Aftermarket B52 diaphragm COMP- 4 CL PETP film diaphragm.

it will fit the following speaker models: MATRIX 2000 newer version ,B- 52 LX 1515 V3, SL 1515 series

OEM part number is Comp-4 CLB, Comp- 4 CLS/B 

Voice Coil Diam: 1.75" 

Nominal Impedance: 8 Ohms