The normal incidence sound transmission loss (nSTL) characterizes the sound insulation performance of the tested sample when it is excited by a normal incidence acoustical wave. It is mainly useful to rank the performance of sound barriers.
Equipment: Impedance tube with transmission
Standard: ASTM E2611, ASTM E1050, ISO10534-2
Method: Three or four microphone transmission tube and the transfer-function method [1,2]
Property: nSTL – normal incidence sound transmission loss (dB)
Tested frequency range
– Small impedance tube (29 mm diameter): 200 to 6600 Hz
– Medium impedance tube (44.44 mm diameter): 100 to 4300 Hz
– Large impedance tube (100 mm diameter): 35 to 1900 Hz
 Y. Salissou and R. Panneton, “A general wave decomposition formula for the measurement of normal incidence sound transmission loss in impedance tube,” J. Acoust. Soc. Am. 125(4), 2083-2090 (2009).
 Y. Salissou, O. Doutres, and R. Panneton, “Complement to standard method for measuring normal incidence sound transmission loss with three microphones,” J. Acoust. Soc. Am. 131(3), EL216-EL222.