the famous B&W nautilus and their ex-designer guy at AvantGarde is it? in South Africa are molding their cabinets in a reinforced epoxy material.
This is generally not recommended for diy'ers as most of the materials are toxic, and smell pretty bad too.
As navin excellently describes the actual mold construction is critically important and very time consuming. All poured, filled epoxy molded parts require extensive finishing for cosmetic appearance, priming, painting, etc. For crude example, look at underside of any Corian sink / vanity or the previously mentioned lab counters; ugly!
The materials are excellent for acoustic enclosures by reason of both material and shape. Fillers: mineral, wood, glass, sand, metals, etc., make the already viscous epoxy extremely so, exponentially increasing mold fill difficuly, curing consistency, and cosmetic finishing.
This is generally not recommended for diy'ers as most of the materials are toxic, and smell pretty bad too.
As navin excellently describes the actual mold construction is critically important and very time consuming. All poured, filled epoxy molded parts require extensive finishing for cosmetic appearance, priming, painting, etc. For crude example, look at underside of any Corian sink / vanity or the previously mentioned lab counters; ugly!
The materials are excellent for acoustic enclosures by reason of both material and shape. Fillers: mineral, wood, glass, sand, metals, etc., make the already viscous epoxy extremely so, exponentially increasing mold fill difficuly, curing consistency, and cosmetic finishing.
tinitus said:
I've found that it's not the resins that cause the problem, it's the mold release. Yes, waxing with mold release wax is important but even more critical is spraying on a nice solid layer of PVA mold release. It's water soluble and will help tremendously. Otherwise you will destroy your mold to remove it. Wax alone will NOT work.
http://www.tapplastics.com/shop/product.php?pid=67
I built a 15 foot kevlar boat hull out of kevlar, fiberglass, and epoxy resin and did NOT use PVA on the plug-mold build and had to destroy the plug (shape on which the mold was originally made) to remove it. When I made the actual hull, I DID use the PVA and it lifted out with zero effort. It even had a polished mirror finish because the mold was polished.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
That's really neat. A friend of mine built a similar boat (canoe) that weighed 38 lbs and was 15'6". How much does your weigh?
An externally hosted image should be here but it was not working when we last tested it.
Ever since I stumbled across this Website I've wondered if this material could be used for enclosures: http://www.winterstone.com/
ezkcdude said:
IT has been done. THe Rockport speakers cabinets are made with epoxy resin and fiberglass.
I have an idea that I think would make a better cabinet than any other and it could be done by the average DIY'er but would be work intensive. And I don't have the time or inclination to do it right now.
There are basically three approaches to this and three types of wall construction.
Rockport type of enclosure is two fiberglass epoxy shells about 1/8-1/4 thick with a poured inner of foamed epoxy resin. The outers should be as stiff as possible and the center should have high hysteresis.
Second type is a composite made of sand, crushed rubber particles, fiberglass or carbon fiber strands and epoxy resin. It is like a plastic cement. THe idea of which is that all the materials have a different acoustic impeadance which randomized the mechanical energy in the cabinet wall.
My method is similar to the Rockport method but more sophisticated. It involves creating a honeycomb stucture that is then filled with high hysteresis foam, sand, lead shot or lead shot and mineral oil.
The idea is to combine a very stiff but relatively low mass with a very effective dampening material. With my method an inner or outer shell is constructed with structural foam and a 1/8 -1/4 inch fiberglass epoxy shell is built up. It can be built up from either the outside or the inside. Whichever is easier. Once the inner or outer shell has been cured the foam form is stripped away and the surface is cleaned up or roughed up depending on what is to be bonded to it.
After the inner or outer shell is made a honeycomb structure is created by using 1/2 or 3/4 inch wide fiberglass tape. Cut in lengths to form hoops which are dipped it epoxy resin and bonded to the inner or outer sheel so that they become part of the inner area. The little hoops are built across the surface in rows or columns. And after they cure each side is laid out on a horizontal surface and the inner dampening material is placed.
Then the inner dampening material it is shaved off so that is level with the top of the hoops. Then the final shell is laid up to the same thickness of the first shell. Using the same type of fiberglass to get the same stiffness as the other outer skin. This should create a structure that is both highly rigid and highly damped.
My speakers have been made in carbon fiber and epoxy as a composite with polyurethane. They are very rigid and very well damped. But I'm not sure that this is necessary as I can't tell a difference from these cabinets and ones in wood or normal fiberglass.
The material that I found that looks very interesting is a polyurethane sheet made in Germany and used to make molds. Its very light and extremely rigid, cuts and shapes very well and when glued with a two part polyurethane glue its basically welded as the board breaks before the glue bond breaks. Downside a single board is about $125. Light and strong is better than heavy since the resonances will be higher in frequency.
All in all, wood is the most efficient material, MDF or partical board is hard to beat for cost and performance. There may be better materials but none that are as cost effective.
The material that I found that looks very interesting is a polyurethane sheet made in Germany and used to make molds. Its very light and extremely rigid, cuts and shapes very well and when glued with a two part polyurethane glue its basically welded as the board breaks before the glue bond breaks. Downside a single board is about $125. Light and strong is better than heavy since the resonances will be higher in frequency.
All in all, wood is the most efficient material, MDF or partical board is hard to beat for cost and performance. There may be better materials but none that are as cost effective.
OT - boats
Aah, a Geodesic Aerolite canoe! I built a Snowshoe 14 - it looks just like the one in the photo.
.
Mine came out a biut heavier than spec, as I couldn't find suitable spruce on the Left Caost and settled for heavier Douglas fir. Still, I can easily carry it one-handed.
ezkcdude said:
Aah, a Geodesic Aerolite canoe! I built a Snowshoe 14 - it looks just like the one in the photo.
Mine came out a biut heavier than spec, as I couldn't find suitable spruce on the Left Caost and settled for heavier Douglas fir. Still, I can easily carry it one-handed.
Over on the talkbass forum there is a person making a composite enclosure using epoxy and fiberglass over a foam core. The goal was primarily light weight. From what little materials testing information he did reveal it appears that the composite stack up was stiffer than plywood (more resistance to vibration?) but wasn't as strong. The failure was delamination of the composite skin from the core. I suspect had he used a core material made for the purpose of composite construction such as CoreCell, rather than foam from the local home center, this would not have been a problem. CoreCell is much more expensive of course.
ezkcdude said:
Nice. My hull as you see was 15 lbs. It was four layers. Problem was that it was all skin and no structure. I hadn't had time to add support structure (laminated-in fiberglass-over-foam ribs) so it's VERY flimsy. Kevlar is not known for its stiffness unfortunately, but it probably would never get a hole from hitting a snag.
The problem using a foam core for a subwoofer is that foam has almost no compressive strength. The honeycomb materials can support large loads though. though there are foams that can support a little load (stiff urethane foams, "surfboard" foams....). but without knowing what kind of foam he used... hard to say why it failed.
Re: OT - boats
Awesome! I've been checking out Mr. Monfort's site for a while now 5 yrs) and may have to bite the bullet.
West coast spruce? Try www.aircraftspruce.com
i just love small boats,
7/10
lousymusician said:
Aah, a Geodesic Aerolite canoe! I built a Snowshoe 14 - it looks just like the one in the photo.
.
Mine came out a biut heavier than spec, as I couldn't find suitable spruce on the Left Caost and settled for heavier Douglas fir. Still, I can easily carry it one-handed.
Awesome! I've been checking out Mr. Monfort's site for a while now 5 yrs
) and may have to bite the bullet.West coast spruce? Try www.aircraftspruce.com
i just love small boats,
7/10
The epoxy, silica sand, wood flour and rubber particulate speaker cabinet was mine.
The sand was there for mass, the wood flour to thicken the resin, add stiffness and stop the sand settling out on slow set resins, and the butyl rubber particulate for it's vibration dampening properties.
Getting the mix right for the highest mass, sitffness, and greatest damping was very time consuming, i made close to 50 sample tiles of varying ratios. Samples were made in sets of five with gross variations in component ratios to start off with. Each subsequent set homed in on the ratios in the best performing sample, with one wild card ratio set added in each time just in case i'd missed a component mixture ratio that offered good results.
It was a UNI engineering project and i've long since thrown away all but one of the tiles, as well as the speaker cabinets.
but the final ratio, by volume was near enough.
epoxy 1
silica sand 1
wood flour 2
butyl particulate 1.8
You'll be surprised how much wood flour and rubber the epoxy can 'eat' as you mix it in.
Use 1 hour set resin otherwise the whole thing will get way hot and ignite, i lost a few samples early in the process.
The butyl rubber particulate was sub 1mm particle size and the wood flour source from a MDF manufacturer, so wear a respirator.
good luck.
The sand was there for mass, the wood flour to thicken the resin, add stiffness and stop the sand settling out on slow set resins, and the butyl rubber particulate for it's vibration dampening properties.
Getting the mix right for the highest mass, sitffness, and greatest damping was very time consuming, i made close to 50 sample tiles of varying ratios. Samples were made in sets of five with gross variations in component ratios to start off with. Each subsequent set homed in on the ratios in the best performing sample, with one wild card ratio set added in each time just in case i'd missed a component mixture ratio that offered good results.
It was a UNI engineering project and i've long since thrown away all but one of the tiles, as well as the speaker cabinets.
but the final ratio, by volume was near enough.
epoxy 1
silica sand 1
wood flour 2
butyl particulate 1.8
You'll be surprised how much wood flour and rubber the epoxy can 'eat' as you mix it in.
Use 1 hour set resin otherwise the whole thing will get way hot and ignite, i lost a few samples early in the process.
The butyl rubber particulate was sub 1mm particle size and the wood flour source from a MDF manufacturer, so wear a respirator.
good luck.
gedlee said:
In India carbon fiber sheet are just becoming available. I saw a 18" x 48" (approx) sheet that was selling for about $225 and found it expensive. Is this in line with international prices?
I agree with usig wood as the mould material. However ply is easier to bend into complex shapes (parabolic) than MDF. 6mm ply bends as easily as 4mm MDF and good marine grade ply is stiffer than MDF. If one is making a one of speaker dont even bother with the PVA. Just be aware that anything that involves resin is messy, anything that involves fiberglass (even if it si woven fabric) is twice as messy.
elseif said:
Using Foam for bass might be the problem. I have used a Foam cylinder (the remains of a foam cored water filter) for the midrange (300Hz+) though. I need to experiment with how low it can go my object (since I have only one cylinder) is to use it for the center channel.
y8s said:
a-ha so that is the reason foam did not work for bass. I did realise that the material is way too soft.
sq225917 said:
I assume what you call wood flour we in India call sawdust.
why would you want to optimise for maximum mass. I thought the idea was to make the cabinet as light as possble and still retain stiffness.
That said I have seen silica being used in concrete to improve the compressive strength of the concrete. I assume the same would be true for epoxy.
Appearantly, getting the foam in the center just right in these foam core designs is the hardest thing. It needs to have high enough hysteresis that it behaves far differently than the outer shells and slows down the internally transmitted forces. But it is still part of the structural assembly and must be strong enough that it increases the stiffness of the outer shells considerably. And it must bond very strongly to the outer shells. This is why a foamed epoxy resin is preferred. It seems that you could also add lead shot into the mix with the epoxy foam if the foam was dense enough to support it.
The reason that I prefer the honeycomb construction method is that it allows the stiffness to become very high without the need for the internal damping medium to be part of the structure. So the damping medium can be further optimized. To me the perfect damping material would be some kind of light oil combined with lead shot. The oil it seems would convert a lot of vibrations to motion and heat and transfer even more energy into a loose collection of lead shot which is allowed to have a small amount of motion since it is not contained in any kind of stiff medium.
The lubricity of the oil further allows the lead shot to slide a bit more to take on energy yet it also quiets the lead shot in it's motion. It would take some kind of oil with good qualities that can be used with lead and not create a hazard. Also, something that is inert to epoxy and fiberglass.
The cheaper solution, but one I think would still be effective is just dry silica sand.
The reason that I prefer the honeycomb construction method is that it allows the stiffness to become very high without the need for the internal damping medium to be part of the structure. So the damping medium can be further optimized. To me the perfect damping material would be some kind of light oil combined with lead shot. The oil it seems would convert a lot of vibrations to motion and heat and transfer even more energy into a loose collection of lead shot which is allowed to have a small amount of motion since it is not contained in any kind of stiff medium.
The lubricity of the oil further allows the lead shot to slide a bit more to take on energy yet it also quiets the lead shot in it's motion. It would take some kind of oil with good qualities that can be used with lead and not create a hazard. Also, something that is inert to epoxy and fiberglass.
The cheaper solution, but one I think would still be effective is just dry silica sand.
In response to the posts suggesting speaker panels ought to be light in weight: I don't think striving for light weight cabinet materials is justified. I understand the argument that decreasing the mass, while retaining the same stiffness, drives the resonance frequencies up but lighter baffles also move more when a given force is applied than do heavy baffles. Whether you're striving to minimize the amount of sound radiated by the cabinet's vibrating walls, or maximize the stability of the baffle the drivers are mounted to, the goal is to minimize the deflection of the panels. I think heavy, well damped panels are more likely to minimize the unwanted deflections than light panels with equal stiffness and damping.
I should confess that I used to be more sympathetic to the "light and stiff" school but a bit of personal experience convinced me that heavier is better. In order to minimize acoustic interference in a very sensitive experiment in my research lab I once made a removable panel for an acoustic isolation box out of 2" thick foam sandwiched between aluminum skins. It didn't provide nearly as much isolation as the thinner (1 inch), but heavier, particle board doors I had previously used. I admit I didn't measure the stiffness or damping of either the foam sandwich or the particle board, but I sure came away questioning the light and stiff argument. A couple of years later I was on the receiving end of a convincing argument and demonstration from Andy Payor of Rockport. Hearing (or actually not hearing) the effectiveness of his very stiff, very heavy, very well damped enclosures pretty much sealed it for me.
Few
I should confess that I used to be more sympathetic to the "light and stiff" school but a bit of personal experience convinced me that heavier is better. In order to minimize acoustic interference in a very sensitive experiment in my research lab I once made a removable panel for an acoustic isolation box out of 2" thick foam sandwiched between aluminum skins. It didn't provide nearly as much isolation as the thinner (1 inch), but heavier, particle board doors I had previously used. I admit I didn't measure the stiffness or damping of either the foam sandwich or the particle board, but I sure came away questioning the light and stiff argument. A couple of years later I was on the receiving end of a convincing argument and demonstration from Andy Payor of Rockport. Hearing (or actually not hearing) the effectiveness of his very stiff, very heavy, very well damped enclosures pretty much sealed it for me.
Few
Few said:
The object is not so much to make the panel light and stiff, but to make the structural part of the panel have a very high stiffness with a moderate mass and to make the dampening part of the panel to have a much lower stiffness to mass ratio but with a high mass. The combined total is still a very heavy panel. Not light at all and perhaps even significantly heavier that standard wood or MDF.
It is easy to see how these seemingly opposite approaches can be confused. It is possible to make a very high stiffness to weight ratio panel that is very light. But as is pointed out. It is not stiff enough or damped enough to do the job. The first priority is that it is stiff enough and damped enough to do a basic job of the work that it is supposed to do.
This is related to my other thread ("Reaction Compliance Couple Mounting"), but it's pertinent here. It is my understanding now that the primary rationale for increasing cabinet mass is to minimize the vibration (displacement, distortion) due to the driver reaction force. If one could magically (or practically) cancel out the reaction force (for example, by rigid back-to-back coupling), the argument for cabinet mass becomes essentially moot. In this case, it would probably still be useful to have a stiff cabinet, but the need for mass should be much reduced. This issue is essentially ignored except by a very few, and most people don't really think about the structural reasons for making cabinets so massive. Take home message: isolate the driver frame from the cabinet, and cabinet mass becomes a relatively unimportant design consideration.
Few said:
You are mixing the problems. Mass is much better for sound transmission loss, but strength to weight ratio is better for less cabinet resonances. They are two different things. So you have to decide which is the dominate source, the cabinet resonances or the sound transmission through the walls from the sound inside. Well since there is a thin piece of paper called a speaker cone placed on one of the cabinet walls, which is virtually wide open to sound transmission through it, lowering the transmission through the rest of the cabinet is going to be a waste of resources. But the driver does structurally excite the enclosure irrespective of the sound in the box, hence the strength to weight property would win.
Isolating the speaker from the enclousre is a bad idea from a number of perspectives, so I don't consider that a solution.
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