louden
verb
loud·en ˈlau̇-dᵊn 
loudened; loudening ˈlau̇d-niŋ
ˈlau̇-dᵊn-iŋ
intransitive verb
: to become loud
transitive verb
: to make loud
Example Sentences
Recent Examples on the Web After Trump's three anti-Muslim retweets, the calls loudened for the trip to be scrapped. 
Michelle Kosinski, CNN, 19 Dec. 2017 Further reading of the thread finds that this operation loudens up the iPhone dramatically: Some posters claim a figure of 40%. Charlie Sorrel, WIRED, 21 Jan. 2008
Michelle Kosinski, CNN, 19 Dec. 2017 Further reading of the thread finds that this operation loudens up the iPhone dramatically: Some posters claim a figure of 40%. Charlie Sorrel, WIRED, 21 Jan. 2008 Word History
First Known Use
circa 1848, in the meaning defined at intransitive sense