try to avoid operation below Fs


as distortion will be increasing rapidly. To determine actual system Fb with a certain enclosure/port configuration, measure the frequency of the lower and upper z peaks. Those are Fl and Fh. Now seal the port, and determine Fc, the single z peak. Fb = sq.rt. (Fl^2 + Fh^2 - Fc^2) Should be about where the dip was between the peaks when vented. Box plot advises keeping BELOW MACH 0.2 with your port velocity...if too high, as you noted, it can be audible under some conditions...Sam


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