I recently posted this on a thread about bracing, but I think it deserves it's own thread / discussion:
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Is Baltic Birch really the ultimate plywood for enclosures?
Since everybody always uses lots of internal bracing anyway, why the heck is the standard enclosure material BB?
I'm not asking about alternative composites now, that was a different thread.
I mean, specifically, WHY NOT SPRUCE PLYWOOD?
Spruce has by far the highest stiffness-to-weight ratio of any of the woods commercially used for ply, and it's almost 1/3 the cost of BB.
Birch is a little bit stiffer, but also MUCH heavier. Again, if you're going to brace the snot out of it anyway, why not go with the lighter product, which is still extremely stiff, compared to standard Pine plywoods?
Plus, 3/4" Sitka Spruce (You only want Sitka or Norway) is as best I can tell, stiffer than 1/2" Baltic, and still almost the same weight. (though my figures may be a little off, as specific gravity charts tend to vary a bit.)
Anyway, you get my point.
And did I mention the price? WISA Canadian Spruce ply looks to be a good bet. That's most likely Sitka, since that's mostly what they have up there.
It does seem a bit hard to source in the USA, though. These guys sell it, but maybe not by the sheet: Plywood and Door. Of anyone has a better source, for just a few sheets, I'd love to know.
Home Depot has “West Fraser” brand 4x8’ 3/4” Canadian Spruce plywood for $48 ! No idea what it's actually made of, though. (Probably slash Pine pulp, cheap glue, and ground up Mexican laborers)
Your thoughts?
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Is Baltic Birch really the ultimate plywood for enclosures?
Since everybody always uses lots of internal bracing anyway, why the heck is the standard enclosure material BB?
I'm not asking about alternative composites now, that was a different thread.
I mean, specifically, WHY NOT SPRUCE PLYWOOD?
Spruce has by far the highest stiffness-to-weight ratio of any of the woods commercially used for ply, and it's almost 1/3 the cost of BB.
Birch is a little bit stiffer, but also MUCH heavier. Again, if you're going to brace the snot out of it anyway, why not go with the lighter product, which is still extremely stiff, compared to standard Pine plywoods?
Plus, 3/4" Sitka Spruce (You only want Sitka or Norway) is as best I can tell, stiffer than 1/2" Baltic, and still almost the same weight. (though my figures may be a little off, as specific gravity charts tend to vary a bit.)
Anyway, you get my point.
And did I mention the price? WISA Canadian Spruce ply looks to be a good bet. That's most likely Sitka, since that's mostly what they have up there.
It does seem a bit hard to source in the USA, though. These guys sell it, but maybe not by the sheet: Plywood and Door. Of anyone has a better source, for just a few sheets, I'd love to know.
Home Depot has “West Fraser” brand 4x8’ 3/4” Canadian Spruce plywood for $48 ! No idea what it's actually made of, though. (Probably slash Pine pulp, cheap glue, and ground up Mexican laborers)
Your thoughts?
And FWIW, member tonskulus replied thusly, on that other thread:
quote:
"I've been using spruce plywood for my PA subwoofers. Light weight and when braced properly, no problems."
quote:
"I've been using spruce plywood for my PA subwoofers. Light weight and when braced properly, no problems."
1)Pretty much the "ultimate" for a number of reasons due to the way it's put together, as much as the material strength.
Ultimate Guide to Baltic Birch Plywood: Why It’s Better, When to Use It – Woodworkers Source Blog
Baltic Birch holds up well to impact, reducing the frequency of surface repairs compared to other plywood subjected to road abuse.
2) Coming across internal voids and warped pieces typical of "standard" plywood can really slow down production and waste money, requiring cutting in to a new sheet to replace a few parts.
Complicated internal bracing can expose defects in plywood (and glue) that may otherwise avoid detection. The construction of BB avoids those problems.
3)I have not found any other plywood product made just like Baltic Birch, which can be frustrating when building from lighter materials. Often, the named material is an ultra-thin exterior veneer, the inside filled with junk wood and voids.
If you can find a good quality Sitka Spruce, go for it!
4)I have not used "real" Baltic Birch in over 20 years due to weight, cost and availability, but still miss it's ease of use and consistent results nearly every project.
Art
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Yeah, Art, I hear you about "not knowing what's inside there." Again, ground up Mexican laborers...
But the WISA product is claimed to be 100% Spruce and void-free, so on a par with the best Russian Birch, construction-wise. (They also use waterproof glue.)
I'm hoping someone here has used it, and can either confirm this or warn us off of it.
But regarding strength, I don't see that as a big factor for anyone but touring companies.
For them, sure, but my subs always have thin padded covers on them, and I don't think I've banged one hard in 30 years. So for me, stiffness (modulus of elasticity) is critical but hardness / strength is not.
That woodworkers blog is for woodworkers, i.e. geared mostly towards furniture making. Slightly different priorities.
Of course, I have never actually built a cab out of Spruce ply, hence this thread. I'm most likely going to use composites anyway, with just BB ply for the driver mount and (if a horn) the higher pressure areas. Still, I think it's well worth discussing / considering.
But the WISA product is claimed to be 100% Spruce and void-free, so on a par with the best Russian Birch, construction-wise. (They also use waterproof glue.)
I'm hoping someone here has used it, and can either confirm this or warn us off of it.
But regarding strength, I don't see that as a big factor for anyone but touring companies.
For them, sure, but my subs always have thin padded covers on them, and I don't think I've banged one hard in 30 years. So for me, stiffness (modulus of elasticity) is critical but hardness / strength is not.
That woodworkers blog is for woodworkers, i.e. geared mostly towards furniture making. Slightly different priorities.
Of course, I have never actually built a cab out of Spruce ply, hence this thread. I'm most likely going to use composites anyway, with just BB ply for the driver mount and (if a horn) the higher pressure areas. Still, I think it's well worth discussing / considering.
Agreed for HIFI/HT or most permanent installs and the primary reason why 'we' recommend 19 mm BB, which is rated 1.8 m, so what is it for this Spruce you speak of? I couldn't find it in a quick search or here: Spruce plywood
GM
I couldn't find it either, so I'm tred to figure it from the s.g. of the raw lumber itself. (figuring that both will use similar glue, if they are AtX & from good companies.)
It's still difficult, because you can find different numbers on different websites, but the difference between species still remains roughly the same.
Here's sort of the "average" of what I found:
Spruce, Sitka & White: spec gravity: .37 Elastic Mod: 1,600,000 lbf/in2
Birch, Alaskan & Russian: spec gravity: 49 Elastic Mod: 1,900,000 lbf/in2
Douglas Fir: spec gravity: 41 1950,000 lbf/in2
Oddly, it seems that raw Doug Fir has a better stiffness ration than even the best Birch.
I forget the formula for stiffness-to-weight ratio, but it's pretty simple.
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Anyway, that was just to get a ballpark idea. All that really matter is trying the actual plywoods themselves. Also, as Art mentioned, finding a brand that is high quality.
(Hence, this thread.)
It's still difficult, because you can find different numbers on different websites, but the difference between species still remains roughly the same.
Here's sort of the "average" of what I found:
Spruce, Sitka & White: spec gravity: .37 Elastic Mod: 1,600,000 lbf/in2
Birch, Alaskan & Russian: spec gravity: 49 Elastic Mod: 1,900,000 lbf/in2
Douglas Fir: spec gravity: 41 1950,000 lbf/in2
Oddly, it seems that raw Doug Fir has a better stiffness ration than even the best Birch.
I forget the formula for stiffness-to-weight ratio, but it's pretty simple.
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Anyway, that was just to get a ballpark idea. All that really matter is trying the actual plywoods themselves. Also, as Art mentioned, finding a brand that is high quality.
(Hence, this thread.)
baltic Birch is a good basic material. You can get higher quality ply.
The species is less important than the number of plies (a generalization, ie bamboo ply).
If you can get spruce ply with a high number of plies, go for it. PArticularily with woofers, stiffness is paramount. Lighter doesn’t hurt.
dave
The species is less important than the number of plies (a generalization, ie bamboo ply).
If you can get spruce ply with a high number of plies, go for it. PArticularily with woofers, stiffness is paramount. Lighter doesn’t hurt.
dave
So much of the big box plywood nowadays is absolute junk with huge core voids and delams. BB is a reliable product with known quality. There are many high quality plywoods available and you want to seek out a specialty shop that caters to cabinet makers and only sells top notch products. Once you find such a supplier you can go with whatever selection of core material, number of plies (more is better) and face veneers to suit your project.
TLDR: birch is not special in Australia. Lots of options are cheaper and/or better.
Australia has a good system for this: our structural 'F' grades are linked to modulus of elasticity.
Birch and most structural ply here gets rated F17, roughly 17,000 MPa. This strength rating doesn't seem to be a hard (costly) target to hit. This linked sheet is F17*, but only the outer veneers are stated to be 'high quality' or 'hardwood', so the rest are probably pine.
SpecRite Formply F17 1800 x 1200 17mm Plywood | Bunnings Warehouse
I can get 'braceply' in F27 from chain stores. Higher ratings exist (to F37) but seem to be a bit more boutique.
Structural grading | WoodSolutions
Plywod Specification Overview
Lots of 'structural' or 'exterior' grade (see 3rd link above) ply seems to meet those criteria, so locally, the only point to buying birch is for the veneer. It's cost literally doubles based on the face appearance - the same shop has:
$107.20 birch core, A-bond (phenol formaldehyde resin), film face**
https://plyco.com.au/products/birch-filmface
$197.99 birch core, A-bond (phenol formaldehyde resin), birch face
https://plyco.com.au/products/birch-premium?variant=36373909136
*The Australian Competition and Consumer Commission (ACCC) gets all up in your grill if you sell plywood that doesn't meet the rating.
**the shop also has non-birch film face that's both cheaper AND stronger than the birch.
Australia has a good system for this: our structural 'F' grades are linked to modulus of elasticity.
The actual properties associated with the F-grades can be obtained from the Timber Structures Code. For example F8 timbers have the following properties (from AS 1720.1 Table H2.1):
f 'b = 22 MPa the characteristic bending strength
f 'c = 18 MPa the characteristic compression strength (parallel to the grain)
f 't = 13 MPa the characteristic tensile strength (parallel to the grain) - hardwoods
f 's = 2.2 MPa the characteristic shear strength
E = 9100 MPa the characteristic modulus of elasticity parallel to grain
f 'b = 22 MPa the characteristic bending strength
f 'c = 18 MPa the characteristic compression strength (parallel to the grain)
f 't = 13 MPa the characteristic tensile strength (parallel to the grain) - hardwoods
f 's = 2.2 MPa the characteristic shear strength
E = 9100 MPa the characteristic modulus of elasticity parallel to grain
Birch and most structural ply here gets rated F17, roughly 17,000 MPa. This strength rating doesn't seem to be a hard (costly) target to hit. This linked sheet is F17*, but only the outer veneers are stated to be 'high quality' or 'hardwood', so the rest are probably pine.
SpecRite Formply F17 1800 x 1200 17mm Plywood | Bunnings Warehouse
I can get 'braceply' in F27 from chain stores. Higher ratings exist (to F37) but seem to be a bit more boutique.
Structural grading | WoodSolutions
Plywod Specification Overview
Lots of 'structural' or 'exterior' grade (see 3rd link above) ply seems to meet those criteria, so locally, the only point to buying birch is for the veneer. It's cost literally doubles based on the face appearance - the same shop has:
$107.20 birch core, A-bond (phenol formaldehyde resin), film face**
https://plyco.com.au/products/birch-filmface
$197.99 birch core, A-bond (phenol formaldehyde resin), birch face
https://plyco.com.au/products/birch-premium?variant=36373909136
*The Australian Competition and Consumer Commission (ACCC) gets all up in your grill if you sell plywood that doesn't meet the rating.
**the shop also has non-birch film face that's both cheaper AND stronger than the birch.
That's a good point. A factor I hadn't considered.
Does anyone know how Spruce ply compares?
^ That's probably mostly true, and as I said earlier, presumably any "ATX" type ply will have similar (waterproof) glue.
- but different wood species can vary widely in their internal structures, (pore structure, etc) as well as the amount of lignin, so there surely must be differences in damping.
- but different wood species can vary widely in their internal structures, (pore structure, etc) as well as the amount of lignin, so there surely must be differences in damping.
In Australia, bond type is part of the specification. Anything specified as marine or exterior grade has an A-bond (phenol formaldehyde resin). The bond type is often stated on the product. There may be similar specifications where you live.
Bamboo ply 'wood' has better damping / lower transmission, and it usually only has 3 layers (the core layer is usually very thick).
I wonder if plywoods whose layers are less consistent are better for damping, e.g. cheap-but-strong plywoods that use soft cores and hard skins.
Note that the damping is pretty low on most of them, so the difference is between different amounts of almost nothing 🙂
This interests me. My regular brain tells me the glue would have to be softer than the wood plies for this to be true. My speaker brain says Dave knows something I don't. Fill me in.
I believe it's the difference in compliance between the layers that matters Constrained-layer damping - Wikipedia
As welterwys said it is the construction more than the species.
I can get BB in the 3/8 inch range but then you have to glue other pieces to get the thickness you need. Not insurmountable but time consuming and expensive.
Has anyone considered the use of oriented strand board? It is heavy and brings along its own foibles for assembling a cabinet. One would not bother making a small cabinet with this since I would want to use glue blocks everywhere with the stuff. But it sure seems to be stiff and stable.
I have only used it as a laminate on those 15 inches woofer boxes that PARTS EXPRESS used to sell. Certainly not an ideal enclosure but works well - mdf on the inside and the osb on the outside. I used massive amounts of good window caulking as the adhesive. I would think it would add damping which I know is not really wanted but with the uneven surface it was the best way to get both pieces in contact with each other.
With many coats of black shellac it can look very interesting.
I can get BB in the 3/8 inch range but then you have to glue other pieces to get the thickness you need. Not insurmountable but time consuming and expensive.
Has anyone considered the use of oriented strand board? It is heavy and brings along its own foibles for assembling a cabinet. One would not bother making a small cabinet with this since I would want to use glue blocks everywhere with the stuff. But it sure seems to be stiff and stable.
I have only used it as a laminate on those 15 inches woofer boxes that PARTS EXPRESS used to sell. Certainly not an ideal enclosure but works well - mdf on the inside and the osb on the outside. I used massive amounts of good window caulking as the adhesive. I would think it would add damping which I know is not really wanted but with the uneven surface it was the best way to get both pieces in contact with each other.
With many coats of black shellac it can look very interesting.
Yes but I believe Dave was discussing the damping within plywood itself. I admit to being confused by his thoughts but it wouldn't be the first time he has set me straight.
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