Systems List › DIY › RE Audio XXX-18D2 Power Ported
The native response curve of this system shows a slightly peaky output with a slow roll off towards 125Hz due to the effects of inductance in the driverís motor. †The impedance minimum was measured at 4.29ohms at 11.4Hz so an input voltage of roughly 2.0v was used for the 1m sensitivity tests and 20v for the 10m test. The sensitivity of this system in the upper bass range is rather low and especially so considering the size of the system. However moving below 30 to 40Hz the efficiency improves, but considering the size of the enclosure and the tuning this is to be expected. interestingly the 10m sensitivity measurement shows a large increase in the results below 20Hz likely due to better integration of the ports contribution so the sub 20Hz sensitivity shown in the 1m sensitivity measurement is slightly understated.
This system can almost run without a rumble filter but since we are doing maximum output testing a filter is required to pad down the frequencies below 10Hz. A Symetrix 551E was used to provide this protection. The roll off of this filter is shown in one of the static measurement charts.†
The peak output and long term maximum output are low in the upper bass range again due to the low efficiency coupled with some thermal compression. This system is very demanding on the amplifier due to the low impedance, low efficiency, small maximum impedance magnitude, etc. However below 40Hz the system comes into its own and produces some very impressive output especially below 30Hz. The distortion results are rather good. The very powerful low frequency output coupled with distortion levels that stay below 10% THD over the full 8-125Hz bandwidth except for a small area right at 10Hz indicate that this system has exceptional deep bass reproduction. Indeed the measurements are extended down to 8Hz for this system due to this. Also notable is the fact that the distortion is comprised primarily of the second harmonic over nearly the entire bandwidth which is generally considered as the least offensive to the ear.†
There is some indication of what are likely to be internal cabinet resonances in the response in the 130-180Hz range due to the extra tall dimensions of this cabinet. Port resonance probably accounts for one of these blips in the response as well. Otherwise in the time domain the results are fairly clean and show nothing of note below 125Hz other than the large increase in group delay due to the vent tuning and rumble filter employed near 10Hz. Still the group delay does not pass 1.5cycles and I'm doubtful of subjectively hearing increases in delay in frequencies almost an octave below 20Hz. This cab can be run up to 120Hz but puts it's best foot forward operating below 65Hz.†