1. Special Fantoni version http://www.4akustik.su/calculator_fantoni_rt60_eng.html (only Fantoni absorbers in data base)2. General version http://www.acoustic.ua/forms/Reverberation-RT60.html (more absorbers in data base)3. Description http://www.acoustic.ua/recommendations/800#104. Sound absorption coefficients table http://www.acoustic.ua/st/web_absorption_data_eng.pdf