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Old 11th February 2011, 07:31 AM   #401
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Location: Bangalore, India
O.K. I want to make jbell's single sheet TH, in a not so single sheet way. I would like to use 18mm ply and use bracing like in the Tuba24 - running through the cabinet, a little off centre and with holes throughout to allow for movement of air through the 2 halves of the cabinet.

My question is, what are the optimal dimensions, not minding that a cab takes more than one sheet?
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Old 11th February 2011, 11:25 AM   #402
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These are the optimum dimensions.
If you use 18mm ply then you will have to recalculate the internal panel points. I made mine with 18mm outer panels and made the sides a half inch bigger in both dimensions to accommodate that. then used half inch ply for internals to keep it the same inside. Worked for me but i am yet to test them and see if they have turned out as good as Jims.
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Old 11th February 2011, 12:18 PM   #403
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Quote:
Originally Posted by Dave NonZero View Post
These are the optimum dimensions.
If you use 18mm ply then you will have to recalculate the internal panel points. I made mine with 18mm outer panels and made the sides a half inch bigger in both dimensions to accommodate that. then used half inch ply for internals to keep it the same inside. Worked for me but i am yet to test them and see if they have turned out as good as Jims.
I just finished my second one. 3/4" exterior panels( 1/2" over on exterior dimensions also ), and 5/8" internal panels . internal dimensions were kept the same and results are very good. I did have to change the baffle corner to back panel dimension from 9.07" inches to 9 1/2" though. The math doesn't add up for me any other way. Unless i'm missing something.
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Old 11th February 2011, 02:05 PM   #404
tb46 is offline tb46  United States
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Hi runrod1948,

Could be that you didn't step the front panel (13") back as in jbells build. Not that it matters.

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Old 11th February 2011, 09:22 PM   #405
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Hi tb46,

well, the front panels in the right place but I think I included it in the 15 3/4" dimension of the speaker panel, therefore the error. fortunately the cab still works right. I'm surprised the design is so forgiving.
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Old 12th February 2011, 02:13 AM   #406
tb46 is offline tb46  United States
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Hi runrod 1948,

When you put a design into Hornresp (or even better int AkAbak) you can check which dimensions are critical, and which can be varied widely. Jbell hit a home run with this one, which doesn't mean you cannot fiddle with it in Hornresp if you are willing to relax the single sheet requirement, but sometimes it is best to leave well enough alone.

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Old 12th February 2011, 02:17 AM   #407
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Thanks everyone for your responses. Did anyone add internal bracing and compensate in internal volume for the braces as well? As I already mentioned, I want to run a brace right through the cross-section, a little off centre, and drill about 3"-4" holes to allow for free movement of air between the two halves.

I also plan to use tar-felt for all internal panels, secured with rubber adhesive. I have found that the panels become very stiff and you can hardly feel any vibrations on the outside of the panels.
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Old 12th February 2011, 03:12 AM   #408
tb46 is offline tb46  United States
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Default To brace or not to brace.

Hi Samuel Jayaraj,

I just entered the data into my Hornresp model to reflect an internal solid center brace. In other words, reduce the internal width by 1/2". There is virtually no difference in the resulting curves between brace or no brace.

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Old 12th February 2011, 06:02 AM   #409
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Oliver, thanks. This is very good news. In your sim, if a solid centre brace does not result in any difference in the curves, in reality, an offcentre brace with enough holes for cross-movement of air should pose no problems and reduce panel flex as well. So it does appear that the internal panels will have to be 1/2", external panels 3/4" (adding the extra 1/4" per panel to the external dimension) and increase internal width by a little less than 1/2" to compensate for an 1/2" solid holey brace.
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Old 12th February 2011, 06:48 AM   #410
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After making a few of the t48s I was dubious about the lack of bracing in the SS15, but having made a pair with the 18mm outer panels and no internal braces, I have to say it is still one solid box. I've gigged with them for a couple of weeks now, (that's almost 30 different bands in that time) and they have shown no problems so far. Crowds up to 200.
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