I've been using tile backer board (I really like "HardieBacker") as a damping material/ mass load. It works well. You could build a box out of that stuff and then stucco the outside with a fortified mortar or even better, an epoxy grout. Although you'd definitely need to wait for it of finish off-gassing.
I've built a bell out of concrete but it needed to be a very specific shape and material density/. You won't get anywhere near that recipe with modern mortars or backer board.
I've built a bell out of concrete but it needed to be a very specific shape and material density/. You won't get anywhere near that recipe with modern mortars or backer board.
Top,
I love concrete. Just put in 3 grand worth for a front patio. They built Rome with it. Fantastic engineering material. By the way, the performance you get on day one will not be the same as a year later. It always changes. No, I am an engineer who has had some exposure to materials science. I look for innovation everywhere. (That is actually my current job) I built my obligatory cinder block speaker in High School. I use MDF, HDF, PB and plywood with various solid woods for bracing depending on the need. What I am saying is cement is a well worn path to nowhere. Look at the OP's project again. He wants to see if he can make substantial improvements over a well respected mid range production speaker by box construction. I agree he can. I am just suggesting he spend his effort in a direction that has promise, not one that is basically stacked against the requirements. Learn the limits of the standard approach, so you know what you want to do different next time.
If one really wanted to try, go get some tile underlayment fiber skin cement boards. and build a box of them. Maybe two or three layers epoxied together. Being sheet goods, it can be worked with diamond blades in a grinder, and sculpted with a diamond cup. Maybe soak in polyester resin. I seriously doubt it would be any better than a conventional approach. Maybe one advantage, no one could lift them, so no one would steal them.
The exact other approach is to try a boat/airplane building composite of end grain balsa with composite skins. Maybe too thick, but it might be worth while to build a sub I could lift.
ScottG,
I think the theory on the sand is the grain to grain friction absorbs the energy. The glue/sheet by it's self provides a laminate of disparate materials, which we know is effective in reducing transmission. Sounds like a reasonable idea, just a little bit of a twist on why it works.
I love concrete. Just put in 3 grand worth for a front patio. They built Rome with it. Fantastic engineering material. By the way, the performance you get on day one will not be the same as a year later. It always changes. No, I am an engineer who has had some exposure to materials science. I look for innovation everywhere. (That is actually my current job) I built my obligatory cinder block speaker in High School. I use MDF, HDF, PB and plywood with various solid woods for bracing depending on the need. What I am saying is cement is a well worn path to nowhere. Look at the OP's project again. He wants to see if he can make substantial improvements over a well respected mid range production speaker by box construction. I agree he can. I am just suggesting he spend his effort in a direction that has promise, not one that is basically stacked against the requirements. Learn the limits of the standard approach, so you know what you want to do different next time.
If one really wanted to try, go get some tile underlayment fiber skin cement boards. and build a box of them. Maybe two or three layers epoxied together. Being sheet goods, it can be worked with diamond blades in a grinder, and sculpted with a diamond cup. Maybe soak in polyester resin. I seriously doubt it would be any better than a conventional approach. Maybe one advantage, no one could lift them, so no one would steal them.
The exact other approach is to try a boat/airplane building composite of end grain balsa with composite skins. Maybe too thick, but it might be worth while to build a sub I could lift.
ScottG,
I think the theory on the sand is the grain to grain friction absorbs the energy. The glue/sheet by it's self provides a laminate of disparate materials, which we know is effective in reducing transmission. Sounds like a reasonable idea, just a little bit of a twist on why it works.
When I saw them on the picture first thought was, "Is his house insured against earthquake?"
Seriously, if you are an engineer you know how badly rectangular house can resonate on some frequencies.
Speaking of glued wonderboards, however it is wrong material. I especially used for concrete gravel with very different sizes of stones. And armored it with old rusted nails and screws. And shape of that box on the picture is like an airplane, and walls are of intentionally uneven thickness. Inside I glued layer of memory-foam. Deadly silent, like in a grave.
There is a very BIG difference in properties between CEMENT and CONCRETE espescially cememt used to make pavers which is absolutely crap. I probably wouldn't use concrete only because it is too heavy. There are many other good options. If you want to experiment with concrete then try it. If you just want sometning that is easy to construct try something else.
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Constrained layer damping is definetly a great way to go about building a fairly non resonant box, the variety of materials that can be used in each layer is quite vast. I have done a pair of bookshelves in baltic birch/ elastomeric compound/ MDF that are very quiet. The main goal in a lot of good designs is materials resonance contol, that is, unless you want the box to add its own voice to the final output. Shifting resonance upwards where it can be controlled with other materials is a good starting point. To argue the merits of many different materials is as useful as arguing religion. The good thing about DIY box building is the satisfaction of starting with a base of good knowledge and proceeding to expiriment with successive designs and see how your perferences in sound guide you. I personally use many different designs in different situations ,horns for some,ported for others sealed in a few cases, ....there is no universal solution to every problem. The situation dictates the parameters needed to solve the problem or at least get the closest approximation of a solution.
Jeremy, do you have further info about this build posted anywhere?
Would like to see how you did that.
WRT learning from building lots of designs, yikes, I want to build one that are great. Last thing I have time for is building speakers as a hobby. I'm thinking a box for the Illuminator woofer mounted in the very top of a 6" wide, tall/deep sealed/ported/transmission line box, and a dipole RAAL tweeter sitting independently on top of it, with external active crossover. Just need to study more first to see what issues are. That's some serious money, so I don't want to start til I'm sure. One issue is how to keep the ribbon close to the woofer, while not having the cabinet interfere with its backward traveling wave. Maybe the top of the cabinet should slope steeply down from the front edge.
Knowing how you made your mdf/birch/elastomeric box would be a help.
Jim
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I haven't had the time to post any build threads for anything that I've made, but I've been trying to get myself to do one for the dual 12" PPSL that I made a couple of months ago. Basically all I did was build the outer shell of 1/2" baltic birch, then "glued" a 1/4" thick sheet of gasket making type rubber to each interior panel with IIRC a proprietary compound made by stinger(I think), keeping each rubber pad away from another walls rubber pad by an 1/8". Then " glued" the 1/2" MDF panels on top of the rubber pads with the stinger compound. I then used shelf braces top to bottom and side to side from the mDF panels. Then I did the same for the baffle board and fixed it in place( otherwise it would have been extremely hard to get all this stuff in the box). It helps If you scuff up the rubber pad to aid adhesion. Oh yeah I used glue for the shelf braces. You definitely have to account for all the material that goes in to get the final box volume.
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Cement is the binder. Concrete is the finished product. There is no such thing as a cement paver, it is concrete, no matter they call it at the store. There are many different types of concrete, depending on the ingredients.
Even a bell doesn't ring if it's flat on the ground or in a stack.
Go tap on things like concrete picnic tables. They ring.
That has more to do with the way the concrete slab is mounted than it does with a speaker box.
In the 35 years since I built my concrete boxes, I have never revisited the idea.
Hardy Board is 90% portland cement, 10% sand. 0.25 and 0.43" thick. 2~3 lbs/ft2
Of course the mounting makes a difference, but the point remains that concrete will ring. It's just that in its usual applications it isn't provoked.
I got reminded of that a few days ago killing time in a park and tapping on the table with my ring. "PONG"
I've heard concrete ring when tapped by a steel hammer but never when a speaker driver is mounted in it. The size of the driver and power it would take to excite concretes natural frequency would be too big to be practical. Also, and I don't know for sure, but it seems the resonant freq of concrete would be very low. When you tap it with a steel hammer you would have to time the decay to see if it is even close to the natural freq.
I only had few problems when i done cabinets out of concrete.
It was posted here too, as it drys out it will shrink.
Allso after few months i did notice the effect of resonatng cement. It starts to disintegrate, leaving a fine powder.
And mounting of speakers is realy hard.
When i was round 20 i did made a nother attempt to make a subwoofer cabinet.
But this time i was smarter. First of all, make the former of the cabinet out of cheap wood.
Let the cement dry out, take your time, depending on the thickness of the walls.
After its done, simply ignite the wood, let it burn out. The heat will allso help the concrete to dry even more, and you allso get rid of the -now useless- wood parts.
At least thats what i did.
Then apply to the inside and outside general purpose casting resin.
This will prevent the cement from gaining or loosing any more water, and allso prevents it to turn into dust due to vibration.
Mounting the driver was done with a bit of cheating, it is actualy mounted to an MDF panel, and this panel is glued with epoxy on the front baffle. What i did "wrong" was not leaving space for the MDF to be in line with the front baffle.
Years had pass, i truly loved the sound, the house got rebuilt, etc..etc.. then we moved to a nother house, and i had to realise that the new doors where smaller, and there is absolute no way to take the sub with me. So it got sold with the house, lol.
Be prepared, a concrete speaker has extreme weight. My 2nd attempt had a 15" PA driver in a sealed box, and it take more than a day to get it into its place.
If i was ever to attempt this again i would surely not build anything "big" out of it.
Finishing the box takes lots of time, and even so the finishling layer and paint was looking.. terrible
probably it can be done better than i did back then.
The pro's are verry rigid walls. And its burgler proof for sure.
The sound is verry clean, the driver fails to excite this high mass.
The con's are..
Takes lots of time, care, and actualy i would compare it to a pet elephant.
It was posted here too, as it drys out it will shrink.
Allso after few months i did notice the effect of resonatng cement. It starts to disintegrate, leaving a fine powder.
And mounting of speakers is realy hard.
When i was round 20 i did made a nother attempt to make a subwoofer cabinet.
But this time i was smarter. First of all, make the former of the cabinet out of cheap wood.
Let the cement dry out, take your time, depending on the thickness of the walls.
After its done, simply ignite the wood, let it burn out. The heat will allso help the concrete to dry even more, and you allso get rid of the -now useless- wood parts.
At least thats what i did.
Then apply to the inside and outside general purpose casting resin.
This will prevent the cement from gaining or loosing any more water, and allso prevents it to turn into dust due to vibration.
Mounting the driver was done with a bit of cheating, it is actualy mounted to an MDF panel, and this panel is glued with epoxy on the front baffle. What i did "wrong" was not leaving space for the MDF to be in line with the front baffle.
Years had pass, i truly loved the sound, the house got rebuilt, etc..etc.. then we moved to a nother house, and i had to realise that the new doors where smaller, and there is absolute no way to take the sub with me. So it got sold with the house, lol.
Be prepared, a concrete speaker has extreme weight. My 2nd attempt had a 15" PA driver in a sealed box, and it take more than a day to get it into its place.
If i was ever to attempt this again i would surely not build anything "big" out of it.
Finishing the box takes lots of time, and even so the finishling layer and paint was looking.. terrible
probably it can be done better than i did back then.The pro's are verry rigid walls. And its burgler proof for sure.
The sound is verry clean, the driver fails to excite this high mass.
The con's are..
Takes lots of time, care, and actualy i would compare it to a pet elephant.
Errrr, cement is the fried limestone that is the bonding agent. When mixed with sand and stone, the composite is called concrete. Various cements do differ. The cement used to build Rome was naturally occurring and contained volcanic ash providing a more elastic material than is typical with kiln fried lime today. Modern concrete won't last 2000 years. This has absolutely nothing to do with how pavers are made.
Do what you will. You can lead a horse to water, shove his face in it, and he still may not drink.
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