WHAT YOU WILL LEARN
Brüel & Kjær began producing microphones in 1945. By the late 1950s they were established as a leading supplier of measurement microphones, due largely to the inspirational enthusiasm of Dr. Per V. Brüel in the field of microphone and general transducer development.
In parallel, Brüel & Kjær also invented, designed and developed complete acoustic measurement systems, analyzers and recorders. The accuracy achieved from our measurement microphones formed an important part in the success of these products.
From humble beginnings, Brüel & Kjær gained an increasingly good reputation amongst microphone users, both in the field of acoustics and in academic research, providing a high standard of service, well-built products and collaborative research and development programmes, ensuring a continuous improvement in the accuracy and performance of new instruments.
Today, this approach continues to deliver innovative measurement instrumentation, including a comprehensive range of measurement microphones in sizes from 1/8-inch to 1-inch. Together these microphones cover all aspects of measurement microphone usage.
Fig.1.1 Range of condenser measurement microphones
By the early 1970s, Brüel & Kjær ’s strong presence in the measurement microphone field had become firmly established with the development of high sensitivity 1/2-inch microphones.
Calibration equipment, such as reciprocity equipment for laboratory calibration and the pioneering hand-held pistonphone, was released. This convenient way of calibration effectively improved the accuracy of everyday microphone usage by allowing users to check measurement accuracy in the field.
In 1973 Brüel & Kjær solidified the position as a leading microphone supplier, meeting a request from Western Electric to supply 1-inch microphones to replace their successful but ageing WE 640AA microphone.
The Brüel & Kjær solution took the form of the classic Type 4160 microphone.
Fig.1.2Sound Intensity probe using a phase-matched pair of microphones
Further innovations ensued, notably in improvements to electret processes during the 1970s, resulting in the production of stable prepolarized microphones which became standard for use with class 1 sound level meters.
The 1980s brought further developments, in particular in the field of sound intensity measurement. The mid 1980s also saw the development of specialized types of sound intensity probe microphone. This microphone made use of a revolutionary and now patented tube system which gives a flat frequency response and allows for measurements in places where access for standard measurement microphones is difficult.
Improvements have continued into the 1990s with the introduction of highly accurate yet robust microphones (the Falcon RangeTM), and outdoor microphones and terminals for permanent outdoor noise monitoring. The outdoor microphones have since proven very effective in harsh environments.
World’s first volume‐produced measurement microphones, Types 4131 (free‐ field) and 4132 (pressure‐field), developed, amongst others, by Dr. Per V. Brüel1967 Type 4138
World’s first 1/8-inch measuring microphone. Due to on‐going product improvements, this type is still availableType 4138 - World’s first 1/8" measuring microphone 1975 Type 4160
Brüel & Kjær is requested to produce a replacement for the Western Electric WE 640 AA Reference Microphone. As a result, Type 4160 and later the ½" Type 4180 were introduced (still the world de facto acoustical standards)Type 4160 - Laboratory standard microphone 1980 Type 4155
Brüel & Kjær launches the world’s first high‐stability, measurement grade, electret microphone, which is now discontinued.Type 4189 - Our best-selling high-precision, and high sensitivity microphone 1984 Type 4179
Using advanced modelling and clever design, this now discontinued microphone had a noise floor of –2.5 dB(A), that was still unbeaten after nearly 30 years!Type 4144 - 1-inch Pressure-Field Microphone 1987 Type 4182
Brüel & Kjær introduces probe microphone for measurement in extremely confined spaces and up to more than 600°CType 4182 - Probe Microphone 1993 Type 4188
Falcon series is introduced. Featuring stainless steel, press‐fitted diaphragms, these microphones result in a step change in microphone technologyType 4188 - ½-Inch Free-Field Microphone 1994 Type 4189
Falcon series at peak performance. Type 4189 is probably the world’s most popular ½-inch free‐field microphoneType 4189 - World’s Most Popular ½" Free‐field Microphone 2000 Type 4297
The world’s only one‐unit Sound Intensity Calibrator enables calibration without dismantling the probeType 4297 - World’s only one‐unit Sound Intensity Calibrator 2003 Type 4948
Surface Microphone – a Brüel & Kjær first: an 'all titanium' sensor originally developed for aerospace applicationsType 4948 - Aerospace Surface Microphone 2004 Type 4949
Surface Microphones now also find their way into the automotive industry, where they break new frontiers in wind‐tunnel testingType 4949 - Surface Microphone for Automotive 2005 Type 4952
World’s first outdoor microphone where all parts exposed to the weather are made from polymer materialsType 4952 - World’s First Outdoor Microphone 2006 Type 4955
Continuing the 'all titanium' concept, this TEDS microphone has 1.1 V/Pa sensitivity and a typical noise floor of 5.5 dBType 4955 - 1/2" Classical Low-noise Microphone 2009 Type 4961
Multi‐field Microphone – Type 4961 was the world’s first ¼" measurement microphone that guaranteed accurate and error‐free measurements in both free and diffuse fields and at any angle, now discontinuedType 4957 - ¼" Array Microphone For Wide Ranges of Temperature And Humidity 2012 Type 1706
World’s first microphone preamplifier that can handle temperatures up to +125°C/+257°FType 1706 - World’s First Microphone Preamplifier 2015 Calibration in
Access calibration data anytime. Calibration data is stored in the cloud for every transducer serviced at a Brüel & Kjær calibration laboratory. Furthermore, correction files for each individual microphone are accessible via the WebOnline Calibration Cloud
Development of microphone products is performed by a dedicated team of engineers. This is something which is not easy to provide given the relatively small and specialist market for precision microphone products. However, at Brüel & Kjær this investment is seen as essential because it allows the design parameters and physical properties of microphones to be based on a solid foundation of knowledge, skills and experience.
Research and development work also encompasses a number of areas that reflect the different aspects of microphone design and construction, in particular, where highly accurate measurements need to be performed. These include:
Development skills and knowledge are also applied in research into the optimum choice of materials and to devise effective forms of testing microphones before they go into full production.
These tests include resistance to shock, vibration, temperature, humidity and in the case of preamplifiers, resistance to electromagnetic fields is also tested. Bump tests in which the microphone is subjected to repeated knocks simulate everyday use, while shock tests reproduce the possible effect of impacts received in transport (typically up to the equivalent of 1000 m/s2).
Finally, microphones are also tested for resistance to corrosion, as proven by the most recent range of condenser microphones which have been found to be very robust in harsh measurement environments.
Microphones are precision instruments and while the design of a conventional measurement microphone may appear to be quite simple, its production must be very precisely controlled to meet specified tolerances. Such tolerances impose great demands on the materials and construction methods used, yet the products created must be extremely reliable and robust.
Speaker: Bin Liu
At Brüel & Kjær the emphasis is therefore on quality rather than mass-production.
Two components which receive a lot of attention during production are the microphone diaphragm and backplate. During production the surfaces of these components are made extremely smooth as a very high electrical field strength must exist across the diaphragm to backplate gap.
Another critical area of production is the distance between the microphone diaphragm and backplate which must be constructed to very small mechanical tolerances. Typically this is set to 20 µ with a tolerance of 0.5 µ. The required distance is monitored and then implemented precisely, once the correct tolerances have been adjusted.