How thick should the front baffle of speakers be?

I use 25mm Baltic Birch for every motorboard I build and if the area of the sides is large there too. Really tough, no outgassing or fear from water damage like MDF and no voids if you stay away from the Chinese stuff and use only real Baltic Birch. Reverberation happens more than people think and thicker plywood is a great answer. Build your cabinet right and all the bandaids for poor cabinets like expensive feet are not needed.

" wheres the proof "  Simonmoon is 100% right and that has been my experience too and measurable through REW and TrueRTA but you can't post results here to prove this because no pictures allowed.
  I had a set of La Scalas that had been damaged and I decided to replace the 18mm sides with 25mm Baltic Birch sides. You don't have to believe me but the perception of much lower bass was startling. What I was actually hearing though was bass without cabinet resonance masking it and it was a real eye opener. Since then everything I build with any area at all gets 25mm wood. Real honest wood and not MDF.

" 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. "
  That's interesting. The old Klipsch Chorus speakers used  1" poplar plywood for the front baffle and I always though that was because it was cheaper. You pick up pieces of differing types of plywood or MDF roughly the same size and tap on them and the range of sound is pretty large so what that guy says makes complete sense. Those old Chorus speakers are my favorite among the Forte, Heresy Cornwall and Chorus.