PS,
The frequency response of any open baffle may derived using the mathematical formulas contained in:
A Model of Open-Baffle Loudspeakers 5025 (H-6)
Juha Backman
Nokia Mobile Phones
FIN-00045 Nokia Group, Finland
Presented at
the 107th Convention
1999 September 24-27
New York
This is available from the AES Website for a modest cost. The calculations are left to the august reader.
For those wishing to take my word for it (I have this paper here), Mr. Backman illustrates a -3db point of around 100Hz for a baffle 30 X 40cm in dimension (this assumes a driver with a perfectly flat frequency response and the baffle in free space), which scales lineary with baffle circumference.
A Spreadsheet based on a simplified version of Mr Backmans mathematics was published by me in the public domain a while back, which combines driver response, baffle response and boundary effects, a google search for xlbaffle.xls will reveal find this easily.
Ciao T