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Old 23rd March 2009, 09:23 AM   #31
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One assumes (I haven't looked at the plans) that it's the thickness of the build material.

Makes no odds to the principle of it. A restriction is a restriction. Period.
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Old 23rd March 2009, 10:02 AM   #32
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OK, I've just taken a quick look for the sake of interest.

The Pensil is certainly a resonant QW line, & not an especially distinguished one at that; looks like only the most rudimentary QW math has gone into it, and it may be regarded in the same vein as the rather similar Zigmahornet. I have dark suspicions about harmonic nulls. F3 will probably be acceptably suppressed by the driver location, but higher modes will likely be more problematic.

FWIW, length / Fp has clearly been set to Fs; for the rest, it looks like raw guesswork, although, Vp appears is roughly in the region of a 4th order (reflex) vented alignment; whether that is accident or design, I wouldn't like to say.

Edit: I've just stuffed it through MathCAD for the sake of providing a few illustrative graphs.

Top plot: driver & vent output of the unstuffed pipe; you can clearly see the confirmation that the first mode is set to the 70Hz pipe tuning. Middle plot: FR of the cabinet when damped ~equivalent to plans. As suspected, note the harmonic null. Lower plot: FR of the cabinet with the same damping, but with the slight mass loading removed. It doesn't make a whole lot of difference, other than fractionally reducing the depth of the null at F5. Still, mass loading as suggested is purely a matter of degree. If there is a restriction, however slight, it's still technically mass loaded. Can't beat the laws of physics.
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Old 23rd March 2009, 10:53 AM   #33
Henkjan is offline Henkjan  Netherlands
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Quote:
Originally posted by raypalmer
Sorry Henkjan that link I posted was completely wrong:S

This is what I meant to link you to
OK, later today I'll run it through the model
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Old 23rd March 2009, 09:27 PM   #34
Henkjan is offline Henkjan  Netherlands
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here is te result if I leave everything but the driver unchanged
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Old 23rd March 2009, 09:30 PM   #35
Henkjan is offline Henkjan  Netherlands
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and here if I reduce the stuffing in the open end to half of that in the original
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Old 23rd March 2009, 09:33 PM   #36
Henkjan is offline Henkjan  Netherlands
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in other words: adjust stuffing to taste
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Old 23rd March 2009, 09:53 PM   #37
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Thanks muchly henkjan. Results look promising




FWIW I looked at the pensil before I built BJohannssen's TABAQ's, there was some conjecture about holes in the response and it being generally a little under-thought, leading me to settle on the TABAQ. Which has worked quite well for me!
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Old 23rd March 2009, 11:47 PM   #38
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Quote:
Originally posted by Scottmoose
OK, I've just taken a quick look for the sake of interest.

The Pensil is certainly a resonant QW line, ...
Thanks for the analysis.
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