What are the benefits/disadvantages of a larger voice coil?

[454Casull]

How does the size (the diameter/circumference) affect motor strength, inductance, etc.?

[KevinLee]

Hello,

A larger voice coil will provide you with an overall stronger motor/cone assembly. There will be more surface are to glue the cone & spider & former together.

A larger voice coil will also help in keeping hte voice coil cool. It will dissipate heat better.

The size will not effect the impedence, the windings do that.

Inductance, not sure. I am sure others will.

Regards

KevinLee

[Bill F.]

Below saturation, the geometry of the voice coil will subtly affect the Le, inasmuch as the ratios of winding width, thickness, and diameter affect the performance of an air-core choke.

I like large-diameter VCs for many apps. For example, I believe the dome mid-bass is a fertile direction for exploration. How about a 10" voice coil? An underhung topology wouldn't need a very thick top plate, and the inherent heat sinking would be awesome--power compression would be a thing of the past...

[454Casull]

An underhung voice coil must fit inside the top plate...

Besides, aren't dome mid-range units hard to do? The few on the market aren't comparable to the better cone midrange units, I've heard.

[thoriated]

Some say that a larger voice coil adds more moving mass, which may have a grain of truth to it, but the JBL E145 combines a moving mass of 55 grams (very light) with a 4" vc and still manages to handle 300 watts music power.

[Bill F.]

An underhung voice coil must fit inside the top plate...

Exactly. So if you take a given 3" VC, unwind it from its former, and rewind it on a 10" former with the same number of layers, the winding height will be 0.3x the original height. Thinner top plate for same Xmax. And the heat sinking would be multiplied.

There shouldn't be much of a weight penalty if any. Since the dome VC it attached around the perimeter (more attachment area), you'd have the makings of a stiffer system without having to increase diaphragm thickness.

It probably wouldn't be cheaper to produce, and there may be other downsides I'm not thinking of, but I think it could be a really great performer.

[Ap]

A 10" VC on what size cone?
If driving a 10" cone then all the force is at the perimeter which just wouldnt work as there would be nothing to hold the apex of the cone.
I think 3" is about the limit, on a 6" cone this puts the 'driving force' iin the middle, any further and I would imagine cone flexure to start creeping in.

[Duo]

Cones flex anyway.

Goodmans designed the cones in their loudspeakers specifically to flex in order to produce the desired frequency response.

I mean, if the cone folds up, you have a problem, but I think it could be made to work. Cones can be made very tough these days, with just whatever properties we want in many cases.

[Vikash]

Originally posted by Bill F.
Exactly. So if you take a given 3" VC, unwind it from its former, and rewind it on a 10" former with the same number of layers, the winding height will be 0.3x the original height. Thinner top plate for same Xmax. And the heat sinking would be multiplied.

There shouldn't be much of a weight penalty if any. Since the dome VC it attached around the perimeter (more attachment area), you'd have the makings of a stiffer system without having to increase diaphragm thickness.

It probably wouldn't be cheaper to produce, and there may be other downsides I'm not thinking of, but I think it could be a really great performer.

Bill has mentioned cost but I think it needs a little more weight. The quantity of steel required to make a >10" motor and the extra magnets required would make this very expensive indeed (relatively speaking), and thus probably only practical in the DIY realm.

Off course the benefits mentioned sounds very appealing

[Bill F.]

A 10" VC on what size cone?

I'm thinking dome, so VC dia.=diaphragm dia.

If driving a 10" cone then all the force is at the perimeter which just wouldnt work as there would be nothing to hold the apex of the cone.

If you're worried about rocking modes, using a spaced pair of surrounds/spiders would take care of that.

If you're talking about deflection under load, IMO, one of the big advantages of a perimeter-driven dome is that as the cantilever distance increases (from the driven edge toward the unsupported center), decreasing amounts of mass are added. This is an improvement over an apex-driven cone where most of the mass is located at the end of the cantilever farthest from the VC, putting greater deflection loads on less material.