[Anthony]

While thinking about a dipole sub, this occurred to me:

Since OB drivers are velocity transducers (as opposed to pressure), wouldn't a mostly flat driver make the best OB speaker?

I imagine the cone shape when pushing the air would have an uneven pressure distribution because it is not all moved together (hard to picture, I'll see if I can draw one up and post it).  Whereas a flat front driver would push the air more uniformly.

I'm not sure how this relates to sonics.  I imagine two effects: turbulence noise and distortion.  This is probably a secondary effect, that is, a really good driver that is cone shaped is probably still preferable to a less-suited one with a flat front.  But all other things being equal . . .

Any thoughts on this?
AC

[hurdy_gurdyman]

In theory, a flat driver would be better. In actual practice, It shouldn't matter much. Bass frequencies are far longer than the depth of the cone. Besides, a flat driver that is stiff enough to hold up to what's needed will be expensive to manufacture, and probably not as efficient due to the extra mass needed to make it stiff.

Dave

[Bob in St. Louis]

Servo motored Contra bass OB?? aa

[D OB G]

Hi Anthony,

I don't know if you are right, but in one design I am using 4 X Kef B139s in parallel per side.  Each has been re voice-coiled to 16 ohms.  They are not very efficient speakers to begin with, but by having four there is obviously an efficiency gain (not to mention the slightly lower Fs due to mutual coupling).

They have a nasty peak at 800 Hz, but I am actively crossing and equalising them at 125 Hz.

Together they move as much air as two 15" drivers and are very linear in response (up to that 800 Hz mark).

They are tremendously dynamic and "open", even though most people wouldn't use them in this application.

David