Concrete Cabinets

[Melon Head]

Originally Posted by tvrgeek

Concrete will ring like a freeking bell. Very bad choice. What are you actually trying to achieve?

Are you serious?
I never heard concrete ring like a bell.
I once heard a sledge hammer ring like a bell but not concrete.

[Alvis]

I was a little suspicious of that too. Assuming the inside walls are damped with something soft.

I suppose it would depend on the size, mass and shape of the particular speaker box.

I can however see how concrete would be more reactive then MDF, I just assumed the mass would over come this at most sound levels.

Resonant Frequency - Concrete Rubblizing - YouTube

[Melon Head]

Concrete is so frickin dense it will be dead as hell.
You would need so much energy to excite concrete it is not funny.

[river251]

Originally Posted by tvrgeek

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....

[Top Shelf]

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

[river251]

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

[ScottG]

Originally Posted by river251

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).


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.

[tvrgeek]

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.

[Wavebourn]

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.

[tvrgeek]

Originally Posted by river251

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.