Speaker technologies

[Mark Schroeder]

Looking for technical info all about speaker technologies from the 20’s through the 50’s. Looking for that “rare” detail about dynamic vs non-dynamic, power handling, load, inductance, etc? Can anyone point me references that can give me these? Almost none of the technical schematics of these eras provide this, nor do the various parts catalogs. These just show a “speaker” and of it is a electrodynamic or not. And what the specifications are for these? Did Jensen ever put together a catalog that would help take any mystery out of what the best speakers are for various radio brands? Did Scott ever provide specs for the speakers they sold or recommended for their radios? If so, where would that be found?  Thanks. 

[Norman S Braithwaite]

EH Scott Radio Laboratories never made speakers.  Specifications of Jensen speakers appropriate for the time frame were published by Jensen and in electronic products catalogs which can be found on line.  I have not seen specifications published for Magnavox speakers also employed by EH Scott Radio Laboratories.

Norman

[Mark Schroeder]

Thanks Norman. Do you have a link to any of the technical specs for the Jensen or Magnavox that you can share? Do you know if EH Scott ever recommended a specific model type from Jensen that they had designed the radios and optimized their designs for?

[David C. Poland]

You are on an antique radio site,  mostly pre-WW2 era or shortly after WW2. The standardization to 4, 8 and 16 ohm speakers with permanent magnets is pretty much a post war development.

Prewar radio design engineers included the specs for the speaker too. Voice coil impedances range widely from 3 or 4 ohms to upwards of 38 ohms depending on the design engineer's choice. Often the output transformer is attached to the speaker frame. Pre war magnets were not very good and so, except for battery radios, there was heavy reliance on field coil speakers through the 1930's - the field coil not only energizing the magnet but also acting, frequently, as a choke in the high voltage circuits.  Field coils can range from a couple hundred ohms to 5,000, 10,000 ohms and more and may be tapped to provide more than one voltage reduction. Some E H Scott radio speaker have two field coils. The field coil is shown on a circuit diagram as part of another circuit and is seldom anywhere near the speaker and output transformer on the diagram.  My point being pre-war speakers are often unique to a particular few or only one radio model.

Departing from the original speaker can involve dealing with more than just a speaker choice - because the output tubes must work in conjunction with a proper output transformer for the substitute  speaker. And a proper substitute for the field coil is required as well. 

In contrast,  1920's era speakers are a whole other world. They are higher voltage, low current devices. They preceded moving voice coils technology of about 1929. The modern speaker is a low voltage, higher current device. The purpose to output transformer was to step down working voltage of the tube circuit to match the speaker to the load needed by the output tube(s). 

1920's horn speakers were derived from telephone technology and later 1920's cone speakers were some improvement.  Both operated with a resistance coil of the order of 2000 ohms (more or less) in series  with the plate circuit of the output tube, meaning in a circuit of maybe 20 volts, or  45 or 90 volts or maybe 135 volts or more depending on the radio design and the batteries and tubes used. No output transformer.  Such speakers had poor frequency response by today's standards. Substituting a modern speaker would require adding a proper output transformer too. 

[David C. Poland]

There is a wealth of information on the various E H Scott models on the archive section at the top of this page. For almost every Scott model, the speaker is unique to that model owing to the tubes and circuit requirements. The Jensen and Magnavox speakers were custom  versions of standard theater size speakers - custom as to the voice coil, attached output transformer, the field coil(s) and for the cable plugs. The speakers are not interchangeable  between models (but for one exception that I know of). 

[David C. Poland]

East E H Scott radio was shipped with the correct speaker(s). 

E H Scott Radio is not to be confused with the H H Scott component HI Fi products of the late 1940's, 1950's and 1960's