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 annoyance response of different communities to aircraft noise has always been difficult to predict. However, in recent years, many studies report extremely high levels of annoyance for the given noise exposure levels. This has led to the belief that people are nowadays less tolerant to aircraft noise than they were a few decades ago.
We’ve looked at the results of 57 aircraft noise surveys conducted between 1961 and 2015, and found that people’s tolerance to aircraft noise hasn’t changed at all.
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.
Noise is, by its very definition, annoying. Intuitively, lots of noise is more annoying than noise that is barely audible. Therefore, the concept of «tolerance» is important: Given the noise situation, can we predict people’s annoyance with this noise?
To answer this question, we first need ways to quantify both annoyance and noise. Annoyance is an emotion, but that does not mean it is not measurable. Researchers have developed very specific questions and answer scales that allow for international comparison of people’s annoyance with specific types of noise.
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
De siste årene har det vært et økt fokus på hvordan musikkspillere kan skade hørselen. WHO gikk i vår ut og sa at over 1 milliard ungdommer står i fare for å få hørselsskader som følge av for høy musikk på ørene. I den forbindelse har det stadig vekk vært slått opp i media, både nasjonalt og internasjonalt, at man bør unngå å bruke øreplugger, såkalte «earbuds» eller «in-ears».
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.