Did the Romans have any other sources of news announcement?
They had "newspapers" of a sort but since they did not have printing at the time, the announcements were hand written.
The urge to inform the public of official developments and pronouncements has been a characteristic of most autocratic rulers. This urge was fulfilled in ancient Rome by the Acta diurna (“Daily Events”), a daily gazette dating from before 59 BCE and sometimes attributed in origin to Julius Caesar. Handwritten copies of this early journal were posted in prominent places in Rome and in the provinces with the clear intention of feeding the populace official information. The Acta diurna was not, however, restricted to proclamations and edicts (or to political decisions taken in the Roman Senate, which were reported separately in the Acta senatus, literally “enactments of the senate,” papers restricted to senators alone). The typical Acta diurna might contain news of gladiatorial contests, astrological omens, notable marriages, births and deaths, public appointments, and trials and executions.
The speaker was useful for providing news to large groups.
In ancient Rome such a person was called as praeco (plural praecones).
Roman “shouters” announced the news mainly during nundiae, that is, on the eight1 day of the week, when people working in the field came to the city to sell and buy products. It was a kind of weekend for the Romans. At that time, the capital was visited by many citizens, who at the time mostly also voted. Praecones thanks to that were able to give the news to a larger group of people.