How thick should the front baffle of speakers be?

3/4" plywood didnt work just fine. Resonance is a bad thing. Think of the surface area of a large speaker cabinet much if not all of which is vibrating. 

   Hi, The speakers that I own (Sonist-"Concerto 4") have two inch thick poplar wood front baffles.    I talked with the designer (Randy Bankert) and he said he tried a bunch of different woods before settling with poplar as it was the best sounding to his ears.
   Instead of mounting the drivers on the outside ,he mounted them on the inside and beveled the wood to create a horn of sorts to help with dispersion. If you look at a picture of them you will see what I mean.
TISH

I've heard the Concerto 4 speakers at an audio show!

They are extremely good, for sure. When I heard them, knowing what I do about speaker cabinets, I made notice of their cabinet construction, and how that contributed to their sound quality. 

The rear mounting with beveled edges is a waveguide, which is a type of horn. 

More traditional horns, tend to be more concerned with gain as first priority, where waveguides tend to be concerned with controlling the pattern of dispersion as first priority. 

Whatever happened to those things you would stick to the sides of your speakers to deaden them? Did those pass into tweak history? (I don't really care) Note that my current speakers, Klipsch Heresy IIIs, tilt back so anything placed on the top just slides off. Keeps things from gathering there.

Randy Bankert passed away a number of years ago. His front panel design was copied from the Zingali speakers that he had previously represented. Like many importers the manufactures always expect more sales and are never completely satisfied with the sales of the importer.