electromagnet driver?

Discussion in 'The Projects Forum' started by telharmonium, Oct 18, 2010.

  1. telharmonium

    Thread Starter New Member

    Oct 18, 2010
    Hi I want to turn a huge piece of sheet metal into a speaker for an art installation, so I want to amplify audio signals to something like a hundred watt 220volt signal to drive a handrolled electromagnet. The voltage was chosen more or less arbitrarily-- it's household current here in the Philippines that I was sending through an electromagnet for my last project, where I made a metal statue ring at 60 Hz. I know sound will bounce and reverberate in the sheet, and that's fine. Does anybody know of an amp design that would be up to this? I don't want to just bolt an off-the-shelf transducer to the sheet.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Frankly, applying line voltage to a project is a great way to making a lethal shock hazard.

    Unless it's sheer noise you wish, using a transducer like the voice coil from a big speaker is going to be a great deal safer. Noise can be done with a big solenoid coil.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    But an off the shelf transducer is what you SHOULD use here.

    Look at a website that advertises 'home theatre sound systems'. The driver you want is a bolt on that is supposed to fit on the bottom of a chair. Going for any high frequency output from a 'large piece of sheet metal' would be a waste of time. Bass notes will be what it wants to radiate and will be good at doing.

    Destroy/modding a subwoofer case and spider/coil would be what I would do.

    Duct tape and RTV silicon are your friends. :)
  4. wayneh


    Sep 9, 2010
    Why not? It's the obvious solution. If you have different design criteria, you'll have to share them to get useful input here.
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
  6. DonQ

    Active Member

    May 6, 2009
    I know big number are exciting, but from your numbers:

    P = 100W
    E = 220V

    From basic electric theory:

    E=I*R & P = I * E


    R = E^2 / P

    That means your 'coil' will need an impedance of:

    R = 484 ohms

    Have you thought this out?

    Maybe that pre-packaged solution would be a better idea.
  7. John P

    AAC Fanatic!

    Oct 14, 2008
    484 ohms, at the frequency of interest and at full power.

    Given that the device will undoubtedly be highly inductive and will operate in the audio range, it's not clear what the d.c. resistance will end up being. Much less than the effective impedance, I'd guess. See Wikipedia article:

    Then again, if the "speaker" is a big chunk of metal, the high-frequency cutoff is likely not to be very high at all. But then we haven't been told how thick the sheet metal part is. In a conventional speaker, the coils move and the magnet is stationary, because the coils are the light part and the magnet is heavy. In this case???

    It's an interesting project, but controlling high voltages isn't very easy, and there certainly are safety issues. I'd consider using a step-down transformer, even though the current requirement at the low voltage will be quite large.