Electrical World, August 2, 1913, page 251:

Loud-Speaking  Telephone  Enunciators  in  Baseball  Grand  Stand

    An interesting trial installation of loud-speaking telephones, which may be made a permanent feature, has been made in the Comiskey Baseball Park in Chicago. It consists of a number of the recently developed telephone enunciators known as "musolaphones" and installed by the Chicago Musolaphone Company. The reproducers of this system are incased in horns or resonators suspended over both tiers of seats in the grand stand. Ultimately about 175 of these reproducers will be installed and about half of that number are in use now.
    By means of this system the announcement of the batteries of the baseball teams, changes in the line-up, or other announcements, may be made to the assembled audience. There is one transmitter booth where the operator sits, and an "amplifier," to build up the tone, is used for each five reproducers. Before the game begins the system is utilized to transmit phonographic music from a Victor record. The music is rather harsh and not particularly pleasant, but the speaking announcements are clear and effective. The musolaphone people say that the "music" could be toned down by introducing more resistance into the circuit.
    The musolaphone is said to be adapted for announcing bargain sales to department-store throngs, giving fire alarms in crowded factories, announcing the departure of trains in railroad stations or varied purposes of like nature. It can also be connected with a commercial telephone service to transmit music to subscribers. An interesting fact, and one which does not seem to be clearly understood, is that where a quartet is singing in the studio or transmitting booth a better effect is obtained if a separate transmitter and an individual source of electricity are used for each performer. A motor-generator set, consisting of a motor and four small direct-current generators, has been devised for this purpose.
alplifier diagram