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 23rd March 2009, 09:23 AM #31 diyAudio Member     Join Date: Mar 2005 Location: UK 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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Join Date: Mar 2005
Location: UK
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.
Attached Images
 pensil.gif (17.0 KB, 219 views)

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Join Date: Jan 2006
Location: Berkel en Rodenrijs
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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Join Date: Jan 2006
Location: Berkel en Rodenrijs
here is te result if I leave everything but the driver unchanged
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 ct222 met andere driver.png (3.9 KB, 168 views)

diyAudio Member

Join Date: Jan 2006
Location: Berkel en Rodenrijs
and here if I reduce the stuffing in the open end to half of that in the original
Attached Images
 ct222 met andere driver en minder demping.png (4.1 KB, 164 views)

 23rd March 2009, 09:33 PM #36 diyAudio Member     Join Date: Jan 2006 Location: Berkel en Rodenrijs in other words: adjust stuffing to taste
 23rd March 2009, 09:53 PM #37 diyAudio Member     Join Date: Dec 2008 Location: Burlington 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! __________________ Wherever you go there you are.
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Join Date: Mar 2009
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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