Noise Characteristics; Sound Composition - TCL TAC-07CS Service Manual

9. Noise characteristics

9.1. Sound composition :

The physical amount of sound is expressed in a logarithm and the sound level (dB) is calculated by simple
addition or subtraction.
Lc, the sum of n sounds L1, L2, ....Ln (dB) is calculated by the following equation.
Lc = 10 log (10 L1 /10 + 10
Generally, the noise level by composing two sounds of L1 (dB) and L2 (dB) is found in the following figure.
3.0
2.8
2.4
2.0
1.5
∆L
1.2
0.8
0.4
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
L L
1
(Figure: Calculation chart of dB composition)
When complex sound (measured sound) is L3(dB) and
background noise is L2(dB), the object sound L1 (dB) is
calculated as follows.
L1= L3 + 10 log (1-10
= L3 - ∆L'(L3 ≥ L2)
Example) While machine sound is measured 65dB, the noise at
machine stopping is 63dB.
Accordingly the noise level of machine itself is
L3-L2 = 65-63 = 2
In the right figure, ∆L' ¡ 4.33
Noise level of machine is
L1 = L3-∆L' = 65-4.33 ¡ 60.7
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L2 /10 + ..... 10 Ln
Example) When composing 60dB and 57dB sounds, the level of
(dB)
2
-(L3-L2) /10)
/10)
complex sound is calculated as follows.
L1-L2=60-57=3
n the left figure, ∆L¡ 1.7
Complex sound level : L3 = L1+∆L
L3 = L1+10log(1+10
= L1+∆L(L1≥L2)
The equation is applied to the sound decomposition method.
(Figure: Calculation chart of dB decomposition)
19
= 60+1.7=61.7dB
-(L1-L2) /10)
7
6.87
6
5
4.33
4
∆L'
3.00
3
2.19
2
1.65
1.25
1
0
1 2 3 4 5 6 7
(dB)
L L
3 2
0.96
0.75
0.58
0.36
0.46
0.26
8 9 10 11 12