Loudspeakers

We're becoming habituated to Klipsch making enthusiastic claims for its speakers' sensitivity (repeated in online 'reviews'), and the RP-600M fits the mould. Klipsch says it generates 96dB SPL at 1m for 2.83V input – which, if true, would be an outstanding result – but our tests recorded exactly 89dB, averaged for the pair, on pink noise. This is still a good result, but the 7dB gap to Klipsch's specification is a vast one. In part the sensitivity is achieved through the use of low impedance. Despite Klipsch's vague '8 ohms compatible' specification, this is a 4ohm design. We measured a minimum modulus of 3.4ohm and sufficiently high impedance phase angles to drop the EPDR (equivalent peak dissipation resistance) to a minimum of 1.8ohm at 129Hz. This makes the RP-600M averagely difficult to drive for a modern loudspeaker, but not as easy as the crib sheet implies.

Forward frequency response was measured at 1m on the axis of the horn-loaded tweeter [see Graph 1, below]. The traces are very uneven – to the tune of L/R response errors of ±5.8dB and ±5.9dB, respectively. A wide suckout between 1kHz and 2.5kHz, and a high treble peak at 17kHz, are principally responsible, the former in particular surely colouring the RP-600M's sound. A pair matching error of ±0.7dB over the same 200Hz-20kHz frequency range is a much better result. Also creditable is the bass extension of 40Hz (–6dB re. 200Hz), determined by diffraction-corrected nearfield measurement. LF output shelves down below 140Hz before falling off at 24dB per octave below 45Hz. Despite the horn-loaded tweeter, the CSD waterfall [Graph 2, below] is mostly clean in the treble, but the 17kHz peak suppresses the level of modes at 2-5kHz. KH