Rhljazz, thank you. I believe the phenomenon referred to in your first paragraph applies to the situation where a y-connector is used to sum left and right line-level outputs to a mono signal, with the resulting mono signal provided to a sub having only a single line-level input. If the outputs which are summed are common with the main signal path, or are just isolated from it via relatively low value resistors, the channel separation of the main signal path can indeed be compromised. Although some people apparently get away with doing that, depending on the specific design. But it is poor practice at best, and conceivably could even degrade long-term reliability.
But none of that is applicable here, as the SB-2000 provides separate left and right inputs. RV’s y-adapters, given that two are being used (as Yogiboy points out should be used), are for the purpose of splitting left and right such that each is routed to the corresponding inputs of the monoblock power amps and the sub.
RV, earlier in the thread I had recommended the Audioquest
"hard y adapters." I feel it would be good practice to use those, or something equivalent, rather than y-cables. Although I suspect the use of the cheap Radio Shack y-cables is NOT a major contributor to the issue you described.
You may have provided some or all of this information earlier, but could you recapitulate a description of the room dimensions, the distances of the speakers to the closest walls, the distance between the speakers, the physical location of the sub, and the location of the listening position within the room.
BTW, I have about 40 or 50 Telarc classical LPs, mostly from the 1980s, which I’ve listened to on several different floor standing speakers that reach down to the vicinity of 24 to 28 Hz, and I am very familiar with their sonics. Although I don’t use a sub, it may be relevant that in my room (see my system description) when deep bass weakness occurred in the past on Telarc bass drum beats and other low frequency notes it was caused primarily by rear wall reflections, even though the central third of the wall behind the listening position is open to another room. Such reflections will result in a suckout at a range of frequencies centered at a frequency (in Hz) of about 281.5 divided by the distance in feet between the listening position and that wall. (281.5 feet per second is about 1/4 of the speed of sound in dry air at room temperature, which would cause a rear wall reflection to arrive at the listening position out of phase with the original arrival at the listening position, for frequencies in the vicinity of 281.5/that distance in feet). I was able to improve that issue significantly in my system when I upgraded my preamp to a DEQX HDP-5, which provides myriad signal processing and room correction functions but costs a pretty penny.
Finally, of course, in addition to placement considerations your sub provides a number of adjustable parameters, which I assume you’re in the process of fine tuning. And I would expect that if those aren’t optimized, especially the phase control, the acoustic output of the sub may even be partially cancelling the bass outputs from the main speakers somewhat.
Good luck. Regards,
-- Al
