178
P. Cardei et al.
L eq (x 1 , x 2 , x 3 , L w , a, b)
= 10 · log
10
L eqZmax (x1,x2,x3,Lw,a,b)
10
+ 10
L eqZ min (x1,x2,x3,Lw,a,b)
10
+ 10
L eqXmax (x1,x2,x3,Lw,a,b)
10
+ 10
L eqX min (x1,x2,x3,Lw,a,b)
10
+ 10
L eqYmax (x1,x2,x3,Lw,a,b)
10
+ 10
L eqY min (x1,x2,x3,Lw,a,b)
10
(3)
The noise level given by the expression (3) is a three-dimensional static field
(variables x 1 , x 2 , x 3 ), dependent on three parameters (L w , a, b). The three parameters
will be determined by minimizing the function built according to the method of least
squares, using the measurements made (a procedure for calibration of the formula (3)
for a certain machine). For the measurement data (see Table 1), the following values
of the noise level parameters are obtained: L w = 100.000 dB, a = 15.725 dB, b =
17.000 dB. In order to obtain these values, the next functional was minimized:
Table 1 Measurement results for the acoustic field generated by the tractor
x 1 (m)
x 2 (m)
x 3 (m)
Leq (dB)
Observations
0.50
0.22
0.00
93.50
Tractor engine
0.00
0.22
0.00
99.10
Tractor engine
−0.50
0.22
0.00
100.50
Tractor engine
0.00
0.23
0.71
93.50
Exhaust pipe, mid
−2.30
0.32
1.30
91.80
Exhaust pipe, up
−2.30
0.00
0.00
83.70
Rear tractor, centre
−1.30
0.15
1.40
73.40
Driver’s ear
11.50
0.00
1.25
69.40
Front tractor
−12.50
0.00
1.25
64.40
Rear tractor
0.00
6.00
1.25
73.60
Right side tractor
0.00
6.00
1.25
75.00
Left side tractor
−3.77
2.00
−0.58
74.60
Worker level ear a
−3.77
0.00
−0.58
75.90
Worker level ear a
−3.77
−2.00
−0.58
78.40
Worker level ear a
−3.80
2.00
0.76
73.80
Worker level ear b
−3.80
1.00
0.76
75.60
Worker level ear b
−3.80
−1.00
0.76
76.20
Worker level ear b
−3.80
−2.00
0.76
74.20
Worker level ear b
−3.35
0.75
0.76
75.30
Worker level ear c
−3.35
−0.75
0.76
74.90
Worker level ear c
a Cucumber harvester
b MPM 4
c MPF1