LABORATORY TEST REPORT

Newport Test Labs first tested the KEF KC62’s frequency response using a near-field technique for all settings of the subwoofer’s equalisation control, at both maximum and minimum settings of the crossover control, the results of which are shown in Graph 1.

You can see that the flattest and most extended response is returned when the KEF KC62 is set for Room Eq, with the maximum crossover setting being shown by the black trace and the minimum setting by the red trace. You can see that overall, at the maximum setting, the KC62’s response extends from 17Hz to 150kHz ±4dB and between about 23Hz and 100Hz, it’s even more linear, at around ±2dB. These are truly excellent results.

When looking at the other traces on this graph (as well as the traces on Graphs 2 and 3) you need to bear in mind that these traces were measured with the subwoofer in the centre of a room, not in the positions it would be for the relevant equalisation settings. This means that for the ‘Wall Eq’ setting (the green and blue traces), the offset downwards in level that’s evident would be compensated for by the subwoofer’s output being boosted by the proximity of the wall, which KEF’s engineers calculate would elevate the traces to that of obtained in the Room Eq mode.

The same would be true of the Corner Eq (purple and blue traces) and the Cabinet Eq (dashed black and dashed red traces) modes.

The traces on Graph 1 that have a completely different appearance are those for the Apartment Eq mode (dashed green and dashed light blue traces) where the low-frequency response has obviously been deliberately rolled off far sooner than for all the other Eq settings.

Graphs 2 and 3 are subsets of the full set of frequency responses that are shown in Graph 1, so you can see the effect of the equalisation more clearly, with Graph 2 showing a set with the crossover at its maximum setting, and Graph 3 a set with the crossover at its minimum setting.

In Graph 4, Newport Test Labs used a pink noise test signal to measure the KEF KC62’s far-field in-room response, using the Room Eq mode and maximum (black trace) and minimum (red trace) settings of the crossover control. Unlike the other frequency responses, where the subwoofer had to reproduce just a single frequency for each graph point, this test requires the subwoofer to reproduce all frequencies across its pass band simultaneously and is thus an extreme test. Nonetheless you can see the KC62 still delivered excellent performance, with the response at the maximum crossover setting extending from 35Hz to 180Hz ±4dB and, with the crossover set at minimum, from 15Hz to 100Hz ±4dB. The increased linearity and extension when the crossover is at minimum reflects the reduced workload on the drivers due to the crossover network reducing the level of the high-frequencies.

The by-pass frequency response of the KEF KC62 is shown in Graph 5 and you can see that it’s exceedingly flat across the audio band, being just 0.5dB down at 5Hz and about 0.18dB down at 20kHz. However, it appears there is a low-pass filter built in that attenuates frequencies above around 22kHz.

The effect of the KEF KC62’s high-pass filter is shown in Graph 6, with the bypass response without any filtering depicted by the yellow trace. The effect of the filter is shown for all its settings: 40Hz (purple), 60Hz (light orange), 80Hz (light grey), 100Hz (light blue), and 120Hz (black). As you can see, it’s a beautifully designed ‘classic’ high-pass filter.

Newport Test Labs measured the maximum volume level of the KEF KC62 with pink noise test signals as being 98dBSPL at one metre, which was a limit imposed by the KC62’s in-built protection system due to the wideband nature of the test signal. When using a single 80Hz test tone, the KEF KC62 was able to deliver 106dBSPL at the same distance, which is 1dB better than specification. Steve Holding