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Old 2nd June 2012, 10:20 PM   #1
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Default Concrete Cabinets

I have all the components from a set of Mission 771e speakers (drivers, crossover, port, terminals etc.). I also have a fully working pair of the same speakers.

I therefore thought it might be worthwhile building cabinets from concrete as it will be interesting to be able to compare otherwise identical speakers - one pair with chipboard / MDF cabinets, the other with something more substantial.

Apart from ensuring I get the internal volume identical, is there anything else I need to think about, such as the position of the rear facing port, its placing within the cabinet - i.e. distance from the back of the woofer etc.?

I was considering making the cabinet of the correct volume but only containing the woofer, with the tweeter mounted above on a narrow open baffle. Any thoughts on this please?

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Old 2nd June 2012, 11:32 PM   #2
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The concrete cabinets I built used plywood as the former which I left in place so they looked like a normal cabinet on the outside. That meant mixing concrete six times. I used heavy mesh attached with staples. I used tapered tubes (cones) in the driver and binding post holes to prevent filling them when I poured and used mini straws (I think) in the mounting screw holes. I taped two layers of wax paper around the perimeter at the rear so I could remove the back after it was poured.

Would I ever do it again? Not that way, very poor work/benefit ratio. You might consider making a form but if you don't have a vibrator, that might be one ugly looking set of speakers without a lot of parging. (is that the right word?)
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Old 3rd June 2012, 01:33 AM   #3
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Interesting. First i was thinking using granit for my next speaker project and an other interesting material is the concrete slabs they make for counter tops but maybe granit can be found cheaper.
In my town pink granit is everywhere and i have large granit rocks in my backyard. Breaking a rock in smaller pieces is not a problem,what i need is someone who can make slabs of the correct size.
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Old 3rd June 2012, 01:37 AM   #4
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Some patio stones would work if your creative, you can glue them together.
Not as nice as granite though.
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Old 3rd June 2012, 01:45 AM   #5
tvrgeek is offline tvrgeek  United States
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Concrete will ring like a freeking bell. Very bad choice. What are you actually trying to achieve?

It turns out, MDF is actually a very good material. Paper. Or you could call it a "cellulose fiber bonded felt composite" if you prefer. Chip board is not so good. You would be better off to build a very well constructed MDF box to see how much better a DIY can do than the OEM. You can build them asymmetrical, slight curves to pre-stress the panels, and all kinds of things you don't do in a factory.
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Old 3rd June 2012, 02:27 AM   #6
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The baffle for both the woofer and tweeter should be the same.. otherwise you'll need to do some crossover work (..a lot actually - likely a total redesign).

If you are going to change a dimension, then cabinet *depth* would be the dimension to change. A bit larger radius (round-over) to the front baffle edges would be a bonus and shouldn't alter the basic design.


Concrete is a good material for the baffle, not necessarily the entire enclosure. (..though be wary of stones where you would connect the driver to the baffle - can't really drill them out. This is one reason why cement with a strengthening additive is often a better choice.) Consider a concrete baffle with a wood box within a box construction and sand damping (between the boxes). The baffle should have a good chamfer for the driver on both the front and rear.
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Old 3rd June 2012, 03:10 AM   #7
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Default concrete enclosures on DIYAUDIO thread

Quote:
Originally Posted by sunbeamgls View Post
I have all the componets.....

I therefore thought it might be worthwhile building cabinets from concrete as it will be interesting to be able to compare otherwise identical speakers - one pair with chipboard / MDF cabinets, the other with something more substantial. Any thoughts on this please?
Cheers
Hi there S: Recommend using the search function herein. Some one extensively documented his construction of a pair of cabinets, this would give you some ideas and the pit falls along the way... as I recall, he was pleased with the results. Personaly, I would not leave the formwork on the finished product, since shrinkage occurs as a normal function of concrete curing, which could cause a buzzing sound. Hope you will post your construction, results, listening experience and measurements (if you do testing)
regards, Michael
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Old 3rd June 2012, 04:04 AM   #8
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Quote:
Originally Posted by sunbeamgls View Post
I would not leave the formwork on the finished product, since shrinkage occurs as a normal function of concrete curing, which could cause a buzzing sound.
My cabinets were built when I was a very young man (read 'boy'), and long before digital cameras were invented, hence no pics) but I didn't notice that but it is a valid point except that the concrete (approx 3 cm.) made it so inert that the plywood was immaterial. There was almost no vibration on the outside of the cabinet but by the time there was, it was so loud you weren't going to hear the cabinet buzzing.
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Old 3rd June 2012, 11:38 AM   #9
tvrgeek is offline tvrgeek  United States
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If you insist going where others have gone before and found it is not the best path.....
Hold up a piece of material. Smack it with something hard. If it goes "pink" it is not a good choice. It should go "dunk". Something like Corian is in between and could have advantages as the baffle. Might track down something made by Wilson Audio, as they have special materials made to be as perfect as they can in their mind. Either that, or you have to be able to advertise SOMETHING for $50K. Places like McMaster Carr have all kinds of thick sheet goods that would be fun to try. The problem is, you can spend really serious money playing around for no real gain, where you could be spending the time and money on perfecting the crossover or better drivers. Don't get me wrong, your starting set is quite good. This is why you are not going to find any easy magic improvement. You would do better studying diffraction, reflection and driver center point issues. Study the effect of different bracing methods. Study the effect of non-regular shapes. Read Olson. Think about what the material has to do. First is be stiff enough that it acts as an enclosure. Second, the resonance is far enough away from anything that can excite it, and third, highly damping of that resonance. These are in conflict, so think about it. You will find 3/4 inch MDF properly braced is a 99% solution unless you need a very small box and the size is a limit, or a very large box like a big sub. ( I use ceramic plates laminated between 1/2 inch plywood for my subs)
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Old 3rd June 2012, 01:39 PM   #10
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im planning to use granite placemats, i got v cheap in a supermarket sale, 8mm thick. I plan to glue and construct using epoxy and 20mm steel box section. Granite, like concrete, rings like ceramic when tapped, and is not well internally damped. I do not totally in agreement with what tvrgeek said, BUT his point was fundamentally valid. I wouldnt attept concrete myself, to much work. Im persueing granite, as its simpler, and follows a similar logic. Im aiming for highest rigidity, thinest panel size. Hoping that the ring will be minimised by thin, and the lightest possible, given the verxt dense nature of stone. I feel thicker may be even worse, due to more vibration inertia if u will. Of course i plan to heavily damp the panels, ana i think its perfectly possible to make them very dead, using thin granite, if it is done right. Just my 2 pence.
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