[Elecraft] headphone impedance

[Joe Subich, W4TV]

> Certainly a higher impedance load will reduce the power available
> from the amplifier, but the output voltage will be higher and the
> current requirement is lower.

Higher impedance headphones (and speakers) have larger voice coils
(more turns) than lower impedance headphones/speakers.  The larger
number of turns produces a larger change in magnetic field for a given
change in current.  Typically the magnetic field increases as the
square of the number of turns while the current in the coil decreases
linearly with the impedance.  In simple terms, because audio is "low"
frequency, doubling the number of turns will increase the magnetic
field by a factor of four while increasing the impedance by a factor
of two.

Thus, although the audio amplifier produces less *power* with higher
impedance headphones, the high-z headphones produce more sound pressure
per unit of audio input ... the higher impedance headphones will be
more *efficient* than low impedance headphones.

Where an audio amplifier is relatively limited in power output (e.g.,
old battery powered "portable" radios) high impedance headphones were
the 'phones of choice.

73,

    ... Joe, W4TV


On 12/28/2015 3:00 PM, Don Wilhelm wrote:
> Steve,
>
> Look closely - that is the *power* that can be developed by the
> amplifier.  Certainly a higher impedance load will reduce the power
> available from the amplifier, but the output voltage will be higher and
> the current requirement is lower.
> Most headphones (other than some audiophile types) do not require much
> power at all.
>
> 73,
> Don W3FPR
>
> On 12/28/2015 1:59 PM, Steve Ellington wrote:
>> K3  uses the.
>>
>> LM4811  Headphone Amplifier
>>
>> Texas Instruments Specs for output Z
>>
>> RL = 16Ω 105 mW
>> RL = 32Ω 70 mW
>>
>> At 60 ohms the output power drops to 20 mw. Per their graphs.
>>
>> 300 ohms is not even considered.
>>
>>
>
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