Table 1. Sound absorption coefficients and NRC of peanut shells

Height	Sound absorption coefficient @ frequency				NRC
Height	250 Hz	500 Hz	1,000 Hz	2,000 Hz	NRC
30 mm	0.039	0.069	0.172	0.638	0.230
30 mm	(0.001)	(0.001)	(0.001)	(0.002)	(0.001)
60 mm	0.079	0.190	0.604	0.859	0.433
60 mm	(0.002)	(0.001)	(0.001)	(0.001)	(0.001)
90 mm	0.172	0.609	0.500	0.849	0.533
90 mm	(0.001)	(0.001)	(0.001)	(0.002)	(0.001)

Parentheses are standard deviation.
NRC: noise reduction coefficient.