Systems List › JTR Speakers › Captivator 212-Pro
NotesImpedance measurements for the Captivator 212Pro show an in band minimum impedance of 3ohms at 42Hz, which indicates that the effective vent tuning for this system should fall close to this frequency. In practice the tuning seemed to functionally be a bit higher as seen by the drivers and closer to 44Hz. The maximum in bandwidth impedance occurs at about 69Hz where it reaches 35 ohms. The impedance doesn’t drop back below 4 ohms until above 110Hz. Effectively this is a 4ohm cabinet.
Voltage sensitivity of the 212Pro is quite high for such a small subwoofer. The measurement with 20 volts applied at 10 meters shows 100 to 103dB sensitivity over the 45-125Hz bandwidth. When measured at 1 meter and 20 volts and then normalized minus 20dB to a 2 volt drive level, the sensitivity is about the same. The 1 meter measurement does show a bit of increase in the output at low frequencies and a bit of loss of output above 100Hz, when compared to the 10m measurement. This is common behavior to see.
The raw, ground plane, 2 meter frequency response of the 212Pro, is quite extended and smooth. The response fits within a 6dB total window from 44-460Hz, which is an impressively wide bandwidth for something intended as a subwoofer. We do see a bit of roughness at about 310Hz which also shows up in the impedance curve. This is likely the vent pipe resonance. Even with that small issue, the 212Pro could operate quite well up to 250Hz and well above that point.
During the high power long term testing a high pass filter was used to protect the woofers below the vent tuning point. After a bit of experimentation an 18dB an octave, Butterworth type filter was set at 35Hz. This seemed to retain a good amount of the useful extension but keep very low frequency excursion under control.
Group delay with the high pass filter in place shows that the delay remains just at or below one cycle throughout the bandwidth of interest of 30-125Hz. The waterfall decay plot also shows that the output decays by 30dB or more very quickly which is what is being looked for.
Long term output measurements start at an input voltage of 1.09v which produces the required 90dB nominal at 50Hz which is used as a baseline for these measurements. Nothing of note happens even after increasing the signal by 25dB to a voltage of 19.3v. The output is compressing less than 1dB to this point and the FR shape is still intact. The next 5dB signal increase to 34.4v causes the output to compress a bit more than 1dB around the vent tuning. Otherwise this level is still uneventful and the response shape and tracking of the output demands are still good. Another 5dB increase to the signal results in 61.1 volts into the cabinet and the onset of a change in the FR shape and compression of 3 to 4 dB near the vent tuning and above 100Hz. At this point there was some driver distress noise and vent air noise. Increasing the drive level a further 3dB to 86.3 volts produced some clear overdrive noises from the woofers and vents and resulted in much less than a 3dB increase in output. Compression of the output reached 6dB around the vent tuning and near 115Hz. During the loudest 86.3v measurement output reached about 117dB at 40Hz, 120dB by 43Hz and 125 to 127dB from 49 to 120Hz. A repeat 6.1v measurement directly after the final 86.3v sweep showed some thermal buildup in the voice coils and motors of the drivers and a sensitivity loss of about 1dB on average. The sensitivity came back up over the next 15min as the system cooled off.
Distortion levels were captured at the same voltages as used for the long term output measurements. With a 10.9v input the THD level is very low remaining less than 3.5 percent above 35Hz. Increasing the voltage to 19.3v does little to increase the distortion despite being a 5dB higher output level. Distortion remains less than 4.5 percent above 35Hz. The next increase to 34.4 volts does trigger an increase in THD but it is still below 10% above 38Hz. The next big 5dB increase in the voltage applied , 61.1 volts, causes the THD to increase mightily. The THD is now reaching 27% at about 120Hz and is rapidly increasing below 42Hz. Some audible distortion was noted from the subwoofer during this sweep. The final increase of 3dB to the signal resulting in 86.3v into the cabinet produced heavy distortion and distress noises. THD has now reached a general level of 10 to 20 percent over 43-83Hz and 31 percent at 120Hz. It would be best to keep long duration signals to less than 60v into this cabinet. The harmonic makeup of the distortion is mostly the 2nd harmonic which is good. The 3rd harmonic does not take over until the 61.1v and 86.3v sweeps where driver is beginning to get high. Even then the distortion recorded above 60Hz is mostly the 2nd harmonic. With a typical low pass filter used at 80 to 100Hz the output requirements above 100hz will be greatly diminished which will lower distortion in that bandwidth.
The short term, distortion limited, burst output measurements start out strong up top. The 212Pro is able to produce 130 to 132dB at 2 meters ground plane at the 80, 100 and 125Hz bands with passing distortion. Output remains high down to 50Hz where it is more than 126dB. At 40Hz the 212Pro came just shy of 120dB with passing distortion. It would produce a bit over 121dB driven all out, but with high distortion levels. At 31.5Hz a respectable output of 109.2dB was recorded with passing distortion and 111.6dB without a distortion limit. The 212Pro even managed a passing result at 20Hz which is an octave below tune. There is not enough output to get a passing result at any of the bands below 20Hz. The limiting harmonic for most of the bandwidths tested was either the 2nd or the 3rd, except for at 80Hz where it was the 4th and 6th equally. The K20 amplifier was completely overkill for the 212Pro cabinet which was never hit with more than 108 volts.
Based on the information here, an amplifier capable of 50 to 65 volts would be a good match for the 212Pro.