MDF Thickness

[harrisni]

Hi,

Just wondering what is a good MDF thickness to build a speaker box? Ive been told that 18mm thickness is a waste of time, is this true?

I understand some speaker manufacturers use 35mm thickness.

[ShinOBIWAN]

18mm is fine for bookshelves but 25mm is better for larger designs.

A better solution is a composite of materials and thicknesses. Such as 18mm MDF + 18mm Ply + 10mm chipboard. Even better is concrete and polymer constructions, although these are difficult to work with.

BTW What really makes a difference when dealing with most sane types of material is bracing, Use plenty of it and the cabinet are really quite dead.

[elfranche]

I once read: 'Make it as close to concrete as possible !'

In my experiences with LARGE boxes, 50mm sidewalls produce almost NO sound when you knock on them, and 32mm does produce a discernable resonance, and needs serious bracing.
So I'd go 38mm for a large box and use normal bracing, and would not hesitate to use 50mm or more for the front baffle. But that's just me.

For a small box, I presonaly wouldnt go under 25mm.



elfranche
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www.stormpages.com/elfranche

[lndm]

I have built boxes of around 30L in 36mm MDF with good results. I like to brace my boxes anyway, and think that bracing is almost (within reason) more important than the choice of panel material. I once also built a 130L pyramid out of 36mm MDF, and this was almost unusable without bracing.

[noodle_snacks]

The (roughly) 45 litre mtms i built have a 36mm thick front baffle and 18mm sides. Then two 12mm horizontal shelf braces, and one vertical one. The enclosure is very dead, however there is not enough physical room to fit the crossover inside! (This turned into a blessing not a curse, i had double binding posts on the back, and things are very easy to tweak when i feel like it)

I also had some problems in that the verticle brace was too close to the port, interfering with its operation, i had to cut out the center brace much better to prevent this from happening.

[ShinOBIWAN]

Originally posted by elfranche
I once read: 'Make it as close to concrete as possible !'

In my experiences with LARGE boxes, 50mm sidewalls produce almost NO sound when you knock on them, and 32mm does produce a discernable resonance, and needs serious bracing.
So I'd go 38mm for a large box and use normal bracing, and would not hesitate to use 50mm or more for the front baffle. But that's just me.

For a small box, I presonaly wouldnt go under 25mm.



elfranche
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www.stormpages.com/elfranche

Yep agreed, well sort of.

I used 5 x 18mm + 9mm(10cm thick) for the baffles on the last set of speakers I built. TBH its not really that much better than 18mm + 9mm MDF with matrix style bracing, there is a definite improvement of course but it has its own problems.

Building up multiple layers of the same material certainly lowers the overall resonance of the material but the primary resonance has a high gain, narrow Q charateristic, your essentially ecxacerbating the resonance signature of the material will lowering the rest. This can be greatly lessened through a composite of materials which each have different resonance signatures as these will tend toward an average. Bracing is something that really does make a big difference, especially if you connect opposing panels as these are effectively out of phase and the resonances tend to cancel somewhat, using a matrix style bracing provides even great improvements.

[Geek]

Keep an eye on your measurements with that stuff. "18mm" made in the US measures 18mm, but the stuff made in Canada is actually 19mm. I learned the hard way and went through a couple of sanding belts the first time out making things even

I dunno if you folk will have the same issues.

[ShinOBIWAN]

Originally posted by Geek
Keep an eye on your measurements with that stuff. "18mm" made in the US measures 18mm, but the stuff made in Canada is actually 19mm. I learned the hard way and went through a couple of sanding belts the first time out making things even

I dunno if you folk will have the same issues.

That's head scratching stuff. Why is 19mm MDF marketted as 18mm?

Are you sure your tape measure isn't faulty?

[elfranche]

Originally posted by ShinOBIWAN



Yep agreed, well sort of.

Building up multiple layers of the same material certainly lowers the overall resonance of the material but the primary resonance has a high gain, narrow Q charateristic, your essentially ecxacerbating the resonance signature of the material will lowering the rest. This can be greatly lessened through a composite of materials which each have different resonance signatures as these will tend toward an average.

That makes ALOT of sense, I'll be sure to use different materials on my next baffle!!!

[lndm]

Originally posted by ShinOBIWAN
That's head scratching stuff. Why is 19mm MDF marketted as 18mm?

We have the same issue here. I suspect it's a metric/cross-system issue.