[ARC5] Fw: Receiver current drain (AF output)

[J. Forster]

The speaker design allowed a much larder displacement of the cone, hence
higher SPL.

The noise pickup is a complex issue.

A high impedance circuit is more susceptible to capacitive coupled EMI.

A low impedance circuit is more susceptible to inductive coupling.

Given that a lot of wiring was shielded, I'm inclined to doubt your
theory. The radio wires usually went nowhere near the spark plug wires
also.

YMMV,

-John

================


> Well, that's true but 4000 ohm units could have been built using the newer
> approach.  And further, magnetic material developement (the higher Hc and
> Br
> Alnico and probably specifically Alnico 5) made possible the newer design
> (decent performance with fewer turns in the coils).  But the lower
> impedance
> audio lines also decreased noise pickup problems (from relatively long
> runs
> in aircraft and AFV's).
>
> In a message dated 1/7/2011 10:26:09 AM Central Standard Time,
> jfor at quik.com writes:
>> I think the headphone impedance change could well have resulted from an
>> earphone design change.
>>
>> Prewar, earphones used a "U" metal structure wound with a coil on each
>> leh
>> and a metal disk diaphragm. I suspect this design does not work well at
>> high noise levels as might be found in AFVs ot planes.
>>
>> So, they went to the small loudspeaker design, and hence a much lower
>> impedance.
>>
>> FWIW,
>>
>> -John
>>
>>
>
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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