Dummy question about plywood materials

Hi everyone, this should be an easy one and I think I may have the answer- but It's just a hunch:


Why are so many ply in the cabinet material so important? I'm thinking the more layers provides the greatest density (no air pockets) and a cleaner sound?

I used 11 or 13 ply baltic birch on my last build and it turned out beautifully. smiley20

Another thought or question I have is and since I'm not a pro is a, say, 5 ply 3/4" birch sheet going to be acceptable in a build. And is it really going to make a difference to a regular Joe like me? What are the advantages and disadvantages? That stuff is readily available down at the hardware store, but I'm wary of buying it.
I'd rather ask and find out as opposed to building "it" and finding out I made a big mistake smiley2 .


smiley5 smiley5 smiley5
Well, thanks for the information. You've taught me more than I already know. Right on!

I already know about the Chinese Birch that is available- it's junk from what I've heard, but I digress....

Cool, then. Thanks for the time.

yes your hunch is right. the more layers there are to the ply the better the density is. I would stay well away from 5 layered ply. And again you are correct there will be pockets of air etc in the ply. The reason birch ply is used, comes down to the smooth finish of the ply and does not need much prep befor spraying. If you are making up a test box befor you build your finished design then mdf can be used. Infact mdf gives the best sound due to its density, but wont last 10 minutes on the road. And your final question is yes again you would notice it. if you where to build 3 boxes 1 in mdf, 1 in 13 lam birch ply, and one in cheap 3 lam ply, the mdf would give the best results. Due to mdf not being up to the strains of taking you boxes out on the road every week, 13 lam birch ply is a good compromise between quality of sound and your boxes lasting 20+ years........ smiley2

On another note birch ply from the likes of b&Q is gonna cost ya 45 to 55 quid a sheet, but from a dedicated wood yard you should be able to get it for about £35 thats a full out sheet i.e. 1220x2440x18mm..... well worth shopping around.

The ply situation is also down to energy transference. Energy is transmitted down the grain and if there is a lot of grain in one piece of wood, there would be a lot of resonance. This is the reason you can't make a bass cab out of solid wood. So with 13 lam ply you get thin layers of Birch separated by a glue line. Birch being a very hard wood also helps. Back in the '70's American cabs were arriving in the UK which were really bad. The ply used on early cabs was douglas fir ply which was soft wood and ended up looking like Weetabix. This is one reason why for many years we made far superior cabs to those available in the States.

adding to what tony has said, each veneer is opposed in grain, so it's a kind of lattice structurally, bound with glue.

this makes it very strong to point loads - it's a similar principal to kevlar bullet vests.

I imagine it would also help in avoiding transfer of any resonances.

Thanks for the info- that's definitely shed a little more light on the subject. I was suprised about the MDF, but it makes sense.

Well, I'm going down to the shop to pick up a couple more sheets of baltic birch this afternoon... smiley17

smiley20

Tony.A.S.S. wrote: ended up looking like Weetabix.

had to see what your talking about

smiley36

Michael, back in the seventies, various cabs were brought over from the States, such as Altec and JBL. The Voice of the Theatre bins were popular, However, they never lasted long on the road. One of the first horn/bin systems I did was my take on the V.O.T. cab, it was twice the weight and had a 200 watt Gauss speaker in it. The porting area looked different because it was tuned for Gauss.
Of course now, America has caught up, because you can use the same ply as us.

Some usefull info on plywood,

Plywood is probably the most popular and versatile man-made woodworking material available in home centers today. Plywood is a laminated product made up of numerous thin strips of wood laid in alternating directions and bonded with glue into strong, stable sheets. Because of this construction method, plywood is less susceptable to expansion and shrinkage. Why?
A board of solid wood hewn from the trunk of a single tree is somewhat unstable and likely to expand or shrink across the grain based upon the moisture content present in the wood. While the board is much stronger and less likely to expand or shrink along the grain, it is much more likely to split with the grain than against.

Plywood Grades:

When buying plywood at your local supplier, you may notice that there are a number of different grades. The normal grading system uses the letters A, B, C & D, where A is the best quality, with virtually no blemishes and very well sanded. Grade D typically contains up to the maximum number of blemishes allowed.
The letter grades typically come in pairs, where one letter refers to the "better" side, called the face, and the other letter to the back side, opposite the face. As such, a sheet of A-C plywood will be very well finished on the face with a relatively unfinished back. Conversely, construction grade plywood would be C-D (commonly referred to as CDX plywood), which is great for structural use but not suited to be finish material.

Plywood Bonding Types:

In addition to the plywood grades, there are four common plywood bonding types. The difference is in the glues that are used to bind the plies, or layers of the plywood.

Interior Plywood:

Plywoods for interior use only are made from various hardwood and softwood species, and can be used only in interior applications such as wall sheathing, furniture (where exposure to moisture is limited), cabinetry and the like. Interior plywood is available in most grades, as well as a number of hardwood species such as birch, oak and cherry.

Exterior Plywood:

The most common type of plywood, readily available at home centers. The glues used in exterior plywoods are much more resistant to moisture than interior plywoods. Once again, nearly all grades are available, with A-C, B-C and CDX the most common. Numerous hardwood species are also available in exterior varieties.

Marine Plywood:

When moisture resistance is a priority, look into marine plywood. This type uses the best adhesives and is manufactured to the highest standards. It also is most commonly graded as A-A, with two top grade faces, but is limited in the hardwood choices that are practical for use in marine settings.

Structural Plywood:

When the appearance of the face is of lesser concern than the strength and stability of the material, structural plywood will typically be the choice. The resins used to adhere the plies are designed for extra strength to avoid separating of the layers. Structural plywood is seldom found in a grade higher than C-D. It is commonly used in concrete forms on construction sites.

Plywood Construction:

Plywood's construction addresses both of these concerns. By gluing numerous thin strips of wood in alternating directions layer by layer, plywood is much less likely to expand or shrink based on moisture in the environment, and the alternating construction creates a board that is much stronger in each direction than a similarly sized board cut from a single tree.
Most plywood is made from an odd number of layers, called plies (typically 3, 5, 7, 9, 11, or 13), with an equal number of plies on each side of the center ply. In this manner, the surface plies are always parallel, and the grain of the surface plies usually follows the longest side of the sheet (although not always). The sheet is strongest parallel with (as opposed to against) the two surface plies.
Surfaces:
In most applications, one side of the plywood is more likely to be seen than the other side. As such, plywood is usually sold with one better side, called the face, and one side that isn't as clean or smooth, called the back. Plywood with two faces is available for projects where both sides of the sheet will be visible.

Tropical plywood

Tropical plywood is always made of mixed species of tropical wood in the Asian region. Tropical plywood boasts its superiority over softwood plywood due to its density, strength, evenness of layers, and high quality. It is usually sold at a premium in many markets if manufactured with high standards. Tropical plywood is widely used in UK, Japan, Taiwan, Korea, Dubai, and other major cities worldwide. It is the most preferred choice for construction purposes in many regions.

Common plywood
Concrete panel
Floor base
Structure panel
Container flooring
Lamin board
Laminated Veneer Lumber (LVL)


Softwood plywood

Softwood panel is usually made either of Douglas fir or spruce, pine, and fir (collectively known as spruce-pine-fir or SPF), and is typically used for construction and industrial purposes.

Floors, walls and roofs in house constructions
Wind bracing panels
Vehicle internal body work
Packages and boxes
Hoarding
Fencing
There are coating solutions available that mask the prominent grain structure of spruce plywood. For these coated plywoods there are some end uses where reasonable strength is needed but the lightness of spruce is a benefit e.g.:

Concrete shuttering panels
Ready-to-paint surfaces for constructions


Hardwood plywood

Used for demanding end uses. Birch plywood is characterised by its excellent strength, stiffness and resistance to creep. It has a high planar shear strength and impact resistance, which make it especially suitable for heavy-duty floor and wall structures. Oriented plywood construction has a high wheel-carrying capacity. Birch plywood has excellent surface hardness, and damage- and wear-resistance.
Coated special birch plywood is typically used as a ready-to-install component e.g.:

Panels in concrete formwork systems
Floors, walls and roofs in transport vehicles
Container floors,
Floors subjected to heavy wear in various buildings and factories,
Scaffolding materials
Birch plywood is used as a structural material in special applications e.g.:

Wind turbine blades
Insulation boxes for Liquefied Natural Gas (LNG) carriers
Smooth surface and accurate thickness combined with the durability of the material makes birch plywood a favourable material for many special end uses e.g.:

Die-cutting boards
Supporting structure for parquet
Playground equipment
Furniture
Signs and fences for demanding outdoor advertising
Musical instruments
Sports equipment

Decorative plywood

Usually faced with hardwood, including red oak, birch, maple, Philippine mahogany(often called lauan) and a large number of other hardwoods.

Plywood for indoor use generally uses the less expensive urea-formaldehyde glue which has limited water resistance, while outdoor and marine-grade plywood are designed to withstand rot, and use a water resistant phenol-formaldehyde glue to prevent delamination and to retain strength in high humidity.

The most common varieties of softwood plywood come in three, five or seven plies with a metric dimension of 1.2 m × 2.4 m or the slightly larger imperial dimension of 4 feet × 8 feet. Plies vary in thickness from 1/10" through 1/6" depending on the panel thickness. Roofing can use the thinner 5/8-inch plywood. Subfloors are at least 3/4-inch thick, the thickness depending on the distance between floor joists. Plywood for flooring applications is often tongue and groove; the mating edge will have a "groove" notched into it to fit with the adjacent "tongue" that protrudes from the next board. This prevents one board from moving up or down relative to its neighbour, so providing a solid feeling floor when the joints do not lie over joists. Tongue & groove flooring plywood is typically 1" in thickness.