Sound Powered Phones for
First a few definitions:
A technology used to reproduce sound and is used in speakers,
and telephone units. First patented in 1918 by Henry Egerton and based
on the 1882 balanced armature telephone patent of Thomas Watson.
Magnetic forces from a
magnet(s) and coil(s) work on a "balanced" or centered "Armature"
or plate. This Armature is connected to a diaphragm. Much more
than the old vintage magnetic headsets because they are "bi polar"
they use both side of the magnetic forces. Also the most sensitive spot
on a diaphragm is the very center. The closer you get to center, the
sensitive the unit. This is why magnetic units try to get their coils
close as possible to each other and to the center. Balanced Armature
achieve this easily by sending the energy from the "Balanced Armature
a "connecting rod" to the exact center of the diaphragm.
A Simple Balanced Armature Unit
Sound Powered unit:
A unit in which the operating power is derived from the speech input
There are no "outside" batteries or power source . The power is
when "sound energy" is converted to "electrical energy" by the "Mic"
These unit were made for the Navy in W.W.II and continue to be made
Balanced Armature is a technology where Sound Powered units
more of a system.
Sound Powered units might
use Balanced Armature
to achieve their goal, but they might also use magnetic elements or
"mics" or other technologies also.
Units like the early 1900's
Baldwin's (vintage headphones) are
considered "Balanced Armature" but not Sound Powered, because they were
never designed for "Sound Powered" applications.
Elements that were designed for
"Sound Powered" application
are more sensitive than magnetic type because they had to be. They had
to work with very low signal levels compared to magnetic sets. Also
the early 1900's to the 1940's technology just got better.
Using Sound Powered
Powered” elements, as they are
by crystal radio designers and builders, are the rage for use on
radios. They have improved performance over the “vintage” style
headphones of the early 1900’s or any other device made since. Even
which are the considered some of the best of the vintage
do not come close to a good set of Sound Powered headsets for Dxing on
a crystal radio. Not always the best for music(some units), they are
more sensitive than any other type of unit for voice, which makes them
invaluable for picking out that very faint station. Please remember
Sound Powered elements reach their "glory" while trying to pick up a
faint signal. This is where they will excell. On signals that are very
strong you might see a very small difference compared to vintage
headsets. In fact
in some cases vintage might sound better such
Most Sound Powered headsets
handsets that are used for this purpose were made for the military
WWII. These units were made for the Navy ships where it was critical
loss of electrical power onboard did not knock out communications
“plane spotters” and the “gunners”, or the bridge and steering or
rooms. Balanced Armature or Sound Powered elements were developed that
used no outside power source. The sound from a person’s voice travel to
the “Mic” unit, which generated a small amount of electrical signal
could be picked up by headset or “ear” unit. No outside power was
because it generated its own power. If a section of the ship was
out by a bomb blast and the wires were destroyed between the spotters
the gunners, a cord could be rolled out on the deck, and the two units
could be reconnected up in an instant. In this way the ship was not
defenseless for very long. Two basic types of units were used by the
“Deck Talkers” which were a headphone and chest mic unit for spotters
gunners, and handsets which resembled a telephone handset.
The very efficient
of these units, due to the small signals that were used, is what makes
them perfect for crystal radios. The main problem with these units is
very low impedance. They must be matched to the radio using matching
to obtain high sensitivity, without “loading” the radio’s circuit. For
more info on matching transformers go to “Matching sound powered
to crystal sets using transformers” link below or to Ben Tongue’s web
The “mic” unit can be
as “ear” piece also. On the main page of this web site are examples of
units as they look before being converted to use on crystal sets. Some
are WWII era and some are post-war era. There are a few units still
made for use today. The fire departments use sound powered units today
because they can be used in areas which may contain explosive gases
the fear of a spark setting the gases off. Also they don’t use
which might go dead at the wrong moment.
Cautionary Notes On
I would like to try and help
clear up a few misconceptions
Sound Powered headphones.
Sound Powered elements will be louder then my vintage magnetic
so I will get a pair.
Please remember that Sound
Powered elements reach their "glory"
trying to pick up a “very faint” signal. This is where they will excel.
Because of their efficiency they will pick up stations that magnetic
not. On signals that are very strong you might see a very small
compared to vintage magnetic headsets. In fact in some cases, vintage
sound better such as music. Sound Powered Elements will continue to
up faint stations where vintage or magnet headsets stop. In this one
only are Sound Powered elements “louder” than vintage. They will
quit nicely on local stations also, but they are at their best at the
level signals because of their efficiency.
I want to get a set of Sound Powered headsets so I can start
If you don't already know, adding
headphones of any kind will
always get you DX. You must optimize the radio first to gain its full
More can be done to the radio to increase efficiency than you can gain
by adding SP headphones. If you are already there then that is another
story. Sound Powered headphones will not instantly bring in “DX”. They
might, but probably not.
I’ll buy a set of Sound Powered and just put them on my set
they will work better than my vintage.
You must match the SP headphones
to the radio. If you do not
a matching transformer, you might as well not use the headphones. The
is low on Sound Powered elements and must be raised to more closely
the radio. For example, a set of Vintage or magnetic headphone are
12k to 23k ohms AC. Not a perfect match to a good radio, but not bad.
a set of Sound Powered elements wired in series will get you about 1200
ohms AC. That is way too low for a radio. By using a transformer to
that to a higher level such as 50k to 100k (or higher) you can “match”
the impedance of the radio. Any loss from the transformer is more than
made up in the matching. Even a vintage headset can be helped with a
transformer. Please see the "Matching" section which is off the "Main"
page for further information.
This is covered a little in the "Comparison"
Now I would like to make a few
comments on comparing Sound
units. I know there is a huge rush to the king of Sound Powered
RCA, but you must please keep some very important things in mind when
to buy a set of Sound Powered units.
When comparing Sound Powered
units there are at least three
to take into consideration first.
Condition, Condition, Condition. Sounds like real
location, location, location! Here is what I mean by “ Condition,
Contition #1-- It depends on the
condition in which they came
of the factory. Did they meet the high end of the factory specs. or did
they just barely pass minimum standards? If they are RCA's and met
standards, (which a lot of them did because there was a war going on
they needed them) then they might not be the "best" but are still very
Condition #2 -- It depends on the
condition they are in now. A
has happened to these units since W.W. II. Salt water, bomb shells
off next to them, sinking ships, laying in someone's back yard or
for 50 years and so. They are very susceptible to rust, corrosions,
blows that can knock the armature out of center, and so on.
Condition #3 – This is my
favorite condition, the condition of
you are comparing yours to. If I have a top of the line set of Western
Electric SP units that are NOS (new old stock) and met the highest
coming out of the factory and I compare them to a beat-up set of RCA's
that just made it out of the factory (just over the minimum standards),
then the WE's will be the "best", but is that true for all WE's ?
NO. You can only tell the true differences by comparing many sets of
brands. Any of the top 4 or 5 SP units on the list could be the "best"
at any given time. So don't get caught up in the "I have got to
RCA's or nothing" syndrome. Most of the Sound Powered units will out
magnet sets. When trying to make a “comparison list” it is very
to do so. The list I have come up with is not from just my knowledge,
from years of experience from people such as Sky or Steve (Baldy).
this experience a list could not even start to be made. I think a list
is sometimes more of a disservice that a service. It makes those who
less experience with Sound Powered units think they must have the best,
and that must be the one at the top of the list, RCA. This can help to
raise the cost of RCA’s and add undue cost to your hobby. I would be
with any of the top 5 brands, or even 6 or 7. They are all good
and great fun!!
Introduction Part 2
What makes a "Sound Powered" element more
a old style "Balanced Armature" element or a