I've been looking into high pass filter design. I'm looking at a basic Sallen & Key format with two two-pole stages switchable for 12dB an 24dB per octave. The advantage of this is simplicity in design and  also it's easy to make one stage variable frequency to tune the response (e.g. set one stage to ~30Hz and the other variable, say 20-50Hz). A two-stage butterworth or chebyshev filter would give a sharper 'knee'. This does mean looking at gain greater than 1. My though