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Genius!2: Brüel & Kjær and the Constant Percentage Bandwidth analyser #21

The technology is still used in the B&K PULSE analyser platform and 2250/70 handheld units

Some scientists set out to explain the world around us and how it works. Others look to develop technologies that make life better. Brüel & Kjær decided to do both through what seems to be the unlikely medium of sound measurement equipment. But their meters and microphones have been used round the world to improve sound quality and deal with the problem of unwanted or potentially harmful noise.

Per Brüel (1915-2015) and Viggo Kjær (1914-2013) met at the Danish Technical University and shared an interest in physics and hi-fi. The two became friends and planned to start an engineering company together focusing on measurement. “Even then we could see that noise is one of the biggest problems of our time,” Brüel was quoted in Journey to Greatness: The Story of Brüel & Kjær. “Our instruments could not only measure noise but also help customers identify and eliminate noise problems.”

Among the devices developed by B&K for measuring response in auditoria, homes and schools was the Constant Percentage Bandwidth (CPB) analyser, which defines the width of the filters relative to their position in the frequency range being tested, something still used in the B&K PULSE analyser platform and 2250/70 handheld units; and the Standing Wave Apparatus, a device Brüel described in his PhD thesis on material testing.”

B&K produced microphones to provide sources for the meters and analysers, which eventually took the company into music recording, initially with the 4000 series. Speaking to Broadcast Systems International magazine in 1989, Brüel said the technology in both types was the same, the only difference being the size. But he said there were communication problems between the two worlds: “We are physicists and we are not used to some of the funny phrases used in music.”

Kjær was the more reclusive boffin looking after R&D, while Brüel became the public face of their company, as renowned for his love of aeroplanes, cars and red wine as his scientific achievements. And combining those is a kind of genius itself.

Published earlier this year and sponsored by QSC Audio, Genius!2 is the second edition of Genius!, celebrating those clever people whose inventions have transformed the world of professional audio. The 30-page supplement is also available to read in a handy digital-edition form