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Old 3rd June 2012, 09:52 PM   #21
tvrgeek is offline tvrgeek  United States
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Wave, that brings to mind Berwin's basement horns. What were they, 20 foot or something?
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Old 3rd June 2012, 10:19 PM   #22
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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.
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Old 3rd June 2012, 10:21 PM   #23
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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.
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Old 3rd June 2012, 10:32 PM   #24
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Quote:
Originally Posted by tvrgeek View Post
Wave, that brings to mind Berwin's basement horns. What were they, 20 foot or something?
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.
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Old 4th June 2012, 12:45 AM   #25
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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.

Last edited by Melon Head; 4th June 2012 at 12:47 AM.
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Old 4th June 2012, 01:28 AM   #26
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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.
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Old 4th June 2012, 02:13 AM   #27
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Quote:
Originally Posted by Top Shelf View Post
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.

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

Last edited by river251; 4th June 2012 at 02:16 AM.
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Old 4th June 2012, 02:48 AM   #28
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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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Last edited by Top Shelf; 4th June 2012 at 02:55 AM.
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Old 4th June 2012, 02:54 AM   #29
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I experimented with sandwich of MDF, Wonderboard, and hardwood plywood glued all together. Does not worth it.
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Old 4th June 2012, 03:00 AM   #30
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Quote:
Originally Posted by Melon Head View Post
There is a very BIG difference in properties between CEMENT and CONCRETE espescially cememt used to make pavers which is absolutely crap.
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.
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