A speaker made of only hardwood

[Paul Carmody]

I apologize for bringing this up because I know this question does come up from time to time, but I can't find it.

Anyway, I have a lot of solid 3/4" oak stock. I used it for the baffles of the Sunflowers (the rest of the speaker was cabinet plywood). But I was curious if it was possible to build a small speaker from the solid oak stock (we're talking like 7 liters max). It's not resonances I'm worried about (I can use braces for that) as much as expansion and splitting. The oak is 40+ years old, but it's flat and true, so I don't think it's going to be doing any more shape-shifting... but I'm not a woodworker; I'm just a musician who likes to build stuff. :o So I need some sage advice.

So woodworking experts, what do you think?

[shawn_a]

Re: A speaker made of only hardwood

Obi Wan Jeffnobi (Bagby) has his Davids which, IIRC, are made of solid oak. There was a split on one of the side panels but it looked to be rather mild and didn't go clear through to the inside. They're floorstanders so I bet the size you're talking about won't be a problem.

shawn

[Jeff B.]

Re: A speaker made of only hardwood

Obi Wan Jeffnobi (Bagby) has his Davids which, IIRC, are made of solid oak. There was a split on one of the side panels but it looked to be rather mild and didn't go clear through to the inside. They're floorstanders so I bet the size you're talking about won't be a problem.

shawn

Yes, you are correct. I have a couple of splits, and a corner that has separated some. Solid hardwoods can do this due to expansion and contraction. This is why I am redesigning the speaker with new tweeters and they will go into new enclosures as well.

Jeff

[philiparcario]

Re: A speaker made of only hardwood

I apologize for bringing this up because I know this question does come up from time to time, but I can't find it.

Anyway, I have a lot of solid 3/4" oak stock. I used it for the baffles of the Sunflowers (the rest of the speaker was cabinet plywood). But I was curious if it was possible to build a small speaker from the solid oak stock (we're talking like 7 liters max). It's not resonances I'm worried about (I can use braces for that) as much as expansion and splitting. The oak is 40+ years old, but it's flat and true, so I don't think it's going to be doing any more shape-shifting... but I'm not a woodworker; I'm just a musician who likes to build stuff. :o So I need some sage advice.

So woodworking experts, what do you think?

they can be done. I like using 3/4 stock as veneer over a 1/2 inch mdf box. a little bigger but rock solid I use glue and thin cork 1/8 inch sheets inbetween the two. I also coat all sides of the oak with 2 or 3 coats of minwax polycrylic thinned with water. this greatly reduces all cracking problems. my avatar is a 2.5 inch curly maple baffle so far so good.

[bobbarkto]

Re: A speaker made of only hardwood

Age doesn't matter!
Wood will always shrink and expand with changes in the environment.
If you restrain it, something will give, sooner or later.
You might be surprised how much force an expaning board can exert. It's pretty amazing.

The difficult part in designing a box is allowing for movement while at the same time keeping things sealed sufficiently for the design and of course not getting any rattles or buzzes. There are no good methods I'm aware of, at least none that I'd be happy employing.

Rigidly connecting braces across the grain and where top and bottom meet the sides (front/back or l/r depending on grain orientation) are where you find the biggest problems. A tightly glued joint there and you restrain the movement and blamo.. something breaks.

Will it happen for sure? No
Is it likely? Yes.
The wider the pieces the more likely you'll see signs.

Oak typically moves a fair amount with seasonal changes. Some oaks more than others.

Do you feel lucky? ;)

I apologize for bringing this up because I know this question does come up from time to time, but I can't find it.

Anyway, I have a lot of solid 3/4" oak stock. I used it for the baffles of the Sunflowers (the rest of the speaker was cabinet plywood). But I was curious if it was possible to build a small speaker from the solid oak stock (we're talking like 7 liters max). It's not resonances I'm worried about (I can use braces for that) as much as expansion and splitting. The oak is 40+ years old, but it's flat and true, so I don't think it's going to be doing any more shape-shifting... but I'm not a woodworker; I'm just a musician who likes to build stuff. :o So I need some sage advice.

So woodworking experts, what do you think?

[bobbarkto]

Re: A speaker made of only hardwood

Just for anyone else really..
The thin cork layer allows for some wood movement.
Without it the boxes would very likely show signs of damage. Especially with only one side exposed to the atmosphere.

It will not prevent any damage where the top/bottom join perpendicular to the sides/front/back.

they can be done. I like using 3/4 stock as veneer over a 1/2 inch mdf box. a little bigger but rock solid I use glue and thin cork 1/8 inch sheets inbetween the two. I also coat all sides of the oak with 2 or 3 coats of minwax polycrylic thinned with water. this greatly reduces all cracking problems. my avatar is a 2.5 inch curly maple baffle so far so good.

[rone]

Re: A speaker made of only hardwood

I haven't done it myself, but I would think that to increase chances of success you would want to limit amounts of seasonal humidity changes by sealing the wood with a waterproof/vaporproof sealant. If not done, the movement in glued cross-grain situations will cause splits. Another way to do it would probably be to fasten the baffle and back with flexible gaskets and slotted screw holes.

[daveh]

Re: A speaker made of only hardwood

I apologize for bringing this up because I know this question does come up from time to time, but I can't find it.

Anyway, I have a lot of solid 3/4" oak stock. I used it for the baffles of the Sunflowers (the rest of the speaker was cabinet plywood). But I was curious if it was possible to build a small speaker from the solid oak stock (we're talking like 7 liters max). It's not resonances I'm worried about (I can use braces for that) as much as expansion and splitting. The oak is 40+ years old, but it's flat and true, so I don't think it's going to be doing any more shape-shifting... but I'm not a woodworker; I'm just a musician who likes to build stuff. :o So I need some sage advice.

So woodworking experts, what do you think?

Paul,

I am no expert but these cabinets are about the size you are talking about and made out of 3/4" inch solid oak. So far so good, I made them for my wife and she has them in the kitchen. Even in this extreme environment (she cooks all the time) I have not had any splits or separating. I guess I finished them about a year ago.

HTH,
DaveH

[bobbarkto]

Re: A speaker made of only hardwood

The very best a suitable finish can do is ~85%.
Some epoxies, 2 component urethanes and some silicone based finishes can achieve those rates.

WB polurethane, acrylic and oil based varnishes and lacquers fall in the 30-50% range at best.

This means the finish buys you some time before the moisture gets in.
Nearly 100% effective finishes exist but they contain fillers that make them opaque and not really suitable for a clear wood finish.

Allowing for movemnet is the only sure method.

I haven't done it myself, but I would think that to increase chances of success you would want to limit amounts of seasonal humidity changes by sealing the wood with a waterproof/vaporproof sealant. If not done, the movement in glued cross-grain situations will cause splits. Another way to do it would probably be to fasten the baffle and back with flexible gaskets and slotted screw holes.

[jims]

Re: A speaker made of only hardwood

I apologize for bringing this up because I know this question does come up from time to time, but I can't find it.

Anyway, I have a lot of solid 3/4" oak stock. I used it for the baffles of the Sunflowers (the rest of the speaker was cabinet plywood). But I was curious if it was possible to build a small speaker from the solid oak stock (we're talking like 7 liters max). It's not resonances I'm worried about (I can use braces for that) as much as expansion and splitting. The oak is 40+ years old, but it's flat and true, so I don't think it's going to be doing any more shape-shifting... but I'm not a woodworker; I'm just a musician who likes to build stuff. :o So I need some sage advice.

So woodworking experts, what do you think?

I would worry most about cracks at the joints. You're aged oak should be pretty stable (in terms of warping) unless it gets soaked or put into an unusually humid environment. However, it will continue to expand and contract with the seasons forever. This is what I would do:

- Orient the grain on the top, bottom and sides so it all goes the same way. Wood expands more across the grain than with the grain (the wood is a collection of little straws the get fatter when there is more humidity, but that doesn't affect their length much). You don't ever want to glue together two pieces of wood that have grain oriented perpendicularly to each other.

- The joints between the sides and top should be something other than b-u-t-t joints, which are quite weak when you're gluing end grain. Preferably something like tongue and groove or biscuits that provide a mechanical interlock in addition to increasing glue surface area.

- The front baffle should be removable and sealed with weatherstripping or whatever you like to use, similar to many cabinet designs. There's no way you can glue on the front baffle without ending up with grain running perpendicularly on two of the joints.

- The rear baffle should also be removable but sealed, similarly to the front baffle. I would cut a rabbet in the back edges of the top, bottom, and sides. Then the rear baffle can be set in without visible joints (except when viewed from the back).

- Finish the cabinet the same way inside and out. The finish only slows down seasonal expansion and contraction, but you won't have unfinished interior moving faster than the finished exterior. However, there is a school of thought that says it really doesn't make that much difference.

Your cabinet should pretty much last forever, IMO.

Best of luck,
Jim

[Wolf]

If you recall my Sir Audinums...

They were made with pine-baffles, and Red Oak 1x6 for the sides/top/bottom. I will say I've not had any trouble either, and they have been finished for about 3 years now.

One thing- you want a slightly flexible adhesive, so that the joints can give a little for expansion. I used the poly-glue method on mine, and nothing has happened to the negative.
Later,
Wolf

[dwigle]

Re: A speaker made of only hardwood

I used solid maple on my Aria 7s - Joe D'Apolito's original MTM design featured in Speaker Builder. That was 20+ years ago and they are fine. The widest panel though was only 9 inches.

I have used oak for a number of different applications. As said by others, make the baffle and rear panel removable, all grains going the same direction and seal the wood inside and out.

For wider panels used in commercial applications, we kerf the bottom or inside of the panel. Cut kerfs about a third of the way through the panel and space a couple inches apart.

[JRT]

Re: A speaker made of only hardwood

I apologize for bringing this up because I know this question does come up from time to time, but I can't find it.

Anyway, I have a lot of solid 3/4" oak stock. I used it for the baffles of the Sunflowers (the rest of the speaker was cabinet plywood). But I was curious if it was possible to build a small speaker from the solid oak stock (we're talking like 7 liters max). It's not resonances I'm worried about (I can use braces for that) as much as expansion and splitting. The oak is 40+ years old, but it's flat and true, so I don't think it's going to be doing any more shape-shifting... but I'm not a woodworker; I'm just a musician who likes to build stuff. :o So I need some sage advice.

So woodworking experts, what do you think?

The short answer is don't do it.

There is some good technical info on moisture related shrinkage, aka wood movement, starting on page 3-7 in the downloadable book at the link, 13.9MB PDF file:

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.pdf

.

[jims]

Yes, but....

The short answer is don't do it.

There is some good technical info on moisture related shrinkage, aka wood movement, starting on page 3-7 in the downloadable book at the link, 13.9MB PDF file:

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.pdf

.

The OP isn't going to be using green wood. If wood is properly dried to begin with, any additional shrinkage/expansion that may occur can be compensated by properly designing the project. I think a small cabinet made with well-dried solid wood could last for decades. It's no different from any other small box.

Jim

Extremely interesting link, by the way. It looks like the sort of thing I'll refer back to.

[edlafontaine]

Barkto knows wood

1) Barkto speaks from experience
2) Removable panels sealed with gaskets obviates the concern for cross-grain joints.
3) Thinner 1/4" hardwood over mdf I can vouch for. The hardwood's need to move wrt moisture changes is restrained by the mdf. After 2 seasons with the Pro C's I have no joint creep.
4) If you construct with solid hardwood, consider coating ALL the interior surfaces with a viscous coating, like duct seal or bed liner.