ici:

" http://www.diyaudio.com/forums/multi...ng-mass-5.html

If you can find a pair I would recommend the Yamaha JA3882, it is not easy to use and won't work in Onkens. The magnetic circuit is 13 kG, 4" VC, mms of 52G. The ideal is horn loaded as it has ultra low Qts and reasonably high Vas.
This driver makes any other 15 I have heard sound fat and slow, it leaves the fabled 515 sounding like an 80 year old dog (if it were possible). This, in a pair of Altec 210 cabs. One side running the Yammies the other the 515's.
This is the best there is. Not that I am biased nor in the slightest one eyed. I will dig out the PDF and post it. If possible I will post some pictures as well.

http://audio-heritage.jp/YAMAHA/unit/ja-3882.html"