We are greatly indebted to those who have rendered assistance for this edition, in particular to Leo Kärkkäinen whose help has been especially pertinent, Noel Lobo for his invaluable guidance in numerical matters, Enrico Pascucci for his many helpful suggestions regarding Chapter 8 and for performing anechoic measurements, Philip Trevelyan for his support and assistance in acoustical measurements, and Rory Stoney for providing impedance tube measurements on absorbent materials in a very short time. We also stand indebted to our wives, Anne Mellow and Gabriella Beranek for their support and enduring patience.

Many improvements and corrections included in the second edition were kindly suggested by: Stephen Bolser, Huiqun Deng, Mads Dyrholm, Alan Feinerman, James Heddle, Mattias Johansson, Bjørn Kolbrek, Joe Ladish, Siegfried Linkwitz, Sidsel Marie Nørholm, Mark Thompson, Paolo La Torraca, Luigi Vigone, and Wojciech Rdzanek.