[AMRadio] Headphones


ne1s at securespeed.us ne1s at securespeed.us
Mon Aug 25 20:03:13 EDT 2014


> It was when I picked up a set made by (for) Telex that a label caught my
> eye.  They had 8 ohms on the label so I looked at another pair made by
> another company and it said 16.  What is the deal, are all manufacturers
> making headphones for audio and the audio builders making outputs the same
> as speakers?  What ever happened to high impedance phones?
>
> Is this common?  He had a Heil headset with mic so that makes me wonder
> the impedance of them.
>
> Can anyone explain.
>

Jim,

Headphone impedances vary all over the place, both in a nominal sense, and
in an actual sense. The impedances usually quoted are all nominal
impedances - actual will be a (rather strong) function of audio frequency.

"High impedance" headsets were the norm back in the days of crystal sets
and regens, and the typical nominal impedance was 2000 ohms. They are less
common today, although I hesitate to say "no longer manufactured" because
I don't know that for a fact.

Headphones with a nominal impedance of 600 ohms were common in and around
the WWII timeframe for military applications.

Really low impedance 'phones, such as 8-ohm nominal, I believe came about
during the early days of high-fidelity.

Bill Guyer provided a good comment about lower-Z 'phones being compatible
with today's direct-coupled solid-state output chips and circuits, so
that's what we encounter mostly today in consumer electronics, for
example. From what I've seen nominal impedances ranging from 8 ohms to
around 100 ohms are common. (BTW, I'm having good results driving a pair
of such 'phones directly, i.e. without an impedance-matching transformer,
from a 6V6 cathode follower - although the math says the impedance of the
cathode follower is too high, I get adequate volume and great fidelity.
The 'phones are coupled to the 6V6 cathode through a big electrolytic
cap.)

Since I'm not a broadcast or recording engineer I can't comment on what's
standard today in broadcast or studio applications, but Bill touched on
that.

73,
-Larry/NE1S



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