A flat panel loudspeaker for mounting in a mounting surface and comprising: a resonant panel insertable into a circular opening in the mounting surface and having a front surface having an outer boundary formed to be circular, the front surface to face outwardly in the mounting surface when the flat panel loudspeaker is mounted in the mounting surface, and the resonant panel further having a rear surface opposite the front surface; an exciter located at an axial centre of the circular resonant panel and coupled to the rear surface of the resonant panel to cause the resonant panel to vibrate, on operation of the exciter, to generate sound; a support frame for mounting in the mounting surface and having the rear surface of the resonant panel fixed thereto around the whole of the outer boundary of the resonant panel, such that when mounted in the mounting surface and when the resonant panel is caused by the exciter to vibrate on operation of the exciter, the outer boundary of the resonant panel is fixed relative to the mounting surface; and mode distribution means configured to induce, in use, non-circularly symmetric distortion of natural modes of oscillation of the resonant panel in response to operation of the exciter in an assembly of the resonant panel, the support frame and the exciter absent the mode distribution means, wherein the non-circularly symmetric distortion of the natural modes of oscillation of the resonant panel is defined by there being no circular symmetry in the distortion of the natural modes of oscillation of the resonant panel, wherein the mode distribution means comprises one or more components (51, 52, 53, 54) coupled to the resonant panel substantially just outside the exciter to add weight thereto to induce the distortion in the natural modes of resonant oscillation of the resonant panel in the assembly of the resonant panel, the support frame and the exciter in response to operation of the exciter. a resonant panel insertable into a circular opening in the mounting surface and having a front surface having an outer boundary formed to be circular, the front surface to face outwardly in the mounting surface when the flat panel loudspeaker is mounted in the mounting surface, and the resonant panel further having a rear surface opposite the front surface; an exciter located at an axial centre of the circular resonant panel and coupled to the rear surface of the resonant panel to cause the resonant panel to vibrate, on operation of the exciter, to generate sound; a support frame for mounting in the mounting surface and having the rear surface of the resonant panel fixed thereto around the whole of the outer boundary of the resonant panel, such that when mounted in the mounting surface and when the resonant panel is caused by the exciter to vibrate on operation of the exciter, the outer boundary of the resonant panel is fixed relative to the mounting surface; and mode distribution means configured to induce, in use, non-circularly symmetric distortion of natural modes of oscillation of the resonant panel in response to operation of the exciter in an assembly of the resonant panel, the support frame and the exciter absent the mode distribution means, wherein the non-circularly symmetric distortion of the natural modes of oscillation of the resonant panel is defined by there being no circular symmetry in the distortion of the natural modes of oscillation of the resonant panel, wherein the mode distribution means comprises one or more components (51, 52, 53, 54) coupled to the resonant panel substantially just outside the exciter to add weight thereto to induce the distortion in the natural modes of resonant oscillation of the resonant panel in the assembly of the resonant panel, the support frame and the exciter in response to operation of the exciter.