution is a well-ventilated motor with a huge gap, huge wire, and lots of windings. Even then, the magnetic field weakens and linearity suffers. Everything is a compromise.
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PostSubject: Re: windings on a voice coil   Mon Dec 03, 2012 2:33 pm

Just have to watch out because with low B and high L you have lots of flux fluctuation (distortion). Inductance will be high as well as the variation of it.
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PostSubject: Re: windings on a voice coil   Mon Dec 03, 2012 3:27 pm

muriloalvares wrote:
Just have to watch out because with low B and high L you have lots of flux fluctuation (distortion). Inductance will be high as well as the variation of it.

With regard to inductance, the voice coil's self-inductance (Le) is pretty low (a couple mH). With a really long wind, it does contribute to the total impedance. The real issue is when the woofer extends too much and the structural metal acts as an iron core. Air core vs iron core inductors is ~100x the permittivity (and therefore the inductance). Woofer data shows ~10x less inductance at full excursion when you use shorting rings.

What SPL woofers use a shorting (Faraday) ring? I've heard about the Sundown Z/SA/NS series, JBL GTI series, Alpine Type R, Dayton Reference series, and the TC Sounds Epic & LMS Ultra. Seems like a slam dunk feature for high end woofers... not just an SQ feature. It does require significantly more magnet (cost and weight), but the linearity is better controlled.

Great post from Jacob @ Subdown:
LINK
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muriloalvares
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PostSubject: Re: windings on a voice coil   Mon Dec 03, 2012 3:52 pm

No doubt about that! (I guess you wanted to type "permeability")

Shorting ring is like a shorted transformer secondary. You want all that wire in the gap but you would rather not have any inductance as it opposes AC.
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chrisbaldelli
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PostSubject: Re: windings on a voice coil   Mon Dec 03, 2012 6:49 pm

You're correct. Permeability.

I've got a project at work, that's effectively a mega-sized voice coil. 0.125" diameter conductive stainless (~8 awg) wire with a coating, 20000 ft wrapped on a 24" spool. That's ALOT of potential for inductance, and sending an AC signal down it is quite the challenge at any useful frequency.

I took a home audio tweeter, midrange, woofer, and sub... and ran them through an impedance analyzer. You could see that the behavior was the same, but the resonant frequency dropped and the inductance rose as the voice coil got larger.

I'm hoping that we can use the well-known behavior of speakers to predict how this 20,000' coil will react. It's a long shot... but this is the kind of research that gets me excited (in my pants?).
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