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Multi-Way Conventional loudspeakers with crossovers

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Old 7th March 2004, 07:53 PM   #1
Andre Baptiste is offline Andre Baptiste  Trinidad and Tobago
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HEy i am building a low q tempest subwoofer.....but i dont have thetempest just yet.....i was wondering.....can i build the box then leave it for about 6 months or so till i get the tempest and ava250amp????? nothing would happen to the mdf if it just sits there with no use right??? ior do i need to treat the wood with some sort of preserve or something?????
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Old 7th March 2004, 08:02 PM   #2
adusson is offline adusson  Finland
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Default Does MDF SWELL

Nothing happends if you keep it indoors dry in roomtemperature.

Reg. Anders
Bort med moms på dill, NU!!
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Old 7th March 2004, 08:03 PM   #3
ingvar ahlberg is offline ingvar ahlberg  Sweden
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MDF is actually thick paper, it atracts moisture, but kept in the same environment as You plan to use the finished speaker, it will last as long with or without driver, if You´ve got a cat the empty cabinet will soon be turned into real estate.
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Old 7th March 2004, 09:04 PM   #4
BrianGT is offline BrianGT  United States
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I had a small sheet of 3/4" mdf in the garage, and through sitting there for 4 months on the floor, it is now 1" thick mdf and in bad shape.

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Old 7th March 2004, 10:24 PM   #5
B.VDBOS is offline B.VDBOS  New Zealand
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Keep it dry and flat, it soaks up water like a sponge, just not as fast

Most types of wood will bend if not stored on a flat surface
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Old 10th March 2004, 02:43 PM   #6
hifidan is offline hifidan  Canada
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Default MDF

Hi, you could paint a first coat of paint/ on both the inside and outside of the box, that would make it inert and less likely to absord humidity.
Happy listening,
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Old 10th March 2004, 10:54 PM   #7
EchiDna is offline EchiDna  Singapore
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it's all about humidity...

here in Singapore it is always 90%+ humidity and MDF always swells unless you seal it after construction with some form of waterproof barrier (Think along the lines of sound deadening bitumen lining inside and paint/varnish on the outside...

simple really, if you live in a dry climate, you would likely never have any such problem.
You can actually buy an impregnated version of MDF here which is double the normal price but is waterproofed.
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Old 11th March 2004, 06:02 AM   #8
Pete Fleming is offline Pete Fleming  Australia
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Default Sealing MDF

Despite some misconceptions to the contrary, MDF is an excellent product to use for speaker cabinets. All wood products will absorb and dissipate water with changes in humidity and in this regard MDF is no different. Unfortunately however the process is somewhat one way with MDF and is compounded by the fact that that the swelling associated with high humidity disrupts the bonding between the MDF particles (ie it falls apart!).

There are two ways to work around this. As mentioned above, either use MDF products specifically designed for high humidity environments, they are generally used in bathrooms etc. Asking your local merchant for “wet area MDF” is nothing kinky.

Alternatively, protect conventional MDF by forming a water barrier. Yes paint and, good grief, tar, will work, but may not be compatible with subsequent finishes, or if you want to veneer the cabinet etc etc. The best way is to protect the edges with PVA glue sizing. That sounds fancy but is simply normal white PVA glue (think white paper glue) that you thin with water until it looks like milk. Use a paint brush and give it a few coats on any exposed edges. By the way, this is also good practice anytime you’re edge gluing MDF as it tends to soak up the glue and can starve the joint. Simply coat as described and allow to dry, then apply glue as per normal.

The faces of MDF rarely need sealing but in REALLY humid environments such as in the tropics you can apply a few coats of shellac. It’s quite extraordinary to think with all the technology there has yet to be anything better developed for this purpose than the old bug poo. Mix shellac flakes with alcohol (you may read about different “cuts” of x amount shellac flakes to y amount alcohol, well that’s fine if you’re French Polishing, for now put some flakes in a jar and pour enough alcohol in to just cover), go pour some of the more tasty alcohol for yourself and come back a few hours later once it’s dissolved, you’ll need to give it a shake every so often. Adopt a French accent and apply with a brush or a rubber … ah no not that kind of rubber, it’s basically a fancy rolled up cloth. It dries VERY fast so by the time you’ve finished you can normally start the second coat.

That’s it. As mentioned you don’t normally need to seal MDF unless it’s in exceptional environments. Unsealed wood you intend to use in projects should never, never, never, did I say never? EVER be left on bare concrete floors as the floor is very high in moisture. Leaving MDF standing on bare concrete will kill it in no time. In a workshop it’s best so seal the floor but if that’s not possible then put some “sacrificial” solid wood “stickers” under the MDF sheets and rest the MDF (or solid wood) on them.

Hope that helps.


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Old 11th March 2004, 03:19 PM   #9
Bull is offline Bull  United Kingdom
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Default reply

What is E1 MDF then?????

Because I got some sitting in a damp shed for about a year and it still is as good as new condition.
Maybe it's special MDF like for use in bathrooms as it's dark brown in colour.Maybe it's the 'wet area MDF' your talking about.
But what does the E1 STAND FOR???
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Old 12th March 2004, 12:46 AM   #10
madinoz is offline madinoz  Australia
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In Australia, there is a product called MR-MDF, the MR meaning moisture resistant. It is used in wet areas. There is, dare I say it, a MR resistant version of chipboard for those who prefer that product ( this is identified by a green thin stripe running through the middle of length of the sheet).
There should be a version of it available in most countries.
The product here is distributed by Laminex which is an american owned company so I wouldn't doubt its availability in USA or even Europe though perhaps under a different brand name.
These products resist swelling but I wouldn't recommend storing the speaker boxes in buckets of water all the same!
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