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In the very early years of radio, headphones was about all there was for sound reproduction. The horn speaker became the  norm in the late teens. Most early horn speakers consisted of a sound magnifying horn with a what was not much more than the sound element of a headphone attached to the base.

When you purchased your new radio in the early 1920's most of them did not have enough power to drive a loudspeaker so headphones was how you listened. Many companies offered one or two stage (some had  three) audio amplifiers that would amplify the weak audio sound enough to drive a load speaker. These (amplifiers and loudspeakers) of any brand of could be attached to the simplest of radio receivers (even crystal sets) so the whole family could listen.

Loud speakers were usually an option and if desired were purchased separately. Most all permanent magnet speakers of the 1920's had an  impedance of around 2000 ohms. All permanent magnet (2 wire type) speakers were compatible with any radio of that era that could drive a loudspeaker. This applies to both the horn and disc type speakers. The disc (or cone speaker) were introduced in the mid late 1920's and were compatible (and proper for use) with any brand 1920's radio. This applies to either battery or the early AC sets. The exception was some of the AC operated sets made in the late '20's required an electrodynamic speaker (more on this type later). It was quite common to have a radio of one brand and a speaker of another as many speaker companies did not make radios and some radio companies did not make speakers. It is proper and ok to use any radio - speaker combination of that era as few sets came with a speaker unless it had one built-in or a combo pack was offered. There were a few (very few) speakers designed (cosmetically) to go with a particular radio, an example was the RCA Radiola 33 receiver that was sold with the Radiola 100B speaker.

Speakers with 3-4 or more wires were usually designed electrically for a particular set and almost always had a special plug that plugged in to the radio chassis. These type speakers were not usually compatible with other radios. You should never apply power to a radio with a proprietary  speaker (electric sets) without the speaker  connected. Doing so will almost always result in damage to the radio's power supply. These 3-4 wire speakers  are "electro-dynamic", that is their magnet is energized by a coil (this is called the field coil) which is part of the power supply circuitry of the radio.  A good example of this type is the Atwater Kent 55. Speakers with only 2 wires will have a permanent magnet.

I should mention that there were certain speakers that were promoted but not included with the purchase of a particular Radio, for example; the Radiola 44 and 60 were both promoted with the Radiola 103 speaker, these are shown on the "Radiola Info" page. The Radiola Super-Heterodyne portable and the Radiola IIIA were sold with the UZ-1320 0r UZ-1325 speaker.

I am often ask if these early speakers can be operated from a modern radio or amplifier, that answer will be found on my Tech Tips page.