Auto Tuba Build Questions...

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Rickisan
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Auto Tuba Build Questions...

#1 Post by Rickisan »

After hours of reading and searching the forum I'm still needing some hand holding on several points of an Auto Tuba build.

Firstly, the plans say "You may wish to back the joint of panels 1 and 2 with a 2-inch wide piece of plywood." The Sketchup view shows this plywood strip on the "outside/large angle" of the joint. Will it be ok to to place it on the "inside/short angle" of the joint? ...located like the dark strip of wood seen in the picture below?
Image

Secondly, I can find nowhere in the plans stating to put screws in the "vertical" dimension of the panels where possible. I'm thinking this is so obvious it goes with out saying.... but just to clarify... Is it best to put several screws through panel 4 in to the vertical (as seen below) ends of panels 1 and 3?
Image

Finally, the panel 5 brace is described as needing half-round relieves to preclude interference with the driver surround during long excursions. This doesn't seem necessary as the driver surround isn't lossy or large enough to allow excursion out that far.

Any comment is greatly appreciated. I came here looking for diy PA speaker plans and turns out to be a whole educational experience on the finer points of sound reinforcement done correctly.

What a cool cool site and forum. Thanks to everyone involved for posting and sharing so much excellent invaluable information, Rickisan
Last edited by Rickisan on Wed Dec 31, 2008 6:14 am, edited 1 time in total.
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LelandCrooks
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Re: Auto Tuba Build Questions...

#2 Post by LelandCrooks »

The brace is fine inside. The loss of chamber volume is pretty minimal the way you did it. Better outside, not worth changing.

Screws, yes.

Depends on the driver. :mrgreen:
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bgavin
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Re: Auto Tuba Build Questions...

#3 Post by bgavin »

Using the MCM 55-2421 driver, the chamber is already much too large. Any reduction of chamber volume from bracing has no effect.
My biggest worry is that when I'm dead and gone, my wife will sell my toys for what I said I paid for them.

Rickisan
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Re: Auto Tuba Build Questions...

#4 Post by Rickisan »

OK I'll keep the "inner" bracing at the join of panels 1 & 2 but leave off cutting half-rounds for the baffle-board brace as I"m installing the MCM driver.

I suspect the recommended Tang Band requires the extra baffle-board spacing but the MCM does not. Also, I'll use screws in the "vertical" joins as confirmed.

Thanks much, If this Auto Tuba does half what I'm reading on the forum it will be Killer Diller!
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Re: Auto Tuba Build Questions...

#5 Post by bgavin »

I used the MCM driver, and did notch the bracing to avoid any possible conflict with the cone. It is a simple step, and takes little time to accomplish. Cheap insurance.
My biggest worry is that when I'm dead and gone, my wife will sell my toys for what I said I paid for them.

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Re: Auto Tuba Build Questions...

#6 Post by DJPhatman »

Fasteners at any/all joints are there only to hold the panels together until the adhesive sets and cures. They do not hold the panels together, the adhesive does. You can use screws, brads, even ring-shank paneling nails to hold the panels until the adhesive cures. After curing, any fasteners may be removed, if you so desire.

As far as notching the brace between the woofer baffle and panel #5, do it! It is much easier to notch it now, than it is to try to notch it after the cab is complete! Only takes a few minutes, doesn't need to be pretty, and is insurance against cone and surround contact.
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AntonZ
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Re: Auto Tuba Build Questions...

#7 Post by AntonZ »

+1 for the notches.
I even added one for the driver dustcap. Probably not necessary, but it was two minutes work while the brace wasn't glued to the cab.

Image

bgavin
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Re: Auto Tuba Build Questions...

#8 Post by bgavin »

Wow, that is optimistic... if the dust cap gets that close, it is only because it is on its way to the house down the street...

:mrgreen:
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Re: Auto Tuba Build Questions...

#9 Post by Rickisan »

Wow thanks so much for all the help. I'll be notching and posting pictures. Can't wait to hear this thing!

This is the Chinese 7/16 plywood from Lowe's... seems awfully soft and the veneer peels away quite easily. I'm hoping the glue holds it all together :) Next build will be with better plywood.

A lot of bubbles are coming up in the glue joints. Is this a concern? The humidity is pretty high here and maybe causes the bubbles?
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AntonZ
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Re: Auto Tuba Build Questions...

#10 Post by AntonZ »

bgavin wrote:Wow, that is optimistic... if the dust cap gets that close, it is only because it is on its way to the house down the street...

:mrgreen:
:D :D :D
Yeah, these AT's do move some serious air :twisted:

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Re: Auto Tuba Build Questions...

#11 Post by gdougherty »

Rickisan wrote:Wow thanks so much for all the help. I'll be notching and posting pictures. Can't wait to hear this thing!

This is the Chinese 7/16 plywood from Lowe's... seems awfully soft and the veneer peels away quite easily. I'm hoping the glue holds it all together :) Next build will be with better plywood.

A lot of bubbles are coming up in the glue joints. Is this a concern? The humidity is pretty high here and maybe causes the bubbles?
You may need the fasteners then. The Auraco isn't much more expensive and will actually hold up. The thin veneer stuff is a problem since you're gluing surface to surface and if the surface is prone to pulling away then you just lost your joint. For all the time and effort put into building these IMO you'd have been better off spending a few more bucks on better plywood. I can understand wanting to do a test run, but why be forced to toss or discontinue use of an otherwise potentially good speaker just because the wood isn't holding up?

The polyurethane glues do bubble some. The more liquid types like Gorilla Glue or Elmer's Ultimate foam quite a bit and I believe all types perform better with humidity or moisture to activate them. My Gorilla Glue recommends dampening the surface to be glued before putting it down. That bubbling though is effectively an indicator of expansion. You want expansion and sealing of all joints.

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Re: Auto Tuba Build Questions...

#12 Post by Rickisan »

I hate it when I lose a joint! :lol:

Yes, if I'd known I would've skipped the Chinese Thin Veneer for sure. Live and learn... it's been a learning experience. The more cuts I made and the more the veneer kept peeling off I came to this same conclusion about half-way through the process.

I will leave the fasteners because of the thin veneer. Hopefully fasteners and liberal glue ooze between the joints will keep the it all together. I think it will be ok.

Meanwhile, next time, and there will be a next time :D I found a nearby lumber source with a nice looking 7-ply 1/2 A/C or B/C (can't remmeber which) for $21 a sheet. Just can't understand why Lowe or Home Depot doesn't carry it???
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Re: Auto Tuba Build Questions...

#13 Post by dbaldock »

Rickisan wrote:...
Meanwhile, next time, and there will be a next time :D I found a nearby lumber source with a nice looking 7-ply 1/2 A/C or B/C (can't remmeber which) for $21 a sheet. Just can't understand why Lowe or Home Depot doesn't carry it???
Their main business isn't selling to furniture and cabinet makers.


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Bill Fitzmaurice
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Re: Auto Tuba Build Questions...

#14 Post by Bill Fitzmaurice »

Rickisan wrote: Just can't understand why Lowe or Home Depot doesn't carry it???
The same reason McDonald's doesn't sell $30 steaks. :lol:

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Re: Auto Tuba Build Questions...

#15 Post by DJPhatman »

Rickisan wrote:Meanwhile, next time, and there will be a next time :D I found a nearby lumber source with a nice looking 7-ply 1/2 A/C or B/C (can't remember which) for $21 a sheet. Just can't understand why Lowe or Home Depot doesn't carry it???
Dan-git!!! I can't find any decent plywood around here, except the 5 ply at one yard. And it's now just shy of US$30 a sheet! :shock:
I know money often seals the deal, but seriously, quality is an investment, not an expense... Grant Bunter
Accept the fact that airtight and well-braced are more important than pretty on the inside. Bill Fitzmaurice

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