Polymer Cabinets

[BurntCoil]

Its Sunday, my day for random thoughts and stupid ideas.

I was wondering if anyone has tried using acetal as a cabinet material. Its got some interesting mechanical properties in that it is very easy to machine, can hold high tolerances, and most interesting of all has a high acoustic attenuation rate. The downside of course is that its heavy and not particularly stiff so any speaker cabinet will need some careful thought on bracing.

I can't find much in the literature, and other than the use of injection moulded cabinets for mass produced speakers and some studio monitors I can't find much on commercial uses of polymers. The is probably due to the weight issue and shipping costs.

I am going to try an experiment with a trial cabinet but wondered if anyone has been down this path before?

Burnt

 

[Flaesh]

POM (=acetal) is typically very difficult to bond.
3D printing is possible )))

 

[BurntCoil]

I agree, it is! I was thinking of an assembly approach that was mechanical - machined surfaces and fastenings, with an internal sealing method using elastomers. Possibly even using gaskets. I have used water cutting services locally for another project and the cost of cutting is very reasonable. The acetal would be milled for a good quality joint.

 

[gedlee]

I had to look up Acetal to find out that it is commonly know as Delrin in the US. It is indeed a very useful plastic often used to make parts for fixturing. But it is too expensive for mass consumption.

I have used polyurethane boards (Renshape) extensively. While extremely expensive compared to plywood or MDF, they are a delight to work with because of their dimensional stability, ease of cutting and machining and they bond extremely well. They will allow for a superior finish as well.

 

[BurntCoil]

Interesting and thank you. When I looked up Renshape I realised I had used it before for modelling in my past life-we used to call it plastic wood! Its a very nice material for machining. However, I recall that if you had a relatively thin sheet of the material and struck it you got a 'ring' a bit like an MDF board but a higher frequency response. If you try striking a Delrin sheet the response is not so pronounced. There are a lot of reports in the literature of polymers used for ultrasonic work where Delrin has a very impressive 30dB per cm attenuation rate, but unfortunately there is nothing for lower frequencies that i can see. However, it does seem like a very 'lossy' material as does Polythene and PTFE.
It might be something best answered by testing some sample, but before I started, I wondered if anyone had tried this before.

 

[gedlee]

I find that Renshape has an extremely high damping factor. I don't think that it rings at all. That's one of its major attractions for me. It does come in several densities and that may be a factor. I use the lightest density but thicker than average panels. This yield an extremely dead cabinet that it actually pretty light - what's not to like? (The cost!!)

 

[BurntCoil]

That sounds very interesting. I will check it out more thoroughly and add it to the list. Interesting about the damping, it might well be the density difference in that that material we used to machine was not light. Thank you for the input!