Which material sounds better for speakers construction? Wood, Ply or MDF?

"Wasn't there a company making cabinets out of cast concrete?"

Maybe you are thinking of different brand, but early Hales speakers had concrete baffles. Paul Hales switched to MDF because of economy in creation and exporting the heavy speakers. I came across an Asian manufacturer making cabinets out of vases. They were trying to find US distribution. Nice people; I hope they didn't struggle too much before quitting the impossible mission of marketing it to US audiophiles.

MDF, if anything is ultimately practical and established. I have not heard a wood box speaker using Scanspeak drivers as good as what YG has achieved, and I welcome the variety and pioneering as MDF is not some panacea. 

RV is a measurement and science based engineer, I can assure you that the 7 cabinet is superior to the 5a in every way.
impossible to overdamp a passive component like a cabinet - you want to hear the Stradivarius or the cabinet ?
the 7 cabinet is a mdf  cabinet within a mdf cabinet with constrained layer damping ( he collaborate s with Michael at HRS, so my guess is that is is HRS supplied ( and you just know they are serious engineers ) and CF wrap cooked in an Autoclave.
in a previous working life I dabbled in advanced composite structures... running arguably some of the most advanced high technology composite shops on the planet- simple stuff like the Hubble optical bench, F-22 wings, 787 fuselage.....
easy stuff...
i can assure you it is more than veneer
now from a musical perspective, while I loved my 5a for many many musical years, the 7 mk 2 are lightyears on....

enjoy....

cueing up some late nite Sunday massed chorale..... perfect for a prayer of discernment....

i checked w RV
he invented the trade secret constrained layer damping material used in Treo up thru model 7 and it’s initial use predates HRS.

motion into heat
simple to say
not so easy to do at the correct range of frequencies.....

i should probably disclose i use a bunch of Vandersteen and HRS products......

Which material sounds better for speakers construction? Wood, Ply or MDF?

I haven’t read any of the answers, but something to ponder over which is material is going to flex the least, and becoming a sound board at certain frequencies in a speaker
In my younger years as a comp surfer, I tried all three in the centre stringer of my comp surfboards, this could be a good indication.
Flex and rebound is a good thing in a surfboard as it gives feel through a turn and rebound coming out of a turn (bit of a kick of speed) bit like snow skii’s when you get a good rhythm going in slalom racing

All three stringers (mdf wood ply) on surfboards being the same thickness, the one with the most initial flex is MDF as it has no grain it’s flexable but it doesn’t rebound (snap back) as good as, single ply of wood, single ply of wood doesn’t have the initial flex of the MDF though.

The stiffest with not much flex or rebound is the 3 ply of wood as all 3 plys are grained if different directions to each other and glued together.

So to me for speakers say thick 15 ply with all grains running in different directions will be stiffer, so not to flex much and become a sound board certain frequencies. Sure they will still have resonances but they should be well down and maybe easy to tune out with strategically placed bracing.

These guys think the same
https://www.google.com.au/search?q=Shahinian+speaker+with+plywood&sa=X&tbm=isch&tbo=u&am...

Cheers George