Subwoofer for classical music listener

Shadorne, thanks for the excellent comments. Regarding cable capacitance I’ll mention that I had raised that issue earlier in the thread, and it turns out that the OP’s existing interconnects are only 2 feet long. Given the preamp’s nominal output impedance of 500 ohms, and assuming the length of the cables to the sub is not unusually long, cable capacitance (which of course is proportional to length) is therefore unlikely to be an issue in this case.

I’ll mention also, as I’m sure you realize but others may not, that the capacitance of the cables connecting the preamp to the sub can affect what is heard from the main speakers just as much as the capacitance of the cables connecting the preamp to the main power amp. The reason being that the capacitance of the cables to both destinations will interact with preamp output impedance and thereby affect the signals that are present at the preamp’s output terminals, that in turn are sent to both destinations. The resulting effects, if any, being most likely to occur in the treble region.

Bob, in answer to your questions I would put it that induced noise can typically be viewed as emanating from a high source impedance. Therefore the lower the load impedance the more the noise voltage appearing across that load will be attenuated, due to the voltage divider effect that will occur between the load impedance and that source impedance. And since the receiving device presumably responds to the voltage appearing across its input impedance, that voltage (and not current) is what matters.

Best regards,
-- Al

I owned REL Storm III and loved it. I tried line level and speaker level connections. I really liked what the sub could do for my system. Bought a measuring mic and learnt how to use REW. So I could measure the impact of varying  placement.

Later I bought 2 Rythmiks 12" kits and built sealed, very heavy (100 lb each), rigid boxes. For less than the REL I got better sound. Rythmiks are servo driven and also have a lot more controls for fine tuning. It was a lot better than the REL.

Eventually I went from the pre (Lamm LL2) to the subs xo and from there to the tube power amp, relieving the amp and speakers from attempting to reproduce below 80Hz. Yet another improvement. Like the article linked to earlier said. 

If you extrapolate the reasoning in that article you arrive at an active system. Later I did without the preamp altogether  abd went active. Running digital xo at the software level, adding time alignment of the sub and midbass woofer, and adding room correction is yet another leap forward. Despite this being a paradigm shift for most audiophiles thinking digital xo are detrimental. I know I'm not going back.

@Steakster, I don't think it's possible to answer your question without a lot of additional information, including the things you mentioned that cannot be determined, and also:

-- The input impedance of your power amp.
-- The length of the cables that connect the preamp and power amp.
-- Whether the outputs of the tube preamp are capacitively coupled or transformer coupled. (Or if it is one of the very few that are direct coupled, e.g., those made by Atma-Sphere).

Generally speaking, though, I would consider using a tube preamp to drive both a power amp and a pair of subs, at least one of which has an input impedance as low as 12K, to be cause for concern. Especially if the tube preamp has capacitively coupled outputs (as most tube preamps do), since the resulting output impedance most likely rises considerably in the bottom octave or two from what it is at higher frequencies. (The impedance of a capacitor increases as frequency decreases).

Something you might consider, though, would be trying to find some sort of buffer stage, that would provide a high input impedance and a low output impedance, and inserting it in the path between the preamp and the subs. Or, if the main power amp also has a low input impedance, perhaps inserting it in the path between the preamp and both destinations. Something like the Burson Audio buffer stage that was marketed some years ago, but is no longer made.

Best regards,

-- Al