Sound field control apparatus and method for controlling sound field

A sound field control apparatus comprising:

• at least two main microphones arranged at points of measurement in a space;
• for each main microphone of the at least two main microphones, at least two sub microphones associated with the main microphone arranged such that the at least two sub microphones are placed in different axis directions about the main microphone that the at least two sub microphones are associated with, where each of the sub microphones is not a main microphone;
• a filtering unit configured to filter an input audio signal;
• at least one speaker configured to output the audio signal filtered by the filtering unit;
• and
• a filter coefficient calculating unit in communication with the filtering unit, the filter coefficient calculating unit configured to calculate a filter coefficient, used to control sound pressure levels and air particle velocities of the audio signal output from the speaker in the space, for the filtering unit on the basis of a sound pressure level detected by each main microphone and the difference between the sound pressure level detected by the main microphone and that detected by each of the corresponding sub microphones;
• wherein the filter coefficient calculating unit is configured to obtain an acoustic system transfer function of sound pressure level on the basis of a sound pressure level detected by each main microphone, to obtain a sound pressure gradient by dividing a difference between the sound pressure level detected by the main microphone and that detected by each of the corresponding sub microphones by a distance between the main microphone and the sub microphone, to convert the sound pressure gradients into air particle velocities to obtain acoustic system transfer functions of air particle velocity, and to calculate the filter coefficient on the basis of the acoustic system transfer function of sound pressure level and the acoustic system transfer functions of air particle velocity.