English: A radio shop in Amberley Working Museum, stocked with old radios and loudspeakers. The 6 speakers on the lower shelf are all horn loudspeakers from the 1920s. They consist of a small compression driver unit containing a small metal diaphragm vibrated by an electromagnet, creating sound waves. The sound is conducted to the open air through the flaring horn. The horn serves to improve the efficiency of the coupling between the diaphragm and the air, so they produce more sound power and are louder than cone speakers when driven by a given signal. The weak vacuum tube amplifiers in early radios couldn't produce much output power, and virtually all loudspeakers from the period used horns to achieve adequate volume. A disadvantage of horn speakers was that the frequency response dropped off below a certain cutoff frequency. Therefore they couldn't reproduce bass frequencies below the cutoff, causing them to sound "tinny". Permanent magnets of the time weren't very strong, so many speakers, such as the Magnavox (right), used electromagnets for the field magnets, usually powered by a 6V lead-acid storage battery.