PMC twenty5.26i Loudspeaker Lab Report

Lab Report

Despite enhancements to the crossover and change of tweeter, PMC has retained the conservative 86dB sensitivity rating of its previous twenty5 flagship and, refreshingly, this is bang on the money with 86.2dB/2.83V achieved at 1kHz and 85.7dB averaged across a representative 500Hz-8kHz. The resulting responses for the review pair [Graph 1, below] show a rising treble output, and minor resonances [Graph 2], though this can be 'tempered' by listening a little off-axis. We've also seen a dip in output at 2kHz-4kHz before, but the ~3dB loss at 2.7kHz is relatively minor in this revised floorstander, these two features resulting in response errors of ±5.1dB and ±4.6dB, respectively. Adding the grille brings further unevenness to the presence band [blue trace, Graph 1] but the pair matching between our two samples over the same 200Hz-20kHz was impressively tight at ±0.7dB. Bass extension is a useful 38Hz (–6dB re. 200Hz), the two 'Laminair' vents actually a single aperture for a transmission line that peaks at a high 86Hz – coinciding with a slight notch in the bass driver output [green shaded area, Graph 1]. Minor resonances in the line were detected at 160Hz and 260Hz.

The modest sensitivity is achieved via a slightly tougher load than might have been expected (or suggested by PMC's nominal 8ohm rating) thanks to dips of 3.9ohm/116Hz and 4.7ohm/3.1kHz although the phase angles are within ±20o here. The biggest swoops in phase angle of +34o/3.8kHz and a significant –69o/60Hz occur at 7.0ohm and 10.5ohm, respectively, but these should not cause any partnering amplifier, of comparable quality, pause for thought. PM


Response inc. nearfield summed driver/port [green], freefield corrected to 1m at 2.83V [yellow], ultrasonic [pink]. Left, black; right, red; w. grille, blue


Major modes decay quite quickly, with just a suggestion of mid and treble driver resonances

Sensitivity (SPL/1m/2.83V – 1kHz/Mean/IEC) 86.2dB / 85.7dB / 84.0dB
Impedance modulus: minimum & maximum (20Hz–20kHz) 3.9ohm @ 116Hz, 30ohm @ 48Hz
Impedance phase: minimum & maximum (20Hz–20kHz) –69° @ 60Hz, 34° @ 3.8kHz
Pair matching/Resp. error (200Hz–20kHz) 0.7dB/ ±5.1dB/±4.6dB
LF/HF extension (–6dB ref 200Hz/10kHz) 38Hz / 28.2kHz/29.9kHz
THD 100Hz/1kHz/10kHz (for 90dB SPL/1m) 1.2% / 0.8% / 0.6%
Dimensions (HWD) / Weight (each) 1040x192x439mm / 25kg
Price £8495-£8995

The Professional Monitor Company Ltd
Supplied by: PMC Ltd
01767 686300