Brüel &amp; KjærBrüel &amp; Kjær Brüel & Kjær Brüel & Kjær (Sound and Vibration Measurement A/S) is a Danish multinational engineering and electronics company headquartered in Nærum, near Copenhagen. It is the world's largest manufacturer and supplier of sound and vibration measurement equipment, systems and solutions. Brüel & Kjær is a subsidiary of Spectris. Founders. Brüel & Kjær was founded by Per Vilhelm Brüel (6 March 1915 – 2 April 2015) and Viggo Kjær (5 June 1914 – 25 July 2013) on 28 November 1942. The two men met while studying at The Polytechnic School in Copenhagen (now the Technical University of Denmark). After receiving their M.S. degrees in  1939 they decided to start a company developing instruments for acoustic measurements. Holger Nielsen joined the company as third partner in 1945, and was with the company until his death in 1978. Products. The most notable products and technologies developed by the company include: Markets. Aero engines. Brüel & Kjær provides tools to overcome noise and vibration challenges. These ensure the quality of new lighter material applications by modal testing and improving the quality and test efficiency in aero engines. Systems include those for development and measurement of new noise-optimised engines, acoustic lining designs and propagation code validation (engine duct  modal analysis, far-field noise measurement, and acoustic panel "in situ" impedance measurement) It also supplies in-flight engine monitoring with flight-certified, high-temperature accelerometers. Aerospace. Brüel & Kjær supplies data acquisition systems and vibration test systems (LDS) to customers in the aerospace industry, such as the LDS V994 shaker, used to test NASA's Mars Curiosity rover. Other systems have tested Astrium's satellite prior to launch, and performed qualification and acceptance testing, such as the integrated LAN-XI data acquisition systems used by the National Institute for Space Research in Brazil INPE. Main customers in this field are  Airbus, Aircraft Strength Research Institute, Boeing, EADS, Eurocopter, Rolls Royce, and Sukhoi. Defence. Acoustic stealth discretion. The company supplies systems for noise signature management: acoustic ranging of submarines and surface ships; noise source investigation during design and build; acoustic trials and self-noise monitoring during operations. It also supplies systems for underwater acoustics, shock testing, noise and vibration testing and structural dynamics testing. Identifying noise sources. Brüel & Kjær offers products covering a wide range of acoustic customer-oriented solutions, ranging from simple sound level measurements to sophisticated microphone array systems using advanced algorithms and hardware. These solutions are provided for  air-vehicle noise certification, exterior noise analysis such as fly-over testing using acoustic holography, beamforming, SONAH and high-temperature sensors, noise source identification to examine e.g., ramp noise or sonic booms, microphone calibration systems and more. Maintaining operational integrity. The company provides products that aid preventative maintenance and manufacturer-specified checks to prolong the health of engines. Real-time multi-analysis capabilities reduce the number of run‑ups/‑downs and gather more data faster for analyses ranging from simple pass-fail overall measurements to in-depth advanced analysis in order to maximize the up-time of aircraft. It offers high-temperature  accelerometers that can monitor the health of operational machinery and provides solutions for maintenance, repair and overhaul tasks such as balancing, trim balancing, on-ground engine vibration checks, vibration diagnostics and re-run production tests using real-time analysis. Furthermore, it provides monitoring systems for engines and gearboxes with permanently placed HUMS sensors and signal conditioners for extreme environments. Environmental noise impact testing and monitoring. Brüel & Kjær supplies systems for occupational health, helmet/cabin/cockpit noise assessment, acoustic and human vibration monitoring, urban noise monitoring and noise-mapping of vehicles in order to test and monitor the environmental noise impact , and to look for ways of reducing environmental noise impact on armed forces personnel and local communities. These activities include helmet/cabin/cockpit noise assessment, human acoustic and vibration monitoring, urban, airport, industrial and construction noise monitoring, and vehicle noise mapping. Wind tunnel testing. Since wind tunnel and test track measurements are often the only way to recreate real-world conditions for model and mule car testing, and are also a good method of validating simulated model data, Brüel & Kjær tries to provide measurement devices that focus on these types of tests, providing specialised solutions for specific needs so that  they can perform vehicle pass-by noise contribution studies for cars, trucks and trains, location of high-frequency engine noise sources, and wind-tunnel measurements. Surface microphones mounted on the exterior of a vehicle measure the pressure fluctuations at different positions of the vehicle without drilling holes. Beamforming can be used for noise mapping at a distance from large objects. The data for all points is acquired in a single measurement, saving time and effort. Setting targets. Brüel & Kjær's sound quality solutions provide the tools for recording, analysing, auditioning, dissecting, and synthesising sounds. The range enables the use of  simulation models and test data to develop modifications to improve the sound quality and to achieve the ultimate objective of designing the desired sound characteristics into the product. Benchmarking. Brüel & Kjær has developed an NVH tool for surreptitious recording and analysis called SoNoScout. It can be carried in the tester's pocket on a train or bus without distracting the passengers or in a competitor's vehicle where it can be combined with a GPS unit to generate a map of the test route, measure speed and even generate an RPM profile. The software runs on a PDA with microphones  binaurally mounted on a headset for quick recording. Telecom and audio. Brüel & Kjær provides products to telecom and audio customers – from transducers to measurement, analysis and reporting for evaluation of electroacoustic devices: Organisational developments. In 1992 Brüel & Kjær was sold to AGIV (a German holding company), and split into a number of separate companies: After the division of the company, a number of former employees left to form G.R.A.S. Sound and Vibration. AGIV included the Brüel & Kjær split companies within its Spectris Division, which comprised Brüel & Kjær, Hottinger Baldwin Messtechnik GmbH (HBM), and BTG Instruments GmbH. In July 2000, the  Spectris Division was sold to the British company Fairey Group Ltd; in May 2001, Fairey Group changed its name to Spectris Plc. Brüel & Kjær acquired LDS Test & Measurement in January 2009 and Lochard Ltd in February 2009. On August 1, 2020, Brüel & Kjær merged with Hottinger Baldwin Messtechnik and changed its name to Hottinger Brüel & Kjær. Brüel & Kjær Brüel & Kjær (Sound and Vibration Measurement A/S) is a Danish multinational engineering and electronics company headquartered in Nærum, near Copenhagen. It is the world's largest manufacturer and supplier of sound and vibration measurement equipment, systems and solutions. Brüel & Kjær is