Exam, acoustic part in MT9473, 20090224
Nr 1
The sound pressure level is measured in octave bands at a point 5m from a machine:
f [Hz] 63 125 250 500 1000 2000 4000 8000
Lp [dB] 73 83 91 84 86 85 80 68
Determine the sound level 150 m from the machine in the same direction as the first
measurement point. (2p)
Nr 2
A rotating machine with mass 550 kg is driven with 2940 r/min. It is vibration
isolated by four springs on a stiff foundation. Dimension the springs so that the
vibrations are attenuated (damped) with 15 dB. (2p)
Nr 3
A sound source with sound power level 93 dBA is located on the floor in a room. The
measured sound level is 83 dBA 3m from the sound source. Estimate the sound level
in the room if the room constant is doubled. (2p)
Nr 4
According to the manufacturer, a machine has the following octave band sound power
levels:
f [Hz] 63 125 250 500 1000 2000 4000 8000
Lw [dB] 85 102 100 98 95 87 65 53
The requirement is that the sound level may not exceed 35 dBA, 200 m from the
machine. Design a suitable housing according to VDI 2711. The insertion loss for the
various classes of VDI2711 is depicted in the figure below. There are no reflections
from buildings etc. (2p)
