Viridian...A properly designed rumble filter eliminates difference signal between channels, which is vertical groove modulation, and which constitutes most of the problem. Some overall attenuation below 20 Hz, such as provided by some preamps, is also desirable, but getting rid of the difference signal is most important.
By the way, when LPs are mastered, for various reasons, low frequency differential signals are cut, so you don't loose any real music signal when you use a rumble filter.
By the way, when LPs are mastered, for various reasons, low frequency differential signals are cut, so you don't loose any real music signal when you use a rumble filter.