Solution for a 100 Hz noise problem with disc resonators

A transformer station could be found beside a Hungarian recreation area where the main noise sources are two shunt reactors. During the investigation, it was found that the shunt reactors' 100 Hz component exceeds the noise limitation at night time by more than 10 dB, as evaluated from the one-third octave spectrum at the receiver points. Near protected residential buildings at 300 m distance, night time noise levels were higher by 8-10 dB. Because the night time noise limit was 40 dB evaluated for half an hour, the environmental authority asked the operators to prepare an action plan. Earlier a 7.8 m high noise barrier was constructed around one of the noise sources, but the noise levels were further above the limits.After detailed noise evaluations, by conscious design - analyzing noise emission, investigating and analyzing directivity, noise mapping - several solutions were worked out. From the mitigation measures, the 100 Hz disc resonator was considered appropriate for the noise reduction at the affected area. In our presentation the planned disc resonator's "laboratorial" evaluation is shown in detail. After the construction of the planned noise reducer equipments, the noise measurements certified the needed noise reduction effect of the additional elements.