1. Handbook of Noise Measurement;Peterson,1954
2. Elements of Acoustical Engineering;Olson,1947
3. Groom, D., Underwood, A. F., Bidwell, J. B., and Lindberg, E.: The Recording of Heart Sounds and Vibrations. I. Historical Review and Description of a New Electronic Direct Contact Vibration Pickup, Exper. Med. & Surg. In press.
4. Munson, W. A.: Bell Telephone Research Laboratories, Personal communication—letter dated April 18, 1955.