This is a guide to using acoustic concrete.
This is a guide to using acoustic concrete. My first set of speakers I built using this method are now owned by a friend. They have never missed a beat in 32 years.
The first thing you need is a list of things to buy.
1 Buy a bag of sand / cement mix. (Should not contain metal, stones, aggregate etc)
2 Buy a can of cement additive. 'Chemstick' is one example. This stuff is a liquid that increases the adhesive properties of cement. Read the safety directions!!!! Read the usage directions!!! If they say use this much, double it!!! Don't triple it, double works, triple doesn't!!! ;)
3. Buy a bag of Ghost Poo. You need it very small. It's the stuff you used to use in bean bags. If your not sure of the size think of rabbit ghost poo. :eek:
4. Buy some wire mesh, the sort that is welded. 25mm (1”) is good. No, not the stuff you used on the house foundations, the sort you would use on a cage for pigeons.
5. Buy some hardwood battens 12mm sq. (½ x ½ )
6. Batten out the rear of the enclosure. Glue and brad nails. Mate, Glue it or it will rattle. Better! Make two of every batten.
7. Mix straight (or as otherwise indicated on your can, but double it!) Chemstick with cement until you have a stiff mixture. It is stiff when you can dip a paint brush into it without drips. Paint this mixture over the inside of the speaker enclosure include the battens. Let it dry for 24 hours or as directed.
8. Precut the mesh to fit the back panel. The mesh sits on top of the battens.
9. Mix a small quantity of (By volume (eq use a cup or can as a measure) ) 1 part cement, 3 Parts sand and 5 parts ghost poo plus double the amount of chemstick that the label says to use. Mix it well by hand, No! Put the cement mixer back in the shed mate, by hand. Gloves are good, bare hands not good. Put the bloody cement mixer away!! Jeez, some people!! :headshot:
10 Fill in the back panel until your level with the battens, Clean the battens, add a layer of precut mesh, then more battens, quickly now, nail guns are good. Tim, brad nailer is good, put that great monstrosity away. Now add the last 12mm (½”) layer of the mixture. Pat it down with the trowel to get any air bubbles out. A 1/3 sheet sander covered in plastic is good to act as a vibrator. It's in the shed mate, not your partners bedside table, yes it would work just as good, But! Let it dry in the shade for 24 hours.
11 Repeat steps 6 through 10 for the sides, top and bottom. Cleanup after each step!!! Keep the speaker covered in plastic, keep the work area very clean!!!
12. Let it dry for at least 7 days before loading drivers.
In use the Ghost poo acts soak up internal vibration, the sand and cement provide a non-yielding surface. I make my enclosures using a high density fibre board such as Laminex Industry's HD3. It is 16mm (3/8 “ ?) and three times the density of a good quality MDF.
There you go mate, Have a tinnie.!!! :drink:
:eek: Now that is a procedure!! I'm thinking my enclosures already weigh a tonne! I'll keep this one in the back of my mind (for a future project), but It may be a while before I try it ;)
Liked the humour too!
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