Testing the active minimization of the total radiated sound power of a vibrating plate

Abstract

This paper presents an experimental investigation of an Active-Noise-Control (ANC) system for reducing unwanted so-called primary sound by destructive interference with sound generated by so-called secondary sources (loudspeakers). In this work the primary source is a vibrating simply supported plate which is radiating sound into the free field. The loudspeakers are placed in front of the plate. The ANC-system utilizes the measured signals of the primary accelerometers which are placed on the surface of the plate. The number of the primary accelerometers corresponds to the number of the loudspeakers. Also, one secondary accelerometer is fixed onto each loudspeaker cone. Furthermore, a microphone in front of each loudspeaker measures the near field sound pressure. An adaptive feed-forward-controller is used to calculate the optimal control signal for each secondary source. The optimal control is achieved by minimizing the radiated active sound intensity in front of each loudspeaker in order to minimize the total radiated sound power of the primary and secondary sources. The ANC-system is tested in different configurations with one or two loudspeakers in front of the plate. Also, an approach for the system calibration is developed to compensate the phase deviation between the true and the measured sound intensity.

Comparing of the analytical investigation with the FEM simulation for minimizing the total radiated sound from a vibrating plate

“…6 at 64 Hz) in front of the plate results in a same amount of the minimized SWL. Hence, positioning one loudspeaker in front of the plate is sufficient when the plate vibrates with only one antinode [6].…”

“…The number and positions of the loudspeakers in front of the plate are determined by the class of the radiated mode of the vibrating plate. Therefore, a modal analysis is carried out for a free vibrating simply supported plate made of aluminium in order to define the number of the antinodes (m, n) involved on the surface of the plate associated with eigenfrequencies [6].…”

“…In this work, the effectiveness of the TASPM-approach in the active noise controller is studies for three different configurations. Figure 4 depicts the configurations schematically [6]. The number of the primary accelerometers, the secondary accelerometers and the microphones corresponds to the number of the utilized loudspeakers in each configuration.…”

“…To verify the results obtained from the analytical investigation [6], the results of the FEM investigations are exploited. The investigations are carried out at the frequencies ranged from 55 Hz to 200 with step frequency 5 Hz .…”

“…The analytical calculation of κ from Eq. 6 requires the analytical investigations of the transfer matrix of the secondary sources H pa (jω) which is given in [6] for a MIMO system as below:…”