Bang & Olufsen Beovox CX50 Loudspeaker Lab Report

Lab Report

B&O's smallest loudspeaker – just 210mm tall and deep and with a mere 2 litre internal volume – was never going to raise the rafters but it still punches above its, er, weight (3.5kg). Rated at 81dB, the CX50's sensitivity is complicated by the uptilted and rather lumpy forward response [see Graph 1], although it seems that B&O was being slightly conservative – our tests showing 82.6dB/1kHz and 83.8dB (500Hz-8kHz) as more representative. Low frequency extension is necessarily limited – just 120Hz (–6dB re. 200Hz) while the limited sensitivity means distortion is high at typ. 5-10% through bass/midrange at 90dB SPL.

One of our pair offered a far flatter and, I presume, more accurate/representative sub-2.5kHz response where the 80mm mid/bass unit takes over [black trace, Graph 1]. Above 2.5kHz the pair matching is still a poor 3.7dB while the response error (good sample) amounts to ±5.2dB, the peaks at 1.6kHz and 2.9kHz linked to cone breakup modes [see CSD waterfall, Graph 2]. The emphasis through presence/treble lends the CX50 something of a subjective 'edge' and while it dips –6dB at 12.7kHz (re. 10kHz) the high treble recovers again to yield a final –6dB extension of ~20kHz. Crucially, the inset grilles, and foam that surrounds the 25mm treble dome, are an integral part of the speaker design and have a marked influence over the uniformity of its mid/treble output [blue trace, Graph 1]. Finally, the CX50's nominal impedance was given as 6ohm and this fits well with the 5.7ohm minimum recorded at 7.5kHz – the speaker being 'toughest', though not especially tough, at HF where the maximum +45° phase angle coincides with a mild 9.5ohm at 20kHz. PM


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


Breakup modes in the 80mm cone are at 1.6kHz/2.9kHz with treble dome resonances thereafter

Sensitivity (SPL/1m/2.83V – 1kHz/Mean/IEC) 82.6dB / 83.8dB / 81.9dB
Impedance modulus: minimum & maximum (20Hz–20kHz) 5.7ohm @ 7.5kHz, 22.6ohm @ 68Hz
Impedance phase: minimum & maximum (20Hz–20kHz) –37° @ 152Hz, +45° @ 20kHz
Pair matching/Resp. error (200Hz–20kHz) 3.7dB/ ±5.2dB/±4.2dB
LF/HF extension (–6dB ref 200Hz/10kHz) 120Hz / 19.2kHz/21.4kHz
THD 100Hz/1kHz/10kHz (for 90dB SPL/1m) 9.5% / 6.5% / 0.7%
Dimensions (HWD) / Weight (each) 210x120x210mm / 3.5kg