With the mike about 1 cm in front of the cone I get a really nice response. The slope above 4 kHz is an artifact, at a distance of 30 cm (and more) the driver keeps going to 16 kHz and then it drops rapidly.
The dip at the 63 Hz mark shows that the pipe is giving increased radiation resistance and thus reduced output from the driver in the 50-80 Hz range. The dB of driver and pipe can not be simply added as phase and radiation surface come into play.
Below is the output from the pipe, a broad peak around the fundamental at 60-70Hz, a dip of the second harmonic of 125 Hz and a second unwanted peak in the 200 Hz range. I will try to increase the damping material in the first half of the pipe to reduce the harmonics and at the same time keep as much as possible of the fundamental, more to follow...
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