Brace material - various woods, steel etc.

[Circlotron]

Suppose we're gunna build our latest shake-the-neighbourhood sub and we don't really like the idea of the enclosure flexing in and out like some kind box-shaped lung. We have to brace the panels to make them nice and rigid. Now, my question is this: pine is quite cheap and you can get it just anywhere but seeing it is a softwood, what is its strength like? There are various kinds of hardwood available - at a price - so what is the strength and rigidity of these like compared with softwoods like pine?

Also, what about steel? I could well imagine a piece of 30x30mm angle or U shape or even box section especially would be very rigid. Actually, one shape I had been thinking about most of all is a T shaped cross section. It can take screws down each side and the centre bit can take a strut from it to the opposite side brace. Only thing is, you cannot glue steel to the panel; maybe some RTV silicone rubber might be ok along with lots of screws.

What's your experience with braces?

[michael]

dont use pine in speakers! it expands and contracts like a russian U-boat, use MDF its plenty stong enough and it wont expand/contract

[Circlotron]

Using MDF for panels of course, but I didn't think it would be strong enough for a brace when you have to put a screw into it's edge.

[tool49]

MDF should be alright but I wouldn't suggest using screws to hold the bracing in place. I personally use little cookies that fit in a slot made in both pieces of wood. You need the proper tool though to make the slots.

http://www.lamello.com/english/hv_sys_e.htm

Coupled with good carpenting glue, this system is flex proof and does a really good job. You will also need several clamps to make that there is enough pressure on the joint to seal the whole enclosure.

Hope this helps!
Sébastien

[michael]

who says you need to screw it, the glue holds much stronger than the screws, if you arent using fitted joints then just use small screws to hold it while the glue dries, or even little nails, my subwoofer box i am currently building use no screws or nails, its all done to fit together and clamped while glue dries.
and MDF is plenty strong enough for bracing, if you are concerned just use alot of it

[Brett]

Try dried hardwood dowel 20-30mm diameter, cut and trimmed to length so that it just fits in and has to be almost jammed into place. The drill a pilot hole through the panel into the end of the dowel and screw up tight. I use epoxy to seal then. You can work out a pattern of the dowels so that they break up the panel modes, and use them between all 6 panels.

If you use some sort of damping material like treated and carded wool, you can "hang" it over the dowels which is much more effective at breaking up internal standing waves.

Only thing is, you cannot glue steel to the panel

Ever tried epoxy resin?
Trouble is steel usually rings, but that may not be an issue at LF.

[Volenti]

I used 16mm hardwood dowel with a looong 16mm drill to go straight from one side to the other, no messy measuring, just slide the dowel in, trim off, and glue in place

[Brett]

Originally posted by Volenti
I used 16mm hardwood dowel with a looong 16mm drill to go straight from one side to the other, no messy measuring, just slide the dowel in, trim off, and glue in place

Of course, once the panel sides are cut, you could clamp them together and use a speedbore before assembly.

Curious Volenti, whats the driver and enclosure type?

[till]

pine, "softwoods" : fine, use very dry quality, use only to take force in one direction. = only F(N) > 0, no F(Q)

steel: problem is to make a connection without a slit between that differen materials. Also it may ring. Bad idea.

MDF, every kind of wood fiber based material: will be less strong against bending / torque than real wood used in right direction. I would call these kind of materials dirt - based.

real hardwood, like maple, wonderfull, but you need to know how to use.

thick construction birch plywood, way to go. stiff on all directions, less problems with expanding uneqal with humidity. Use PVAC glue.

[Volenti]

Originally posted by Brett


Of course, once the panel sides are cut, you could clamp them together and use a speedbore before assembly.

Curious Volenti, whats the driver and enclosure type?

good point.

I'm using 2x JL15w-6 (car audio long throw subs, very similar to Adrie's tempest, but with dual 6 ohm voice coils) in push push with a driver on either side to cancel mechanical vibrations, the enclosure is divided in 2 with each sub in a seperate 85L sealed enclosure(stuffed with dacron and lined behind the drivers).