Rogers LS3/5a Classic Loudspeaker Lab Report

Lab Report

Rogers is unusual in quoting the sensitivity of its Classic to 0.5dB – but when a speaker is this insensitive, every half dB counts. The specification says 82.5dB SPL for 2.83V at 1m and our measured pink noise figure is reassuringly close at 82.3dB. This low figure is due in significant part to the high 15ohm nominal impedance. Although that doesn't quite square with our measured minimum of 7.9ohm, the Classic is unquestionably a high-impedance loudspeaker by today's standards. While this hurts its sensitivity, it makes the Classic easy to drive. Despite quite large low frequency impedance phase angles, the high modulus ensures that the EPDR (equivalent peak dissipation resistance) never falls below 4.2ohm/128Hz. There's a second dip to 4.3ohm/46Hz but no worthy amplifier will struggle driving this speaker.

The forward responses [Graph 1, below] were measured at 1m on the tweeter axis with the grille in place [red/black traces] as this should minimise reflection effects from the raised edge of the inset baffle. The notch at 6.5kHz is exaggerated once the grille is removed [grey trace]. The overall trend is flat and, while there are many undulations, errors are modest at ±3.4dB and ±3.3dB. Pair matching error over the same 200Hz-20kHz span is high at ±2.2dB but this is caused by a very narrow-band disparity at about 13kHz. Ignoring that, the matching error reduces to a fair ±1.2dB. Diffraction-corrected nearfield bass measurement shows a rising output as frequency falls to 145Hz, before the expected 2nd-order roll-off kicks-in below 100Hz. Bass extension is limited to 73Hz (–6dB re. 200Hz) but boundary gain can be exploited to improve the effective bass extension. The CSD waterfall [Graph 2, below] shows some treble resonances. KH


Resp. is essentially flat despite undulations. Removing the grille brings a notch in presence [grey]


Small cabinet is almost necessarily well-damped while driver modes are limited to the treble

Sensitivity (SPL/1m/2.83Vrms – Mean/IEC/Music) 83.1dB/82.3dB/82.2dB
Impedance modulus min/max (20Hz–20kHz) 7.9ohm @ 20Hz, 68.9ohm @ 90Hz
Impedance phase min/max (20Hz–20kHz) –55° @ 104Hz, 52° @ 76Hz
Pair matching/Response Error (200Hz–20kHz) ±2.2dB/ ±3.4dB/±3.3dB
LF/HF extension (–6dB ref 200Hz/10kHz) 73Hz / 33.4kHz/>40kHz
THD 100Hz/1kHz/10kHz (for 90dB SPL/1m) 1.7% / 0.5% / 0.9%
Dimensions (HWD) / Weight (Each) 305x190x165mm/5.4kg
Price £2750-£2799

Rogers International UK Ltd
Virginia Waters, Surrey
Supplied by: Rogers International UK Ltd
01344 844204