subsonic filter for turntables

[danger boy]

can someone explain what the subsonic filter does on a pre amp and why it's important to have/use it when listening to albums.

it seems modern day pre amps/receivers don't have that subsonic filter... is that a bad thing then?

[strider]

The way understand it, the subsonic filter removes the signal in the lower, inaudible, frequency range. Ever noticed your midrange drivers jumping up and down when you first put on an album? It's designed to tame that. Some people see it as a work around to a problem. I found I didn't need to engage mine after I made certain my platter was absolutely level.