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I'm helping a friend get started in loudspeaker design and a question came up about estimating acoustic offset. He doesn't have measurement gear so we're using manufacturer IB files and Jeff's Response Modeler to sim the baffle step, low end woofer response and the modified impedance curve.
He's decided to use XSim and we'll use that to create the minimum phase (derived phase in XSim) .frd and .zma files. Which brings me back to the estimated acoustic offset (mod delay in XSim). I seem to remember that an estimate for a "typical" 6 ½" woofer and 1" tweeter was about 1 ½". And I don't remember if that estimate was valid for minimum phase files or not. Do you guys have any opinions or guestimates? I suppose we could always punt on the acoustic offset, but I feel an estimate based on the experience of this group is better than none.
Finally, I don't use XSim that much and always get confused on the sign of the mod delay. Do you put a positive mod delay value in the woofer? I'm used to the negative value used by PCD.