QUESTION:
Calculate the total sound pressure level caused by a combination of sounds with the following
SPL,s (a) 25db and 39db (b)60db+60db+60db
SOLUTION:
The sum level of sound pressures of non-coherent sound waves is
2
  p 2  p 2

 p2  p22  ...pn2 
  1    2   ...   pn  

L total  10 lg  1

10
lg
2







  pref   pref 
pref


 pref  

2
2
L1
 p 
 p 
As L1  10 lg  1    1   1010 , hence
 pref 
 pref 
L2
Ln
 L1

L total  10 lg 1010  10 10  ...  10 10 


L2
39
 L1

 25

a) L total  10 lg 1010  10 10   10 lg 10 10  10 10   39.17 dB




L1
L2
L3
60
60
60
60






b) L total  10 lg 1010  10 10  1010   10 lg 10 10  10 10  10 10   10 lg  3 10 10   64.77 dB






ANSWER:
a) 39.17 dB
b) 64.77 dB