I wish to try making a composite consisting of 3/4" MDF on the outside with a layer of Bitumen and then a 1/2" sheet of cement board on the inside for speaker cabinet wall construction. I have been looking at the roofing tars and driveway fillers/sealers at Home Dumpo wondering what might be a suitable filler that will not run away in a mess after laminating and will provide the viscous damping needed. Most of the sealer products want to be exposed to air dry or cure. Anyone have a brand or type they had good experience with in this sort of application? I would prefer something that works at room temperature but could heat the Bitumen if necessary to apply it.
I think this sort of thing is good fun and one of the big advantages of DIY but just a word of caution with the bitumen. I seem I recall reading in Collums book on High Performance Speakers (or maybe some where else) that if the bitumen is not allowed to dry sufficiently there have been cases where the solvent vapour ruined the adhesive to the centering spider. Grief ensured. Given any thought to mixing sand or some other aggragate with the bitumen?
hello!
sandwhich is a compromise solution. you want to meet half-way result as well. unpredictable damping factor, logarithmic decrement.
what do you think about more resolute decision?
let's make speaker cabinet, using real marble coffers
it's realy not expensive, but you'll completely satisfied of quality and by sight
sandwhich is a compromise solution. you want to meet half-way result as well. unpredictable damping factor, logarithmic decrement.
what do you think about more resolute decision?
let's make speaker cabinet, using real marble coffers
it's realy not expensive, but you'll completely satisfied of quality and by sight
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Yury said:hello!
sandwhich is a compromise solution. you want to meet half-way result as well. unpredictable damping factor, logarithmic decrement.
what do you think about more resolute decision?
let's make speaker cabinet, using real marble coffers
it's realy not expensive, but you'll completely satisfied of quality and by sight
Yury,
Good idea for compact sized speakers ....but. Have you seen the large speakers in my avatar? They weigh 300 lbs each! That is with 125 lb. of sand in filled L & R side surfaces. In marble these behemoths would easily weigh 1200+ lbs each.
I don't know anybody that has forklift and loading dock to their living room. I used to but that is another story.
you're right, but I made big cabinet ones. I'd assembling it on the place, in the room of customer. it's one way.
second one is - makes it by thin panel. paste it on the wood cabinet. 6mm-10mm. you'll get nice design, best acoustic parametres and not very heavy.
ok. I see. it's not easy, but the same as sandwhich....
good luck.
second one is - makes it by thin panel. paste it on the wood cabinet. 6mm-10mm. you'll get nice design, best acoustic parametres and not very heavy.
ok. I see. it's not easy, but the same as sandwhich....
good luck.
Jonathan Bright said:
Johnathan,
I also had a concern for the outgassing of solvents that would be an issue if store bought roofing treatments were used as bitumen. The untreated surface of the MDF would absorb some of this in time and it could end up lifting the paint or outer finish while potentially making an eternal bad/hazardous smell to anyone with sensitive olfactories or solvent intolerance.
I've seen municipal road crews undertaking asphalt road crack repair with a small trailer that has a propane fired heat source to melt the tar they use and they just pour it into the cracks as a liquid which then cures as it cools. This stuff would probably work very well but to use it I suspect one would have to set up a time consuming and costly to prepare industrial process in the shop.
I do not know that adding sand to the bitumen would be helpful as one wants this zone to be a semi-viscous shock absorbing layer.
I'm sure two part silicone electronics casting compound from Dow Corning would be a hot trick to use in this application but it is about $50/pint last time I bought some about a decade ago.
It could work, but I'm not sure that the adhesive side is adequate structurally; by design it's intended to seal the rubber to the roofing substrate but it's the nails/staples attaching the shingles above that provides the major structural strength. I'd still use screws every 6-8 inches to be sure.
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I know this might seem retarded, but how about styrofoam?
Polystyrene insulation sheets are sold at HD in various thicknesses and it's pretty cheap and SUPER light.
How about a sandwich going from inside to outside:
styrofoam
adhesive
roll roofing
adhesive
MDF
Am I WAY off here?
Let me know...
Polystyrene insulation sheets are sold at HD in various thicknesses and it's pretty cheap and SUPER light.
How about a sandwich going from inside to outside:
styrofoam
adhesive
roll roofing
adhesive
MDF
Am I WAY off here?
Let me know...
I don't really have a solution, but I might help clarify things about the roofing materials.
GM mentioned #50 roll roofing. This is nothing more than a compressed organic felt saturated with blown asphalt. Has very litlle elastic qualities. Probably not suited for damping.
Bill F mentioned rubber roll roofing. If it is the product used for ice dam protection then it might be peel and stick. If so it is an asphalt product with plasticizers and solvents and not too likely to work either because of the gas-off and the smell. If there is such thing as a synthetic rubber self adhesive system (EPDM) then that may work. You will have to go to a roofing supply place to get EPDM or neoprene glue as well as instructions on how to prep the surface and bond your panels. Contact cement will work but the actual glue is better. It's black in colour, same application.
If that's the case why noy get some regular 60 mil EPDM and glue both sides?
How much elasticity are you looking for?
Cal
GM mentioned #50 roll roofing. This is nothing more than a compressed organic felt saturated with blown asphalt. Has very litlle elastic qualities. Probably not suited for damping.
Bill F mentioned rubber roll roofing. If it is the product used for ice dam protection then it might be peel and stick. If so it is an asphalt product with plasticizers and solvents and not too likely to work either because of the gas-off and the smell. If there is such thing as a synthetic rubber self adhesive system (EPDM) then that may work. You will have to go to a roofing supply place to get EPDM or neoprene glue as well as instructions on how to prep the surface and bond your panels. Contact cement will work but the actual glue is better. It's black in colour, same application.
If that's the case why noy get some regular 60 mil EPDM and glue both sides?
How much elasticity are you looking for?
Cal
rcavictim said:
I guess between you and Cal, I'm misinformed as to what 'bitumen' and '50lb roll roofing' is. Anyway, I'm referring to the large rolls of asphalt roofing that's used instead of many small shingles. It isn't a tar like 'glue', so a few randomly placed screws are required to hold the 'sandwich' together, but as a whole it's so massive that the localized 'hot spots' are so well damped it's a moot point.
WRT outgassing, petroleum based tars can destroy drivers in a sealed cab (been there, done that
), but I haven't experimented with vented so YMMV. I haven't had any problems with the asphalt based roll roofing in a 'sandwich' though. I assume it's because it has sufficient time to outgass during manufacturing, etc., and the speaker cab environment isn't harsh enough to continue the process enough to be an issue, whereas the 'tar' has a higher percentage of petroleum products to keep it soft over a long period of time in a harsh environment.If you still prefer a tar-like material, there's a synthetic one made for waterproofing/damping aluminum trailer tops that works well, with no outgassing issues, according to a number of folks years ago on the old basslist, but again YMMV. Don't know if it has sufficient glue-like qualities to hold the 'sandwich' together over a long period of time though since I never got around to doing any testing.
Probably the best reasonably priced product to use, though I don't know if it's available in bucket quantity form for rolling on, is the non-hardening glue used to install subflooring normally bought in caulk tube form, such as 'Liquid Nails for Subfloors'. This is my fave for spot damping. I smear some on a cheap adhesive backed linoleum floor tile, slap it on the 'hot spot' and I'm done. Note that I use very rigid contruction materials, so if MDF or other low rigidity material is used, then the damping material must be rigid to ensure a good impedance mismatch to the glue and each other.
GM
Went to bed and never posted this: Roll roofing.
In this case he's referring to organic felt mat saturated with an asphalt compound..
It's used as a roofing underlay. It's either tacked or glued. I don't think it's the ideal thing to glue between MDF and cement board because it's basically got no mecanical strength in a useful direction and will sag over time if it has a load attached. OTOH, GM says it works well so maybe he's had success.
Linoleum has a similar sort of density to rolled roofing and you can buy ends of roll cheaply. Instead of bitumen you could just use contractor's adhesive which you can buy cheaply at HD. It has reasonable shear strength, doesn't stink, and you get your constrained layer: the linoleum.. And it might keep your cement board attached to the top side of the speaker. (DAP, Loctite, etc.,etc., all make contractor's adhesive).
An MDF-X-cement board composite might be a good idea, perhaps, but what are your objectives?
If you're trying to make a sandwich material with a constrained layer which will absorb vibration, then linoleum is probably nicer to use than bitumen or roofing felt and should work pretty well.. (JUst make sure you scuff the shiny side of the linoleum before you glue it).
If you're set on cement board-bitumen-MDF, there are bitumenous adhesive used for attaching flashing and are allowable for vertical application and that MIGHT keep the cement board attached to the top of the speaker and might damp the sound transmission.
But three layers glued together hard/heavy-soft-hard/heavy are the way to go, I think.
This is interesting towrds the end:
http://www.earsc.com/HOME/engineeri...uietVibration-freeOperation/index.asp?SID=145
In this case he's referring to organic felt mat saturated with an asphalt compound..
It's used as a roofing underlay. It's either tacked or glued. I don't think it's the ideal thing to glue between MDF and cement board because it's basically got no mecanical strength in a useful direction and will sag over time if it has a load attached. OTOH, GM says it works well so maybe he's had success.
Linoleum has a similar sort of density to rolled roofing and you can buy ends of roll cheaply. Instead of bitumen you could just use contractor's adhesive which you can buy cheaply at HD. It has reasonable shear strength, doesn't stink, and you get your constrained layer: the linoleum.. And it might keep your cement board attached to the top side of the speaker. (DAP, Loctite, etc.,etc., all make contractor's adhesive).
An MDF-X-cement board composite might be a good idea, perhaps, but what are your objectives?
If you're trying to make a sandwich material with a constrained layer which will absorb vibration, then linoleum is probably nicer to use than bitumen or roofing felt and should work pretty well.. (JUst make sure you scuff the shiny side of the linoleum before you glue it).
If you're set on cement board-bitumen-MDF, there are bitumenous adhesive used for attaching flashing and are allowable for vertical application and that MIGHT keep the cement board attached to the top of the speaker and might damp the sound transmission.
But three layers glued together hard/heavy-soft-hard/heavy are the way to go, I think.
This is interesting towrds the end:
http://www.earsc.com/HOME/engineeri...uietVibration-freeOperation/index.asp?SID=145
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