Grundfos Motor Book
9. Installation
# x x x { | } x z| |x{ ~ What to know about sound
Sound pressure from several sound sources Sound pressures from two sound sources are added according to according to the formula below.
Example: Lp1
LP total = 10 • log ( 10
10
Lp2
10
+ 10 )
45
10
50
10
LP total = 10 • log ( 10 + 10 ) = 51.19 Sound source 1: 45 dB (A) Sound source 2: 50 dB (A) 0 -5 -10 -15 -20 -25 -30 -35 100
Sound pressures from two sound sources are added
Sound pressure in relation to speed The sound pressure of a fan rises with the motor speed. The resulting sound pressure change can be estimated by means of the following formula ∆Lp = 50 • log
n2 dB (A) n1
Delta Lp is the sound pressure change resulting from a speed change from n1 to n2. The formula applies both to speed increase and speed reduction.
208 Grundfos Motor Book
90
80
70
60
50
25
The sound level decreases when the motor speed decreases