There's a general fixation of large scale audio devices used by government and military. And on Taiwan's Kinmen island there are several of 30 foot speaker banks that due to the close proximity of mainland China, were used to blast propaganda messages across the 4 miles of water that separate the island from China.
Consisting of large concrete structures, around 30 feet tall, with banks of 48 piercing mid range horns, a small desk and a microphone that the announcer would sit at to give their message.
Must have been incredibly loud - we have no information on power output was, but they were designed to throw the anti-communist messages up to 25 kilometres and when weather conditions were favourable, much further. Inhabitants of the island must have been exposed to high sound levels too - though its not clear how often they were used. This technique is still used in Korea between North and South, with South Korea only recently agreeing to stop blasting K-Pop over the border 24-7!
The speakers have been in place for around 60 years, and this year on August 26th, a group of artists are to power up one of the towers for a different kind of transmission. Berlin based Augustin Maurs and four Taiwanese artists are calling the installation piece "Sonic Territories". Those expecting soothing ambient tones (would would be quite nice) may not get what they want, at least from Maurs - his work is more challenging and avante garde.
Britain also has its own audio installations - the acoustic mirrors at Kilnsea Grange, West Yorkshire and Denge in Kent were used in wartime to listen out for approaching aircraft, before radar was developed.
Original item - Artnet.com