The question of sand. Yes ordinary sand will work quite well for dampening and mass but because the sand particles are more rounded in shape than crushed rock the particles do not bind together as tightly as particles that are flatter and uneven. But the sand is very inexpensive and easy to get and easy to mix and the epoxy bonds to it well so it will work quite well.
Calculate the volume of the material and then mix enough sand or crushed rock so that it completely fills the mold. Then the epoxy should be of sufficient quantity to fill in all of the voids in the sand or crushed rock.
A thick wall of fiberglass mat and epoxy would be the best for high rigidity and would be the ultimate for a subwoofer wall since at low frequencies strength and rigidity are the most important. A better compromise for cost and one that works better at higher frequencies would be to pour the material out of sand or crushed rock filled epoxy and then skin both sides with fiberglass mat as thick as you can afford.
An other idea would be to build up the wall out of fiberglass mat and epoxy on the inside mold surface and then once the wall is thick enough install the outer mold and pour epoxy into the mold to fill in the remaining voids and make the final form.
You can make the braces out of MDF or plywood and then skin the braces with fiberglass mat and epoxy to make the braces ultra rigid for strength. You would have the best made sub enclosure out there plus one that could be made in any shape you wished.
Hezz
Calculate the volume of the material and then mix enough sand or crushed rock so that it completely fills the mold. Then the epoxy should be of sufficient quantity to fill in all of the voids in the sand or crushed rock.
A thick wall of fiberglass mat and epoxy would be the best for high rigidity and would be the ultimate for a subwoofer wall since at low frequencies strength and rigidity are the most important. A better compromise for cost and one that works better at higher frequencies would be to pour the material out of sand or crushed rock filled epoxy and then skin both sides with fiberglass mat as thick as you can afford.
An other idea would be to build up the wall out of fiberglass mat and epoxy on the inside mold surface and then once the wall is thick enough install the outer mold and pour epoxy into the mold to fill in the remaining voids and make the final form.
You can make the braces out of MDF or plywood and then skin the braces with fiberglass mat and epoxy to make the braces ultra rigid for strength. You would have the best made sub enclosure out there plus one that could be made in any shape you wished.
Hezz
Hi,
I was taken by the concept of the ceramic sphere
based concrete type products on my earlier post because
all you add is potable water and the dust is not dangerous
like many other options. The product I mentioned is experimental
but I am sure that similar experiments and similar ideas are being
tried around the planet including Canada. Also if you were into
making spherical subs or moulding panels the History Stones Abs
moulds are worth a look and they are in your part of the world.
regards
AnthonyPT
http://historystones.com/index.html
I was taken by the concept of the ceramic sphere
based concrete type products on my earlier post because
all you add is potable water and the dust is not dangerous
like many other options. The product I mentioned is experimental
but I am sure that similar experiments and similar ideas are being
tried around the planet including Canada. Also if you were into
making spherical subs or moulding panels the History Stones Abs
moulds are worth a look and they are in your part of the world.
regards
AnthonyPT
http://historystones.com/index.html
morbo said:
May be you are right.
I assembled my new sub cubes just with simple multiplex plates and
I don't observe anything wrong with them. All their dimensions
are 5-10 times below the relevant wave length.
And the wood intrinsic resonance ability seems to be in frequencies
well above my use case (just listening to the noise, when knocking on the wood). But this knocking noise would theoretically vanish much faster if sand would damp it.
Also I think that sub frequencies can also trigger the higher resonances of the used materials
...but that's just a guess, my practical results indicate that these effects seem to be of minor importance....
In car audio if you want wicked curves you use fiberglass.. I think it would be much easier to make a fiberglass box then a concrete one and more reasonable. You can do searches on car audio forums and get a lot of information on making a box out of fiberglass, and you can make it as thick as you'd like.
Its about 12 bucks a quart and around 30 dollars a gallon. How far that gets you I'm not sure. Its been a while since I've built a fiberglass box... You also have to buy fiberglass matt. A fleece blanket, and some drops to make it cure faster. None of which is all that expensive either, but definately more expensive then building a wooden box. A whole lot more time consuming too. Especially if you paint it. If you vinyl or something like that it wouldn't take as long. I'm just rambling now.
Bruce
Bruce
Hi,
Gilbert Briggs investigated sand filled panels for full range speakers. His information was from a time when deep bass was not even recorded never mind able to be reproduced. There may well be more recent research that supercedes his work.
I believe this does give a dead sounding box and that will apply at any frequency. The inside could/should be braced just like any other comparable speaker space.
The little Acoustic Energy AE1 (mk1 & 2) uses plaster (of paris?) as a thick coating inside the box. This deadens the panels and adds weight (cheaply). I don't have any info on the current mk3 or the bigger brethren.
Fibre reinforced concrete will improve the tensile:compresive strength ratio above the 1:10 (approx) ratio inherent in standard concrete. Another major advantage of reinforcing is crack control, fibres will reduce the tendency for major cracks to form in the shell as curing /shrinkage proceeds, to be replaced with micro cracks that holefully will be inconsequential. But adding fibre changes the mix from cheap to quite expensive, but nowhere near as expensive as GRP. Getting a gas tight mix may be difficult, particularly if you use foamed aggregate although a painted on sealing coat could solve this.
Gilbert Briggs investigated sand filled panels for full range speakers. His information was from a time when deep bass was not even recorded never mind able to be reproduced. There may well be more recent research that supercedes his work.
I believe this does give a dead sounding box and that will apply at any frequency. The inside could/should be braced just like any other comparable speaker space.
The little Acoustic Energy AE1 (mk1 & 2) uses plaster (of paris?) as a thick coating inside the box. This deadens the panels and adds weight (cheaply). I don't have any info on the current mk3 or the bigger brethren.
Fibre reinforced concrete will improve the tensile:compresive strength ratio above the 1:10 (approx) ratio inherent in standard concrete. Another major advantage of reinforcing is crack control, fibres will reduce the tendency for major cracks to form in the shell as curing /shrinkage proceeds, to be replaced with micro cracks that holefully will be inconsequential. But adding fibre changes the mix from cheap to quite expensive, but nowhere near as expensive as GRP. Getting a gas tight mix may be difficult, particularly if you use foamed aggregate although a painted on sealing coat could solve this.
concrete subwoofer
Hello,
I made an ACI Titian subwoofer using concrete. It was simple to make and much, much stiffer than a box enclosure. I purchased two laminated wood tubes (available on the internet from several vendors), then sleeved one tube inside the other and glued a MDF plate on the bottom pre cut for the driver. I poured a concrete epoxy slurry in the cavity between the two tubes--about 1.25" and then glued on a top plate cut from MDF. I purchased the exterior tube prefinished with a wood veneer and placed the plate amp in a small box outside the driver enclosure. It weighs about 80lbs, a guess, and is extremely stiff. Placing one tube inside the other and filling the cavity with something stiff creates a stress skin construction which is very ridged. You could also pour a high density foam into the cavity, which would make a stiff enclosure but wouldn't have the weight.
Drew Harty
Hello,
I made an ACI Titian subwoofer using concrete. It was simple to make and much, much stiffer than a box enclosure. I purchased two laminated wood tubes (available on the internet from several vendors), then sleeved one tube inside the other and glued a MDF plate on the bottom pre cut for the driver. I poured a concrete epoxy slurry in the cavity between the two tubes--about 1.25" and then glued on a top plate cut from MDF. I purchased the exterior tube prefinished with a wood veneer and placed the plate amp in a small box outside the driver enclosure. It weighs about 80lbs, a guess, and is extremely stiff. Placing one tube inside the other and filling the cavity with something stiff creates a stress skin construction which is very ridged. You could also pour a high density foam into the cavity, which would make a stiff enclosure but wouldn't have the weight.
Drew Harty
My first draft attempt at a concrete sub box
Made with no rebar, 1.5" thick walls, Sackrete 5000+ pre-mix. No internal bracing. This is the first attempt. A friend and I are working on testing samples of different mixes including concrete, ground rubber, and structural fiber in varying proportions. The mold for the 2nd version is already in the works.
Subjectively, several people including my girlfriend have guessed about a 3db in-room gain, compared to the 1.5" thick mdf box that the same guts (Rythmik DS12) were swapped from. Presumably, this is due to reduced backwave bleed-thru causing cancellations. I will run the Audessy EQ and compare the levels for the sub and report back.
PS: 200 lbs, in case you were wondering.
Made with no rebar, 1.5" thick walls, Sackrete 5000+ pre-mix. No internal bracing. This is the first attempt. A friend and I are working on testing samples of different mixes including concrete, ground rubber, and structural fiber in varying proportions. The mold for the 2nd version is already in the works.
Subjectively, several people including my girlfriend have guessed about a 3db in-room gain, compared to the 1.5" thick mdf box that the same guts (Rythmik DS12) were swapped from. Presumably, this is due to reduced backwave bleed-thru causing cancellations. I will run the Audessy EQ and compare the levels for the sub and report back.
PS: 200 lbs, in case you were wondering.
Attachments
Concrete is a novel idea and an interesting project to try. It definitely has downsides. Firstly, it will always shrink - I'd be wary of a construction that does not allow for this. Secondly, very heavy. This makes for more difficult construction, and you have to factor in the cost of chiro visits after! It's probably the heaviest way to get a given result, so it justifies itself more on the basis of novelty and the "why not factor" than it's technical merits. I read about one guy making concrete kitchen benchtops - an inspirational effort but the effort involved put me off.
Did I hear the word "easy" in the first post? That word definitely doesn't belong on this thread!
The Rythmik kit is a great choice (I have 2 of them). If you are going to go to this kind of effort in making the box, you should make sure the sub itself is worth the effort. Often the driver itself is the limiting factor and putting too much into the box doesn't make sense in that case.
Want the most cost effective and simple way to get a solid, stylish curve box? Laminate 3mm MDF sheets together. Use the internal bracing to create the curve, bend the sheets around to create curved sides. Similar to B&W subs in appearance. The cost isn't too bad and the complexity of moulds and mixing materials and construction methods is avoided.
This is shown in the image minus the side curved walls. The top in this one is a bit more difficult!
Ed mentioned foam - I'd be considering this perhaps before concrete. Geddes talks about a combination of a fibreglass skin with foam being better for enclosures than MDF (however I suspect this applies more to fullrange than subs). Lots of work to do it this way. In effect you create it twice. By the time you have created a mould you could have finished the MDF version.
An alternative. Built it using the curved MDF approach. Create a few layers to give an internal skin wrapped around the bracing. Now put in some spacers so that you get a big gap between the sheets - 20 to 50mm (depending on how extreme you want to go). Now continue to wrap a few more layers of 3mm MDF. Pour in urethane foam (choose a dense version, not the stuff you buy in a spray can). Let it ooze out the top and bottom, or put holes in the inside skin and let it expand and ooze inside. You can cut it back shortly when it stops expanding.
Did I hear the word "easy" in the first post? That word definitely doesn't belong on this thread!
The Rythmik kit is a great choice (I have 2 of them). If you are going to go to this kind of effort in making the box, you should make sure the sub itself is worth the effort. Often the driver itself is the limiting factor and putting too much into the box doesn't make sense in that case.
Want the most cost effective and simple way to get a solid, stylish curve box? Laminate 3mm MDF sheets together. Use the internal bracing to create the curve, bend the sheets around to create curved sides. Similar to B&W subs in appearance. The cost isn't too bad and the complexity of moulds and mixing materials and construction methods is avoided.
This is shown in the image minus the side curved walls. The top in this one is a bit more difficult!
Ed mentioned foam - I'd be considering this perhaps before concrete. Geddes talks about a combination of a fibreglass skin with foam being better for enclosures than MDF (however I suspect this applies more to fullrange than subs). Lots of work to do it this way. In effect you create it twice. By the time you have created a mould you could have finished the MDF version.
An alternative. Built it using the curved MDF approach. Create a few layers to give an internal skin wrapped around the bracing. Now put in some spacers so that you get a big gap between the sheets - 20 to 50mm (depending on how extreme you want to go). Now continue to wrap a few more layers of 3mm MDF. Pour in urethane foam (choose a dense version, not the stuff you buy in a spray can). Let it ooze out the top and bottom, or put holes in the inside skin and let it expand and ooze inside. You can cut it back shortly when it stops expanding.
Attachments
Sub enclosure made out of concrete
Hi Rafal,
This sounds like an interesting field of investigation, as a general comment-if you haven't yet-google for:
- ferrocement,
- fabric cast concrete, (e.g.: http://www.umanitoba.ca/cast_building/assets/downloads/PDFS/Fabric_Formwork/Kenzo_Unno_Article.pdf),
- concrete stepping stones (http://www.concretegardenleaves.com/concrete-leaf.htm)
- hypertufa,
- Lafarge Ductal (shells seem to have been cast down to a minimum thickness of 10mm), steel fiber and PVA fiber reinforced concrete.
The way I see it, for your standard subwoofer use standard construction methods and materials.
For your concrete subwoofer I would suggest stepping away from the beaten path, and trying to come up with something a bit different in shape and assembly, e.g.: as the individual parts of a concrete enclosure will be quite heavy, it might be interesting to see if an enclosure can be build that can be knocked apart and assembled reasonably quickly; e.g.: you could combine wooden edges that fit together with cloth forms into which you shape your concrete.
For build-in horn enclosures (including subwoofers) concrete can be quite impressive, just make sure that your model is correct, and the foundation strong enough
(http://www.audioavid.de/projekte6.htm).
Regards,
Hi Rafal,
This sounds like an interesting field of investigation, as a general comment-if you haven't yet-google for:
- ferrocement,
- fabric cast concrete, (e.g.: http://www.umanitoba.ca/cast_building/assets/downloads/PDFS/Fabric_Formwork/Kenzo_Unno_Article.pdf),
- concrete stepping stones (http://www.concretegardenleaves.com/concrete-leaf.htm)
- hypertufa,
- Lafarge Ductal (shells seem to have been cast down to a minimum thickness of 10mm), steel fiber and PVA fiber reinforced concrete.
The way I see it, for your standard subwoofer use standard construction methods and materials.
For your concrete subwoofer I would suggest stepping away from the beaten path, and trying to come up with something a bit different in shape and assembly, e.g.: as the individual parts of a concrete enclosure will be quite heavy, it might be interesting to see if an enclosure can be build that can be knocked apart and assembled reasonably quickly; e.g.: you could combine wooden edges that fit together with cloth forms into which you shape your concrete.
For build-in horn enclosures (including subwoofers) concrete can be quite impressive, just make sure that your model is correct, and the foundation strong enough
(http://www.audioavid.de/projekte6.htm).Regards,
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