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Old 14th November 2012, 04:02 PM   #31
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I have used pine battens and MDF battens with similar results, although the pre tension of the grain in pine may be a slight advantage. Ive also used ally angle to good effect. I plan to use square box in either steel or ally in my next build since windowed braces arent practical in my case..
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Old 14th November 2012, 05:57 PM   #32
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I would say that bracing material choice would depend on bracing strategy, or vice versa. You could try dowels of metal or perspex, strips of dense real wood across panels, a plywood holey brace, clamping the front panel to the rear with threaded rod.

when you say bracing I immediately think of bracing the driver, which is the source of all energy/resonance in the speaker.
I agree with this. To be honest I dont totally agree with the MDF arguement. Like for like then BB is stronger. Mass damping is useful tho. I work in an engineering job where both added stiffness and added mass are both used to tame problems. Both are valid approaches. Ive used 12mm MDF for a 17 liter box, heavily damped with lath lining to great affect, so i wouldnt say MDF is verboten. It is more transparent to sound though, and that needs to be taken into account during design, and tackled appropriately. Next build im using sapele ply and steel box bracing, and i think ill have no trouble getting the box vibrations down to a decent level. We shall see if i achieve it!
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Old 14th November 2012, 06:07 PM   #33
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Show pics of any of your solid wood or ply builds.
I'm betting you can't.
You lose.

You can start here: miniOnken/Fonken gallery pictures only. For every one you see there there is at least one that is someone else's design.

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Old 14th November 2012, 06:12 PM   #34
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Quote:
Originally Posted by mondogenerator View Post
It is more transparent to sound though, and that needs to be taken into account during design, and tackled appropriately.
Hey Mondogenerator, what do you mean by 'more transparent to sound'?
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Old 14th November 2012, 06:29 PM   #35
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Making anything but fire out of pine is a waste, except its nicer for kindling
Pine can be made to work fine. More care with bracing and build topology is required.

Woden Design Victor for FE166En

Click the image to open in full size.

these too:

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Old 14th November 2012, 06:43 PM   #36
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Well... The 'low level mush' that can be present with MDF, (theyre close to P10s words to me on the subject), I reckon is due to transparency. MDF has no pre tension, unlike ply or solid wood, and isnt up to par with ply under tension stresses. It still resonates but the lack of inherent elasticity means it is a more wideband resonator. Large bandwidth but low Q and thus benign harmonic signature. With the correct design it could be better than ply, trouble is that its a whole load more effort to get there.

Consider a box made of 1 inch cork or hard rubber. Would it sound bad? Perhaps the opposite. Would it leak sound like a sieve due to high panel compliance? Likely. Suitably braced though and the same could actually be rather good. A little like CLD, there are 2 other ways. Very rigid skeletal internals, compliant panels OR joints coupling them to frame. Or the opposite, weak compliant skeleton with very rigid panels. Both lend themselves to self damp due to the contrast in material attributes.

My main bugbear with MDF is its composition, which ive read is largely pine sawdust, and i avoid pine at all costs. Heavy card tube is better, but there may be many types of pulps used which would account for this. I ruined a brand new tenon saw recently cutting card tube... Hardboard (HDF?) would be far better than MDF, if it was available in more useful thicknesses.

@P10, that pine looks ok. Not at all like the balsa like pine over here. There is logic behind at least some of my assertions. Honest. Ive even gone as far as using angle iron for all battens, rather than pine. With the 'corners' particularly the rigidity was greatly improved. I guess im saying that the corner joint strength is more important if a rigid build philosophy is to be a success. If i get the corners strong enough then the panel rigidity is less important or more easily addressed, minimally.
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Old 14th November 2012, 07:01 PM   #37
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Old 14th November 2012, 07:40 PM   #38
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Stolen from the net:

Production Process:
MDF is a mixture of refined wood chucks and shavings that are ground into a fine fiber.The wood is heated prior to refining to give the finished product a stronger and more moisture-resistant surface. During refining, the wood is rubbed apart into fiber bundles (Reference 1). A binder or wax resin is added, which is usually urea formaldehyde, and the product is then heat pressed, sanded and sawed into very dense sheets. It requires about 23 inches of a fiber/resin mix to create one -inch sheet of MDF, whereas it only takes about 4 to 6 inches of wood chips and sawdust to create one sheet of -inch particleboard.
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Old 14th November 2012, 08:36 PM   #39
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Thanks Cal.
The 'rubbing apart' is the worst part since it destroys the natural fibrous adhesion of woodgrain in favour of a homogenous felted adhesion. Id guess that this trades high uni directional strength for weaker structure which is strong in all directions, but to a lesser degree.

Since the OP is concerning braces, id postulate that in brace apps, the rigidity of the material, ply or MDF is compromised.

Ive heard 'translam' designs criticised for using ply in its weakest dimension, yet window braces in ply or MDF both use the material in the weakest dimension. In this method of use, neither are as effective.

A fixed and welded skeleton of box tubing, placed just so, will out perform its equivalent.

A window brace in ply or MDF is itself a compromise, using a 'frame' of 2" or larger in 10mm LDPE would work too.

But a window brace of almost any rigid homogenous material would work way better.

Ply is cheap to some, not me.

The advantage in window bracing with ply rather than MDF, is alot closer to none.

Both are weak perpendicular to their stratus (strata?) Its the WAY the window brace uses the material to create strength is the key to its effectiveness, not the choice of ply or MDF
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Old 14th November 2012, 08:53 PM   #40
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Man, you've got me running to Google.

I know of Microllams, Parallams and even Timberstrands but the only Translam I know is when you stack your own cut outs together to make a cabinet, aka laminated.

The window braces I know are made of metal.

Can you help out the uninitiated here?

Ta.

EDIT: By window brace, do you mean something holds up your window mounted A/C unit?
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