Easy HPF for bass cab?

[JMFahey]

I tend to agree with you Juan, not that it matters much. What does sanity have to do with playing music anyhow though? 😎

You can hear the harmonics just fine and the harmonic series is different from any normal bass. There's a semi-viable niche market and at least a few people are successfully gigging and recording with these things. Synth bass can also go very low, as you of course know.

Yes, it's harmonics you hear, even on conventional 5 string bass.

I make Bass amps and one part of the flavour my customers like is that I add 10/20% second harmonic in the first stages, not only to enhance final audibility, but for tone controls to have something to "grab".

Not perceived as distortion at all, but as grind/growl/unpoliteness.

They play an open 5th (6th) string or the very lowest notes and say "now I hear it loud and clear" , truth is the brain reconstructs the fundamental from the much louder 2nd harmonic.

As of the highpass filter needed by the OP, the Preamp/Filter he mentioned in a link , can be built inside a pedal and powered by a 9V battery.
The schematic is in the thread.

Looks very reasonable:

https://sites.google.com/site/hpftechllc/home/technical-diy-stuff