Speaking tube A speaking tube or voicepipe is a device based on two cone s 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 This device was also known as a " megaphone " , but that use has since become superseded . Design . 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 . 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 switch ing 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 telephone s . 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 bell s 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 intercom s 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 employs tubing connecting sound horns or other speaking boxes to allow voices to travel to separate points , for the amusement of the children .