Subwoofer voice coil size

prodjay

DJ Extraordinaire
Dec 13, 2009
488
Bossier, Louisiana
Hey who can tell me what the difference between 2 subwoofers if both have the same power rating and very close sensitivity ratings, but 1 is a 3" voice coil and the other 1 is a 4"?
 
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steve149

Veni, Vidi, Lusi
Staff member
Sep 26, 2011
33,151
Prospect, CT
Theoretically a larger voice coil can produce a higher magnetic field to drive the cone. But there are different kinds of winding, sometimes multiple voice coils, and all the other differences in the construction. It's sort of like horsepower .. sort of meaningless unless you know the weight of the vehicle, how the torque is transmitted to the drive system, etc.

Generally larger cones have larger coils and magnets. More important would be SPL (measured consistently between the 2 subs), frequency linearity, and overall build quality.
 

prodjay

DJ Extraordinaire
Dec 13, 2009
488
Bossier, Louisiana
Theoretically a larger voice coil can produce a higher magnetic field to drive the cone. But there are different kinds of winding, sometimes multiple voice coils, and all the other differences in the construction. It's sort of like horsepower .. sort of meaningless unless you know the weight of the vehicle, how the torque is transmitted to the drive system, etc.

Generally larger cones have larger coils and magnets. More important would be SPL (measured consistently between the 2 subs), frequency linearity, and overall build quality.
This is for replacements for my 18" subs and new boxes that I will also need drivers for.

I was just trying to compare the difference between the Eminence Kappa Pro 18 LF-8 and the Omega Pro 18A

I've been using the Omega Pro 18A for years and never had any problems.

I will be adding some new boxes to my large system and will need to change out some older drivers (now wrong ohm load).
 

steve149

Veni, Vidi, Lusi
Staff member
Sep 26, 2011
33,151
Prospect, CT
Looking at the specs, there's a difference in box needs, so it depends on the box size and design you're fitting them into ...

According to speakerparts.com

The Kappa needs a 2.44 cubic ft sealed box or a 5.5 cubic ft vented box (optimal).

The Omega is designed for a .99 cubic ft sealed box and a 2.19 cu ft vented box (though the spec sheet shows a larger volume .. still smaller than the Kappa).
 

oldschool

DJ Extraordinaire
Jun 25, 2018
186
58
A bigger coil will put the location of where the coil is mounted to the cone, closer to the edges of the cone. It should reduce the cone flex and produce a cleaner sound.
Not always but more offten then not, bigger coils mean they can handle more power. It's kinda like a car. HP sells cars, torque wins races.
 

Handinon

DJ Extraordinaire
Oct 1, 2014
2,033
72
All things being equal (and they never are) the larger diameter voice coil can dissipate more heat. The voice coil is cooled by the pumping action of the woofer moving back and fourth, forcing air through the voice coil /magnet gap.The larger diameter VC has more surface area, thus better cooling IF it is made out of the same material as the smaller one.
 
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sawdust123

DJ Extraordinaire
Nov 10, 2006
240
56
Ventura County, CA
Steve has the best advice, when replacing drivers, look at the Thielle-Small (TS) specs. They will tell you if the driver is a match for the box.

As far as voice coils go, there are MANY parameters to consider than the diameter. In fact, there is an industry magazine called VoiceCoil that specializes in driver design. The parameters to consider include:
* Former type (the material the voice coil is wrapped on such as paper, kapton, aluminum, etc)
* Winding type (underhung, overhung, dual layer, etc)
* Wire cross section (round, rectangular)
* Tinsel type (the wires that go from the coil to the driver frame)
* Gap venting
* Thermal circuit

Cones come in hundreds of materials with different stiffnesses and weights and mechanical construction methods, All cones will have breakup modes where the cone is no longer exhibiting pure pistonic motion. The coil size will determine where, when and how the breakup modes start occurring. A lot of this will also depend on the surround and spider materials too.

Finally, when testing coils, one needs to look at the centering, impedance, rocking motions, rub & buzz and other issues. Like with any other product, some companies are better at quality control than others.
 

steve149

Veni, Vidi, Lusi
Staff member
Sep 26, 2011
33,151
Prospect, CT
Steve has the best advice, when replacing drivers, look at the Thielle-Small (TS) specs. They will tell you if the driver is a match for the box.

As far as voice coils go, there are MANY parameters to consider than the diameter. In fact, there is an industry magazine called VoiceCoil that specializes in driver design. The parameters to consider include:
* Former type (the material the voice coil is wrapped on such as paper, kapton, aluminum, etc)
* Winding type (underhung, overhung, dual layer, etc)
* Wire cross section (round, rectangular)
* Tinsel type (the wires that go from the coil to the driver frame)
* Gap venting
* Thermal circuit

Cones come in hundreds of materials with different stiffnesses and weights and mechanical construction methods, All cones will have breakup modes where the cone is no longer exhibiting pure pistonic motion. The coil size will determine where, when and how the breakup modes start occurring. A lot of this will also depend on the surround and spider materials too.

Finally, when testing coils, one needs to look at the centering, impedance, rocking motions, rub & buzz and other issues. Like with any other product, some companies are better at quality control than others.
I've got to get a t-shirt made with "Pistonic" .. got to be a hidden joke in there .. :)