English: Drawing of an early cone loudspeaker, the "Farrand Inductor" by Acoustical Engineering Associates, New York, from an advertisement in a 1929 radio magazine. Loudspeakers that used a paper cone for a diaphragm replaced horn loudspeakers in the mid-1920s. Although many cone speakers from this time used older moving-iron drivers, this one used the "electrodynamic" moving coil mechanism invented in 1924 by Chester Rice and Edward Kellogg, and so worked similarly to a modern speaker. The two horseshoe magnets that generated the magnetic field are visible. It was sold in two sizes: the 10" model 6-G for $10 and the 12" Model 10-G for $11.

Part of ad copy: "An entirely new principle is involved in the Inductor unit. The armature, instead of moving from side to side in the direction of the pole pieces, as happens in the ordinary magnetic units, moves like a piston along the length of the air gap and maintains a steady distance from the pole pieces. As the sensitivity is extraordinarily high, the gap is made wide and the armature will not strike the pole pieces."