Except for the KEF B139 (and discounting the few odd Japanese novelty offerings) no piston-type drivers seem to have ever caught on, and apart from expense - which shouldn't be excessive anyway - are there any reasons not to make 'cones' this way for LF applications, and any reasons they should be? I could see a Kevlar/Nomex honeycomb/Kevlar piston as having some merit.
In theory a flat front piston would be "better", by creating a geometrically flat wave source; in practice at Sub frequencies, wavelengths are WAY larger than the 5-8 cm difference between cone apex (where the voice coil is) and edge, so no difference= no advantage.
When 2 solutions reach exactly the same end, the simpler cheaper one is preferred.
Does the cone not amount to a larger SD than a flat piston given the same diameter? In this regard a better performer?
At these extreme pressure gradients, a cone would be more rigid than any flat surface driven at its center
It's really quite SIMPLE.
A CONE will contain and capture a LARGER amount of air than a flat cone of the same diameter.
This results in a larger amount of air being 'heaved' or thrown from it into the room.
And that translates to increased efficiency.
Additionally, a CONE is more rigid than a flat diaphram.
A CONE will contain and capture a LARGER amount of air than a flat cone of the same diameter.
This results in a larger amount of air being 'heaved' or thrown from it into the room.
And that translates to increased efficiency.
Additionally, a CONE is more rigid than a flat diaphram.
If it worked better than a conventional cone I feel sure the folks at KEF would have continued to use it and many others would have followed behind.
And, yes, if you ever saw a B139 unmounted you would see it starts as a cone, an oblong cone, but a cone nonetheless.
And, yes, if you ever saw a B139 unmounted you would see it starts as a cone, an oblong cone, but a cone nonetheless.
The "would have" means KEF obviously did not feel the need for them for whatever reason.
Technics/Panasonic, Sony, among others got on the bandwagon with that for a while... it didn't last.
More of a 'trendy' marketing thing than practical.
No to the first part. Yes to the second.
Take a dome tweeter, for instance. Stretch out the shape to a ridiculous extent, so that the "dome" now looks more like a geometrical cylinder (with the flat face pointing forward). Do you really think that the effective Sd of the diaphragm has changed? Invert this shape if you prefer, so that it now looks like a super deep flat-bottomed cone.
The BD139 foil faced solid expanded polystyrene flat diaphragm is backed with a tapered foamed plastic structure which joins it to the voice coil.
Without the cone backing, the flat front piston would not remain flat under pressure.
In what way would it flex? What if it was a mass of foam shaped like a rectangular box attached to the vc?
And why would you want that? It would be much heavier than an equivalent cone.
Regardless, no material is infinitely stiff. Everything will deflect to some degree under any load, regardless of how thick it is. So you have to balance all factors, not just "shape" or "thickness".