Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electromagnetic Speakers

  1. Apr 9, 2010 #1
    Well I have tried a different approach to make speakers.

    Normally speakers contain permanent magnets for producing sound using the property of electromagnetism when electric signals are passed through a coil kept in the magnetic field of Permanent Magnet. (ref: How Speakers Work frm How Stuff works).

    now what i have tried to do here is replaced the permanent magnet of the speaker with an electromagnet.

    keeping the principal of speaker in mind i hav even left the minor air gap between the core and coil (of electromagnet) for letting the coil with electric signals vibrate in the influence of magnetic field producing sound.

    the basic idea while performing this was to reduce the weight of speaker along with obtaining difference in sound just by changing the strength of electromagnet.

    i hav used a soft iron rod of 0.75" dia., 28 awg enameled copper wire, 12 V 500 mAh DC power supply for electromagnet.

    the problem being faced here is i am unable to get the similar strength of electromagnet as that of Permanent magnet of the speaker. though i have achieved the sound objective but volume remains very low.

    even increase in no. of turns of the coil and changing source to 12 V 3 Amps DC has not solved the problem.

    what am i missing, should i go for any different approach in order to increase the field and sound volume
  2. jcsd
  3. Apr 9, 2010 #2
    In the 1940's I disassembled pre-war (WW II) (vacuum tube) AM radio sets with electromagnet speakers. The electromagnet was a dc filter coil for the B+ (high voltage) dc supply.........

    Bob S
  4. Apr 9, 2010 #3


    User Avatar

    Staff: Mentor

    I believe that's why permanent magnets are used in speakers -- that's the best way to get the very high short-range fields needed to get loud volume.
  5. Apr 13, 2010 #4


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    I don't think you will achieve the field strength of modern speaker magnets easily with an electromagnet. There is also the 'green' issue of power consumption as you will need lots of current-turns which will involve higher voltages etc.. It could be real 'steam radio'!
  6. Apr 14, 2010 #5


    User Avatar
    Science Advisor
    Gold Member

    What is known as a hum bucker.
  7. Oct 28, 2010 #6
    Has anyone ever tried just using the same AC power signal coming to the speaker voice coil to power the electromagnet? You would have to plan for the correct resistance of course.

    It would have to be the opposite phase of the coil of course which would make them repel and attract.

    I believe you would get the amps required and only be using them when necessary rather than trying to power an electromagnet the whole time.

    Basically it would work like an AC motor.
  8. Oct 28, 2010 #7


    User Avatar

    Staff: Mentor

    The magnets in speakers are permanent magnets, not electromagnets.
  9. Oct 28, 2010 #8


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    If you tried to excite the Electromagnet with the audio signal then the self inductance would only allow significant current at the low frequencies. That would make the frequency response very glubby, not to mention the relative phase shift between the current in the voice coil and the varying magnetic field. Then, of course, you'd need a hugely powerful amplifier, compared with what's needed for a standard permanent magnet speaker. Hardly a serious engineering proposition.
    If God had intended us to do it that way he'd never have given us neodymium magnets.
  10. Oct 28, 2010 #9
    I understand that. I was initially proposing to replace the permanent magnet with an electromagnet.
    The answer below is great.

    Great answer. I didn't even think about the inductance. Doop!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Electromagnetic Speakers Date
Speaker power Dec 16, 2017
Electromagnetic Ring Expansion Test Jul 4, 2017
MOSFET or Rheostat or Potentiometer pros and cons? Jun 20, 2017
Permanent magnets May 24, 2017