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.
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.
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
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
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.
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.
elfranche said:
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 said: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?
Andy Graddon said:
My guess is it left the manufacturing plant as 18mm but subsequently was left for months in less than perfect conditions.
I've got a few scraps of 18mm in the shed that have been kicking around for about a year and they look more like 25mm now!
Or it could just manufacturing tolerances
I would suggest that that over there, they are still being manufactured at 3/4" = 19.05mm
I know that down here, they "generally" are manufactured to 18mm thickness. Maybe there is a slight expansion after they leave the presses?
Ps, those 18mm offcuts that got left out in the rain are now about 40mm +/- 20mm... interesting experiment ! ;-)
I know that down here, they "generally" are manufactured to 18mm thickness. Maybe there is a slight expansion after they leave the presses?
Ps, those 18mm offcuts that got left out in the rain are now about 40mm +/- 20mm... interesting experiment ! ;-)
mmmm I cant help but think that the thickness of the material is more of an issue as you use more reactive speakers, the bigger the voice coil, the more shake is produced as a by product, ie a 4" voice coiled speaker demands thicker and better braced boxes than a 2". ect.
concrete is the ideal as stated above. I do find bracing and structral stregth very very important!
concrete is the ideal as stated above
. I do find bracing and structral stregth very very important!
Andy Graddon said:
Quite probable. Our lumber industry is so intertwined with the US, it would be a disaster is we converted it to metric. AFAIK, it's the only product we make still sold in imperial measurements.
But as to why the MDF stamped "Made in the USA" and shipped here to US owned lumber yards is 18....
I have read about people making a gap and filling it with sand works well too. Bag of sand would be less suspicious for apartment dwellers than a wheelbarrow and concrete going in the front door
I did once experiment with 1" concrete slabs, and almost made an entire enclosure.... I had the molds ready
http://www.stormpages.com/elfranche/photos/Concrete2.jpg
(refresh the page using F5 if the link doesnt work the first time)
what finally drew me back is the 800+ pound weight for a large speaker.. but for a smaller speaker it would be a very good idea to use it imho, especially if poured in a hollow wooden baffle
elfranche
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www.stormpages.com/elfranche
http://www.stormpages.com/elfranche/photos/Concrete2.jpg
(refresh the page using F5 if the link doesnt work the first time)
what finally drew me back is the 800+ pound weight for a large speaker.. but for a smaller speaker it would be a very good idea to use it imho, especially if poured in a hollow wooden baffle
elfranche
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www.stormpages.com/elfranche
I once knocked up a concrete enclosure. I was in the process of improving my house, and I made up a standard mortar of sand and cement and poured it into a simple form made from one large box and one small one. I was planning to dynabolt the front baffle on.
Anyway, after a week I removed the form. I walked around it prodding and kicking. It rang like a bell when struck with a steel toe cap. It made a distinct 'tink' (I also tried whacking it with a piece of pine). This box was around 50L and the walls were 5-6cm thick.
I'm sure I don't know enough to speak with authority on this matter, but there was obviously more to it than I expected.
BTW elfranche, I can't get your link.
Anyway, after a week I removed the form. I walked around it prodding and kicking. It rang like a bell when struck with a steel toe cap. It made a distinct 'tink' (I also tried whacking it with a piece of pine). This box was around 50L and the walls were 5-6cm thick.
I'm sure I don't know enough to speak with authority on this matter, but there was obviously more to it than I expected.
BTW elfranche, I can't get your link.
harrisni said:
Hi,
The point of the cabinet is to separate the sound from the speaker rear from the front sound waves.
Obviously, any thickness does that.
Well, sort of.
The more effectively you can control the sound, the better.
What to consider?
Thicker cabinet walls do a better job.
Stiffer cabinet walls do a better job.
As you increase the cabinet size, the wall sides will flex more.
So, as cabinet size increases, use thicker material, or bracing (or both).
Use the thickest material that is practical for you.
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