The 375 was only one component of the system developed for the Westrex project. A unique bass driver, the 150-4C was also produced. This driver had a deep, straight sided cone to provide the stiffness required for horn loading while remaining light in weight for maximum efficiency. Four of these drivers were mounted in a massive new enclosure - the T550A. John Frayne worked with Bart Locanthi to develop new acoustic lens to be used with the 375 driver and two of these driver/lens combinations were mounted on top the the T550A. For the first time, JBL had produced a theatre system of a scale that could compete with the largest Altec VOTT systems. The T550A was sold directly by JBL as "Jim Lansing Theatre Sound System" and was also manufactured by Ampex as the C6000.