The 1920s saw much development in horn loudspeakers, and loudspeaker in general. Western Electric already had their microphones, amplifiers, straight exponential horns, and very good balanced armature transducers. At this time, much research was also put into disc recording and reproduction at the Western Electric Engineering Department, and simultaneously, optical recording of sound was also in progress, using Wente’s Light Valve. The time seemed ripe to attempt sound film. The story has been told elsewhere, but in short, most of the industry turned down Western Electric’s offer. They “knew” sound film would not work. But the Warner Bros found in the WE system something that could help them beat the big guys in the industry, and after the success of their first sound film, the rest is history.
It is hard to tell when horns first were used. They have been in use for thousands of years as instruments, and man must early have discovered the amplifying effect of a pair of cupped hands in front of his mouth, or behind his ears. Ear trumpets were early implementations of this, and the first hearing aids.
Horns were used on phonographs and gramophones from the start. This was the only way to get the required volume from the tiny motions of the needle. The theoretical understanding of horns was still small though, and most of the work was experimental. Early models used conical horns, but as theory progressed, the superiority of the exponential horn was recognized.
The 39th Scandinavian Symposium on Physical Acoustics will be held at Geilo Hotel from January 31 to February 3, 2016. This year it is organised by Ulf Kristiansen and Erlend Viggen, both at ARC. The theme for the meeting will as usual be physical acoustics, with emphasis on hydroacoustics, nonlinear acoustics, ultrasound, general sound propagation and applications in technology, medicine and fisheries.
The purpose of these meetings is primarily to stimulate contacts and exchange information between different Scandinavian teams working in this research area. Although the symposium is Scandinavian, foreign participants are most welcome, and the meeting language will be English. As usual, we expect a rather informal tone, the main goal being to create contacts, not only during sessions, but also by social activities, indoors and outdoors (cross country and downhill skiing). The meeting normally attracts about 50 participants holding about 25 talks throughout 5 sessions.
Reis’ telephone was perhaps the first loudspeaker of any kind, as it employed a magnetostriction driver mounted in a resonating box. But it would still take many years before inventors discovered the virtues of baffles and enclosures. As Hunt puts it, the baffle is probably the most frequently rediscovered feature of loudspeaker art. Stokes, in 1868, pointed out that the radiation efficiency could be improved by preventing air circulation around the edges of a vibrating surface (the acoustic short-circuit). Rayleigh, a few years later, gave the now classic analysis of the radiation from a piston in an infinite baffle. But by the time loudspeakers were being produced in great numbers, Rayleigh’s Theory of Sound had been out of print for more than two decades, and many inventors discovered the baffle before they discovered Rayleigh.
Nå på mandag holder jeg prøveforelesning i forbindelse med professorstillingen etter Ulf. Den har ikke blitt annonsert veldig tydelig av IET, men her er en antydning:
Prøveforelesning: «Aeroacoustic sound generation mechanisms» i Elektro B418 på mandag 14/9 kl 1015-11 anbefales for fysikkstudenter som vurderer å ta et eller flere akustikkemner – og for alle andre som vil lære noe om hvordan lyd skapes. Eksempler er hentet fra NTNU og SINTEF akustikkmiljøet: Syngende rør i oljeindustrien, støy fra nye F35 jagerfly, og også noen mye mer nærliggende eksempel. Dermed er dette også en anledning til å bli litt kjent med akustikkmiljøet i Trondheim.
For de med teoretisk fokus kan det tilføyes at teorien er knyttet til beskrivelse av turbulens – et fenomen som er utfordrende å modellere og forstå. Her kan det nevnes at blant annet teorien for kritiske fenomener og faseoverganger fra statistisk mekanikk brukes (e.g. «Universality of rare fluctuations in turbulence and critical phenomena», Nature 1998). Forelesningen her vil imidlertid holdes elementært (MSc course in engineering acoustics level) med vekt på konkrete eksempel. Rommet B418 er et lunsjrom, så det er begrenset plass.
Det vil være fint om noen flere enn komiteen er tilhørere. I tillegg kan det hende at noen av dere synes temaet er artig; det er det!
I forbindelse med Forskningsdagene 2015 åpner vi akustikklaben til SINTEF for alle som vil se og høre. I denne laben, som du ser avbildet på toppen av denne nettsida, har vi så mange og så kraftige høyttalere at vi til og med kan gjenskape lyden av et helikopter som lander rett ved deg.
Har du lyst til å komme en tur? Det er i Strindvegen 4 det skjer, mellom klokka 13:00 og 13:45 den 16. september.
Illustrasjonsfoto: Geir Mogen / SINTEF
The invention of the telephone set off a wave of creativity, and almost all conceivable transducer mechanisms were tried out in the 1870s and 80s. Some of them developed into usable devices, others serve mainly as illustrations of man’s creativity. In this part, some of them will be presented, ranging from useful, mainstream designs to the downright bizarre.
I løpet av denne uka har vi vært i media med MAUS-prosjektet, som handler om auralisering av utendørs støy. En sak om prosjektet, skrevet av Åse Dragland, har blitt publisert tre steder på norsk:
Saken har også blitt oversatt og publisert i flere internasjonale medier. Du finner en liste nedenfor.
I tillegg har Erlend og Jakob vært i Norgesglasset på P1 og vist fram og snakket om verktøyet. Du kan høre klippet her, men raska på; klippet er bare tilgjengelig i seks måneder.
In Part 4, we looked at various early variants of moving coil (or moving conductor) loudspeakers, including predecessors of the modern moving coil cone driver. In this part I will present two specific designs that made a lasting impact on loudspeaker technology. One is a direct radiator; the other is a horn driver.
In the early part of the 1920s, many researchers were working on loudspeakers, based on various principles. E.C. Wente at the Western Electric Engineering Department (to become the Bell Telephone Laboratories) worked on a small direct radiating moving coil loudspeaker that was later patented (US patent 1812389, filed April 1, 1925 and granted the same date 1935). In England, Paul Gustavus Adolphus Helmuth Voigt at Edison Bell also worked on moving coil loudspeakers and microphones. In May 1924, he applied for a patent on a moving coil loudspeaker, but unfortunately a little to late. He was beaten at the finish line by two engineers at the General Electric Company, C.W. Rice and E.W. Kellogg.
The moving coil loudspeaker is without doubt the most common electroacoustic transducer in use. It consists of a circular coil suspended to move freely in a radial magnetic field. This transducer principle was first described by Ernst W. Siemens in his 1874 patent. He describes his transducer as a means for “obtaining the mechanical movement of an electrical coil from electrical currents transmitted through it.” He also mentions that the coil could be used to move visible or audible signals, but he had obviously nothing more elaborate in mind than a bell or buzzer.