Posted by Lynn Olson on another forum
Discussion open to all, I'm particularly interesting in hearing from our acousticians or anyone with experience.
One of the real differences between direct-radiator bass and bass horns is the much higher directivity index (DI) for bass horns; by comparison, direct radiators in the 100 Hz ~ 500 Hz region are nearly omnidirectional.
Since room response is dominated by very severe modes and standing waves in the 100 Hz ~ 500 Hz region, there's a big difference between a near-omnidirectional radiator and one that is pretty directional. The modes will be at their worst with the near-omni radiator, since all the wall reflections are driven. With a higher DI, much less energy goes into the rear, side, floor, and ceiling reflections, and modes are not as strong.
In practical terms, when you allow for the contribution of room modes, the higher-DI horn system may deliver flatter response, even if the horn itself has rougher response compared to a simple direct-radiator.
Discussion open to all, I'm particularly interesting in hearing from our acousticians or anyone with experience.