Aktiv bullerdämpning i ventilationssystem
Active headsets have been on the market for years and now it is time for
something else to enter the stage. The technology of active noise reduction can
for exmple also be used in ventilation systems for reducing ventilation noise.
An active control system principally consists of four important components,
namely the downstream error microphone, the upstream detection or reference
microphone, the digital signal processor (DSP) and a loudspeaker.
The upstream reference microphone listen to the primary ventilation noise and
sends it to the DSP which makes a phase shift to the signal and sends it to the
loudspeaker. The loudspeaker sends out the opposite waveform of the incoming
one and reduce the primary ventilation noise. To adjust the sound radrated from
the loudspeaker so low reidual soundlevel is obtained a downstream error
microphone is used. The residual sound is a sum of the primary ventilation
noise and the secondary sound generated by the loudspeaker.
In noice reduction systems today there are not many systems that use the active
technology. Passive silencers have low noise attenuation at low frequencies,
approximately under 250 Hz, and that is why the active technology should be
used. The aim with a silencer based on active noise control is to improve the
reduction of the low frequency noise below 250 Hz.
In this project we also have a passive component that reduce the higher
frequencies. The active control system should make the system better in the low
frequency range.
The use of both active and passive noise reduction at the same time makes an
even better system and the goal with this work was to implement a system with
high performance to a low cost.