A speaking tube or voicepipe is a device based on two cones connected by an air pipe through which speech can be transmitted over an extended distance. While its most common use was in intra-ship communications, the principle was also used in fine homes and offices of the 19th century, as well as fine automobiles, military aircraft, and even locomotives. For most purposes, the device was outmoded by the telephone and its widespread adoption. This device was also known as a "megaphone", but that use has since become superseded.
Early voicepipes consisted of two cones, of wood or metal, one end shaped to fit the speaker's mouth, connected to the other which was flared to amplify the sound. Later designs of the voicepipe inserted a removable cork-mounted whistle, which could be sounded by blowing into the tube from the other end. On naval vessels, this created a distinctive sound associated with urgent intra-ship communication on old warships. The sound of the whistle would summon the listener, who would remove the whistle and answer the call.
Voice pipes could be used over distances as long as 300 feet (90 m). However, very long speaking tubes might use an electrical signalling device to indicate a call, as the large volume of air in the pipe would make it difficult to blow with enough pressure to sound a whistle at the far end. Despite this, a pipe with a larger internal diameter was desirable for longer runs as the signal loss is inversely proportional to the pipe's cross-sectional area.
Voicepipes have no switching mechanism and so, to provide multiple destinations, separate voicepipes with dedicated transit pipes have to be provided between all pairs of desired endpoints.
The technology continues to be used into the electronic age due to its reliability and low cost. Voice pipes are unaffected by a complete electrical power loss or by an Electromagnetic pulse. Warships built as late as the 1950s continued to incorporate voicepipes alongside more advanced technology.
Maritime use 
Voice pipes, the maritime term, served to transmit reports from lookout positions aloft to the deck and from the bridge to the steering position and engine room. These were somewhat larger in diameter than the domestic version and were often covered in sound absorbent material to increase their efficiency. About 1780, one captain removed a canvas voice pipe installed by an imaginative midshipman saying he was sure the topmen would “use it for an improper purpose”.
One disadvantage of voice pipes is that they may breach the integrity of watertight spaces. This led to the introduction of shut-off valves on both ends of voicepipes to prevent water from a flooded compartment from entering other compartments via its voicepipes.
Permanently fitted, rigid voice pipes are still in use and are generally covered with heavy lids to avoid ingress of water. The speaker has to place the mouth in the "horn" or bell-shaped end of the pipe and the receiver has to 'bend an ear' to hear what is being said.
Voice pipes have generally been replaced by sound powered telephones. Even on modern ships, however, they may still be found linking wheelhouse and binnacle for communication of magnetic compass heading to the helmsman in the event of a blackout.
Domestic use 
In domestic applications, voicepipes were smaller and referred to as "speaking tubes". The ends of the tube were often flexible for convenience of use. The speaking tube supplemented the array of remotely controlled hand bells that were operated in the upstairs rooms and rang in the servant's quarters in even modest houses in the 19th century. The phrase "get on the horn" and "give him a blow" as well as the use of "blower" as a synonym for "telephone" are generally accepted as having their origin in this feature of speaking tubes.
Speaking tubes were employed in some offices, with whistles at either end and were therefore also known as whistling tubes. Several speaking tubes could be hung from the edge of a desk to communicate with different locations.
Speaking tubes were also used in fine automobiles, allowing communication between the separate passenger and driver's compartments when desired.
Gosport tube 
A 'Gosport Tube' was a voice tube used by flight instructors in the early days of military aviation to give instructions and directions to their students. It was invented by flying instructor Robert Raymond Smith-Barry at the School of Special Flying he opened at Gosport in 1917.
Modern usage 
Acoustic tube headphones (also called pneumatic earphones or air earphones) are used especially in two-way radio. These are useful because a clear tube can be used to hide the earphones. They are also used to provide music to patients undergoing an MRI scan, as it would be dangerous to use metal wiring in the scanner's magnetic field.
Pneumatic intercoms can be applied to motorcycle helmets for pilot-passenger communication. Similar systems are common on ultralight aviation too. They are sometimes preferred over bluetooth or other radio technologies due to their simplicity and absence of batteries.
Up to the 2000s acoustic tubes were in use in some civil aircraft for movies audio and other audio broadcasting in-flight entertainments.
The principle of the speaking tube can be found on certain playground equipment, which employ tubing connecting sound horns or other speaking boxes to allow voices to travel to separate points, for the amusement of the children.
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See also 
- Acoustic transmission line
- History of the telephone
- Pipe (fluid conveyance)
- Pneumatic tube
- Tin can telephone
- "Voicepipes and Speaking-Tubes". The Museum of Retro-Technology. March 15, 2010. Retrieved October 17, 2012.
- Pseudo. 'Suffolk Coast' (1933). Memories of an Old Ipswich Mariner Capt. R. H. Gower. Suffolk Chronicle 2nd December.
- Vincent Orange, "Barry, Robert Raymond Smith- (1886–1949)", Oxford Dictionary of National Biography, Oxford University Press, 2004 accessed 12 September 2007
- The Amplifier Institute: