concrete enclosures?

[sparky77]

I have a friend that is a master mason and is interested in hifi, he had an interesting question pertaining the use of concrete for a speaker enclosure. The design would involve acrylic coating on the inside of the enclosure to deal with the pouressness of the concrete and a marbalized finish on the outside (which I think would look pretty cool), and of course a lot of damping inside to deal with the reflections, and the front baffle would be heavy wood attatched with t-bolts set in the concrete.

Any Ideas or opinions?

 

[Johnd]

I have a friend that is a master mason and is interested in hifi, he had an interesting question pertaining the use of concrete for a speaker enclosure. The design would involve acrylic coating on the inside of the enclosure to deal with the pouressness of the concrete and a marbalized finish on the outside (which I think would look pretty cool), and of course a lot of damping inside to deal with the reflections, and the front baffle would be heavy wood attatched with t-bolts set in the concrete.

Any Ideas or opinions?

Yeah, how would you move it, crane?

If that's your cup of tea, go for it. Certainly a novel idea. I've always understood that the cabinetry was good for more than containment of the speakers, it also supplies some coloration and resonance. How would concrete effect the coloration of a subwoofer? I don't know, but I can't imagine that it be good...or forgiving. Probably not all that different than a glass enclosure. Try it, but perhaps first with a cheap woofer...just to see. Post back if you would with any results. Maybe we'll be pleasantly surprised.

 

[WmAx]

I have a friend that is a master mason and is interested in hifi, he had an interesting question pertaining the use of concrete for a speaker enclosure. The design would involve acrylic coating on the inside of the enclosure to deal with the pouressness of the concrete and a marbalized finish on the outside (which I think would look pretty cool), and of course a lot of damping inside to deal with the reflections, and the front baffle would be heavy wood attatched with t-bolts set in the concrete.

Any Ideas or opinions?

If done properly, this could easily out-perform a traditional MDF box for mid-range use. The most effective method would be to make an outer shell, then put many layers of a dampening material such or similar to Dynamat on this interior shell to build up to say, at least 1/3" the thickness of the exterior wall, then glue some type of material to the Dynamat to facilitate a second layer of concrete being poured and adhering to the Dynamat. This wold make a constrained layer system. If the concrete is of sufficient thickness(probably 3/4" for each layer) and re-enforced with some hidden re-bar to ensure a durable cabinet, and if sufficient bracing is used internally - this should result in an enclosure with little to no coloration; something not many cabinets can accomplish. For subwoofer use, this is not needed. You can easily use conventional materials to build a coloration-free subwoofer cabinet.

-Chris

 

[jinjuku]

It would most likely reduce the need for internal bracing. A concrete enclosure would likely be super inert.

 

[stratman]

Doesn't Wilson use cement/concrete in some of their speaker components? I'll see if I can find info.

Check this out:

http://www.engadget.com/2007/01/23/germans-build-concrete-cast-5-1-speaker-set/


and this:

http://technabob.com/blog/2007/11/06/concrete-speakers-from-25togo-heavy-duty-sound/


Can't find info on Wilson, it could have been Legacy, too many years ago, can't remember now.

 

[avaserfi]

Stratman, it was B&W in their older matrix series speakers the midrange portion. They would use a composite of concrete and fiberglass.

Concrete on its own is a bad idea as it is extremely resonant, but if a mixture of concrete and the right material (tar roofing shingles for example) would likely make an inert enclosure with proper internal bracing.

 

[stratman]

Stratman, it was B&W in their older matrix series speakers the midrange portion. They would use a composite of concrete and fiberglass.

Concrete on its own is a bad idea as it is extremely resonant, but if a mixture of concrete and the right material (tar roofing shingles for example) would likely make an inert enclosure with proper internal bracing.

I could have sworn that Wilson or Legacy used concrete in the front speaker panel.

 

[sparky77]

This is actually intended for full range 3-way tower speakers, the cabinet may be built in two pieces that joing together with a tounge and groove around the perimeter and sealed with a gasket, the weight of the top portion should be enough to keep it sealed with out any fasteners to the bottom half.

The concrete material we would be using is actually spraycrete, it is a very brittle form of concrete and our preliminary test panel resonates at a very high frequency so I don't think resonance will be much of an issue, but it reflects a lot of sound back from it. The walls would be 3/4's to an inch thick, and reinforced with wire mesh. Definately need some sound absorbing material all around the interior of the cabinet. The spraycrete isn't as pourous as poured concrete so it may not even require any sealer on the inside.

 

[avaserfi]

I could have sworn that Wilson or Legacy used concrete in the front speaker panel.

It is very possible - I was just informing you on what I know .

This is actually intended for full range 3-way tower speakers, the cabinet may be built in two pieces that joing together with a tounge and groove around the perimeter and sealed with a gasket, the weight of the top portion should be enough to keep it sealed with out any fasteners to the bottom half.

This unit would be incredibly heavy if you are looking for a true three way with full range capabilities. I would recommend building two separate modules: the subwoofer/midwoofer module and a midrange-tweeter module. The lower module could be made from high quality ply wood or HDF. With proper bracing and dampening it will be completely inert in the passband and be far lighter than with concrete. Then mold the upper layer from the concrete mix and have them sit together. This will have the same sonic end results with a far lighter system.

The concrete material we would be using is actually spraycrete, it is a very brittle form of concrete and our preliminary test panel resonates at a very high frequency so I don't think resonance will be much of an issue, but it reflects a lot of sound back from it. The walls would be 3/4's to an inch thick, and reinforced with wire mesh. Definately need some sound absorbing material all around the interior of the cabinet. The spraycrete isn't as pourous as poured concrete so it may not even require any sealer on the inside.

How did you test the panels resonance exactly and what is the high frequency you are referring to? Also, what is the panels size? WmAx's mention of using a constrained layer along with oak bracing to remove resonance is a very good one.

As far as internal dampening goes I strongly recommend OC705 or 6-8lb mineral board applied liberally within the cabinet.

 

[sparky77]

We casted a panel 44inches by 12 inches and 3/4 inch thick, whick would be the size of the back panel of the box just for the resonance test although the halves of the box would be casted seamless which would probably raise the resonance of the concrete a little more. Hung the panel with a c-clamp on a chain and thumped it with a dead blow mallet, and watched the rta, it had a definate spike at about 1.2khz which should be high enough for the 800hz crossover frequency of the woofer.

 

[Kolia]

Interresting.

The only concrete "speaker" I saw was a huge light house fog horn...

Need more spl than that?

I'm looking forward to updates on this project.

 

[sparky77]

I think I'm finally getting the hang of my new cad software, here's a model of the top portion. Just haven't figured out how to do recesses with this program yet.

[/IMG]

 

[WmAx]

I think I'm finally getting the hang of my new cad software, here's a model of the top portion. Just haven't figured out how to do recesses with this program yet.

[/IMG]

If you mold in ample steel bracing, you will raise panel resonances even higher than the 1.2khz you measured, insuring no substantial amount of resonance is present in your crossover transition band.

BTW, what was the weight of that single test panel you created?

What is the mid-range? Is this open backed or closed back mid you will be using? If closed back, be certain to mount it on a suspension to prevent vibrational excitation of the enclosure. I can give you specific suggestions if you give me more information.

-Chris

 

[sparky77]

The midrange is a sealed back so that shouldn't be a problem. The test panel weighed just shy of 20 pounds so the top portion will likely weigh in at about 50 pounds when it's finished. I was thinking about adding some ribs to the concrete about an inch tall and an inch thick about every 4 inches.

 

[fmw]

My father did it back in the early 1960's. He had a concrete wall in his listening room that was covered with natural stone. On each stereo side there were 4 15" Bozak woofers, 2 6" Bozak midrange drivers and 4 1" tweeters mounted directly into the concrete wall with the back wave vented outdoors through a chimney flue. No enclosure resonances and no back waves. The listening room itself was octagonal to optimize acoustics. Here we are nearly a 1/2 century later and still haven't heard a better speaker system anywhere at any price.

 

[-knife fight-]

My father did it back in the early 1960's. He had a concrete wall in his listening room that was covered with natural stone. On each stereo side there were 4 15" Bozak woofers, 2 6" Bozak midrange drivers and 4 1" tweeters mounted directly into the concrete wall with the back wave vented outdoors through a chimney flue. No enclosure resonances and no back waves. The listening room itself was octagonal to optimize acoustics. Here we are nearly a 1/2 century later and still haven't heard a better speaker system anywhere at any price.

can we get pics of that, id really love to see it.

 

[WmAx]

The midrange is a sealed back so that shouldn't be a problem. The test panel weighed just shy of 20 pounds so the top portion will likely weigh in at about 50 pounds when it's finished. I was thinking about adding some ribs to the concrete about an inch tall and an inch thick about every 4 inches.

I recommend mounting the mid-range on a suspension in this case. Do not allow it to couple mechanically to the enclosure. Since this is a sealed back mid, then it is not important to have an air tight seal - which makes this easier. For the mid-range, have a small cavity that is sealed from the rest of the enclosure volume. Now use a high grade latex cushion foam with a medium rated ILD(stiffness to surface area pressure resistance) in a ring behind the driver, about 1/2" thick, between mid and enclosure. Cleanest looking way to mount the driver will probably be to use a screw head for each screw hole, using a machine screw that is very short(cut just long enough to hold a nut on the back side) and glue (using super glue) an elastic band(as you find in a craft store) string to the back of the screw. Pull the elastic band trough the small sealed cavity behind the midrange, then through some small holes drilled through this cavity into the main enclosure volume. Pull the elastics through and tie them off on washers, or just knot them, etc.. so that tension is pulled sufficient to hold the midrange in place. Use a dot of silicone caulk on the interoir volume where each elastic pulls through to prevent air breach. There are other ways to do this - but this one will end up looking like a standard clean screw mount - but have no effective mechanical coupling.

From the weight vs. panel size you specified, this particular concrete will have a density of 2-3x of MDF. To increase stiffness appreciably, if this is your concern, just go ahead and mold metal re-enforcement into the concrete. Don't forget large surface area cross bracing - this is the most efficient way to raise resonance further if this is your goal.

-Chris

 

[sanjithjoseph]

Here is the picture of concrete enclosures I have. They are made for Tannoy HPD385 drivers.

Sent from my SM-G950F using Tapatalk

 

[123Toid]

I was at midwest audiofest this past year and a builder used concrete enclosures. It really is a good idea, and his sounded fine. However, he used cinder blocks. I think it might be nice if you could form it as one whole concrete design and then polish it, so you won't have diffraction off of it. I think it could not only look nice, but have a lot of acoustical benefits.

 

[Verdinut]

This is a true story:
In the 1950's, one guy had built a concrete enclosure in a corner of his basement. It was ported at the bottom junction between baffle, floor and walls.
He had a cat and this animal used the enclosure as a litter, so the owner had no option but to demolish it.