Jon Waller wrote on Wed, 22 July 2009 15:05 |
Phillip, I think you are right. Clever of them and you...
But for this to work, the turbulent flow conditions in the small ports could give rise to 'chuffing' noises (a Richard Small term, I believe) at high power levels. Perhaps this drawback, combined with newer, larger xmax drivers, are why they were not included on the new SB1002 model.
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Jon,
I've read a couple of papers on these turbulence effects, and the change in the resistive component of the acoustic impedance of an undersized port can be extreme, like more than 2
orders of magnitude!
If the change in these small ports was similarly extreme (likely), they would nearly shunt themselves out of the practical acoustic system w.r.t. the large port.
Clearly, though, air has to move through them to cause the rise in acoustic impedance. If the effect is pronounced very near the inside end of the tube, perhaps there would be no "chuffing" at the outlet of the port tube. I truly don't know.
Not having experience with this particular SB1000 variant first hand, I don't know if this is audible or not. I know that if I was the manufacturer I would do a series of nearfield acoustic measurements of the cone, large port, and small port, at different power levels and signals, and I would try to correlate this to the impedance spectra taken under the same stimuli.
Academic musings worth probably less than 2 cents.