File:Early home radio loudspeaker.jpg

English: An early loudspeaker used with home radios around 1920.. This is similar to early Magnavox loudspeakers and may be a Magnavox Telemegaphone (1920, $75) or R3 (1922, $45). It is a horn loudspeaker, consisting of a driver unit (bottom) containing a small metal diaphragm vibrated by an attached voice coil. The sound waves were conducted to the open air through the flaring horn. The purpose of the horn was to increase the acoustic impedance loading of the diaphragm, coupling it more efficiently to the air. Horn loudspeakers produced much more sound power than cone speakers. The vacuum tube amplifiers in early radios had low gain and produced very weak output power, in the milliwatt range. So virtually all early speakers used horns to produce adequate volume.

Before 1920 radios were listened to with earphones and didn't come with speakers. When radio broadcasting began in 1920, it created a desire for family listening. So separate loudspeakers like this one were sold which plugged into the earphone jack. Permanent magnets of the time weren't strong enough to create the magnetic field needed for the voice coil, so electromagnets were used in the driver to create the field. The speaker had four terminals; the pair in the front was the signal input from the radio, while the pair in the back (one visible at right) was connected to a battery to power the field coils. The small box next to the front terminals was an audio transformer to match the voice coil's low impedance with the higher impedance of the earphone output.

The caption of the picture read: "A popular small-sized type of loudspeaker used with the usual two-stage amplifier of the radio receiving set. A 6-volt storage battery is used to energize the field coils."