Ivanov, N. I.; Malozemov, V. N.; Omel’chenko, A. V. On an extremal problem from technical acoustics. (English. Russian original) Zbl 1041.76554 Vestn. St. Petersbg. Univ., Math. 32, No. 4, 28-32 (1999); translation from Vestn. St-Peterbg. Univ., Ser. I, Mat. Mekh. Astron. 1999, No. 4, 34-38 (1999). MSC: 76Q05 Hydro- and aero-acoustics PDFBibTeX XMLCite \textit{N. I. Ivanov} et al., Vestn. St. Petersbg. Univ., Math. 32, No. 4, 28--32 (1999; Zbl 1041.76554); translation from Vestn. St-Peterbg. Univ., Ser. I, Mat. Mekh. Astron. 1999, No. 4, 34--38 (1999)