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.

  • Alexander@sopuli.xyzEnglish
    0·
    3 months ago

    Could be doable with just a hall sensor chip, you have one in your phone, just check it out quickly. Large coil will probably catch slow vibrations too. Also try just filtering audio signal, like get only sustained bass sound, footsteps and voice have short lived low frequency components compared to most music except for percussion I suppose.

    • einfach_orangensaft@sh.itjust.worksOPEnglish
      0·
      3 months ago

      I tryed with the magnetometer in my phone before and sadly it didnt pick up anything, i think the polling rate may be to low too. But ima search around for some more sensitive hall effect sensors