RDZANEK, W.J., and W.P. RDZANEK. “The Real Acoustic Power of a Planar Annular Membrane Radiation for Axially-Symmetric Free Vibrations”. Archives of Acoustics, vol. 22, no. 4, Jan. 2014, pp. 455-62, https://acoustics3.ippt.pan.pl/index.php/aa/article/view/969.