[jk@home]

Hey Folks, I'm preparing to build a pair of PAP Trio style OB speakers, and have a question regarding baffle material. Looks like most folks use baltic birch, but the availability of that is hard to find now. I have some scrap pieces that would do 3 panels, if I go with 1-1/2" thick baffles.

So my question; is there a problem if I laminated 3/4" MDF on the 3/4" BB pieces I have now, with Titebond, to make the 6 panels I need? Each piece will be 21 x 16-1/2, so laying together should be easy with concrete blocks. Not really looking for a sonic advantage, just negatives. If I use the BB on the back, I can back install the drivers, then the front MDF holes will be easy to round over.

[Peter J]

I did what you're suggesting on these:

https://www.audiocircle.com/index.php?topic=139529.0

Some years later, no sign of any structural problems. I laminated the blanks in vacuum bag and actually cut driver holes in one layer prior to lamination, then flush trimmed second layer after. I can be more specific if need be.

[jk@home]

Thanks for that, good news. I had read on another forum about vacuum pressing, not a big woodworker so wasn't familiar. Don't think I will go out and buy one for this job (already have a stack of blocks in the yard) 

I plan on cutting the MDF slightly larger than the properly sized BB boards, gluing together, then use the flush trim bit to match them up.

[WGH]

Not really looking for a sonic advantage, just negatives.

The MDF/Baltic birch laminate is guaranteed to warp during humidity changes like winter into humid summer.

If the relative humidity varies from 35 to 85 percent, the change in size (width and length) for MDF is about 1/2 percent. 3/4" Baltic birch with 13 plies has barely any movement with moisture content changes but will tend to warp more, sometimes pieces stay flat, sometimes not. So you will have a 1-1/2" baffle that will change dimensions up to 1/2% on one side and 0% on the other side. 1/2% of 24" is almost 1/8".

The side braces should be extra beefy and the big speaker hole in the middle of the panels should keep everything from going too wacky. It might just work but don't laminate the panels this week and wait 6 months to start cutting. Warped panels cannot be made flat again. The surface the panels are laminated on has to be absolutely dead flat too. If commissioned, I wouldn't make a PAP speaker with a two layer laminate because I have no idea what would happen. I've been known to tell my clients "no" all the time.


The rule is to keep laminated panels symmetrical, say Baltic birch in the center and MDF (3/8") on both sides. Tightbond will keep the laminate together but Tightbond is also very flexible and will not stop any warping. The only time laminating only one side works is when the panel is locked in place and braced like in the open baffle woofer thread above.

I've been doing custom laminating for over 30 years
https://www.wghwoodworking.com/current.html

[jk@home]

OK. We keep the house at 45-55 percent humidly, but I see your point. Since I haven't bought the MDF yet, could do what you propose. Next week I am going to try and locate some BB ply, one fellow in town said he had 4 x 8 sheets for $60 (not Russia BB). Sounds too good to be true, I know most BB sheets come in 5x5, and cost a lot more. Would there be another sheet material you could recommend?
BTW for finishing the boards, most likely will use some (ugly) black Duratex I have laying around, which should seal up the wood.

[Peter J]

BB situation is definitely weird right now. First shipping problems, now Ukraine situation.

 As of last week, one distributor I use has opted out of selling it altogether. Has some kind of similar thing in 1/2", although I have not seen it. Sounds like North American ply that probably has softwood core where BB has all same thickness birch cores. I'm guessing primarily used for cabinet drawers.

I did check with another distributor I've used, and they have both 5x5 and 4x8 in 18mm BB/BB grade. A few sheets of B/BB.  Not cheap though, 4x8-$152, 5x5-$122. I queried as to future supply and really didn't have an answer. Only that they have 1000+ sheets in their system now.

Where are you JK?, They have several warehouses.

[WGH]

I'm not familiar with the PAP design. Can you make the L&R baffles from one 4x8 sheet? I always bought 4x8 sheets of 3/4" from my supplier, don't know if it was officially Baltic birch but it had more plys than construction plywood and suited my purpose. The 16 ply doesn't have any voids like construction plywood. The $60 sheets may have only one good face or both faces will have patches and "footballs," my supplier called it cabinet grade, it was perfect for the inside of projects that would never be seen (or covered in Duratex). Store the sheets horizontally (8' side on the floor) against a flat wall or laying on a very flat surface, never upright at an angle.

Birch plywood grades
https://www.woodworkerssource.com/blog/woodworking-101/tips-tricks/your-ultimate-guide-to-baltic-birch-plywood-why-its-better-when-to-use-it/

I would skip the MDF, make the baffles all plywood. There is a reason all open baffle speakers are made from baltic birch ply, it works without surprises.

I have also used ApplePly plywood made in Eugene, OR.

BTW for finishing the boards, most likely will use some (ugly) black Duratex I have laying around, which should seal up the wood.

Why? Sand the Baltic birch to #220 and apply a clear sealer. No stain, birch is notoriously difficult to stain, the grain changes direction and gets blotchy. Interior wood doesn't have to be sealed, it will hang out just fine unfinished but will get dirty and waterspot. Some cabinetmakers just waxed their furniture, it's a lot of work and not durable but can look great. A coat of shellac and then wax, old school.

[jk@home]

BB situation is definitely weird right now. First shipping problems, now Ukraine situation.

 As of last week, one distributor I use has opted out of selling it altogether. Has some kind of similar thing in 1/2", although I have not seen it. Sounds like North American ply that probably has softwood core where BB has all same thickness birch cores. I'm guessing primarily used for cabinet drawers.

Without getting too political, the US has sanctions against Russian, evidently including Baltic Birch. I've read they use a run around through China, who knows. Don't think things will change any time soon.

I did check with another distributor I've used, and they have both 5x5 and 4x8 in 18mm BB/BB grade. A few sheets of B/BB.  Not cheap though, 4x8-$152, 5x5-$122. I queried as to future supply and really didn't have an answer. Only that they have 1000+ sheets in their system now.

Where are you JK?, They have several warehouses.

The fellow I talked to today said it was "B" grade (?) furniture quality, but 13 ply. We had a kitchen remodel done a few years back and the contractor left some extra 3/4" shelving. It appears to be Baltic, but not quite....probably the same stuff.

Without getting too political, the US has sanctions against Russian, evidently including Baltic Birch. I've read they use a run around through China, who knows. Don't think things will change any time soon.

I live in Virginia Beach, there is a supplier in Norfolk (next door) that I bought my other "real" BB from. Wasn't open today, will try again on Monday.

[jk@home]

I'm not familiar with the PAP design. Can you make the L&R baffles from one 4x8 sheet? I always bought 4x8 sheets of 3/4" from my supplier, don't know if it was officially Baltic birch but it had more plys than construction plywood and suited my purpose. The 16 ply doesn't have any voids like construction plywood. The $60 sheets may have only one good face or both faces will have patches and "footballs," my supplier called it cabinet grade, it was perfect for the inside of projects that would never be seen (or covered in Duratex). Store the sheets horizontally (8' side on the floor) against a flat wall or laying on a very flat surface, never upright at an angle.

Birch plywood grades
https://www.woodworkerssource.com/blog/woodworking-101/tips-tricks/your-ultimate-guide-to-baltic-birch-plywood-why-its-better-when-to-use-it/

I would skip the MDF, make the baffles all plywood. There is a reason all open baffle speakers are made from baltic birch ply, it works without surprises.

I have also used ApplePly plywood made in Eugene, OR.


Why? Sand the Baltic birch to #220 and apply a clear sealer. No stain, birch is notoriously difficult to stain, the grain changes direction and gets blotchy. Interior wood doesn't have to be sealed, it will hang out just fine unfinished but will get dirty and waterspot. Some cabinetmakers just waxed their furniture, it's a lot of work and not durable but can look great. A coat of shellac and then wax, old school.

PAP stands for PureAudioProject, you can google them...many many examples of OEM and clones out there. I like the fact that it is a modular design. This is my 1st diy OB (although I have built many subs), and can switch around any of the drivers installed without a major teardown. I will not be using the usual suspect drivers...nuff said. 

I will set up the speakers nude (no finish) at first. Then finish if the results are passible. Thanks to all the subs I built, I've pretty much perfected roll-on Duratex. And I have a gallon + (at $100 per gallon) here already.

[Peter J]

The fellow I talked to today said it was "B" grade (?) furniture quality, but 13 ply. We had a kitchen remodel done a few years back and the contractor left some extra 3/4" shelving. It appears to be Baltic, but not quite....probably the same stuff.

I live in Virginia Beach, there is a supplier in Norfolk (next door) that I bought my other "real" BB from. Wasn't open today, will try again on Monday.

There is a similar looking product that I not-so-fondly call "China birch" which is, you guessed it, made in China. I was all jacked about it years ago because it was relatively inexpensive. I used it till I realized it was no bargain. Delamination was the biggest problem, sometimes massive. Maybe it's changed...dunno. Something else kinda funny, it smelled weird when machining. I've also seen it or similar at big boxes but am gun shy now.

[jk@home]

LOL, I googled China Birch

https://techtalk.parts-express.com/forum/tech-talk-forum/54472-say-no-to-chinese-birch-plywood

[Openly Baffled]

MDF/Baltic birch laminate is guaranteed to warp

Hi WGH,
Thanks for your detailed reminder that dissimilar laminated materials will warp.
Particularly of interest was your quantisation of the impact.
regards,
Rohan

[jk@home]

Birch plywood grades
https://www.woodworkerssource.com/blog/woodworking-101/tips-tricks/your-ultimate-guide-to-baltic-birch-plywood-why-its-better-when-to-use-it/

Thanks for the link. A printed copy of the grade scale will be helpful when shopping. The ply I already have has a side marking of BB/BB.

EDIT: I went ahead and ordered the six 20 x 30 pc set from the same web site, with free shipping! 
So I'm good to go, thanks for all the help.

[jk@home]

After working on the construction options and efforts involved, decided to skip the modular design and go with a single slab per side. Mainly because I want to fit three 15" drivers in a WWM configuration and still maintain a "not too high" FR driver to ear level, with the drivers I already have. This is in a 12' x 15' x 8' high room, with the speakers 5' from the front wall. Almost near field. Using a couple of test baffles, I have pretty much decided on where the speakers are going for now.

I know there is software out there that can help design baffle sizing, the drivers I am starting with are one Fii Xisi Fast 15 and two Eminence Beta 15s, per side. Want the option of upgrading the Lii later to a better/more $$$ unit like a coaxial. I have researched lots of OB pics and designs, including the barrel shapes that are popular with the Fii drivers now. Personally the lower height what the barrel would result in didn't work in my room (using the test baffles).

Ordered a pair of these birch countertops from Home Depot:
https://www.homedepot.com/p/HARDWOOD-REFLECTIONS-4-ft-L-x-25-in-D-Unfinished-Birch-Solid-Wood-Butcher-Block-Countertop-With-Eased-Edge-BBCT1502550/300688696

Nice looking slabs for the price. Here is a front and back view:


The manufactured supplied size is 1-1/2" X 25" x 50". I can work with the height, I plan on mounting the slabs on double or triple layers of BB birch platforms (I already bought the material for that, see above  ). Thinking I will start with no wings, with the option to add later. Already have IB subs in the ceiling, with optional pairs of 2 and/or 3 cubic foot unfinished boxes already made if I need to add more lower bass. So good there.

So my question to the group...anyone see a problem with keeping the 25" width?  I know Pure Audio uses a 21-1/2" width, Perry Marshall Bitches Brew (which I could upgrade these baffle drivers to later) uses 21-22". Steve Decware's medium barrels are much wider. It would be nice not have to cut the slabs at all, except for the driver holes. I'm good there, with router and bits. So is 25" too wide, or no biggie?

[Early B.]

So my question to the group...anyone see a problem with keeping the 25" width?  I know Pure Audio uses a 21-1/2" width, Perry Marshall Bitches Brew (which I could upgrade these baffle drivers to later) uses 21-22". Steve Decware's medium barrels are much wider. It would be nice not have to cut the slabs at all, except for the driver holes. I'm good there, with router and bits. So is 25" too wide, or no biggie?

As Danny would say, "You may as well build in-wall speakers."
It might be helpful to watch this video: https://www.youtube.com/watch?v=jsAw6jSdQrQ

It's cool to go DIY, but do plenty of research beforehand so you don't waste time and money. If this is your first DIY OB speaker build, I'd suggest following a proven OB DIY design and save those birch countertops for your second or third build. 

[jk@home]

Thanks for the video link, that was helpful.

Decided to cut the baffles to 20-3/8" wide. That gives me room for the 15-1/2" driver flange mount holes, plus the 2-1/2" heavy duty L-brackets (x 2) used to connect the base plate.