Table 2. The sound absorption coefficient values of samples

No.	Conditions	Sound absorption coefficient (α)			SAA	NRC
		Low frequency (Hz) 63–1 k	Middle frequency (Hz) 1 k–3 k	High frequency (Hz) 3 k–6 k
1	SB100-A	0.30	0.48	0.49	0.37	0.43
2	SB100-B	0.33	0.50	0.51	0.40	0.46
3	SB100-C	0.36	0.53	0.52	0.42	0.50
4	SB75-CS25-A	0.30	0.50	0.48	0.37	0.45
5	SB75-CS25-B	0.35	0.52	0.52	0.42	0.49
6	SB75-CS25-C	0.38	0.55	0.55	0.44	0.53
7	SB50-CS50-A	0.30	0.51	0.51	0.37	0.46
8	SB50-CS50-B	0.33	0.57	0.58	0.42	0.51
9	SB50-CS50-C	0.36	0.61	0.60	0.45	0.55

SAA: sound absorption coefficient average, NRC: noise reduction coefficient, SB: sugarcane bagasse, CS: coffee silver skin.