Wooden (MDF) vs. Plastic speaker casing

No. It's not what you make it from that matters, it's how you make it.

Unless you're going for looks,

then id go for wood speakers. :)

That's misleading (if not outright wrong).

Cabinet resonance can have a considerable effect on sound. Is there some mixture of bracing and Nylon 5 that might match MDF's qualities? Maybe: but there's a reason that almost every speaker from the $50 pioneer at BestBuy to the $24,000 B&W 800D is made (primarily) of MDF.

There are some people who go other routes. I have speakers here at home made of cast marble, for example; and the 800D above doesn't use MDF for it's midrange (only it's bass cabinet).

Good cabinets have little to no resonance. Achieving that has little to do with the material the cab is made of. Of course some materials aren't suitable, like sheet metal. There's nothing the least bit special about MDF, other than it's inexpensive and takes veneer well.

and it's reasonably stiff.
and reasonably strong.
and very consistent (don't have the problem with voids you would with, say, plywood.
and it can be gotten very straight (as opposed to, say, hardwoods)
and it's dense (which affects resonance and vibration)
Based on my experience in tiled rooms: It seems like different materials might reflect sound differently too.

It certainly not that other materials cannot be used (I've seen glass, brass, steel, concrete, various polymers, and fabricated marble used for enclosures); but nothing's been shown to be clearly superior.

What kind of plastic? I imagine that in the near or maybe far future, 3D printing would make cabinets a lot more interesting while keeping all the desirable properties for audio production. I don't think you can 3D print MDF, but who knows what the future holds.

Properly made (low resonant) plastIc speaker cabinet will be much more expensive than one from plywood or MDF. All cheap plastic speakers you can find are small and use very thin walls without internal bracing. That is why these are cheap. When you start talking about 100 pounds of plastic for each speaker, it will be completely different money.

Nor is MDF superior to other materials. If it was I'd use it. I don't. The only reason manufacturers use it is because it's cheap and it's heavy. Being as heavy as it is they can make a non-resonant cabinet from it with minimal bracing, if any. That minimizes labor costs, which maximizes profit margins, and in the speaker business as in all businesses profit is the name of the game. The downside is weight and durability, but for cabs that aren't meant to be portable weight and durability aren't issues. Where weight and durability is an issue, as in pro-sound, high quality cabs are made of anything but MDF. You do see MDF used in pro-sound, but only in cheap entry level cabs, where the only consideration is cost.

ABS plastic is a great material for enclosures and speaker/woofer baskets as well. ABS you can make the entire enclosure as a mold and can be very strong and non-resonant and light.

True, the major disadvantage is the $250k or so that it costs to make the mold. Of course not all ABS enclosures are as strong and non-resonant as they should be, but neither are all those made from any other materials either.

You mean like in move theaters? (http://www.klipsch.com/kpt-435-n)

Maybe professional concert line-array boxes (http://www.electrovoice.com/product.php?id=20) That one is from plywood.

OTOH: I wonder if considerations like cabinet resonance isn't actually *less* important when you are running over 110db to an audience tens-of-meters away.

Theaters don't consider 167 pounds a problem, nor durability, as they typically only move it once, the day they install it.
Plywood is more or less the pro-touring standard., but JBL Vertecs and others use composites, for lighter weight. Saving 50 pounds per box is significant when you fly upwards of eight in an array, and fuel prices aren't going back to a buck a gallon. It's even more of a consideration, seeing how high internal cab pressures are to realize the output required.

Based on what? http://www.linkwitzlab.com/builtown.htm has zero internal pressure (open baffle) and is 87db.

How is the cabinet resonance (added sound output) a bigger problem when there are dozens of speakers, very high volumes, and the listeners are tens-of-meters away?

Why would you believe that the internal pressures would be higher? The chambers are (generally) larger, often ported, and (because of the use of a large number of drivers), the XMax is generally smaller (a simple look at the surround roll will tell you that).

So if my speaker is moving less (smaller XMax) in a larger space: the cab pressure will be less, not more.

Personal experience. I design loudspeakers for a living, so I have a fairly good grasp of these matters.

Did you design *these* loud speakers?

Am I right that a driver with a lower Xmax-Xmin distance in a larger ported enclosure will have less pressure than a driver with a higher xmax-xmin distance in a smaller sealed enclosure?

Are you asserting that pro audio uses smaller enclosures (relative to driver size), or drivers with a larger xmax-xmin distance?

What are the actual numbers (since you know them?) Is it measured in PSI?

ABS/PC-ABS, PPE, Fiberglass, Carbon, Nylon, etc. The plastic industry has more materials available to it than the metals industry. There's also an entire section of composites which have the media suspended in resin, and don't get me started on different types of resins. Just because a speaker is 'plastic' doesn't mean it's junk. MDF is a composite btw and so is carbon fiber. Plastic composites can be cheaper, lighter, and less resonant. Material selection is always improving and from what I've seen plastic is the now.

+1. It's used because it's less expensive than other materials while giving just as good, if not better, results. But the molds are so expensive that if unit sales of less than 4,000 speakers within the first year can't be realized the high tooling costs won't be eclipsed by the reduced materials and labor costs. If the tooling cost for plastic was the same as that for wood based products you'd see plastic take over almost completely, save probably for the very high end market, where people would be willing to pay more for wood based construction based purely on the perception that it works better, even if it doesn't.
Edited by Bill Fitzmaurice - 11/23/12 at 7:36am

That's where 3D printing, SLA type building comes into play. Rapid prototyping eliminates the mold and leaves the design only to the imagination. I've used it at work where we make plastic parts for a major auto manufacturer and from design in Solidworks to a real 3D plastic part takes less than a day.

*edit: The SLA part is for assembly equipment, the actual car parts are still made with injection molding. Just in case there was confusion.

How much does the 3D printing hardware cost? No doubt when it's less than current methods it will be adopted by the speaker industry. Perhaps it already has, just not with anyone I work with yet. It's all about money, and even the smallest auto manufacturer's sales dwarfs the largest speaker manufacturer by a huge margin.

Not cheap. I think our machinist was saying that each rapid prototyped part was in the 5k to 10k range, maybe more. The price of needing a fixture right now.

So perhaps I shouldn't be quick to criticize PSB for using polycarbonate for the enclosures for their new Alpha PS1 desktop speakers? I too always just assumed a plastic enclosure was automatically inferior.

My DR series pro-sound speakers were originally designed with the intent of being molded. The party who commissioned the first prototype DR250 couldn't come up with the million or so that it would have taken to fund the enterprise, so it didn't go into production. The DIY version built of wood takes about thirty man hours to build; an injection molded version would take perhaps three, and if anything the injection molded version would sound better, as there are things you can do with plastic that you can't do with wood.
60 years ago, when it was proposed that a car body be made of plastic rather than steel, skepticism abounded. This is what the fuss was all about:

Edited by Bill Fitzmaurice - 11/24/12 at 9:41am