Hey all,

I posted a series in the Audio Forum DIY speaker category, but really it could have gone here.  I have tried a number of drivers in my 1952 Imperials, and have tried to understand some of the math/formulas too.  If interested, please check this thread:

http://www.audiophiletalk.com/cgi-bin/yabb2/YaBB.pl?num=1234718168

The short version is that there is a formula for calculating throat dimensions, and the apparent matches/mismatches I found seem to correlate with subjective impressions. Most BLH throats are too large for the drivers!   The same seems to be true with compression chambers, which ought to be a lot less than the driver Vas to get compression prior to the throat.

I believe one could do a more efficient search for the right driver by going this route.  I'm currently using an Altec 515E with earth-shattering results.