Hardwood vs. MDF for a DXT-MON build.

[carbidetooth]

Boston Jack, I think there's an important thing to consider in your boat analogies concerning waterproofing. Bulk water is a larger molecule than is water vapor. For reference think of Gore-Tex or similar fabric that breathes vapor yet repels water. What you're dealing with in a home environment is vapor (humidity). That is unless you intend to float them in the bathtub!
I doubt you could ever achieve a perfect seal in a project such as yours that would encapsulate wood to the point of being vapor impermeable. Again, the best you can hope for is to slow down and minimize that natural "respiration" of ambient humidity in and out of wood.
This is all pretty deep into theory but is helpful is determining what the best path to the destination is. As with many things, there are trade-offs. Determining which trade-offs are acceptable for the project at hand becomes the decision maker.

 

[puppet]

... and with age, many finishes do check if only on a microscopic level. Fabricating a solid wood project with an eye toward wood movement via humidity is always good practice. That will dictate the design in most cases. If you allow for the inevitable, the design will be a success.

 

[Morpheus]

Thanks for sharing that. Unfortunately I have 4/4 walnut and 8/4 Brazilian cherry (aka tigerwood) sitting in my apartment coming to moisture equilibrium, so the die is cast. I think my approach is going to be to 1. consult with some local cabinetmakers, as making boxes isn't exactly a new thing and they might know tricks that work and 2. really pay attention to surface treatment.

I did find one builder online who had speaker cabinets produce small cracks after moving from a dry climate to a humid coastal climate. He provided pictures (sorry don't have the link handy) and was able to repair by injecting epoxy, so some small cosmetic damage but not terrible result.

Just to summarize, I wasn't able to find any data that solid hardwood is worse than MDF in acoustic terms. I appreciate your advice and I'm going to steer in the direction of taking whatever mitigating steps I can.

So here is a strange case: I've owned a couple of small sailboats: J30 with teak rub rails and hand rails, 26' Columbia with custom teak cockpit seats, and a 1960's Lightning with mahogany, ash, and mahogany plywood decks (entirely wood construction). All three boats were exposed to marine environment, dry stored in winter New England climate, basically put through a torture test for years. Result: no cracking or failed joints. What's going on there?

Teak is a very resin rich wood (as is Brazilian cherry), so that is part of the story. Mahogany and ash are not.

What was your failure? Joints failing? Cracks across panels? What adhesive was used on the joints, do you know? Thx.

No cracks or bulgin on the pieces themselves, just the failure of the glued joints due to different expansion rates.The top and bottom had grown to be more than a mm longer than the side cheeks wich were the same dimension depth wise, same plank and same grain orientation ( paralell to floor, whereas baffle and back was perpendicular to floor).
And there is also that, in a box, two sides are always gonna be in diferent orientation in anysotropic materials and therefore expansion/contraction axis.
Can't remember the glue , but it was the one he used for super humid in-bathroom cabinetry.
By the way, great choice of project, DXT MON really looks state of the still attainable art measurements wise.

 

[BostonJack]

Cabinetmakers have used regular wood glue(s), be they hide or resins, for centuries. If your completed loudspeaker cabinets will be used to get you across the Atlantic, go with the epoxy
Don't forget, some of these makers are building for harsh commercial environments. They buy their adhesives in bulk and frankly begin to use them for everything they might make. Nothing wrong about it but one has to bare in mind that some adhesives will have adverse effects on certain woods. They might stain and discolor. Always good to check this stuff out first.

To add: old wood working techniques have been lost to some degree, which is a shame. Today manufacturing is geared toward production. Hand tools aren't used as they once were. You're building a custom piece. The skill level you have will make or break your project. If you don't want it to fly apart, crack some books on the older techniques. I worked at this for over 40yrs ... took the first 10yrs to find my ass with both hands.

you're right, it pays to be humble. boats, epoxy... they are like a religion with me. (not kidding)
I'll follow some of the threads you have laid out.
I'm also a stubborn student so I'll accept responsibility for my mistakes.

 

[BostonJack]

No cracks or bulgin on the pieces themselves, just the failure of the glued joints due to different expansion rates.The top and bottom had grown to be more than a mm longer than the side cheeks wich were the same dimension depth wise, same plank and same grain orientation ( paralell to floor, whereas baffle and back was perpendicular to floor).
And there is also that, in a box, two sides are always gonna be in diferent orientation in anysotropic materials and therefore expansion/contraction axis.
Can't remember the glue , but it was the one he used for super humid in-bathroom cabinetry.
By the way, great choice of project, DXT MON really looks state of the still attainable art measurements wise.

Thanks. and thanks to everyone for their responses. when the flaws in my work are apparent, I will post pictures.
this is an empirical site, right?

 

[mightycicadalord]

I haven't had any problems with using hardwoods on speakers. I just got these together but can't decide on how to finish them, can't really decide on what to do, just and oil finish or poly coat? They're pine boards from lowes.

Here's to hoping they don't expand or contract too much, got plenty of bracing in there. I have some stands I made a few years ago out of pine and they haven't changed in the slightest. I flush routed a lot of it so if there problems I'd see them. Thread is making me consider grabbing some metal l brackets and spreading them out over the inside joints.

 

[BostonJack]

I haven't had any problems with using hardwoods on speakers. I just got these together but can't decide on how to finish them, can't really decide on what to do, just and oil finish or poly coat? They're pine boards from lowes.

Here's to hoping they don't expand or contract too much, got plenty of bracing in there. I have some stands I made a few years ago out of pine and they haven't changed in the slightest. I flush routed a lot of it so if there problems I'd see them. Thread is making me consider grabbing some metal l brackets and spreading them out over the inside joints.


View attachment 178393

nice looking speakers! i vote a poly based varnish.

 

[mightycicadalord]

nice looking speakers! i vote a poly based varnish.

Sounds interesting, I'll have to buy a few different finishing products and see what I like. seems like one can get lost in deciding what's best.

 

[BostonJack]

Yes. Testing two or three options on samples of the original stock is my plan.

 

[mightycicadalord]

Huh, I just got back from Lowes and grabbed some metal L brackets, but I didn't see any poly based varnish, or any varnish for that matter. Maybe I was in the wrong section but it seemed like it should be there. I will probably just make a new thread asking for advice on finishing.

 

[D!sco]

Thought I’d share one of my favorite diy speaker designers videos on enclosure materials. I have often thought about making a set of paduak, wenge, or zebra wood speakers, but they need special consideration for their “natural timbre” or resonances. As many have mentioned, these will stretch , fight, and ultimately destroy any joinery you do to it. These will lead to sound leaks. I have seen a lot of builds using a second piece of 4/4 exotic lumber jointed to the front baffle forming roundovers, waveguides, decorative shapes, etc. That seems a more reliable way to assemble a speaker with exotic woods. That or a fully open baffle which can’t leak in the first place.

 

[muskrat]

Birch is oddly considered a hardwood, but as someone who has a lot of experience with burning it in fireplaces and woodstoves I can tell you it is actually rather soft and burns very fast compared to say Oak - which is indeed hard. In the woods there is a joke that when you plan to cut down a Birch tree it falls over on its own before you can get the saw running - cuz it's scared. In fact you see a lot of Birch trees fall each storm, on their own. Whenever I buy seasoned firewood I never accept much Birch content in the load because Birch burns too fast, and I always demand as much Oak content as I can get in the load of firewood. Lately that's been easy due to all of the Gypsy Moth attacks we've had on the Oaks.

If it has leaves it's a hardwood. Balsa is a hardwood. Basswood, woodcarver's favorite, also hardwood. Needles=softwood, you know hemlock, tamarack.

 

[Andrej]

I recommend that you do not worry about which material will vibrate the most - they will all do it more than you want. For longevity, I recommend MDF, which can then be made beautiful with addition of solid wood panels on various speaker sides. For less vibration I have used "matrix" internal bracing with some success. Here is a small satellite speaker and a small sub, during construction. Adding an additional 1/4" thick board with green glue between the box and the panel (could be solid wood, furniture grade veneered plywood, or anything you can paint/veneer) might help a little too. The problem with resonances is that they keep ringing. Green glue will speed up the energy dissipation and reduce the ringing time, but removing the ringing in the first place wins, in my "common sense" opinion.
Or moving them to very high frequencies, which are getting lower and lower in my case

 

[antennaguru]

Has anyone ever tried using OSB (Oriented Strand Board) for making speaker cabinets?

They are using OSB now for building homes as sheathing, and the claim is that it has better shear strength than other sheathing materials. It is made from random size chunks of wood, from tiny all the way up to as large as your hand, that are compressed in a form with glue between all of the chunks to make the board. It would seem that from a damping standpoint the irregularly sized internal structure of the OSB chunks might offer a potential advantage.

Many years ago I built a component isolation platform from a section of OSB, spray painted a uniform color on the top/bottom, and then edged with walnut veneer. For isolation feet I bought two rubber sports balls and sliced them in half, and glued the four halves to the bottom side as "bouncy" feet. It was dirt cheap to make and worked every bit as well as the store-bought isolation platforms I tried - including the "Townshend Sink" that has a tire inner tube between two metal halves. The sports balls had the advantage of not having to periodically get air pumped into them like the tire inner tube...

 

[carbidetooth]

Has anyone ever tried using OSB (Oriented Strand Board) for making speaker cabinets?

They are using OSB now for building homes as sheathing, and the claim is that it has better shear strength than other sheathing materials. It is made from random size chunks of wood, from tiny all the way up to as large as your hand, that are compressed in a form with glue between all of the chunks to make the board. It would seem that from a damping standpoint the irregularly sized internal structure of the OSB chunks might offer a potential advantage.

Many years ago I built a component isolation platform from a section of OSB, spray painted a uniform color on the top/bottom, and then edged with walnut veneer. For isolation feet I bought two rubber sports balls and sliced them in half, and glued the four halves to the bottom side as "bouncy" feet. It was dirt cheap to make and worked every bit as well as the store-bought isolation platforms I tried - including the "Townshend Sink" that has a tire inner tube between two metal halves. The sports balls had the advantage of not having to periodically get air pumped into them like the tire inner tube...

Someday I'll do this. Here's some food for thought.

As delivered, OSB has some challenges from a precision machining and cabinet making standpoint. It wasn't really engineered for such.
Assuming one wants something close to a furniture finish, the surface is kinda hilly and pocked up...even after significant leveling via sanding or routing.

I do like the mottled looks because it's out of the ordinary. My thought was to coat with either polyester or epoxy resin to level surface but leave the chock-a-block appearance.

This workbench top was machined on both sides and subsequently coated with shellac, which I renew from time to time. I'll probably put some toner in clearcoats to mute and blend a little for speaker cabs.

Sonically, I suspect the high resin content of OSB would work to an advantage and may be similar the properties of Baltic Birch plywood.

 

[mightycicadalord]

Make some out of osb and just call them "raw" versions like genelec lol.

So my classix ii out of pine are three years old now, had no finish for a year, we have terrible windows and live in ohio so big fluctuations in humidity. You can definitely feel it, the woofers are impossible to get out when it's cold, but fall out when it's warm. Applying danish oil seems have to have done wonders for keeping the wood stable. So far no cracks or joints separating. I am now considering a coat of polyurethane.

 

[antennaguru]

I have seen OSB in other applications stained to show off the texture. Here is a picture of some different colors all painted in a two step process using a base color and then a white-wash to show the texture:

 

[DeruDog]

One great way to do it is to make your own plywood. Cut the 4/4 and 8/4 boards in to 1/8" plys on a bandsaw, rotate every other ply 90 degrees and glue together. Lots of cauls and clamps required. In the end you will have your beautiful hardwood panels, and the endgrain (which is usually ugly anyhow), will match the face grain. Would look cool when finished!

 

[mightycicadalord]

Well looks like everyone was right, my pine classix II speakers have begun pulling themselves apart at the seams. The baffles have begun to warp. An fairly cheap but costly in time lesson to learn. At least I learned it now before embarking on other projects. I tried repairing this epoxy but it just kept pulling. These cabinets even have L brackets inside on all joints and it wasn't enough. Don't make the same mistake I did.

Guess I'll be picking up some MDF here soon.

 

[BostonJack]

Personally, I would go with Baltic Birch, stable, fairly dense (overlaps with available MDF's, according to my google searching), and much more pleasant to work with than MDF,
plus could be brought to a good finish without veneer work.

I've heard supplies are getting tight due to Ukrainian/Russian war.