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Old 26th January 2013, 08:06 PM   #1121
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...it is still at trial and error stage?
Yes. The iBIBk is a concept needing empirical detailinhg. Must be an even number of years ago i did it.

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Start small and expand as needed?
That is the best plan. Up to about a 3rd the length of the pipe (ie 2/3rds of the box height). If i was doing it i'd accomplish it with an increasing number of drilled holes. And i'd put half the slot on each side (i can't remeber what i drew.

dave
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Old 26th January 2013, 10:48 PM   #1122
rock12 is offline rock12  United States
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yes the cornu tang bang 318
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Old 27th January 2013, 05:29 AM   #1123
freddi is offline freddi  United States
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a Sapkowski patent holey Karlson port straight cross-section line might be something to investigate with foam board - - don't know how it might work overall - "???????" ??? ??????????. - ?????? ??? ??????
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Old 28th January 2013, 02:24 AM   #1124
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a Sapkowski patent holey Karlson port straight cross-section line might be something to investigate with foam board - - don't know how it might work overall - "???????" ??? ??????????. - ?????? ??? ??????
Klassno link. I like the Karlson-evolution approach, taking into consideration the possible (real IMO) quarter-wave action and the tapped horn aspect of it. I skimmed through the paper you linked about Helmholtz resonators with large apertures - the math was heavy, interesting nonetheless

I wonder, can one attenuate the 3/4, 5/4, 7/4, etc, modes in a pipe by drilling small de-Q'ing holes at the corresponding anti-nodal points - without affecting the fundamental QW mode too much? I suppose I could test it easily enough.

IG
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Old 28th January 2013, 02:46 AM   #1125
xrk971 is offline xrk971  United States
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IG,
Drilling small de'Q'ing holes would indeed reduce the other modes but at the expense of collapsing the strength of the fundamental mode - as anyone who has played a flute knows how the smallest leak in one of the pads or finger holes will make the low note disappear. I discovered this first hand in my recent BIB (FIB) build when I did not seal the bottom on well because I was adjusting stuffing. There was no deep bass at all. Once it was sealed properly the low note came in strong.
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Old 28th January 2013, 03:00 AM   #1126
IG81 is offline IG81  Canada
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IG,
Drilling small de'Q'ing holes would indeed reduce the other modes but at the expense of collapsing the strength of the fundamental mode
Might reduce the QW mode too much to be worth it I suppose. It might only work for real far-up modes, like 7/4 and more, where the holes could be well away from the pressure antinode for the fundamental (mouth), but this is easily dealt with using stuffing.

IG
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Old 28th January 2013, 12:11 PM   #1127
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The use of foam for lightweight enclosures is reminiscent of my first speaker project...in 1955. The November 1955 issue of Popular Electronic featured an article, by the now noted author David Weems, on building a corner labyrinth style enclosure using a sheet of Celotex. I remember this enclosure well, as my mother was very angry that I messed up her Kitchen when cutting out the panels for same. It used an 8 inch driver, of which mine came from a junked Zenith TV set. As I recall it worked very well with my Alliied Radio S 723 10 Watt amp.

Some other material which you might like to try is the 1/2 foam paper backed insulation board sold under the John Mansville name. It very light weight, cuts easily with a carton knife, and can be cemented with Tacky Craft glue or the caulking gun type of glues made for foam products. Another, some what heavier and dense product is Homasote, It is used for sound deadening and insulation. It cuts with a saw and takes most wood glues and can even be nailed. There are a lot of materials that can be used as an alternative to MDF or wood for enclosures, just keep your eyes and mind open for them.
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Old 28th January 2013, 12:45 PM   #1128
xrk971 is offline xrk971  United States
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KlBIrd,
Thanks for the tip on the half inch foam board from John Mansville. Is this something available at Lowes or HD, or is it mostly available for building contractors? Is this that pink egg carton like foam with paper cover? I seem to recall seeing it at construction sites. So the famous Weems did foam core speakers back in 1955? And I thought I was on to something new
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Old 28th January 2013, 01:04 PM   #1129
KLBIrd is offline KLBIrd  United States
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You should be able to find it a Lowes or your local lumber dealer. Its called Johns Mansville AP Sheathing. The outer paper is white with yellow inner foam Contact me via my web site at; Ken Bird.com and I will send you a PDF of the 1955 Weem's article.
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Old 29th January 2013, 03:38 AM   #1130
xrk971 is offline xrk971  United States
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Ken Bird,
I saw this foam which is very cost effective and has a poly facer sheet. This just may be the thing to try for a larger Cornu horn build. It will keep things light weight yet provide more rigidity since it is half inch thick. Just need to cover with wall paper or the like as the markings are pretty ugly compared to plain white foam board. Have you used polyisocyanurate foam before? Maybe the John Mansville stuff is similar?
Shop Insulfoam 1/2-in x 2-ft x 4-ft Expanded Polystyrene Insulated Sheathing at Lowes.com

http://www.lowes.com/pd_42729-236-26...ard&facetInfo=

Last edited by xrk971; 29th January 2013 at 03:40 AM.
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