BB Ply vs MDF vs Corian

[tommus]

You are right, you can't really "overbuild" a cabinet to the detriment of sound quality. My definition of "good enough" however doesn't imply much if any compromise - I think (but cannot prove) that these differences would be difficult to measure and even more difficult to hear. Perhaps I should say "excellent enough" instead Still, I am going to say that geometry trumps materials by a large margin. Mass is an inelegant way to get stiffness.

I would put minimizing diffraction near the top of that list of things worth losing sleep over...

 

[Cal Weldon]

tommus, your thoughts and mine are similar. Personally, I think it's a bunch of hooey. If you're doing a simple braced box, make the braces out of anything you have on hand. MDF shelf braces or softwood stick braces, it's all an improvement (usually). How you do it is 10 times more important than the material used and I bet anyone here can find 10 things on anyone's set of speakers that are more important to improve than the brace material.
Sometimes, too much thinking is just that.

 

[GM]

Also, Ive seen an Austrian manufacturer using Corian for their baffles. Is there any reason for this other than just marketing and foo-foo dust?

Corian is much more massive than MDF, but with nearly the tensile strength of BB ply, so an excellent speaker box material, but not much of a selling point without a buying public that's well educated in the underlying physics.

GM

 

[GM]

It probably doesn’t matter what the bracing is. The corian is very inert and machines well. I typically use birch ply for cabinet and bracing and mdf for the baffles because it machines better than plywood. I would think the corian would be a nice upgrade to the mdf.

For most non true sub woofer DIY cabs, no bracing beyond a motor support would be required if built with 1/2" Corian with its scrap used for glue blocks.

GM

 

[vinylkid58]

Corian is much more massive than MDF, but with nearly the tensile strength of BB ply, so an excellent speaker box material, but not much of a selling point without a buying public that's well educated in the underlying physics.

Cost of Corian vs MDF might have something to do with it. Corian has always been quite expensive.

jeff

 

[GM]

Yes, there is that, though for those of us with little patience can be a bargain when a fine furniture finish is required. I burned myself out early on hand sanding many coats of primer, then rubbing out 20-30 topcoats of nitrocellulose lacquer on various pieces of furniture, vehicles to get that 'piano black', hot rod, show car finish that a fly lands on and busts his a$$ sliding off!

GM

 

[brianco]

......... (BTW I always put a well-fitted brace on edge right behind the driver magnet - give it a pad of foam gasket and compress the chassis between the baffle and brace when you screw the driver in.)

A better (much more expensive) option is to use a space filler between magnet and brace made from pure carbon block. It really does clean up the sound.

 

[planet10]

Any disadvantage to using MDF as interior bracing for BB cabinets?

Lots. MDF is a bad speaker building material, and worse for bracing. It is not stiff enuff.

Corian is also not stiff, but it can be nice to have a scrap or 2 for the top (particualrily if you don’t have enuff veneer.

MDF also brings safety hazards. Its only real asset is that it is cheap.

dave

 

[planet10]

From what I gather making the bracing from another material than the box creates a mechanical impedance mismatch which impedes the transmission of vibrations.

That is true. I suggest a dissimialr material — even MDF — for th event spacers on my miniOnkens.

But for a brace letter to go with something stiffer than BB — like some hardwoods, but that is usually only suggested for stick braces, full 4-sided braces might have issues and be expensive.

dave

 

[planet10]

Material is cheap, labor ain't.

+1

 

[planet10]

I tend to use bracing (whatever piece of extra is about the right size) as a full blown shelf brace with holes jigsawn out, rabbetted into the walls, where it's fully constrained and rigidly coupled. Not a lot of use hoping a butt joint stuck between walls provides much bracing.

If you are using proper glue a butt joint is just as good as one that is rebated in.

My braces typically tie 4 walls together, are placed off-centre, and the orientation is such that the aspect ratio of the subpanels ar ehighe rthan the panel being braced.

The 1st brac ei put into a cabinet braces the driver itself, and often the baffle to 3 other walls.

dave

 

[planet10]

.. 3/4" is fine for subs. Bracing should be intelligently designed

With a well-braced box and push-push loading to cancel driver reactive forces i easily got away with 15mm (58”).

dave

 

[planet10]

Yes, I've done that, but used cork between magnet and brace

I aim for as stiff, and tight up to the magnet as possible before loadin gthe basket. I want as much of the driver reactive energy as possible to be routed to multiple panels.

dave

 

[planet10]

...but I certainly hear a quality from low diffraction systems...

Indeed, the decrease in the diffraction signiture is audible across the standard variations of my miniOnkens. The signature decreases as you move from the rectangle ClassicGoldenRatirapezoid version, to the Rectangular miniOnken with the big side chamfers, to the trapezoid version which mimics a teardrop shape in its plan view.

dave

 

[planet10]

Mass is an inelegant way to get stiffness.

:^)

 

[planet10]

Corian is much more massive than MDF, but with nearly the tensile strength of BB ply, so an excellent speaker box material, but not much of a selling point without a buying public that's well educated in the underlying physics.

We never found Corian (or other materials in the solid surface material class) to work well as speaker enclosures.

(we had lots of scraps to play with)

dave

 

[GM]

Not sure what you mean by not 'work well', but its physical specs work and for sure the two different huge multi-way high end speaker systems that I auditioned in the late '80s? sure impressed me [dead as a door nail], but the brands/models evade me ATM.

For sure there was no plywood or anything else tone except its many eigenmodes/reflections that created a sort of aura for lack of a better description, i.e. basically a bunch of individual driver boxes stacked to try and create a focused array that was more than the sum of its parts. Worked for the paying customers, but not me other than the cab's construction.

Anyway, probably academic on these forums.

GM

 

[scottjoplin]

I aim for as stiff, and tight up to the magnet as possible before loadin gthe basket. I want as much of the driver reactive energy as possible to be routed to multiple panels.

Yes, I should have been more explicit, this was in a u-frame subwoofer, so the brace was glued top and bottom but had no rear support, therefore I didn't want to put too much lateral strain on the joints and the cork is 4mm thick and slightly compressed by the magnet. I consider it to be a good compromise, certainly using foam never crossed my mind as a useful option, what do you think?

 

[twinter]

Material............................Stiffness (Modulus of E).................Damping Factor
Laminated Bamboo Lumber....1,500,000 psi..............................0.2 (good damping)
Corian.................................1,400,000 psi..............................0.04 (little damping)
Baltic Birch Plywood..............1,100,000 psi..............................0.04 (little damping)
MDF.......................................450,000 psi..............................0.02 (little damping)

 

[planet10]

Not sure what you mean by not 'work well', but its physical specs work

Where Chris worked did a lot of solid surface material. The guys who work it are specially trained. It was advised that we not use corian unless we did an initial substrate of something else. Just too expensive & hard to work.

Wilson, with their development of spealer box specific solid surface type materials for their speakers shows that it cn be used.

dave