The four mile p.a. system...

[pucho812]

A prototype horn loudspeaker driven by compressed air and an "artificial larynx" used as a portable public address system in Los Angeles, California, USA in 1929. The inventors tried to imitate human vocal cords. It could reportedly project voice or recorded music 4 miles. A vacuum tube audio amplifier powered 4 "artificial larynxes" which modulated compressed air going into the horn provided by a 50 HP gasoline engine and compressor. The owners rented out the powerful system for $300 per hour.

https://www.americanradiohistory.com/Archive-Radio-News/20s/Radio-News-1929-05.pdf

 

[emrr]

So awesome

 

[JohnRoberts]

$300 an hour was real money in 1929.

JR

 

[pucho812]

$300 an hour was real money in 1929.

JR

true. in a lot of places it still is.