1. ASTM standard: Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones and a Digital Frequency Analysis System. ASTM standard E1050-19
2. ASTM standard: Standard test method for measurement of normal incidence sound transmission of acoustical materials based on the transfer matrix method. ASTM standard E2611-09
3. Directorate General of Mines Safety, Ministry of Labour (1975). Protection of workers against noise and vibration in the working environment. Technical Circular no. 18 of 1975. Dhanbad. India
4. Gelfand, S.: Essentials of Audiology. Thieme. p. 87. ISBN 978–1604061550. “hearing is most sensitive (i.e., the least amount of intensity is needed to reach threshold) in the 2000 to 5000 Hz range” (2011)
5. ISO Standard: Determination of sound absorption coefficient and impedance in impedance tubes-Part 2: Transfer-function method. ISO 10534–2 (1998)