I'd suggest one of two types, either a DI matched two-way or a three-way with a simple conical midhorn. The advantage of the two-way is simplicity and the advantage of the three-way is reduced bandwidth for each driver. Either will provide uniform coverage if done right, because the two-way is DI matched and the three-way is horn loaded down to a relatively low frequency.If the woofer is a JBL 2226 or equivalent, which seems to be the popular alignment for 15" pro woofers these days, then you'll want a cabinet between 2.0ft3 and 5.0ft3 tuned to 40Hz. Pick the port with the Helmholtz formula below and you're set.