[Elecraft] headphone impedance

[Joe Subich, W4TV]

 > Headphone efficiency clearly has other dependencies than
 > impedance.

Yes, there are other dependencies like the weight and "stiffness"
of the diaphragm, the strength of the magnet, the coil geometry,
etc.  However, there is still a strong correlation of efficiency
with impedance in well built headphones.

73,

    ... Joe, W4TV


On 12/29/2015 4:55 AM, Barry N1EU wrote:
> Jim, I think it would be great if you would clarify your comment to
> Steve.  I've looked at the data sheet and everything Steve said seems
> correct to me???
>
> And I'm not sure I'm willing to totally buy (per Joe) that there's
> necessarily a proportional relationship between headphone impedance
> and efficiency that makes up for the inverse relationship between
> output power and load impedance.  I just don't observe this efficiency
> rule consistently in my collection of headphones with varying
> impedance.  Headphone efficiency clearly has other dependencies than
> impedance.
>
> 73,
> Barry N1EU
>
>
>
> On Tue, Dec 29, 2015 at 6:46 AM, Jim Brown <jim at audiosystemsgroup.com> wrote:
>
>> You clearly don't understand what you're reading on that data sheet, nor the
>> design of audio output stages. I refer you to my earlier posts, and to those
>> by W4TV, W2RU, and W3FPR.
>>
>> Those numbers you quote are NOT the output impedance, they are the minimum
>> LOAD impedance that the output device is designed to work into. Modern
>> output stages are essentially constant voltage sources. That's what Bud is
>> telling you with his discussion about damping factor -- the output Z (source
>> Z) is typically 50-100 times the load Z.
>>
>> With headphone amplifiers, a good designer will add some small value of
>> resistance in series with the output to prevent the output stage from
>> failing if a short is connected to its output (which could occur when a plug
>> is being inserted, or with an improperly wired plug). Line level outputs use
>> a series output resistor to prevent the output stage from seeing the
>> CAPACITANCE of a long cable, which could, by interaction with the feedback
>> network, cause the output stage to oscillate.
>>
>> Executive summary -- simply buy good quality headphones, and don't worry
>> about impedance.
>>
>> 73, Jim K9YC
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