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Shorting speaker terminals...

Externet

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Hi all.
If the terminals of a standalone dynamic speaker or headphone transducer are shorted together, what do we have ? A movable coil in a magnet field.
If there is an audio 'loop' transmitting audio in proximity; would the shorted speaker receive and reproduce the audio as with a wireless induction ?

Or; how to induce audio to a speaker or headphone that is in a magnetic field from a 'loop' ? Shorting its terminals ?

Or; If a shorted earphone transducer is placed near/inside an active speaker coil with its cone removed; will it emit sound... perhaps faint, but emit ? Call the contraption an audio 'loop' and its receiving passive transducer.

-No active electronics/amplification involved for 'reception'-
 

KlausST

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Hi,

If there is an audio 'loop' transmitting audio in proximity
What doe this mean?
What is an audio loop?
"Transmitting" as sound, as magnetic waves?

I don't understand.

Klaus
 

Externet

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Thanks.
Replacing a speaker with a number of turns of wire around the perimeter of a room, creates a magnetic loop that can be picked by a coil in a receiver and amplified. There is no RF carrier.

----> https://assistivetechnologyblog.com/2016/09/induction-loops-what-are-they-and-how-they-work.html

The RX coils are typically

----> https://loopseattle.org/loops-in-seattle-2/what-are-telecoils-or-t-coils/
----> http://megaspectr.net/en/rehabilitation-and-physiotherapy/hearing-aids/telecoil-for-hearing-aids

And related :

----> https://goughlui.com/2014/10/04/project-audio-induction-loop-receiver-part-1/
 

Audioguru

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A speaker is a motor. If you short a speaker then it is difficult to move its cone. The same as if you short a DC motor then it is difficult to turn it.
The shorted coils also prevent picking up a magnetic field.

My hearing aids have a tiny coil that picks up an audio loop around a room then the hearing aid amplifier amplifies it. The coil in each hearing aid also picks up the very small magnetic audio from a telephone earphone.
 

BradtheRad

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For the receiving loop to be more sensitive, it should be high impedance. A speaker coil is low impedance therefore it's not very sensitive for magnetic fluctuations at a distance.

If you disconnect the high impedance lead going into a sensitive amplifier, it may pick up ambient mains hum from nearby appliances, or perhaps from wiring in the walls.

There is the store-bought telephone pickup coil. Attached to an earpiece it detects audio frequencies. I measure mine having DC resistance 300 ohms. The housing looks as though it has room for a couple hundred turns. It's a more likely bet to act like a telecoil.

telephone pickup coil.jpeg
 

FvM

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-No active electronics/amplification involved for 'reception'-
None of the existing "telecoils" works without an amplifier.

If the terminals of a standalone dynamic speaker or headphone transducer are shorted together, what do we have ? A movable coil in a magnet field.
If there is an audio 'loop' transmitting audio in proximity; would the shorted speaker receive and reproduce the audio as with a wireless induction ?

Or; how to induce audio to a speaker or headphone that is in a magnetic field from a 'loop' ? Shorting its terminals ?
Did you notice that the voicecoils of a speaker or headphone are completely shielded by the surrounding magnet system? Even a loop operated with high current wouldn't induce perceptible audio signal because the field doesn't reach the coil.

You need a high current loop plus a large coil to receive anything without amplifier. Achieving a flat frequency response would be another challenge.
 

betwixt

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I think there is a fundamental misunderstanding of magnetics here.
Typically, the sound source is amplified many times then impedance matched to the induction loop transmitter. For a simple short circuit across a loudspeaker the magnetic field would be miniscule and even with a sensitive amplifier, would probably have a range no further than a few mm.
The radiated magnetic field has to cover the entire 'listening' area and that could require many Watts of power into a relatively high impedance in some circumstances.

Brian.
 

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