That big wavy thing was done using layers of 3mm mdf and LOTS of pva glue.
It's a dual tapered quarterwave pipe, so the volume is not necessary, only the smooth increase of the chambers from one end to the other.
You can also buy ply which is more bendable than your normal ply.. called bendable ply, but 3mm ply works well so long as you only work with gentle curves, also, you would be amazed how few layers you need to get something that is very non resonant ! There are a couple of examples of using ply in the curved speakers section.
Other volumes can be estimated using mathematical integration or slices etc.. I do have a degree with a major in pure and applied mathematics from when I was younger (1978), so its not really an issue to find some way of finding a reasonable approximation.
Also understand that those laser cut things are not mine, they are pics donated by others to show examples.
Anything noted as ARGOS is mine though.
