I have been on the fence about posting on this. These things get nasty at times and I lack the energy to argue with folks.
I have done extensive testing on cabinet materials in the startup of my company. One straightforward approach was too build the same cabinet out of multiple materials. You would be shocked at how much energy goes back into a cabinet and how much strength is really required to damp it.
The frequency with which the cabinet resonates is also extremely important. The lower the frequency, the greater the vibrations that are created and the more it impacts the ability for sound to travel forward from the cabinet and secondarily, the amount of distortion that muddies the sound coming from the drivers.
I used the same drivers, crossover and stuffing in cabinets that were identical other than the material and fine exterior measurements to variances in thickness of the materials.
When you do this, you will find that when you use stiffer materials like Carbon Fiber or even fiberglass stiffened by resin, the sound coming from the speaker will be more natural and fine detail is clear. When the cabinets are less rigid, but still resonate at a high frequency separation of detail will still be good but sound will be damped and dark. The solution is to alter the crossover and make the tweeter slightly more forward.
When the cabinet materials are less stiff and resonate at a lower frequency, the sound will be both dark and muddy. No matter how stiff the drivers are, there is nothing that a manufacturer can do to stop this.
Wood, no matter how heavy, stiff and dense, can’t match it. Some perform better than others, no question. But manufacturers are cost conscious and want to keep prices down. Take a stand mount speaker that is 8"w x 15"h x 10"d. Normal size. The cost of the MDF in that pair of speakers is about $7.50. Baltic Birch plywood will be about $40 and a hardwood would be $100-$400 depending on exactly how rare or exotic it is.
Composites will start above that plus the cost of a mold and much more expensive machining. Same for metal.
There is a reason why Magico’s, Wilson’s, Marten, Vivid, Wilson Benesch, etc... sound so good. The materials they use, whether composite or metal, resonate less and/or do it at a much higher frequency.
Given all that, what material do you think a manufacturer is going to pick when making a cabinet? Especially when everyone is using MDF and it is the industry standard. Unless you are going for high performance, even stepping up to Baltic Birch will add about $100 to your retail price and in hyper competitive markets where there are 80 speakers to choose from, every nickle counts.
MDF is used because it is cheap. And layered MDF does not significantly outperform solid MDF. It bends easier which is why it is used. Strength comes from layers with oriented strands of grain being laid down in opposite directions. OSB or standard plywood are examples of this. By it’s vary nature, MDF does not have oriented strands. It is stronger than particle board but well short of plywood. Having 7 or 9 layers of thin MDF glued together only makes sense when bending