Our neighbors are harassing us and we believe are using a low frequency audio attack.
When you say "are harassing us", do you mean that they have been antagonizing you deliberately in other ways, and now just up the game by playing loud music?
Do they have any reason to show hostile behavior? Do the attack manifest itself as an audible rumble, or do you go purely by a suspicion?
Have you tried talking to them in a calm manner?
My sound meter records a dBA reading of 0, but the same meter records a dBC reading of 30-45 dBC. I assume this implies they are emitting a low frequency audio signal in the less than 0-2k range. Is this dangerous? I am sensing a small level of ear ringing. How can I prove it (equipment and method)? I’m a novice, not a professional.
I assume you mean "in the 0-2k range". Less than 0Hz can't really be done
30-45 dB doesn't sound like much, even with C weighting. I'm thinking it's simply road noise and/or rumble from building utilities.
I suggest doing the same measurements both outside and other places inside the building to gain some perspective.