I want to count and log the BPM of a rather large bass speaker (250-400W RMS range i assume).

BUT there is a mostly wooden/stone wall (~40cm) between me and the speaker + a 50cm air gap.

I managed to detect the speaker with a normal microphone, but that gets confused once there are other noises like talking or foot steps in the room.

So my idea was to build a large coil around some graphite rod to build a sensor for electromagnetism. Then connect that to a audio amp and feed the result into a audio card microphone input.

Would that maybe work? Any guesses how far the magnetic field of a bass speaker is detectable? How much wire should i use for the coil?

Edit:

So i found this video https://www.youtube.com/watch?v=83edokt3K5c of someone using a giant coil to pick up a very small speaker from a few feet away, so i assume its 100% possible, and the speaker i am trying to pick up has like 200-300x the power of what he is picking up in the video.

  • OwOarchist@pawb.socialEnglish
    4·
    1 month ago

    Interferometry, maybe?

    Two microphones, side by side. Signals that come from directly in front (or directly behind, unfortunately) will hit both microphones simultaneously. But sounds coming from the side or any other angle will hit each microphone at slightly different times. If you then have a hardware or software solution to filter out any sound waves that don’t match, you’ve got a highly directional microphone that should work well in any frequency range. (Can also use this setup with 3 microphones if it needs to be 3D and filter out noise from above and below as well.)

    There are commercially available setups that do this, but in theory it shouldn’t be too hard to build your own, either. I mean, in theory, you could just feed the outputs of both mics through an and-gate transistor into a single output, and that very simple hardware would do the filtering for you – you’ll only get the outputs from when both mics pic up the same sound at the same time.