Origins of electrical sound

Live amplification begins with the telephone, because the telephone first turned a voice into a current. Bell’s liquid transmitterAlexander Graham BellLiquid transmitter1876Alexander Graham Bell's liquid transmitter used a needle attached to a diaphragm and dipped in acidulated water, so that sound moving the needle varied the circuit's resistance. It is described in his US patent 174,465, 'Improvement in Telegraphy', filed 14 February and granted 7 March 1876. Bell used a version of it on 10 March 1876 for the first intelligible transmission of speech by wire, to Thomas Watson.Open profile → of 1876 proved that a varying resistance could follow speech, and the fragile Reis telephoneJohann Philipp ReisReis telephone1860–1861Johann Philipp Reis, a German schoolteacher, built a make-and-break transmitter modelled on the human ear and a receiver using magnetostriction in an iron needle, demonstrated to the Physikalischer Verein in Frankfurt in October 1861. He coined the word 'Telephon'. It sent musical tones reliably, but speech reproduction was inconsistent.Open profile → had already hinted at it. The Bell magnetic receiverBell TelephoneTelephone receiver1876Bell's receiver placed a permanent magnet wound with a coil near an iron diaphragm; line current changed the magnetic field and vibrated the diaphragm. His cylindrical 'iron-box' receiver of spring 1876 replaced a less efficient tuned-reed design, and was shown at the 1876 Philadelphia Centennial Exhibition.Open profile → could turn that current back into sound, but only for one ear pressed against it.

Alexander Graham Bell Liquid transmitterCodeName47km · CC BY-SA 4.0Johann Philipp Reis Reis telephoneScience Museum Group · CC BY-SA 4.0Bell Telephone Telephone receiverAlexander Graham Bell · Public domain (US patent)

The carbon microphone made the signal strong enough to be useful. Edison’s carbon transmitterMultiple inventorsCarbon transmitter1877Sound pressure varies electrical resistance through compressed carbon granules.Open profile → and carbon buttonThomas EdisonCarbon-button transmitter1877–1878Thomas Edison's transmitter placed a button of compressed lampblack carbon beneath the diaphragm, so sound pressure varied its resistance and a battery supplied most of the signal power. Filed in 1877, the patent was not granted until 1892 (US 474,230). Western Union marketed the design before selling its telephone business to the Bell interests in 1879.Open profile →, Berliner’s loose-contact transmitterEmile BerlinerLoose-contact transmitter1877Emile Berliner filed a caveat on 14 April 1877 for a transmitter that varied the pressure, and so the resistance, at a contact between a vibrating plate and a fixed point. His patent was not granted until 1891 (US 463,569) after long Patent Office proceedings. Combined with Francis Blake's design, it became the Berliner–Blake transmitter used by Bell licensees in the 1880s.Open profile →, the Blake transmitterFrancis BlakeBlake transmitter1878–1879Francis Blake Jr., a former US Coast Survey physicist, developed a carbon transmitter patented in Britain in January 1879. Paired with Emile Berliner's contact principle, the Berliner–Blake transmitter became the Bell standard for most of the 1880s, mounted as the top box of three-box wall telephones.Open profile → and Hunnings’ granulated-carbon transmitterHenry HunningsGranulated carbon transmitter1878–1881Henry Hunnings, a curate near York, developed a transmitter using loose carbon granules between two platinum electrodes behind the diaphragm, patented in Britain in 1878 and the US in 1881. On 27 January 1880 it was demonstrated over about 45 miles of telegraph wire between Darlington and York. Hunnings sold the patent to Edison, but the granule principle became the long-term standard.Open profile → each raised output and stability. That extra level later let carbon microphones drive the first public-address amplifiers directly. On the reproducing side, Lodge’s 1898 moving-coil patentOliver LodgeMoving-coil transducer patent1898Oliver Lodge's British patent 9712 of 27 April 1898 refined the moving-coil transducer, using non-magnetic spacers to hold a precise air gap between the magnet's poles, as part of a 'telephone relay'. It built on Siemens's 1874 moving-coil patent and became practical only once valve amplifiers could supply power.Open profile → described the motor that every dynamic loudspeaker still uses, decades before anyone could feed it enough power.

Multiple inventors Carbon transmitterH. R. Van Deventer · Public domainThomas Edison Carbon-button transmitterGerry Ashton · GFDLEmile Berliner Loose-contact transmitterEmile Berliner · Public domain (US patent)Francis Blake Blake transmitterPopular Science Monthly, vol. 70 (1907) · Public domainHenry Hunnings Granulated carbon transmitterHenry Hunnings · Public domain (US patent)Oliver Lodge Moving-coil transducer patentOliver J. Lodge · Public domain (US patent)

Power came from the vacuum tube. Fleming’s two-electrode valveMarconi / J. A. FlemingFleming valve1904John Ambrose Fleming built the first oscillation valves in October 1904 and patented them that November (US equivalent 803,684): an evacuated bulb with a heated filament and a separate plate that conducted current one way only. Marconi used it as a radio detector.Open profile → could only rectify. De Forest’s three-electrode AudionDe Forest WirelessThree-electrode Audion1906–1907Lee de Forest added a third electrode, the grid, to a two-electrode vacuum tube in 1906, creating the Audion, the first device able to amplify as well as detect electrical signals. Early Audions used a lamp-style glass envelope built by incandescent-lamp maker H. W. McCandless.Open profile → and the Lieben–Reisz valveRobert von LiebenLieben-Reisz valve1906–1913Robert von Lieben, with Eugen Reisz and Sigmund Strauss, developed a mercury-vapour valve with a control grid intended to amplify telephone signals; his German patent 179,807 was published on 18 November 1906. The 'LRS relay' was demonstrated for telephone amplification by 1911–13 and then manufactured by the Lieben Konsortium.Open profile → added a control grid. Once Arnold and others made that grid work as a true gain stage, the Audion amplifierDe Forest / later developersAudion amplifier1906 patent; amplification demonstrated laterA control grid modulates plate current, allowing a small signal to control a larger one.Open profile → could lift a carbon microphone’s output to loudspeaker level. Microphone, amplifier, loudspeaker: the chain every modern live system follows was now complete on paper, and the next era would wire it into public halls.

Marconi / J. A. Fleming Fleming valveGerald F. J. Tyne · Public domainDe Forest Wireless Three-electrode AudionPaul Thompson · Public domainRobert von Lieben Lieben-Reisz valveDrahtlos · CC BY-SA 4.0De Forest / later developers Audion amplifierLee De Forest · Public domain

Wired loudspeaker distribution arrived before the valve amplifier. In 1910 Automatic Electric of Chicago announced its Automatic EnunciatorAutomatic ElectricAutomatic Enunciator1910Automatic Electric of Chicago announced the Automatic Enunciator in 1910, a loudspeaker for wired telephone-line distribution, and a separate company was formed to sell it. It was used for announcements in hotels, stores, factories and railway stations before outdoor installations followed.Open profile →, first pitched as a hotel paging system. In August 1912 an outdoor installation of 72 loudspeakers covered about half a mile of grandstands at a Chicago water carnival, and in 1913 units were installed at Comiskey Park, the Musolaphone stadium system.

Automatic Electric Automatic Enunciator© FOH magazine; photographer not credited · Rights retained by the rights holder; reproduced for historical commentary