声学基本概念 - 图文 

Two Sound Sources

Lp1= X dB

Lp2= X dB

Lp1+ Lp2= X + 3 dBBA 7666-11, 26

Addition of dB Levels

L+dB3Example:L1L2?LL+Lt=55 dB=51 dB=4 dB=1.4 dB=55 + 1.4 = 56.4 dB21.4 dB

100

4 dB

BA 7666-11, 27860512/2

51015

?LdB

Subtraction of Noise LevelsLS+N[dB]LN[dB]BA 7666-11, 28

Subtraction of dB Levels

L?dB654321

123456

7

8910LS ~ LS+N

?LdB

Ex:LS+NLN?LL?LS=60 dB=53 dB=7 dB=1 dB=60 ?1 = 59 dB??

BA 7666-11, 29

?

Addition of many dB values

Addition of sound levels :L1+ L2..... + LN = ?

For L1= L2= L3..... = LN

10 log N1210864200

BA 7666-11, 30

LTotal=L1+10logN

Examples:

N = 2: LTotal = L1 + 3 dBN = 10: LTotal = L1 + 10 dB

51015

N