resin loudspeaker cabinets

[cowanrg]

i was in my car today and an idea popped into my head... wouldnt it be cool to mount a midrange driver inside a bored out bowling ball? i figure, cant get much more dense that that, and there would be almost NO resonance.

then i thought, wait, isnt a bowling ball just pure resin? why not make an entire cabinet out of it.

if you made a typical loudspeaker (floorstander) cabinet from resin, it would be MUCH denser and heavier than wood or MDF, it would have a lot less resonance, be fairly easy to make into different shapes, and very flexible in design.

is there downsides to this? cost really isnt a factor. it would almost be cheaper than MDF if you could just plan out the molds right. foam is cheap, and so is resin. finishing it would be a dream. you could just sand and polish it, and basically paint it. or, just dye it before it hits the molds.

seems to me that a very complex structure with vented ports, chambers, etc, could be made without too much effort with resin.

anyone else have any comments on this?

[pinkmouse]

A few thoughts...

1) Your enclosures would be very heavy...

2) Building the mould would be more complicated than building the box initially from wood, and it all needs to be finished very well to give a good surface to the resin. Also resin gives off very large amounts of heat whilst curing, so your mould design needs to take this into account.

3) Estimating from the price of resin in the UK I think you might find it is very expensive for the quantity you would need.

4) To prevent the cabinet becoming brittle you may need to load it with fibre in such a large and complicated structure.

But bearing all of that in mind, my favorite speakers of all time, the B&W Nautilus use resin for the cabinets, because they would be just about impossible to make from wood.

So, in conclusion, if you have the time and money, go for it, but as always it is probably worth building a test piece first, maybe a mid enclosure, or a small full range box.

Good luck

[jackinnj]

Of course, you can fashion cabinets out of concrete or you can use clay drainage tile for cabinets.

[cowanrg]

actually, ive done some checking...

weight wouldnt be a HUGE issue. im looking at using areospace resin. its lightweight (relatively), strong (not brittle like you say), and its low temp curing. plus, a 5-gallon bucket of the stuff is like $50 or so. molds are easy. i know a guy who makes all sorts of parts for his model airplanes from it. you just use styrafoam blocks, cut out the shapes, and pour it. a lot of work would go into the design though... if you were talented enough, you could make one mold for the speaker, but you would probably need multiple ones. but with resin, you can join then easily, and chemically, it would be one peice once fused.

and from what i understand, sanding and finishing it is as easy sanding wood. you can get a polished mirror finish from it without much effort.

lastly, if everyone here uses 1/2" or 3/4" MDF, if you used that same thickness of resin, it would be about 4x as dense. sure it would be heavy, but isnt that the point? the meridian dsp8000's weigh in at like 500 pounds EACH. its a resin/granite thing that the cabinet is made out of. i dont see weight as a downside, except if it got absurdly heavy.

i think ill take your advice and just make a prototype mini-monitor or something first, then maybe look into doing some towers. a mini-monitor or bookshelf should really only need about 5 gallons of resin. so the cost would be nice.

correct me if im wrong here, but would i need internal bracing if i made the cabinet at least 3/4" thick with resin? wouldnt that be more than enough to warrant bracing?

oh, and btw, the watt cubbII's use high density MDF AND resin as their cabinets. i think the baffles are mdf, and the cabinet itself was resin. it seems like the big boys use resin instead of wood... even the b&w 800, 801's use resin for the midrange enclosure.

[cyclotronguy]

Hiya

What you are proposing has been done many times commercially, with various amounts of success (financially). Currently in the US a firm doing business as Poly-crystal does small runs of speaker cabinets for constructors.

US Enclosures at one point had hollow resin spheres available to the DIY community, though with a reputation of poor service.

Could very well be a fun DIY-Audio project!

The weight issue of the resin may be addressed by adding glass balloons to the resin mix, these are often sold as "micro-balloons".

When choosing resin care must be exercised to assure compatibility with the foam core. Not only can heat cause problems but some castable materials will attack plastic foam.

Cyclotronguy

[BrianGT]

Originally posted by cowanrg
actually, ive done some checking...

weight wouldnt be a HUGE issue. im looking at using areospace resin. its lightweight (relatively), strong (not brittle like you say), and its low temp curing. plus, a 5-gallon bucket of the stuff is like $50 or so. molds are easy. i know a guy who makes all sorts of parts for his model airplanes from it. you just use styrafoam blocks, cut out the shapes, and pour it. a lot of work would go into the design though... if you were talented enough, you could make one mold for the speaker, but you would probably need multiple ones. but with resin, you can join then easily, and chemically, it would be one peice once fused.

and from what i understand, sanding and finishing it is as easy sanding wood. you can get a polished mirror finish from it without much effort.

lastly, if everyone here uses 1/2" or 3/4" MDF, if you used that same thickness of resin, it would be about 4x as dense. sure it would be heavy, but isnt that the point? the meridian dsp8000's weigh in at like 500 pounds EACH. its a resin/granite thing that the cabinet is made out of. i dont see weight as a downside, except if it got absurdly heavy.

i think ill take your advice and just make a prototype mini-monitor or something first, then maybe look into doing some towers. a mini-monitor or bookshelf should really only need about 5 gallons of resin. so the cost would be nice.

correct me if im wrong here, but would i need internal bracing if i made the cabinet at least 3/4" thick with resin? wouldnt that be more than enough to warrant bracing?

oh, and btw, the watt cubbII's use high density MDF AND resin as their cabinets. i think the baffles are mdf, and the cabinet itself was resin. it seems like the big boys use resin instead of wood... even the b&w 800, 801's use resin for the midrange enclosure.

Worth a try. Another easier option would be to make a shell out of 1/2" mdf, and then just layer the resin inside that, making a hybrid speaker. You could get a really solid cabinet from this. I have a friend that used to make car subwoofer cabinets this way. Sure, this wouldn't give you an impressive looking speaker, and would look like a normal box, but I would imagine that it would be one rigid box speaker.

--
Brian

[cowanrg]

yeah, i know that certain resins will NOT be compatible with the foam molds.. but even so, i will be treating the foam somehow just to be safe. it will be an interesting little adventure. just gotta finish the aleph2's first.

[cyclotronguy]

Coating. PVA glue followed by mold release works just great.

Cyclotronguy

[herm]

US Enclosures

[Austin]

Are all of the B&W speakers using resin Transmission Line speakers? I think there would be a problem in small sealed enclosures made out of resin because the energy inside the speaker has to go somewhere and that somewhere is usually out the speaker cone. TL's don't really suffer this problem so they can benefit from the most dense cabinet possible. I don't know how vented boxes are affected by this. Dense wood is generally the best thing to use in sealed speakers IMO because it absorbs enough of the energy into the cabinet walls without transmitting it through the walls therefore not requiring that the energy escape through the driver cone. I did a little research on this during the summer in my acoustics class, but never really came to a conclusion of whether the benefits of the resin enclosure was worth it. (This does not apply to TL's because it obviously was better). Hope you can follow that. Has anyone done any experiments along these lines?

Austin