You are speaking about 515-G which I believe is a circa 1994 Altec Lansing ferrite version in the 515 line. I have not mentioned this model as one of the models I was considering using- but that could change. At this point, it's not clear to me why you brought this model up. The 515 types I'm considering are the GPA 515-LF and GPA 515C. I see now that I had wrong info in my previous post- when I wrote "515B", I meant GPA 515C ("Classic")- my apologies. So, the two LF drivers that came to mind for my A7/828s are GPA 515-LF and GPA 515C.
"need for extra efficiency". About 2 years ago, I got a set of drivers that were originally belonging to some 1966 A7/825s: 416A LFs, N-500-E Xovers, 511B horns, and 802D HF drivers. The Xovers were not working, so I repaired them with some MBGO Russian caps- otherwise original. I bought a pair of 828s to install the components into. The 416As were pretty tore up, and rather than getting them reconned, I bought some 416-16Bs from GPA. The porting is original 828 spec- 205 sq in (I think)- not the more popular 90 sq in. Frequency response curves I generated showed overall same efficiency for the two port configurations- with some difference in the tow, of course.
This setup has always been aggressive in the high end- I believe for more than one reason. And HF attenuation knob on the Xovers almost always at max attenuation position. With the JBL 2446/2360 or JBL 2446/2397 horn setups I am substituting, I believe the SPL gap between LF drivers and HF drivers will even widen. In any event, I would prefer my A7s not to need any attenuation- and I had assumed that's possible. This is based on an uneducated hunch that the horns will sound better without a resistor in series. That's why I want more efficient LF drivers. I already know I'm a dumbass, and that some (many?) people may believe my hunch is silly.
This has been a long-winded way of asking: do you believe the GPA 515-LF or GPA 515Cs are appropriate drivers for my A7/828s? Other LF drivers I should consider? TAD? Also, FWIW, I've noticed that in original LF driver specs, 416As and 515s types are designated for 825/828 box use.
Thanks.......