Loudspeakers

'Our planar drivers', says Chris Brunhaver, PSA's Senior Loudspeaker Design Engineer, 'are "standing on the shoulders of giants". Learning from Infinity, my father (Richard Brunhaver) and David Graebener's planar magnetic driver work at Speakerlab in the 1990s and from my former colleague, Igor Levitsky, of Bohlender Graebener (BG), shaped our design approach.

Well-made planars, with their symmetrical magnet layout, resistive impedance, inherently high damping and superior decay performance side-step many causes of midrange distortion and break-up modes in traditional dynamic drivers'.

Nevertheless, Chris is acutely aware of the practical trade-offs in the design of 'real world' planar magnetic drivers. 'Certainly, we paid very careful attention to their assembly and mechanical damping at the diaphragm edges, as reflections and plate modes can cause narrow band buzzing and resonances.

'We use a proprietary corrugation for the planar film and a number of damping methods including adhesive tapes, Dupont Twaron fibre damping felt, and a reversed voice coil turn at the diaphragm's periphery. We also use acoustically resistive cloth screens very close to the diaphragm to damp the output around their fundamental resonance'.

Optimising sensitivity and treble response was also a priority. 'We use thin ultra-high strength N52 magnets', reveals Chris, 'and a phase plug design to minimise/tune the cavity resonance and the low pass filter behaviour formed by this front magnet structure'. PM