Generally speaking, almost any transducer that can pick up infrasound will have almost zero response to ultrasound anyway, so this is unlikely to cause you any problems.
200Hz is not considered infrasound, so depending on what frequencies you want, a normal microphone may be suitable. Down below 20Hz it gets more difficult, so you will need to look at specialised tools. This site shows an example for seismic detection.
But in general, what is used is a low pass filter. This example from Audacity has a cutoff at 250Hz. And Audacity is in fact a useful tool to do this, rather than worry about building a filter yourself.