I am building a Troels larger box design and he uses quite a bit of internal bracing with nice round routed holes etc. With the current price of lumber in the US I found that steel bracing would be much cheaper on a cost per stiffness basis. Plus I prefer welding and cutting to routing.
So I am thinking of a rigid space frame internal construction and with front mdf baffle and sides attached to the frame. Still keeping the designed internal volumes.
Any big drawbacks to this plan?
So I am thinking of a rigid space frame internal construction and with front mdf baffle and sides attached to the frame. Still keeping the designed internal volumes.
Any big drawbacks to this plan?
I have done this for subs, like you I really like working with steel. 1”x1” box tube works great. It ready has round over edges
How did you attach the panels to the frame? I am thinking about using constructive adhesive along with a few screws to pull it in.
I'm for minimizing weight. I can't lift 94 lb onto poles, if I ever could. Up on poles worked great for my SP2-XT, but cost $100 to hire a man to put them up there. The burglar that took them removed them for free.
A 1" steel bar cube sounds heavy, too.
All those plywood braces inside of plans annoy me. I've been thinking sheet metal joist hangers at the corners of the box with machine stop nuts glued or welded inside. Requires good measurement to line up the holes but what doesn't? I've been thinking 1/2" mdf panels since HD doesn't sell the "baltic birch" all the Europeans hyperventilate about. Then stiffen the panels against vibration in the middle with 2 cross braces of 1/2" steel rod threaded for 10-24 screws on the ends.
I bought 3/4" "sema" plywood, full dimension, @HD, for the front since the 15" driver vibrates so much.
A 1" steel bar cube sounds heavy, too.
All those plywood braces inside of plans annoy me. I've been thinking sheet metal joist hangers at the corners of the box with machine stop nuts glued or welded inside. Requires good measurement to line up the holes but what doesn't? I've been thinking 1/2" mdf panels since HD doesn't sell the "baltic birch" all the Europeans hyperventilate about. Then stiffen the panels against vibration in the middle with 2 cross braces of 1/2" steel rod threaded for 10-24 screws on the ends.
I bought 3/4" "sema" plywood, full dimension, @HD, for the front since the 15" driver vibrates so much.
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If you just want stiffness at low weight the advantage of using steel is stunning.
A 16" wide by 0.75" MDF stiffening panel would weigh 4.3lbs per foot length.
The same stiffness is achieved with 3/4" 14ga steel square tube at 0.61 lbs per foot length.
A 16" wide by 0.75" MDF stiffening panel would weigh 4.3lbs per foot length.
The same stiffness is achieved with 3/4" 14ga steel square tube at 0.61 lbs per foot length.
Tek's wood to metal screws work great for this application.
Attachments
Is it bad that I go to Home Depot and obsess about fasteners the way that my wife obsesses about clothes?
You haven't really descended into the depths until you are poring over fastener options and specs on McMaster-Carr 🙂
I LOVED when I could order big batches of specialty fasteners and fittings from McMaster-Carr when I managed a science lab…
I really like the idea of steel or aluminum square tubing frames for loudspeakers.
I really like the idea of steel or aluminum square tubing frames for loudspeakers.
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Weight for weight magnesium, aluminium, titanium, iron/steel and tungsten all perform about the same, Young's modulus scales closely with density for these and many other metals. Steel is just much the cheapest.
Beryllium is a total outlier, far far more stiffness per unit weight (alas very toxic, making it impractical).
Diamond is even more extreme, although carbon fibre is a much more affordable way to get lightweight stiffness from carbon!
I suspect pre-tensioning with high-tech high-modulus fibres like Dyneema/Spectra is another interesting way to add stiffness at low mass.
Yep, very true. Strength to weight ratio can vary quite dramatically, but stiffness to weight is much more consistant with metals.
The interesting thing about steel and aluminum is that it is commonly available in form factors which have high stiffness. Box section and I-bean sections for instance.
With wood products, we are somewhat limited to solid round sections (i.e. dowell rod), or bar section (1 x 2 timber), or panels (plates).
A steel or aluminum box beam has a great deal of form-factor stiffness. I-sections and C-sections are useful as well, but they are only stiff in one direction.
I would use a two-part epoxy , I would drill 1/2” holes in the tubes and use 1/2 oak dowel rods . I would drill a very small hole in the wood and then I would place the steel bars over those holes. I would cut the dowels about 3/4 of the what diameter of the steel tubes are. And when it’s all in place, put a small amount of wood glue on one end of the dowel and tap it into the hole of the speaker cab, and then mix up some fast dry epoxy and fill up the hole of the steel tubes and let it dry. It’s a lot of work, but after it’s done, nothing will pull them apart.
I’m not too fan of metals in my speakers. It’s enough metal in the drivers. I try to even avoid screws as much as I can now and try my way around glue with proper bracing. I like the idea of using a single throw of a sledgehammer before tossing the rubble of the speaker into the fireplace when you’re done with it (ready for the next project). Unfortunate the drivers themselves have more environmental impact than the cabinets but I’m sure you could get some dollars for alu castings.
That is excellent joinery for sure! I am not sure I can get the requisite precision on the space frame welding for that. Unless I match drill.
If I was going this route, I'd pick an overall design that made the steel perform multiple functions.
e.g. use a pair of side mounted LF drivers on opposite sides of the box.
Instead of mounting them with screws, use threaded rod which span the box and tie these drivers together.
For the regular front mounted drivers , do the same thing - fasten these drivers with threaded rods (or very long bolts) than go right through to anchor plates on the back of the box.
Anchor plate - Wikipedia
MDF is a poor choice for this comparison, it is among the least stiff types of "timber".
Look at hardwoods or bamboo instead. The values are about the same as steel or alu (see stiffness to weight at the bottom of this page).
6061-T6 Aluminum vs. Bamboo Plywood :: MakeItFrom.com
I chose MDF because its the far and away most popular building material, I don't like it. However I am after stiffness not necessarily stiffness to weight.
I can make a stiffer box out of MDF and steel than a box made of 100% bamboo, volumetric-ally. And cheaper too I imagine.
I am going to CAD up a design. I am thinking of a traditional six sided MDF box but braced internally with a steel "spider", rather than a steel framed box with MDF sheathing. I think the former will be less expensive, but still may go that way. First I would like to generate some concepts.
I can make a stiffer box out of MDF and steel than a box made of 100% bamboo, volumetric-ally. And cheaper too I imagine.
I am going to CAD up a design. I am thinking of a traditional six sided MDF box but braced internally with a steel "spider", rather than a steel framed box with MDF sheathing. I think the former will be less expensive, but still may go that way. First I would like to generate some concepts.
"I can make a stiffer box out of MDF and steel than a box made of 100% bamboo, volumetric-ally."
If you look at the 3-way classic (a 102 litre box), the braces take up about 3 litres.
if you slimmed these down by using steel instead, you might reduce the external volume to a mere 100 litres.
Faital-3WC
If you look at the 3-way classic (a 102 litre box), the braces take up about 3 litres.
if you slimmed these down by using steel instead, you might reduce the external volume to a mere 100 litres.
Faital-3WC