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Old 31st July 2006, 12:09 AM   #1
gtb is offline gtb  France
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Default mdf+concrete ?

What is the effect of coating say a 1/8" or 1/4" of concrete inside a 3/4" mdf speaker ?
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Old 31st July 2006, 12:48 AM   #2
RJ is offline RJ  United States
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I've been usin 1/4" tile backer board made of concrete and using a thin layer of PVA glue to stick it on. Still being put together so I won't know for another week if it was worth it...
http://www.jameshardie.com/backerboa...ardibacker.php
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Old 31st July 2006, 01:03 AM   #3
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Default Re: mdf+concrete ?

Quote:
Originally posted by gtb
What is the effect of coating say a 1/8" or 1/4" of concrete inside a 3/4" mdf speaker ?
The concrete will crack and separate from the MDF, because concrete is fragile if that thin and the 2 materials have different expansion/contraction rates.
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Old 31st July 2006, 06:15 AM   #4
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Most speakers live in places where temperature remains somewhat steady...
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Old 31st July 2006, 11:17 AM   #5
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http://www.hsi-luidsprekers.nl/Kastm...nonderzoek.htm

Use web-translater from Dutch to your language like this http://www.freetranslation.com/free/web.htm

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Old 31st July 2006, 03:45 PM   #6
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try a couple layers of roofing felt instead -- tack it in there with a power stapler -- decades ago folks were making pads of roofing felt, sand and tar, then tacking to the side of the particle board cabinet -- unfortunately tar stinks when it warms up -- there are acrylic adhesives which will do a good job today.

i did the concrete thing with my second pair of KEF B139 Reflex enclosures -- used 1/2 " layer of Quick-Crete -- to get the concrete to remain in place just drill some #6 pan-head self threading machine screws into the interior of the cabinet -- these will anchor the concrete in place -- and just be patient with the concrete -- doing one side then waiting about 48 hours to do the next. these were the darned heaviest cabinets I ever made and I had to whack them apart with a sledge-hammer when we moved.
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Old 31st July 2006, 07:28 PM   #7
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For part of the liquid in the concrete mix add flexable PVA glue (white fabric glue, Mud-pooge, book binders glue, etc.) Good way to bond new concrete to old, BTW.

Cyclotronguy
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Old 31st July 2006, 07:44 PM   #8
Taco is offline Taco  Netherlands
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Quote:
Originally posted by Michail Bugaria
http://www.hsi-luidsprekers.nl/Kastm...nonderzoek.htm

Use web-translater from Dutch to your language like this http://www.freetranslation.com/free/web.htm


I do not want to translate from Dutch to Dutch, but thx for the link now I can read russion sites .

Ply wood attached to concrete or masonite board seems to work best. One thing what is not covered by the article is the way the board is attached. Martin only used one constrained sheet for his tests. For cabinets/ enclosures the panel is clamped at the edges.
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Old 31st July 2006, 10:01 PM   #9
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Quote:
Originally posted by cyclotronguy
For part of the liquid in the concrete mix add flexable PVA glue (white fabric glue, Mud-pooge, book binders glue, etc.) Good way to bond new concrete to old, BTW.

Cyclotronguy
I don't understand how that would work -- additives interfere (purposefully) with the hydration of concrete --
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Old 1st August 2006, 12:22 AM   #10
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You add % of PVA to supplant the water, not replace. Very common in construction to bond new concrete to old or to make for waterproof concrete.
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