[Elecraft] audio amplifier/speaker/headphone impedance matching

Thu Mar 7 15:47:05 2002

-----Original Message-----
>From: [email protected]
[mailto:[email protected]] On >Behalf Of Rick Shindley

>People sometimes are confused about impedance (Z) matching. They
mistake the 
>need to do so at rf frequencies with the conventions used at audio
frequencies.
....
>The zero Ohm source impedance of most audio amplifiers assures that the
speaker >voice coil will be forced into position with authority.  That
means low acoustic >distortion. If the amplifer had a non-zero output
impedance, the voice coil 
>would not accurately track the voltage signal and acoustic distortion
would 
>result.

>Rick  KC0OV
>K2 1360
-------------------

This is an interesting topic that is raised here. I have often wondered
about the practice used in most ham equipment of using series resistors
to feed the headphones (e.g. separate 82 ohm resistors to feed the R and
L headphones in the K2). It does make the output short-circuit proof. 

But what are the side-effects? Does it cause the headphone to ring at
some undesired resonance frequency? Could it distort CW, by distortion I
mean color it with some unknown frequency response which is the effect
of the design of the headphone and the series resistor? At the very
least we don't get the advantage of damping the headphone coil with the
low output impedance of the amplifier.

Any comments?

73 Sverre

Sverre Holm, LA3ZA
Asker, Norway (59.8N, 10.4E)
---------------------------------
www.qsl.net/la3za