Sorry, if this is only of interest for my fellow Europeans
but
I want to share my experience with a very interesting and affordable midwoofer for OB use: the Monacor SPH 176:
http://www.monacor.com/int/en/produktseite_suche.php?artid=4084&spr=EN&typ=fullUnusual for a stamped metal basket it features a rear vented spider and venting holes in the coil former. So no vented pole piece is necessary.
I found some measurements, which are independent from the official ones and they showed a shallow dip at 300-2000 Hz.
Simulating this driver at the top of a 30-40 cm wide OB, EDGE showed a shallow peak (thin red lines) just in the same range as the dip (other lines).
I put the real driver in a real 40 cm wide OB (Don´t mind the tweeter in front of the SPH-176. I took it off for measurements)
and applied an active 230 Hz HP and a passive 2.7 kHz LP filter. 30° off axis I got this measurement:
Without the LP filter and on axis SPL looks like this:
Of special interest is the added measurement of the output to the rear (red line). Regarding the stamped frame both front and rear output are very well in line up to 2 kHz.
While I am still struggling with that coax tweeter alignment I much appreciate the very natural rendition of the SPH from 200-2500 Hz.
Rudolf
BTW: If you fill the back side of the hollow U-shaped rim of the driver with hot-melt adhesive (as I did), the distortion peak of the original driver at 3-4 kHz is significantly reduced (compare red and blue peak in the first diagram).
