Loudspeakers

A founding Perlisten principle, though not one it shouts from the rooftops, is its management of low frequency group delay and, by inference, bass phase distortion. There’s a body of (subjective) opinion that cites group delay – the frequency-dependent time delay associated with all filters – as a blot on the sound quality landscape, influencing everything from perceived transient attack, musical ‘smoothness’ and listener fatigue. Linear-phase filters introduce a time delay that is constant with frequency but minimum-phase filters, including a loudspeaker’s bass roll-off, have a non-constant time delay – a phase distortion – that modifies the shape of complex (multi-frequency) signal waveforms.

Sealed-box designs have low frequency group delay, but this distortion is exacerbated by the higher 4th-order roll-off of reflex-loaded cabinets. Without resorting to active drive, and complex DSP, Perlisten’s ‘passive’ approach means pushing its low frequency tuning, and associated group delay, down to as low a frequency as possible. In the A4t this is achieved with a trio of 215mm bass drivers, mounted very closely to minimise combing, that are ‘tuned’ to a sub-20Hz [see PM's Lab Report] via a deep, grille-covered channel in the base of the enclosure. PM