Large horn loudspeaker from 1928 built for use in movie theaters and concert halls. Because early vacuum tube audio amplifiers couldn't produce much power, and horn loudspeakers can produce about 10 dB more sound power from an amplifier than a cone speaker, loudspeakers in theaters until WW2 were horn speakers. In order to reproduce bass frequencies adequately the horn had to be large, with a wide mouth and a sound path of 12 - 18 feet. This was a standard theater horn made by Bell Telephone Laboratories in New York for sound research. Scientist S. P. Grace holds a replica of Alexander Graham Bell's original telephone "loudspeaker" transmitter for comparison.