Okay, now I realize not all the PMC speakers are the same, but looking at this one PMC speaker measurement, I'm not very impressed with these $2,250 PMC GB1:
@ 150Hz, it's down like -12dB???
And from ~ 1.5-4kHz, it's down ~ -4dB??
http://www.soundstagemagazine.com/measurements/pmc_gb1/
You can't measure a TL with one mic placed like that. There is too much output from the port. You have to mic the port output separately and sum it with the woofer response.
That is a very small TL and it is not properly damped by the look of the impedance curve. I suspect this was done to increase bass output from the small driver.
Unlike a reflex enclosure, the pipe will assist the driver over 1.5 to two octaves. I suspect at the mic position there was cancellation between driver and port at the mic position.
As far as the 2 to 4 kHz smiley, I guess that is because Peter Thomas is an ex BBC engineer.
The BBC have long maintained that a slight 2 to 3 db droop centered on 3 kHz is desirable for a more spacious sound stage.
I agree to an extent, but I don't deviate much from flat. I will tell you one thing, even a tiny excess in output in that range, makes for a terrible speaker. So I never allow any excess in energy in that region. If I have to choose I always come down on the side of a dip, never a peak, not even a small one of a half db.
