[Elecraft] audio amplifier/speaker/headphone impedance matching

Thu Mar 7 18:43:01 2002

The main concern is that of damping of the headphone vibrations. After
it has been excited, the membrane will keep on oscillating unless it is
being damped by the low output impedance of the audio amplifier. This is
common practice in audio engineering. One computes the ratio of the load
impedance (e.g. 8 ohms), and the output amplifier's impedance (say 0.1
ohm) and finds a damping factor of in this case 8/0.1 = 80. If the
resistance of the cable adds say 0.3 ohm, the system has been
compromised because now the damping is reduced to 8/(0.1+0.3) = 20.

My concern is the effect of adding 82 ohms to the output impedance of
the output amplifier. We are talking of a minor effect here, but I think
the idea that was brought up by Rick's (KC0OV) posting is worth
pursuing. If there is something we can learn from the audio people that
can improve overall sound quality, then why not?

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

-----Original Message-----
From: David A. Belsley [mailto:[email protected]] 
Sent: 7. mars 2002 23:14
To: [email protected]; 'elecraft digest'
Subject: RE: [Elecraft] audio amplifier/speaker/headphone impedance
matching

If the resistor is pure R and no X, it should have no effect on
frequency 
response.

best wishes,

dave belsley, w1euy

--On Thursday, March 7, 2002 9:47 PM +0100 Sverre Holm - LA3ZA 
<[email protected]> wrote:

>
>
>
>
> -----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