Axiom Home Page Forums General Discussion Stereo M3 with TubeCube

Dan, you're correct that one possible benefit of using a sub is to relieve the mains from trying to reproduce low frequencies which they can't do cleanly. However, this can't be accomplished in the way discussed here. A sub doesn't have a "high pass filter"; the control on the back(sometimes incorrectly referred to as a "crossover"), is only a low pass filter which rolls off the sub response above the selected frequency, but which can have no effect on the response of the mains. This is the case regardless of whether the mains are connected directly to the amplifier terminals or are connected to the speaker level outputs on the sub(which are simply straight-through connections to the amplifier).

Relieving the mains of the bass burden requires a multi-channel HT receiver or separate processor having bass management circuitry, with the mains set "small" at an appropriate frequency, typically 80Hz. The sub would then be connected to the sub out with coaxial cable.

Thanks for the clarification John. I use the traditional setup with bass management in my HT receiver. However I (mistakenly) thought the low pass filter for the sub also acted as a high pass filter to the speakers. Good to know for future reference.

Just to add to the confusion, some subs *do* include a crude high-pass filter in the pass-through speaker connections, but it typically does not track with adjustment of the main crossover and does not have the same cutoff slope either.

So not recommended except for very basic systems.

That's right, John, but I didn't want to add to the confusion. A very few subs have a separate high pass filter on their speaker level outputs, fixed roughly(very roughly)around 100Hz. However, this has nothing to do with the low pass filter control on the back. Again, the frequent usage of the incorrect term "crossover" for the low pass filter leads to a fairly common misunderstanding that it's also a high pass filter to mains connected to the speaker level outputs, creating a crossover.