There's an AES 1991 convention paper by JBL staffer D. Button that compares 15" woofers.
It's a technical discussion rather than a sales pitch so the drivers aren't identified by brand or model.
One is clearly a JBL but I can't identify the model.
The specifications are identical to a 2227 frame - 600W, 4" VC, 0.5" thickness top plate, pole vents etc.
But the Xmax is much more than a 2227 and Mms is 150 gm so it looks a 2226/2227 cone with extended VC and more mass.
This doesn't match any model in the JBL Pro Thiele/Small parameter list.
But some subwoofers are not in that list, consumer ones for example.
Anyone know what this is?
David