Re: Hearing aids, Inductive loops question

To avoid the possibility of amplitude distortion it is best to load an
amplifier with a resistance of about the same value as what the
amplifier is designed for.

So a resistance of roughly 8 ohms can be connected in series with the
low impedance loop.

The resistance has a beneficial effect - it levels the frequency
response. It allows more turns to be used in the loop without loss at
the higher audio frequencies.

The loop thinks it is being fed from a constant current source with an
internal resistance of 8 ohms. This is considerably higher than the
impedance of the loop itself even when it has several turns. It is
this constant current characteristic which maintains the frequency
response.

The amplifier is also happy because it thinks it is driving an 8 ohm
loudspeaker.

The smaller the room area to be covered, the greater the number of
turns allowed. The number of turns can be increased until the loop
impedance is several ohms at the higher audio frequencies, say 4 ohms
at 6 kHz if the amplifier has been designed for an 8 ohm loudspeaker.
But it is very non-critical.

The loop impedance is that of its inductance which can be calculated
prior to installation. or measured afterwards.

Reasonable hi-fidelity can be expected.

But performance ultimately depends on the sensitivity of the pick-up
receiver and on the level of noise, interference and 50-60 Hz mains
hum and its harmonics.
----
Reg.


.

Relevant Pages

  • Re: Advice on speaker wire needed.
    ... An 'ideal amplifier' has zero output impedance so a speaker ... connected to it with cable of minimal resistance gets highly damped. ... impedance as we are talking about the low frequency damping) is 6 ohms. ...
    (rec.audio.tech)
  • Re: Hearing aids, Inductive loops question
    ... amplifier with a resistance of about the same value as what the ... The load resistance of an amplifier is dictated by its power supply ... It allows more turns to be used in the loop without loss at ...
    (sci.electronics.design)
  • Re: Advice on speaker wire needed.
    ... An 'ideal amplifier' has zero output impedance so a speaker ... connected to it with cable of minimal resistance gets highly damped. ... impedance as we are talking about the low frequency damping) is 6 ohms. ...
    (rec.audio.tech)
  • Re: Hearing aids, Inductive loops question
    ... Any idea how much drive is required for the loop. ... You can use a standard stereo amplifier to drive a loop. ... Ohms, whatever the amplifier is designed to drive. ... An extra resistor can be ...
    (sci.electronics.design)
  • Re: Hearing aids, Inductive loops question
    ... Any idea how much drive is required for the loop. ... You can use a standard stereo amplifier to drive a loop. ... Ohms, whatever the amplifier is designed to drive. ... Definitely no. Using thin wire causes the loop to have some resistance ...
    (sci.electronics.design)