Open Baffle Speakers: Question About Materials

I am wondering whether the materials and construction methods used for the frame/baffle of these designs matters. In other words, is it necessary to build the frame/baffle so that it does not vibrate/flex/move in response to driver excursion/vibration? If so, what are some of the popular open baffle designers (Spatial Audio, Pure Audio Project, ETC) doing to mitigate this issue? 


Yes, it is just as important for open baffle speakers as box speakers to have a stiff baffle. Spatial uses a thick wood material (I think it is a composite of some kind). PAP uses metal bracing to reinforce their baffle panels.

My open baffle speakers (based on GR-Research designs) use a separate enclosure for the woofers to handle the bottom three octaves, built with 1.5" high quality MDF. The second enclosure handles everything else and is built using a composite material.

When @ricevs (Ric Schultz) was making open baffle/dipole speakers and subs (employing the Rythmik Audio/GR Research Sub DIY kit) he made his baffles by gluing together three layers of 3/4" MDF, using Green Glue iirc.

One great method for creating very non-resonant baffles is to put a layer of ASC Wall Damp material between two layers of MDF or Baltic Birch Plywood.