The need for quantitative information on piping noise reduction obtainable by various devices such as flexible couplings, isolating hangers, or pipe‐wall damping treatments led to the development of a test setup for making the desired measurements. The setup consisted of a long, straight length of pipe in which the test device was installed. Broad‐band noise was introduced into the water or the pipe wall at one end of the system. Pipe‐wall vibrations were detected by accelerometers and were analyzed by means of an octave filter set. It was found that flexible couplings could be rated in terms of the difference in vibration levels at two points on opposite sides of the coupling. Differences of 20 to 45 db were found for some couplings at high frequencies and at atmospheric pressure. The effectiveness of damping treatments which extended along a considerable length of the pipe ranged from 0.2 to 0.5 db per foot. The isolation provided by resilient hangers was measured by comparing pipe‐wall and support structure vibrations, but test results must be used with caution since mounting conditions found in practical installations often vary widely from those provided by the test set‐up.