Systems List › KRK Systems › 12S2
NotesMeasurements of the KRK 12S2 were taken with the controls in the following positions. Volume Max, Polarity zero, Input sensitivity High.
The first set of measurements taken are the frequency response measurements with settings of the low pass filter. The crossover only has 4 settings: 50 ,60, 70 and 80Hz. No matter what setting the crossover is set at we can see that the 12S2 has a dramatic roll off above 70Hz. Even with the crossover set for 80Hz the output is down by 6dB by 80Hz and 12dB by 100Hz. Even more troubling is that the output changes dramatically depending on the setting. Switching from an 80Hz setting to a 70Hz setting drops the overall output by almost 9dB! Switching from 70Hz to 60Hz drops the output by another 10dB! Overall the output difference between the 50Hz setting and the 80Hz setting is a whopping 22dB! I tried every input type and there is no way to bypass the crossover or this effect. Regardless of the crossover setting the response isn’t very flat. The flattest setting is 50Hz where the response manages to stay within a 6dB window from 28-75Hz, but there isn’t too much difference between the settings. 80Hz offers the most upper frequency bandwidth by a small amount, with a 35-78Hz range falling within a 6dB window, so it was used for testing. The response shape of the 12S2 appears to be due in part to some inductance effects in the driver and perhaps a high Qts causing a peaking in the response near 50-60hz. The undefeatable low pass filter is combining with this to roll off the top end and further peak the response.
The group delay measurement indicates that the delay hovers around 1 cycle or a bit more below 60Hz. This may or may not cause anything audible. The waterfall decay does not show anything of note however. The output decays by 20 to 30dB quite quickly.
The long term output testing proceeds uneventfully from the 90dB through the 110dB nominal sweep where the output has just started to compress but is still 1dB or less. The 115dB sweep caused some distress noise from the subwoofer due to high excursion from the driver and possibly amplifier limiting or clipping. Compression of the output starts to be significant at 1 to 3dB over the 25-100Hz bandwidth. Increasing the output demands another 5dB beyond this puts the subwoofer at maximum output over the whole bandwidth and causes a lot of distortion from the driver where excursion was high, but otherwise the system took it in stride and did not blow up or otherwise damage itself. Since the 12S2 was nearly at its maximum output during the previous measurement the 120dB nominal sweep indicates massive output compression of 4 to 8dB over most of the bandwidth. A repeat 100dB sweep indicated that there was some heat built up in the driver and a temporary loss of about 1dB in output. During the loudest measurement taken the output reaches about 100dB by 26.5Hz, 105dB by 32.5Hz, 110dB at 42.5Hz and a maximum of 114.4dB at 52Hz.
Distortion results captured at the same drive levels as the long term output measurements are a mixed bag. In general the overall THD from 35 to 200Hz is quite acceptable. Distortion below 35Hz grows very quickly and rapidly goes beyond 20%. During the nominally 110dB sweep the THD stays below 7% from 36-200Hz. The nominally 115dB sweep causes THD to increase a bit, but it still stays below 11.5% above 35Hz. The loudest 120dB measurement does cause much more output from the 12S2 except at the frequency extremes. That being the case the overall THD doesn’t increase much. It remains below 15% above 34Hz. The harmonic makeup of the distortion is almost all H2. This is good since the 2nd harmonic is generally considered the least audible and most benign. Even the loudest 120dB sweep is dominated by H2 everywhere above 22Hz.
The burst output measurements for the 12S2 indicate that the subwoofers useful extension with good headroom is about 30Hz. The 12S2 was unable to produce any useful output below 20Hz. At 20Hz a passing result of just under 90dB was recorded which isn’t really enough to be meaningful. At 25Hz the 12S2 would produce just over 96dB with passing distortion and 102.5dB when driven all out. At the 31.5Hz band the headroom starts to show up and an output of 108dB was recorded. From 40 to 100Hz the maximum short term output is beyond 110dB. The maximum output recorded was 115.7dB at 50Hz.