Domino or Tongue-N-Groove?

[Nestor]

Hi all!

I'm going to be building a pair of folded-horn subwoofers, dimensions: 18" X 36" X 72", with the opening at one of the 18X36 ends. For those unfamiliar, see pics below. (Pics from the interwebs)

The Festool bug bit me about three years ago with the purchase of a TS55 and a couple of rails. Recently, I added an MFT, parallel guides, and a Kapex. I've become smitten  [drooling] by the Domino, OF1400, and an RO90DX, and figure this new project makes for a good excuse for my next acquisition.

1. The speaker is typically built from 1/2 inch 5 ply Baltic Birch. The problem I'm going to have for this design is I can only get 5' X 5' sheets locally, so this means joining. Which will result in a stronger joint, Dominoes or Tongue And Groove? The most important aspect of this design is that joints must be airtight. No leaks. I should add that exterior finish isn't important at this time.

2. The plans are designed for a bare minimum of tools. (circular saw and drill). It's obvious how the TS55 and parallel guides will make things easier and more accurate. How about the Domino? Would it help for "mirroring" side panels? Can one use it to "transfer" the first layout to the next subwoofer?

The chaos of life kept me off this site for the last couple of years. With the recent purchase of some more tools, (and a house), I hope to hang around much more! I've forgotten how much great info is on this site.

 

[vkumar]

You did say air tight joints.  My vote would be for tongue and groove, it will be airtight and strong.  I am a fan of the domino, but in this case a tongue an groove would be better.

You just have to come up with a way of coming with an exact size groove to fit your plywood, using a smaller bit router and moving it a little bit to make the groove. The OF 1400 with fine adjustment ont he guide rail stop should make this easy.

Best on the project.  Lets know how it turns out.

Vijay

 

[mouppe]

I would use the Domino, and rely on a good finish to provide a seal. A few coats of shellac should do it. After gluing the frame together, sand lightly and then work the shellac in. When you scuff-sand again, do not clear the dust. As you work the next layer of shellac in, it will bind with the dust and close the pores and seal the joints.

This trick was taught to me by an old master.

 

[semenza]

Hi,

I guess my first question is why 1/2" Baltic birch? I am by no means an expert on speaker enclosures, but I have had an interest in audio, and built a subwoofer enclosure. It has always been my understanding that MDF and particle board are better choices because of there density and sound absortion / deadening. If the plywood is needed for a finished exterior you could go with wood veneered MDF core.

The tightness will be more of a factor than strength since the sides will be attached to other sides and pieces.

I think that  the T&G would be a better gaurantee of having an airtight fully closed joint in this situation.
With the T&G I don't think you would need to worry about any type of joint filling. Those interlocking surfaces all coated with glue should seal it up very well.

But the Domino would be really handy for the interior baffle joining.

Seth

 

[BobKovacs]

If you're considering T&G, look at doing a spline instead- that way you've only got one router setup to make.

 

[semenza]

If you're considering T&G, look at doing a spline instead- that way you've only got one router setup to make.

That would be good. More likely to get a flush surface with less fiddling and adjusting. Nestor you would need to be able to make the spline or find exact thickness material to use for the spline.

Seth

 

[Nestor]

Hi,

I guess my first question is why 1/2" Baltic birch? I am by no means an expert on speaker enclosures, but I have had an interest in audio, and built a subwoofer enclosure. It has always been my understanding that MDF and particle board are better choices because of there density and sound absortion / deadening. If the plywood is needed for a finished exterior you could go with wood veneered MDF core.

The tightness will be more of a factor than strength since the sides will be attached to other sides and pieces.

I think that  the T&G would be a better gaurantee of having an airtight fully closed joint in this situation.
With the T&G I don't think you would need to worry about any type of joint filling. Those interlocking surfaces all coated with glue should seal it up very well.

But the Domino would be really handy for the interior baffle joining.

Seth

You could use MDF, but it would make an already heavy box even heavier. There is little to gain from the higher density in this application, as most of the box is "horn".

The speaker is a home theater variation of a PA cabinet design, where strength weight ratio and moisture resistance is important when schlepping from gig to gig.

And let's not forget the "nastiness" of MDF dust.  [scared]

 

[tbellemare]

I'm also curious about the tonal qualities of MDF.

I don't think an MDF guitar or violin would go over too well. My understanding is that a new Martin guitar doesn't sound as rich as an old Martin.

Is the same true of speaker enclosures?

Thanks,

Tom

 

[Kevin Stricker]

Tom, we are talking about a subwoofer not a Stradivarius.  I agree with Seth, you should be looking into MDF not Baltic Birch.  I also think that joining the exterior is going to be a big mistake.  Neither dominos or a T&G are going to be strong endgrain to endgrain in 1/2" ply and will likely both fail in your application.  The T&G or spline would work great in 3/4" material, but I don't think you will have a lot of luck on 1/2" BB as the tongue would be less than 3/16" if you wanted to keep the sides equal.   If you must join I would look at doing a shiplap, at least 1" long to join the boards.  As for the interior partitions use dados.

if you must use plywood I would ask your local lumber dealer if they have any Apple Ply or Russian Ply, both come in 8 foot lengths.  Most of the Baltic Birch I see these days is crap, if you don't cut it up and use it the day you pull it out of the big stack at the lumber yard it is warped by the next morning.  

 

[semenza]

Hi,

I guess my first question is why 1/2" Baltic birch? I am by no means an expert on speaker enclosures, but I have had an interest in audio, and built a subwoofer enclosure. It has always been my understanding that MDF and particle board are better choices because of there density and sound absortion / deadening. If the plywood is needed for a finished exterior you could go with wood veneered MDF core.

The tightness will be more of a factor than strength since the sides will be attached to other sides and pieces.

I think that  the T&G would be a better gaurantee of having an airtight fully closed joint in this situation.
With the T&G I don't think you would need to worry about any type of joint filling. Those interlocking surfaces all coated with glue should seal it up very well.

But the Domino would be really handy for the interior baffle joining.

Seth

You could use MDF, but it would make an already heavy box even heavier. There is little to gain from the higher density in this application, as most of the box is "horn".

The speaker is a home theater variation of a PA cabinet design, where strength weight ratio and moisture resistance is important when schlepping from gig to gig.

And let's not forget the "nastiness" of MDF dust.  [scared]

As for the MDF dust... Using Festool should take care of that  [smile]

OK, so this is going to be moved or is it sitting in a home theater?  Not quite sure from yor post.

Also, upon reading Kevin's post I think he is right that the joint might be quite weak in 1/2". But perhaps the baffles will add enough strength to keep it together?  [unsure]

Seth

 

[bellnarak66]

Hi,

I guess my first question is why 1/2" Baltic birch? I am by no means an expert on speaker enclosures, but I have had an interest in audio, and built a subwoofer enclosure. It has always been my understanding that MDF and particle board are better choices because of there density and sound absortion / deadening. If the plywood is needed for a finished exterior you could go with wood veneered MDF core.

The tightness will be more of a factor than strength since the sides will be attached to other sides and pieces.

I think that  the T&G would be a better gaurantee of having an airtight fully closed joint in this situation.
With the T&G I don't think you would need to worry about any type of joint filling. Those interlocking surfaces all coated with glue should seal it up very well.

But the Domino would be really handy for the interior baffle joining.

Seth

You could use MDF, but it would make an already heavy box even heavier. There is little to gain from the higher density in this application, as most of the box is "horn".

The speaker is a home theater variation of a PA cabinet design, where strength weight ratio and moisture resistance is important when schlepping from gig to gig.

And let's not forget the "nastiness" of MDF dust.  [scared]

As for the MDF dust... Using Festool should take care of that  [smile]

OK, so this is going to be moved or is it sitting in a home theater?  Not quite sure from yor post.

Also, upon reading Kevin's post I think he is right that the joint might be quite weak in 1/2". But perhaps the baffles will add enough strength to keep it together?  [unsure]

Seth

[eek] [eek] [eek]

 

[semenza]

Hi,

My mistake I meant Kevin's post not Ken's,  fixed it.

Seth

 

[PeterK]

I have built a few subs and all my main speakers. Always used mdf and would laminate layers to have a minimum 1 1/4" thick wall. Half inch Baltic Birch may work with all the internal braces but there sure isn't much material at the edges to make a joint. Being this is really an exotic ported sub - not a sealed sub, you are not having to contend with all the internal pressures of a seled design. This design has no where near the airtight joint requirements so small leaks really won't hurt as much. If you can add a square board, maybe a 1x1 or larger, you could add significantly more glue surface at the corners. You definitely need to t and g or spline the joints just to have some strength to be able to move it around. I would sure prefer using 3/4" material for the cabinet and would use mdf for sure if you ever plan on adding an exterior finish of some sort. Of course, my ideas will make it very heavy!