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Alpair 11MS pensil questions
Alpair 11MS pensil questions
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Old 29th June 2020, 01:00 PM   #1
airkitty is offline airkitty  United States
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Default Alpair 11MS pensil questions

Hi Guys,
I've built a set of Pensil cabinets out of Birch ply, not Baltic Birch alas. I need to mount the drivers on the wide side of the cabinet not the skinny as the instructions specify. Several years ago I recall one of the gurus (Scott or Dave or?) blessing this driver location. I've made the backs and bottoms removable so internal stuffing or lining will be easy. The Pensil specs call for some level of stuffing. I'm happy to use poly-fill or some other variant but am curious of the intent. Are we stuffing the cabinet to dampen cabinet vibrations to reduce unwanted coloration, slowing or speeding up the air flow to the terminus or something else? Also, should I still put the port on the same face as the driver? My plan is to have them painted by a car shop that painted my Fried subwoofers which have held up really well.
Thanks for any and all input.
Mark
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Old 29th June 2020, 04:30 PM   #2
Scottmoose is offline Scottmoose  United Kingdom
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Acoustic damping, not panel. If it were panel damping it would be high mass material fixed to the panels (not necessarily a particularly good idea for LF enclosures). It kills the pipe harmonics and linearises the LF response to the target alignment, along with flattening the impedance load.
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Old 29th June 2020, 08:32 PM   #3
airkitty is offline airkitty  United States
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Thanks Scott. You operate on far superior technical level than me for speaker building. Thank you for making the Pensil plans.
Can you tell me if the port on the same side as the driver is the way to go with the modified orientation I proposed?
Thanks again for any and all help.
Mark
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Old 30th June 2020, 09:07 AM   #4
Scottmoose is offline Scottmoose  United Kingdom
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Well, I don't actually recommend shifting the driver as such; you can do it, and it won't affect the internal box loading, but it will alter external factors (diffraction & step-loss frequencies) away from what was anticipated / designed. Some of these may be swamped by system effects, & it should be 'OK' but as noted, it will change things a little.

With that said, re the vent, you can keep it on what would now be the side if you wish, or shift it to what is now the front, providing you do not change the vent CSA and aspect ratio.
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Old 8th July 2020, 05:41 PM   #5
airkitty is offline airkitty  United States
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Thanks Scott.
I used to own Fried C3Ls and Wilson Audio Watts. I recall the both had rounded edges on the front baffle. I recall Bud Fried telling me he did the rounded edges to reduce the diffraction issues. Have you heard anyone trying to round over the front edges of the pensil cabinets? Does this idea have any merit 30 years after Fried described it to me? Thanks for your help.
Mark
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Old 8th July 2020, 06:25 PM   #6
planet10 is offline planet10  Canada
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Alpair 11MS pensil questions
Rounding or chamfering the front edges is never a bad idea, it does affect diffraction but for that to get into a low enuff useful frequency it has to be very large (3-4” D), much larger than you can put on a Pansil unless special constrcution measures were taken when building it to accomodate such a large edge treatment.

dave
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