Table 1. Sound absorption coefficients at 250, 500, 1,000, and 2,000 Hz frequency, and NRC for different filling heights of Acanthopanax senticosus wastes inside the impedance tubes

Filling height (mm)	Sound absorption coefficient (Hz)				NRC
	250	500	1,000	2,000
40	0.103	0.124	0.226	0.402	0.214
60	0.114	0.169	0.393	0.391	0.267
80	0.134	0.244	0.486	0.599	0.366
100	0.161	0.367	0.416	0.841	0.446

NRC: noise reduction coefficient.