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Old 22nd December 2012, 07:40 PM   #1
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Default Kongo build questions

Hi this is my first speaker build and i have decided on the kongo but i have a few questions i am thinking of making a sandwich of ply mdf and chipboard for the contraction and possibly having a thin layer of lead in there i think its 1.3mm thick would it be worth doing?

secondly would it be worth making the sides top and botton 25mm instead of 19mm

and thirdly here is a picture i would like to sort of copy Click the image to open in full size.

my question is how can i add a baffle like that does it matter if the driver is another 20mm out?

anyway i would appreciate any help
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Old 22nd December 2012, 09:51 PM   #2
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It would very likely just be more effective to use quality plywood as specified. The top and bottom have the least pressure and with the deflector are well braced so increasing their thickness would be moot. A lot less work too. Adding a supraBaffle is not a hardship.

dave
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Old 22nd December 2012, 09:57 PM   #3
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Adding a supraBaffle is not a hardship.

dave
if you don't mind me asking how would be the best way to do that would i make the baffle an extra 19mm thick so it would be 46mm or wold i have it just 19mm but the driver stands out

am i right in saying that all people do is add say 19 to the front attach the speaker to that then add side peices to ake it look like it say 60mm thick if so will any internals have to be changed thanks

Last edited by arnoldx3; 22nd December 2012 at 10:06 PM.
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Old 22nd December 2012, 10:35 PM   #4
chrisb is offline chrisb  Canada
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Originally Posted by arnoldx3 View Post


if you don't mind me asking how would be the best way to do that would i make the baffle an extra 19mm thick so it would be 46mm or wold i have it just 19mm but the driver stands out

am i right in saying that all people do is add say 19 to the front attach the speaker to that then add side peices to ake it look like it say 60mm thick if so will any internals have to be changed thanks
AFAIC, for drivers of this size class and physical mass the thickness of extra layer of baffle does not provide any sonic advantages, and indeed adds extra complication to the fabrication to avoid creating a very narrow "tunnel" immediately adjacent to the rear side of cone.



I've built several different designs with supra-baffles, and would not consider them and afterthought, but should be accommodated in the build of main enclosure by cutting a much larger hole in the front panel than required by the driver. Actually what I usually do is to cut the front panel as 2 shorter pieces and overlap with the suprabaffle. You can either screw them on and seal with closed cell weatherstrip tape, or something like 3M high strength double edge tape.


Whether or not you decide for a SB- don't forget to chamfer the rear side of driver cut-out, which is much easier to do with a 45dg bevel bit before assembly.

And to echo Dave's earlier comment, I don't think there's anything to be gained from material thicker than 18-19mm, or the heroic efforts to laminate materials and include panel damping for these enclosures. They're well braced by design, and even with the low frequency gain provided by the BLH/manifold, the FE126E is not likely to cause any objectionable cabinet resonances. If concerned about that, I'd be inclined in add a narrow brace between the side panels in the mouths, oriented to approximately bisect the angle between deflectors and horizontal panel that forms last leg of the manifold.
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Old 22nd December 2012, 10:53 PM   #5
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thanks for all of your help i guess i am only doing it for looks but do you think it would be bad idea to add a superbaffle?

if i add a superbaffle to the outside of the speaker and cut the hole out for the driver and then chamfer how big does the hole in the front of the speaker need to be would it work being 20mm bigger i hope this makes sense
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Old 23rd December 2012, 02:17 AM   #6
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Originally Posted by arnoldx3 View Post
thanks for all of your help i guess i am only doing it for looks but do you think it would be bad idea to add a superbaffle?

if i add a superbaffle to the outside of the speaker and cut the hole out for the driver and then chamfer how big does the hole in the front of the speaker need to be would it work being 20mm bigger i hope this makes sense


Looking at the Kongo plans, the internal width is 130mm, and the driver through hole required for FE126 is 102. I build this type of enclosure with the sides overlaying the internal panels, which in this case would leave 15mm margin either side of the front side of driver through hole.

Some quick doodling arrives at the following figures - surface mounting the FE126 on 19mm suprabaffle, and using a 10mm deep chamfer on back side, the driver cut-out would flare out to approx 122mm. Even without continuing the flare, that would make the front panel a bit delicate to move around, which is why I'd suggest cutting it in 2 pieces, to be overlapped by the supra baffle panel, and sealed with gasket / tape

As to shapes & dimensions for the SB, I happen to be partial to elliptical, but have the advantage of access to a CNC machine, which makes those very simple. Try to avoid square or rectangles that are even multiples of height to width. Ratios such as 1.414, or 1.618 are my favorites for both the width of SB relative to enclosure width, and the H/W of the SB. Once again using 19mm material, that would make the SB either 238x336 ( @ 1.414 * 168mm) , or 272x440 @ * 1.618.


Of course those numbers would change with different material thickness. I happen to use 15mm "baltic" birch type multiple for builds with smaller drivers such as these. While I also like to rebate all drivers for flush mounting, the Fostex FE series drivers have thin enough metal frames that they can be surface mounted with no discernible ill effects (at least to my ears), and don't really need any thicker material than that for baffles. The same cannot be said of Mark Audio drivers, or for that matter Fostex such as FX120 or F120A
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Last edited by chrisb; 23rd December 2012 at 02:26 AM.
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Old 23rd December 2012, 02:18 AM   #7
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Quote:
Originally Posted by arnoldx3 View Post
thanks for all of your help i guess i am only doing it for looks but do you think it would be bad idea to add a superbaffle?
As well as it is done well, a supraBaffle can bring aesthetic and sonic benefits.

One will need to adjust the panel that controls air cavity volume, but if one wants to go to town a sculptured back air cavity panel is a good idea.

dave
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Old 23rd December 2012, 02:50 AM   #8
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As well as it is done well, a supraBaffle can bring aesthetic and sonic benefits.

One will need to adjust the panel that controls air caity volume, but if one wants to go to town a scultured back air cavity panel is a good isea.

dave

I think Dave means to add pieces of material to the back panel of the driver chamber equal in volume to the amount of material displaced by the SB - which isn't really a whole helluva lot, and as he notes would provide an opportunity to add irregular contours to the rear surface of the chamber. Several builders of similar designs have gone to town on that.

Dave - get that keyboard fixes, or start watchinf what yoi typw
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Old 23rd December 2012, 03:57 AM   #9
chrisb is offline chrisb  Canada
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I think Dave means to add pieces of material to the back panel of the driver chamber equal in volume to the amount of material displaced by the SB - which isn't really a whole helluva lot, and as he notes would provide an opportunity to add irregular contours to the rear surface of the chamber. Several builders of similar designs have gone to town on that.

Dave - get that keyboard fixes, or start watchinf what yoi typw


geeze Dave, it kinda deflates the message when you post-edit your typos
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Old 23rd December 2012, 04:34 AM   #10
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thanks guys for the help i know i am probably asking stupid question but i jyst want to get it right so what you are saying is that the first chamber behind the driver i should extend everything by the thickness of the baffle?

by the way how do you calculate the size of baffle i was thinking either round or elliptical
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