A method of making an acoustic device having a diaphragm having an area and having an operating frequency range, the method comprising: choosing diaphragm parameters such that it has resonant modes in the operating frequency range; coupling a plurality of electro-mechanical transducers to the diaphragm to exchange energy with the diaphragm; selecting a number of resonant modes; selecting positions and a mechanical impedance of the transducers so that a net transverse modal velocity being quantified by a root mean square (rms) transverse displacement tends substantially to zero over the area where a relative mean displacement is less than 25% of a rms transverse velocity to thereby balance the selected resonant modes in the operating frequency range; characterised in that the method includes: selecting a shape or an aspect ratio of the diaphragm so that there are a plurality of nodal grouped locations at or around which nodal lines of the selected resonant modes are clustered, some of said nodal lines intersecting within an area smaller than a drive part coupling of the transducers; mounting each transducer at one of the plurality of the nodal grouped locations; the balancing of the selected resonant bending wave modes is achieved substantially by the positioning and mechanical impedance of the transducers alone such that, for the selected resonant modes and starting with a high order mode, all succeeding lower order modes are dealt with as a group; and mounting the diaphragm so that it acts like a free plate where support and suspension components for the diaphragm are so light in action that they do not interfere with a required radiation balanced mode behaviour. choosing diaphragm parameters such that it has resonant modes in the operating frequency range; coupling a plurality of electro-mechanical transducers to the diaphragm to exchange energy with the diaphragm; selecting a number of resonant modes; selecting positions and a mechanical impedance of the transducers so that a net transverse modal velocity being quantified by a root mean square (rms) transverse displacement tends substantially to zero over the area where a relative mean displacement is less than 25% of a rms transverse velocity to thereby balance the selected resonant modes in the operating frequency range; characterised in that the method includes: selecting a shape or an aspect ratio of the diaphragm so that there are a plurality of nodal grouped locations at or around which nodal lines of the selected resonant modes are clustered, some of said nodal lines intersecting within an area smaller than a drive part coupling of the transducers; mounting each transducer at one of the plurality of the nodal grouped locations; the balancing of the selected resonant bending wave modes is achieved substantially by the positioning and mechanical impedance of the transducers alone such that, for the selected resonant modes and starting with a high order mode, all succeeding lower order modes are dealt with as a group; and mounting the diaphragm so that it acts like a free plate where support and suspension components for the diaphragm are so light in action that they do not interfere with a required radiation balanced mode behaviour. selecting a shape or an aspect ratio of the diaphragm so that there are a plurality of nodal grouped locations at or around which nodal lines of the selected resonant modes are clustered, some of said nodal lines intersecting within an area smaller than a drive part coupling of the transducers; mounting each transducer at one of the plurality of the nodal grouped locations; the balancing of the selected resonant bending wave modes is achieved substantially by the positioning and mechanical impedance of the transducers alone such that, for the selected resonant modes and starting with a high order mode, all succeeding lower order modes are dealt with as a group; and mounting the diaphragm so that it acts like a free plate where support and suspension components for the diaphragm are so light in action that they do not interfere with a required radiation balanced mode behaviour.