TY  - RPRT
TI  - Letter Circular 870: sound absorption coefficients of the more common acoustic materials (supersedes Letter Circular 714 and 715)
PY  - 1947
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 870
DO  - 10.6028/NBS.LCIRC.870
ER  -