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More magnets!

  1. Nov 16, 2004 #1
    hi I found this forum on the net... . figured Id give it a try.

    I'm a musician/audio guy working on a quirky project. my goal is to turn normal objects into speakers by painting them with some magnetic paint I found at my local art store. The other end of this, however, requires that I build a fixed electromagnet capable of handling an audio signal (presumably from an amp) and also capable of moving the object. (my first target is the base of a metal wash bin)

    so far....
    using magnet wire and a nail seems to yield sub par results. the insulation melts and smokes within 5 minutes and the magnet is rendered useless. the sound is also very distorted. it sounds as if there is a rectifier of some sort on the signal. it is also heavily weighted toward bass (which is ok and to be expected.... hell its not like the bottom of a washboard is a paper cone)

    whats the trick to converting electric audio signals to magnetic signals?

    thanks for your time

  2. jcsd
  3. Nov 16, 2004 #2


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    Science Advisor

    Your impedance is too low. Need more turns/finer wire. Take a speaker apart to find out typical combinations.

    I would imagine the idea of turning ordinary objects into speakers is so that they can impart some of their own character to the sound, so isn't distortion desirable?
  4. Nov 16, 2004 #3
    Your impedance is too low. Need more turns/finer wire. Take a speaker apart to find out typical combinations.
    ----NEAT I'll buy more magnet wire today. maybe link three reels up?

    so isn't distortion desirable?
    --------- yes, however, I've held a mic up to this monstrosity and (it will reacts to the magnetism before the sound.) and the waves are rectified. very strange. however I think its simple enough to deal with it. (just squeeze the whole wave above 0)

    I'll post back when I get results
  5. Nov 18, 2004 #4
    out come for the record

    well I've wrapped approximately 450 feet of 26 and 30 gauge magnet wire around an iron bar which is about 3/4" thick. connected to this bar is connected to two consecutive amps. (the alesis RA-100 which is "100 watts per channel into 4?, 75 watts per channel into 8?") both channels are clipping and the results are interesting.

    clipping the amp produces more frequencies at one time which seems to make it louder however makes the original sound virtually undefinable. this frequencystack-to-loudness correlation seems to be in spite of the fact that the amp literally clips the wave form

    Obviously I thank anyone and everyone for their help (as I have only knowledge of music and sound to repay) but if there is anyway I can get this darn thing loud/strong enough to reproduce sound well please post it. :)
  6. Nov 18, 2004 #5


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    Homework Helper

    Couple things.
    You want the DC coil resistance to be somewhere around 3 to 4 ohms.
    This is to keep the Amp from being damaged.
    Look up on a wire table for ohms per foot for the wire you are using.

    The magnetic circuit is also important.
    A U shaped bar will be better than a straight bar.
    The gap between the ends of the U and the moving surface should be as small as possible without hitting.

    You could also try cutting the cone off of a standard speaker and gluing the voice coil to the surface you want to move.
  7. Nov 18, 2004 #6
    Maybe you should have a look at this http://www.afrotechmods.com/cheap/hdspeakers/hdspeakers.htm [Broken]

    I hope it ll help
    Last edited by a moderator: May 1, 2017
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