KEF LS50 Meta Loudspeaker Lab Report

Lab Report

To ensure the validity of our comparisons, new samples of both the LS50 and LS50 Meta were tested 'back-to-back' under identical lab conditions. So, while the LS50's pair matching is within 1.3dB and response uniformity good to ±2.9dB and ±4.0dB [grey/orange traces, Graph 1] the new 'Meta' delivers an improved response flatness of ±2.1dB and ±2.2dB [black/red traces] with even tighter 0.5dB pair matching (all 20Hz-20kHz). The sharp Uni-Q tweeter breakup mode at 40.2kHz (+22dB re. 1kHz) cannot be avoided but this is still impressively out-of-band for an alloy dome [see interview sidebar, p61].

Sensitivity is rated at 85dB for both models but the LS50's boosted 2-6kHz band gives it an edge here, yielding 85.0dB versus 84.5dB for the LS50 Meta (averaged, 500Hz-8kHz). The new crossover also sees a change in the Meta's impedance/phase trend above 200Hz where there's a slightly tougher upper bass/midrange load. The LS50's modulus is <8ohm over a narrow 125Hz-630Hz [min. 4.09ohm/213Hz; grey trace, Graph 2], while the Meta is <8ohm over a broader 115Hz-980Hz [min. 3.65ohm/242Hz; black trace, Graph 2]. Swings in phase angle are largely unchanged at circa –60°/+50° but the Meta's load [red trace, Graph 2] is more reactive at midrange than bass freqs.

The –6dB bandpass of the LS50's mid/bass cone is 80-650Hz, that of the Meta a wider 72Hz-900Hz, though both ports remain tuned to a sharp and clean 50Hz (–6dB bandpass of 38-80Hz, LS50; 38-85Hz, Meta). This yields a steep 4th-order roll-off but usefully low extension of 42Hz for the 'standard' LS50 and a slightly deeper 40Hz for the Meta (both –6dB re. 200Hz). Note also the generally 'flatter' more uniform bass output of the Meta [green shaded area, Graph 1]. PM


Response inc. nearfield summed driver/port [green], corrected to 1m at 2.83V [yellow], ultrasonic [pink]. LS50 Meta, black/red; LS50 grey/orange


Impedance magnitude (black/grey) and phase (red/orange) for LS50 Meta and LS50, respectively

Sensitivity (SPL/1m/2.83V – 1kHz/Mean/IEC) 84.6dB / 84.6dB / 82.4dB
Impedance modulus: minimum & maximum (20Hz–20kHz) 3.65ohm @ 220Hz, 31ohm @ 93Hz
Impedance phase: minimum & maximum (20Hz–20kHz) –62° @ 110Hz, +48° @ 860Hz
Pair matching/Resp. error (200Hz–20kHz) 0.5dB/ ±2.2dB/±2.1dB
LF/HF extension (–6dB ref 200Hz/10kHz) 40Hz / 54kHz/59kHz
THD 100Hz/1kHz/10kHz (for 90dB SPL/1m) 1.2% / 0.2% / 0.7%
Dimensions (HWD) / Weight (each) 302x200x280mm / 7.8kg
Price £1000

GP Acoustics (UK) Ltd
Maidstone, Kent
Supplied by: GP Acoustics (UK) Ltd
01622 672 261