Of course this is not "new'.
Thought I'd mention that one can simulate these filters in LTSPICE, which is a free download.
A bit of a learning curve, but you can tweak the values and see the resulting graph!
These are a class of filters now known as "elliptic" or "Cauer" filters, iirc.
Basically they work by creating a notch filter to "suck out" energy at some frequency.
The notch is usually very sharp, and can be very deep (as in >60dB) compared to the usual
filter of a cap-choke-cap with is rolling at a slope of 18dB/octave. So for practical values,
one might have maybe -36dB of reduction at 120Hz, perhaps more - but the addition of
the paralleled L+C creating the notch drops
some frequency (chosen by the values)
down into a deep crevasse. The response higher up in frequency lifts and more or less
returns to the original slope of the basic filter.
The attached file is NOT exactly the same, since it uses two elements, but it shows more or
less how it works - look carefully at the dB scale!
I had an LTSPICE screen capture of an actual LF filter I had designed and used, but can't find
that jpeg at the moment.
In the example below, the response pops back up too far, in my
example it followed the same black line after the deep dip...