I suspect that an impedance compatibility issue is contributing to the problem. Your BAT VK-3iX (I assume that is what you meant) has output impedances for its XLR and RCA outputs that are very high and that also vary widely across the frequency range, at least if your unit does not have the optional Six-Pak upgrade. From Stereophile’s measurements:
Also, I suspect that like most JL subs your subs probably provide only line-level inputs, and you are either driving the power amp from the preamp’s XLR outputs and the sub from the preamp’s RCA outputs, or vice versa. Many and perhaps most preamps providing XLR and RCA outputs do not drive the two pairs of outputs from separate output stages, and the signal provided to the RCA connector for each channel is the same signal that is provided to one of the two signal pins on the corresponding XLR connector. If that is the case with the VK-3iX the input impedance of the subs and the capacitance of the cables to the subs (especially if those cables are relatively long) can both have audibly significant effects on the signals received by the main power amp, that are reproduced by the main speakers. So if you already haven’t done so assessing the sonics provided by the Sophia with the sub cables disconnected from the preamp may provide useful insight into the issue.
Good luck. Regards,
-- Al
The VK-3iX’s output impedance was also high, and this might well have an effect on sound quality, depending on the input impedance of the partnering preamplifier [I assume he meant "amplifier"]. The unbalanced source impedance varied from 7k ohms at 20Hz to 1460 ohms at 1kHz and 2650 ohms at 20kHz, while the balanced figures ranged from a very high 14k ohms at 20Hz to 1850 ohms in the midband and above.You didn’t say what amplifier you are using, but those numbers definitely indicate that sonic issues **will** arise with many and perhaps even the majority of solid state amps.
Also, I suspect that like most JL subs your subs probably provide only line-level inputs, and you are either driving the power amp from the preamp’s XLR outputs and the sub from the preamp’s RCA outputs, or vice versa. Many and perhaps most preamps providing XLR and RCA outputs do not drive the two pairs of outputs from separate output stages, and the signal provided to the RCA connector for each channel is the same signal that is provided to one of the two signal pins on the corresponding XLR connector. If that is the case with the VK-3iX the input impedance of the subs and the capacitance of the cables to the subs (especially if those cables are relatively long) can both have audibly significant effects on the signals received by the main power amp, that are reproduced by the main speakers. So if you already haven’t done so assessing the sonics provided by the Sophia with the sub cables disconnected from the preamp may provide useful insight into the issue.
Good luck. Regards,
-- Al