1) Radio Corporation of America (RCA) headset &
handset elements
2) Western Electric (WE) handset & headset elements
(sound powered)
3) US Instruments (USI) handset elements
4) Automatic Electric (AE) handset elements (sound powered)
5) Stromberg Carlson (SC, Strombergs) handset elements
6) Stromberg Carlson (SC, Strombergs) “Deck Talkers”
“mic” elements (HS-200U)
7) Stromberg Carlson (SC, Strombergs) “Deck Talkers”
“ear” elements (HS-200U)
8) TA-1/PT field phone elements (various makers)
9) Dynalec handset elements
10) Dynalec headset “mic” elements (HS-200U)
The following are sound powered units generally considered to be notably less efficient than the others for crystal radio use. They will, however, probably outperform any conventional headphone.
11) Sound Powered Communications Co. (SPCC) handset
12) Wheeler handset
13) Dynalec headset “ear”elements (HS-200U)
14) Remler
Not in this rating are the headsets made by Nathanial Baldwin. They
are indeed Balanced Armature units, although they are not considered "sound
powered" units. First patented 1910 in Utah, they are the best of the vintage
sets then and now.
A unit that is in excellent shape might perform better than a higher rated unit that is in need of repair.
New old stock (NOS) might be better than one that went down with the ship!
Most sound powered units are better than magnetic headphones if the sound powered unit is in good working order.
It should be mentioned that old sound powered elements frequently need to be readjusted and cleaned to achieve working status or best operation. An element that has continuity but weak, distorted, or no sound, probably just needs servicing, but is otherwise OK. Always seek advice before tearing into them. Irrepairable damage is disappointing, and will cost you your investment. Advice can always be obtained at the Crystal Set Radio Club on Yahoo Clubs. Just join and ask, it's free!
Sound powered units are difficult to rate. They are subject to personal preferences, quality of construction, condition of units, and how easy it is to adapt elements into headsets. The above comparison is only a guide, and care must be taken in its use. This evaluation cannot be accurate 100% of the time, due to so many factors that affect these units. Of course, the most important factor is proper impedance matching of the unit to the crystal set. A proper matching transformer is a must for optimum performance of the unit. See Ben Tongue’s web page on impedance matching at http://uweb.superlink.net/bhtongue/index.html (a must see site for sound powered units).