Loudspeakers

It isn't often these days that we encounter a speaker which is distinctly conservative in its sensitivity specification but the L100 Classic harks back to earlier times in more ways than one. JBL claims 90dB at 1m for 2.83V input, but we measured an even stronger 91.6dB on pink noise, which would be more than enough for others to claim 92dB. On the face of it JBL has not resorted to punishingly low impedance to achieve this – the L100 Classic is honestly specified as 4ohm nominal (no '8 ohms compatible' nonsense) and we measured a minimum impedance of 3.5ohm. Unfortunately its low frequency impedance phase angles are very high as a result of which the EPDR (equivalent peak dissipation resistance) dips to a low of 1.3ohm at 82Hz. In other words, this speaker does present a pretty tough (low frequency) amplifier load even for a modern design.

The forward frequency responses, measured on the tweeter axis with the HF and MF level controls set to 0dB, show peaks and dips of ±3.1dB and ±3.5dB respectively [see Graph 1]. The peak at 2kHz and plateau between 4kHz and 6kHz probably explain why, during the listening sessions, both controls were dialled back to 12 o'clock, which shelves down the output by a few dB above 700Hz. Pair matching was fair at ±1.1dB. Diffraction-corrected summed nearfield driver and port outputs show a bass response that's flat to 70Hz, rolling off with a roughly second-order slope immediately below before the full fourth-order roll-off kicks in at about 40Hz. The 'official' bass roll-off point is at 42Hz (–6dB re. 200Hz). Finally, the CSD waterfall [Graph 2] shows a tightly packed group of treble resonances from 4kHz to 8kHz. KH