A little OT but speaker design?

[R.G.]

it's hard to get ALL the specs to input, unless ya find a speaker whos specs are documented to the tiniest detail... easier said than done.

The hifi speaker builders' common wisdom these days is to measure the actual speakers you get. Almost like germanium transistors, eh?

The measurement isn't all that hard, but it does require some study.

There should be something in this world where you select the brand/model speaker and it tells you the optimum box.

The older I get the more I recognize that the words like best, worst, optimum, and so on have no meaning whatsoever without a stated context. In fact, they probably ought to be replaced with "most X" or "least Y", which is how they should be used, but aren't. Which is just my long repeated version of Rob's

There's no such thing as an optimum box because the meaning of  "optimum" varies!!

At one point in my life I thought that guys who trade brands and models of speakers through their cabinets were doing the musical equivalent of shopping for new wallpaper. But it makes sense that the quirks of a speaker are its voice, and what is more natural than a musician trying out new musical instruments?

One last item. Other than diffraction loss and lobing from multispeaker placement in cabinets, the design of a speaker cab is about bass response only. The volume and shape of a cabinet has little effect on treble, given only that it's not done so poorly that sound reflects back out of the speaker cone.

[petemoore]

  We're talking about 'solid' cabs, ie not going for lots of 'wood sound' like Jensen 13ply 1/2'' birch or Fender [old cabs made from many-ply 1/2'' wood].
  We're looking to mount the frame solidly, and have an enclosure which seals the back of the speaker in a cavity with a certain volume of air in it.
  The dimensions are not that critical. ie as long as the enclosure volume is X amount...and extreme rectangles aren't chosen [I've heard cabs with really shallow depth..short from front to back sound...shallow]..
  The only thing I think youd hear a 'preferrable difference' in is:
  poor wood quality
  poor joinery
  too small a cabinet
  I've made cabinets using baffle board w/styrofoam / paper mache enclosures...sound great, like fine enclosure...I just pull the alnico drivers and pre-made baffle boards from salvaged consoles, then put any fairly solid sealed enclosure behind..basically anything can work for holding air, I just wouldn't sit on the mache' or styro cabs, styro cabs have a little bit of 'styro sound'...which is cool, the thick mache' is pretty much nulling to soundwave penetration'.
  Suggestions to buy a pre-made are good because all the joinery is hopefully really tight and solid, everything is figured out down to 'thousandths' as far as the woodworking jigs etc. doing the joinery, something that is generally done consistantly well...by those set up to do it, and who are doing it consistantly.
  I can't tell if you still want to DIY it but..A frontboard to backboard strut [2'' x 2''  seen inside marshall 4x12'' cabs]...keeps the middle of the backboard held solid to the frontboard [baffle] with a long screw.
  It's not rocket science, all you really need is something that holds a volume of air behind the speaker, separating the back of the speaker from the surrounding air, which puts an 'air shock' effect on the speaker cone which helps prevent over-excursion of the voice coil, deepens bass response. Most guitar speakers can do well in open back or enclosure designs.
  If the cabinet is a well made, 'normal shape' unit, it'll sound great.
 

[Chuck]

After dwelling on it a few days, I'm going to try and build two cabinets as close to an existing 2x12 as I can, with oak or birch plywood.

If they sound good, I'm going to take them to Line-X and have them sprayed with that carbon fiber/kevlar stuff they spray truck beds with.
That should tame any remaining resonance.

[runmikeyrun]

that's the other option- go to the music store and measure a marshall (or whatever brand you like the sound of) cab and then build from that.  It will sound different if you get different speakers but you'll get a better result than just guessing.  And be sure to use good wood- particle board  mdf will crack if someone drops it carrying it, try to get top grade 3/4" plywood.

[Somicide]

But the popular trend is over-sized cabs, more like the Recto cabs from Mesa!

[Chuck]

But the popular trend is over-sized cabs, more like the Recto cabs from Mesa!

Why?

All the 2x12s I've been looking at:  Ear Candy, etc are ported.

[Meanderthal]

 Just don't include the port... or copy it exactly(speakers and all). Either way you'll do fine.

On guitar, I'm not sure extended bass response is a good thing. I never got one to sound right thru my SVT coffin cab.