My thinking was if I used a square thoat, the flare transition would be pure. The path length differences are within the compression chamber, but without a phase plug, there are path length differences using any throat shape. The compression chamber forms a low-pass filter, and the path length issues add to that. It becomes a variable, where cone and dust cover size and shape affect the response. This set of variables is hard to model without FEA, so you pretty much have to build and test. Every model of driver will be different.