"sound-4". Oxford English Dictionary. Archived from the original on 19 August 2012. Retrieved 3 March 2013.
thefreedictionary.com
"sound-3". TheFreeDictionary.com. Retrieved 3 March 2013.
unesco.org
"Baltic Straits". Legal provision for integrated coastal zone management, Chapter 2.3: International straits and canals. UNESCO. Retrieved 3 March 2013., archived version
web.archive.org
"sound-4". Oxford English Dictionary. Archived from the original on 19 August 2012. Retrieved 3 March 2013.
"Baltic Straits". Legal provision for integrated coastal zone management, Chapter 2.3: International straits and canals. UNESCO. Retrieved 3 March 2013., archived version