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I'm restoring an old RCA radio from the 1940's. From looking the schematic I have this question: What is the theory behind this speakers connection arrangement? What's the benefit of using an electrodynamic speaker with a permanent magnet speaker? enter image description here

Envidia
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Asaf Smilan
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  • Before inexpensive strong AlNiCo magnets were possible, they used electro-magnets , here with the option for either. – Tony Stewart EE75 Jun 25 '21 at 19:32
  • As the PM speaker plugs in, perhaps it's an optional extra to provide sound in another room. See https://electronics.stackexchange.com/questions/423864/em-vs-pm-speaker/423881#423881 for more about the wound-field speaker. (note the NEUT. COIL on the field armature : it cancels out hum induced by ripple in the field winding/PSU choke –  Jun 25 '21 at 19:32
  • The Speaker electromagnet was used as a filter choke in many radio power supplies. That way they got a two for one. The major benefit is it is easier to mount a speaker rather then a cumbersome chjoke. The electrodynamic speaker in that time frame sounded better especially at the lower frequencies. – Gil Jun 25 '21 at 20:06

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