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Archived from groups: rec.audio.high-end (More info?)
While I was thinking about circuits to drive headphones, it occurred
to me that I have never in my life seen a graph of headphone impedance
v. frequency. As far as I know headphones have an impedance, and
that's it. As we all know, loudspeakers are designed to be driven
with a source impedance as close as possible to zero ohms. This is
because of wild impedance variations wrt frequency that are typical of
all speakers. My question is: Does this same issue crop up with
headphones? i.e. will there be a gross difference in frequency
response if headphones are driven by a high source impedance?
The sensitivity of speakers is usually specified as SPL when driven by
2.83 volts. With headphones, it's almost always SPL when driven by 1
milliwatt. Because headphones vary in impedance from about 16 ohms to
600, there will be a 6 to 1 variation in voltage required to produce
that 1 milliwatt. Any voltage divider that has to drive the entire
range of impedances will be quite a compromise in performance if the
headphone impedance varies significantly.
Anyone out there that can throw some light on this situation?
Norm Strong
While I was thinking about circuits to drive headphones, it occurred
to me that I have never in my life seen a graph of headphone impedance
v. frequency. As far as I know headphones have an impedance, and
that's it. As we all know, loudspeakers are designed to be driven
with a source impedance as close as possible to zero ohms. This is
because of wild impedance variations wrt frequency that are typical of
all speakers. My question is: Does this same issue crop up with
headphones? i.e. will there be a gross difference in frequency
response if headphones are driven by a high source impedance?
The sensitivity of speakers is usually specified as SPL when driven by
2.83 volts. With headphones, it's almost always SPL when driven by 1
milliwatt. Because headphones vary in impedance from about 16 ohms to
600, there will be a 6 to 1 variation in voltage required to produce
that 1 milliwatt. Any voltage divider that has to drive the entire
range of impedances will be quite a compromise in performance if the
headphone impedance varies significantly.
Anyone out there that can throw some light on this situation?
Norm Strong