Electromagnetic emission of audio...

A loudspeaker coil is wound on its magnet core, and does cause an audio-frequency magnetic field across its magnetic gap.

At a certain power, the electromagnetic emission from the voice coil gap (not the acoustic vibration of the cone) should be able to be picked by a 'receiving' inductor nearby. Is there any experiments or studies about such, or your opinion ?

In other words, a speaker with the cone removed; only its coil 'glued' in place.

Audio induction loops work similar; and the audio electromagnetic wave is picked by the telecoils in hearing devices.

These are 'telecoils' :
----> https://www.grupopremo.com/111-telecoils



[found at hearingwellclub .files .wordpress .com /2015 /05 /hearing -aid .jpg ?w = 191 &h = 237]

And the induction loop is like :




[found at americanhearingloop .com /wp -content /uploads /2014 /10 /HearingLoopDesign1 .jpg]

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[found at 1 .bp .blogspot .com /_dqeG9o9oFfA /THCJnOJi1cI /AAAAAAAAAAM /CjFP -1jZ7tw /S760 /DSCF0010 .JPG]

Which is capable of reaching many meters away to a 'telecoil'. The loop is fed by a plain audio amplifier.

A loudspeaker coil is wound on its magnet core, and does cause an audio-frequency magnetic field across its magnetic gap.

Audio frequency magnetic field will generate in the magnetic gap when audio signal applied to coil !!!!!

If we place a cone on the moving coil, the audio signal (electrical energy) converted to mechanical energy, With the help of cone this mechanical energy converted to sound (Vibration).

If you remove the cone, the coil will vibrate but no sound if you place a telecoil near by, you may receive EMI (electromagnetic interference) not the sound wave.

Telecoil loop systems are working with principles of electromagnetic induction or mutual induction. Induction loop (driven by audio amplifier) act as a primary of a transformer and receiving coil act as a secondary of transformer.

I would like to share my wonderful experience in audiophile . Once i testing a PA amplifier with a speaker suddenly the speaker got shorted and no sound from speaker but i heard the music still , finally i found that the output transformer making sound like speaker!!!!!!!!!!!!!!!

Keep on thinking you may get a new idea


Hope it is helpful to you

You get probably a stronger external magnetic field from the loop spanned by the speaker cables than from the voice coil, because the voice coil is almost completely shielded by the embedding magnet system. Only a small part of the voice coil at the speaker front side is exposed to free field.

Both field components are detectable. Not sure what's your specific question in this regard.

FvM said:

...Not sure what's your specific question in this regard.

Click to expand...

Thanks, FvM.
In other words, if a speaker with its moving parts removed; only its coil 'glued' in place would emit EM audio detectable by a 'telecoil' nearby.

Some calculations would be needed to find a range given power at the speaker voice coil and properties of the telecoil.

Or, if to say it simpler, instead of an 'air cored' room induction loop; a voice coil alone wound fixed on an iron core. Will its audio EM field be detectable by a telecoil nearby ? Have any experiments/tests ever done ?

The field of a small coil won't have a range larger than a few 10 cm or may be half a meter. A loop is much better suited.

Externet, I think you have invented the air cored transformer!

As shown in the graphics, the normal method is to build a loop around the whole area so the pick-up point is always inside it. My local hall has the loop half way up the walls rather than on the floor and it avoids doorways by rising over then inside conduit. The pick-up circuit is just a coil and audio amplifier although in most instances a filter is needed to reject AC line interference. Power distribution cables unfortunately also produce low frequency EM fields and tend to be located around the perimeter of rooms where they behave in a similar fashion to audio loops.

Brian.