Concrete speaker cabinets

Hi All,

This is my first foray into speaker building and I think I picked a bit of a tough one. After three iterations I finally got a decent result.

I order the seas drivers and crossover gear from madisound in the states:

http://i830.photobucket.com/albums/z...ents_step1.jpg

Constructed the internal mould for the speaker cabinet using styrofoam, just to make it easy to gouge it out at the end I wrapped the main piece in clingfilm:

http://i830.photobucket.com/albums/z...outs_step3.jpg

missing from this pic is the internal piece for the connection terminal

Then I shoved the port tube in the back of the big piece of styrofoam and assembled the mould:

http://i830.photobucket.com/albums/z...ould_step6.jpg

After a couple of days of drying I pulled it out:

http://i830.photobucket.com/albums/z...ould_step8.jpg

and after a bit of sanding, painting and crossover assembly, I put the whole thing together:

http://i830.photobucket.com/albums/z...mble_step9.jpg

I still have to build a set of stands for them, which will have to be pretty strong as the speakers weigh about 45-50 kilos a pop, as well as that I have to give them another coat of paint and put the crossover into a protective box.

As regards the sound, will know a heck of a lot better when I manage to put them on proper stands and position them correctly, but other than those obvious problems of context, they sound fantastic.

I had the idea of sticking a set of casters on the bottom of the stands that I build, any opinions on whether that would be a good idea or not?

Thanks,

Nathan

I don't know why concrete isn't routinely used.

Wharfedale made kit many years ago that dropped inside a drainpipe. Column loudspeakers on the cheap!

A friend of mine was raving about how great a cabinet material concrete is, so instead of exhausting my limited woodworking skills, I thought I would give concrete a go. After a couple of mistakes I managed to get it about right, its a learning game.

There are, of course, a number of things I would have done differently. In the latest incarnation I increased the depth of the mould internals by about 15mm, which was not matched by an increase in the depth of the mould externals. This put a bit more stress on the mould than there should have been and caused a warp in the walls of the resulting cabinet. I thought the mould would be able to cope with the small increase, but this was not the case. The pressures inside the mould mean that any mistakes in measurement become exaggerated. Sometime, again, when I have the time/inclination, I will have another crack at it and produce a perfectly symetrical pair.

That is brilliant! well done you for even attempting it!

There have been a few commercial designs in the past, but none seemed to break the mould if you wil pardon the pun!

Yours look fab though.

Quote:

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Originally Posted by Labarum

I don't know why concrete isn't routinely used.

Wharfedale made kit many years ago that dropped inside a drainpipe. Column loudspeakers on the cheap!

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:) The weight, the cost, consistancy of finish etc. Imagine the shipping costs for a large floor stander and then having to man handle them at the customers....god help him if he lived in a top floor flat! Just don't drop one and pray the shipping Co. hasn't already done so.

:lolsign:

And then the floor may need reinforcing as well! :doh: Maybe OK for DIY but not a good commercial proposition.

Quote:

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Originally Posted by NRG

:) The weight, the cost, consistancy of finish etc. Imagine the shipping costs for a large floor stander and then having to man handle them at the customers....god help him if he lived in a top floor flat! Just don't drop one and pray the shipping Co. hasn't already done so.

:lolsign:

And then the floor may need reinforcing as well! :doh: Maybe OK for DIY but not a good commercial proposition.

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Yea, this is more of a problem than you would initially think. They are very heavy and a lot of work. Mass production of something like this would be a major engineering feat, not really feasible unless you gave your cabinets ultra thin reinforced walls.

The big problem I found was creating a solid set of holes for the screws holding the drivers. The driver recess and the holes for the screws are so close together that the brittle concrete would need a lot of time to dry out and develop the required strength. I tried two different methods before I finally gave in and included pieces of wood dowling in the mould which would remain embedded in the concrete. The driver screws could then be driven directly into the dowling.

If anyone fancies having a go at this I have a number of tips which can make things a lot easier.

My next task is to build some decent speaker stands. I wonder has anyone any tips on how to go about this.

Nathan

That's a great idea as concrete would not be resonant like wood.

A couple of things. You can colour the concrete using oxides and you can buy a bag of reinforcement that you just mix in with it. You must of course vibrate it when you put it in the mould.

The other thing is that if you mix the beans from bean bags with it, it makes the concrete lighter.

Only concrete speakers i remember were from Avance yonks ago, i think they were Danish..

Focal used to offer a driver kit with plans for concrete enclosures.

Now this appeals - here in Spain concrete is THE main building material, so it could be cheap to try out.
Anyone got any ideas about dimensions, drive units etc - all need to be cheap as chips and guaranteed to produce a decent, if not neigh-on perfect sound.....
Any ideas ?