Concrete Cabinets

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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?

Cheers
 
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. :D 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?)
 
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.
 
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.
 
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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concrete enclosures on DIYAUDIO thread

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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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. :)
 
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)
 
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.
 
read where?

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)


This seems like an emminently reasonable post. Tvrgeek, where can I read about that stuff? Presume you mean Lynn Olsen, what of his is good?

Thanks for any pointers....
 
The statement that concrete will ring like a bell is ridiculous. If concrete had the same molecular structure as metal which it obviously does not, then that statement would be valid. Take a hammer, go down in your basement and hit the concrete wall( if its concrete and not blocks). The wall will make a "thunk" and not a "bing" then grab a patio stone and do the same, its not as thick so it will resonate a little more. Concrete is a fantastic material for making stuff out of. There are two major camps in the diy box building scene, MDF and Plywood .TVRGeek is obviously in one of them. As with any subjective view opinions should be taken with a grain of salt until a thorough review of all available information on the subject is accounted for. Definetly use the search function to your advantage as you will find a few hidden gems pertaining to this subject. Good luck
 
I think that the double box with sand in between sounds like nothing else could be so non-resonant.

Yeah.. sometimes it doesn't get "through" though (to others). :eek:


Here is basic suggestion that I did for GregOH1 (12" AE driver sealed cabinet with an integrated crossover "box"):

Greg's Box by ScottG - Google 3D Warehouse

Selecting "3d" view allows you to rotate the model in the browser, but downloading Sketchup and then downloading the model allows you a LOT more detail to play with the model.

It basically substitutes the weight and rigidity of a cement baffle for a plywood-damped 1/4" steel plate baffle. (..and of course it's a double box model.)

Note: generally you should use a soft pva glue like Elmers to coat (roll-on) and then adhere some fabric to the walls adjoining the interior "fill" space for the sand. (..when shopping, I found that discount flannel sheets were about the right thickness and were cheap while providing more than enough material.) This provides a little bit of compliance for the added mass to "work-on", further improving damping.
 
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River, Just Google Diffraction. Everyone who does a book on speaker building references his work. Here is one example: True Audio TechTopics: Diffraction Loss

Mellon, Pick up a 1 inch patio paver and give it a tap. Go see how well a block wall lets sound through. If you want dense, then just get some 2 inch steel plate. Of course, 2 inch lead would be a better speaker box. I'll stick with MDF and plywood. I would like to play with UHMW Poly or Hydlar Z, Garolite, or good old Delrin for a baffle. Maybe someday. Today, instead of several hundred for a baffle, I concentrate on the real problems, the crossover. If anyone would like to investigate alternative materials, this is a better place to start than cement.

A speaker box is a set of trade-offs between modulus. It is also something to live with. For the project in question, far more could be gained in understanding if it is better to decouple the driver from the baffle or rigid mount, if that big expensive 1 inch router bit is any better than the 1/2 inch, if a non-regular shape or angle reflection back through the woofer matters. These are things that do matter and are well within the DIY range. There are also a lot of things that are good enough, look somewhere else. When I can afford that pure Be dome with pure silver voice coil maybe I'll quit using zip cord inside my speakers. Until then, any imperfection in the wire is just not relevant. A speaker is a complicated system. Back up and look at it as a system. Realize the amp is part of it. Don't get carried away with the problems that are in the noise. A basic engineering rule: Fix the first 90% problem and move on. Keep doing that until that last 10% of the first problem is your 90% problem. It almost never goes that far.
 
The best stationary enclosures that I saw and heard were made from concrete, period.

First I made horn subwoofer under the floor, because it was easy and logical to use concrete for horn. Then I made woofer in rough boxes, to try. Last I made shelf size arrays, with 6 of 2"x6" drivers, they were sold to one audiophile that loved them despite of ugly appearance.

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I think that the double box with sand in between sounds like nothing else could be so non-resonant.

Warfdale ( I think) tried this in the 50's. Transcendental Sound did some woofer enclosures of Sono tunes and sand in the 80's. 4 cu ft with a pair of cheap 8's, sealed. F3 of 35 Hz or something. This is long before "subs". All in all, just not worth the effort. Sand settles leaving the thin walls to vibrate again.
 
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