An excellent book for an acoustic consultant or anyone trying to solve a problem in noise control. Bies and Hansen have gone through several editions with improvements and corrections that have fine tuned this book. (Edition one had a mistake in a valve noise equation 11.27, which has been corrected and the section expanded in edition four.) The section on instrumentation has been updated to include things like holography and beamforming. Silencer design is well covered. Fan and jet noise predictions are useful but somewhat over simplified. Noise metrics are well summarized. It is the first book I reach for when confronted with a new problem or to brush up on technology I haven't used for awhile.