Voice coil and formers[bobbins]

[Bull]

Boring subject,but you have to consider it when buying a loudspeaker.Thats the part which will handle the thermal heat.

Paper formers are usually rubbish,because they can catch on fire at high volume levels; only good for cheap drivers where u don't wack up the volume,or guitar drivers,to give a special vintage tone.

Aluminium formers are okay,but they also deform[change shape] at high volume levels,at least they don't catch fire.

Kapton formers can take 250 o C Continuos,without any deformation.

Normex formers can take 800 o C continuos,without any deformation,and i know these are used in the Precision Device PD1840 driver.

Kelvar/Fibreglass/Carbon fibre/Teflon [composition type]

Now moving on to coils,there is polyamide-imide coated copper types,aluminium types,different windings such as hexagenal,square,and ribbon windings,also underhung and overhung types.

Could someone tell me what is Overhung and Underhung voice coils are.
And also what does 2 layer voice coil mean?
And how do they put two coils on one former in the dual voice coil arrangement?
Last but not least,can you tell the wattage by the number of turns of the coil,someone told me each turn = 1w rms,so 150 turns = 150w rms.

Please help me out,because i'm very confused.Also unlike a big heavy magnet,vented pole piece,and good wattage and freq responce spec sheet you can see.You can't tell whether the speaker your buying has a paper,or aluminium or kapton former,without tearing apart the speaker to see.But sometimes it is clearly stated on the spec sheet like Eminence use Kapton formers and Polyimide-imide coated copper voice coils.

[pinkmouse]

Hi Bull

Could someone tell me what is Overhung and Underhung voice coils are.

Underhung- the coil is completely contained within the polepiece of the driver when the driver is at rest, not very efficient, but can give a very linear response within strict perameters

Overhung- the voice coil extends past the polepiece in both directions, gives greater efficiency and linearity with larger excursions, but has a greater coil mass and therefore often a lower Frequency response.

The wattage of the driver is proportional to both number of windings, and thickness of wire used.

I have seen dual voice coil drivers with both the coils wound parallel, and one on top of the other, but I suspect parallel will give a better result, as the motor influence will be more symetrical between channels.

If you are just using your drivers for normal household volumes, you do not really need to worry about the temperature handling of the voice coil former, as they will not get that hot, this is mostly just marketing speak, and only really important if the driver is run at maximum power for a long period of time.

The only real difference is in wether the voice coil is conductive or not, conductive voice coils tend to have a slightly rolled off high frequency response, but you would see this from the published or measured response anyway.

If you want a more detailed description of driver design, may I suggest you buy a copy of the new edition of the Loudspeaker Cookbook, as it has a whole chapter on driver construction.