AES Munich 2009
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Heyser Lecture

AES Munich 2009
Recording Industry Event

Thursday, May 7, 18:30 — 19:30

Heyser Lecture
followed by
Technical Council

The Richard C. Heyser distinguished lecturer for the 126th AES Convention is Gunnar Rasmussen, a pioneer in the construction of acoustic instrumentation, particularly of microphones, transducers, vibration and related devices. He was employed at Brüel & Kjær Denmark as an electronics engineer immediately after his graduation in 1950. After holding various positions in development, testing, and quality control, he spent one year in the United States working for Brüel & Kjær in sales and service.

After his return to Denmark in the mid-1950s he began the development of a new measurement microphone. This resulted in a superior mechanical stability, increased temperature, and long term stability. The resulting one-inch pressure microphone soon became the de facto standard microphone for acoustical measurements to replace the famous W.E. 640AA standardized microphone.

The optimized mechanical design of the new generation of measurement microphones opened up the possibility for reducing the size of the microphones, first to a ½” microphone and then to ¼” and 1/8” microphones with essentially the same superior mechanical, temperature and long term stability. Notably the ½” microphone is still the most widely used measurement tool today. Since the beginning of the 1960’s, this microphone design has been preferred for all types of acoustic measurements and has formed the basis for the IEC 1094 series of international standards for measurement microphones.

Gunnar Rasmussen received the Danish Design Award in 1969 for his novel design of the microphones that were exhibited at the New York Museum of Modern Art. He also developed the first acoustically optimized sound level meter, where the shape of the body was designed to minimize the effect of reflections from the casing to the microphone. This type 2203 Sound Level meter was for many years seen as the archetype of sound level meters and its characteristic shape became the symbol of a sound level meter.

Other major inventions and designs include the Delta Shear accelerometer, the dual piston pistonphone calibrator for precision calibration, the face-to-face sound intensity probe and hydrophones, occluded ears, artificial mouth, etc. Rasmussen is also the author of numerous papers on acoustics and vibration and has served as chairman and vice-chairman of various international organizations and standard committees. In 1990 he received the CETIM medal for his contribution to the field of intensity techniques. He is also a Fellow of the Acoustical Society of America.

In 1994 Rasmussen started his own company, G.R.A.S. Sound and Vibration. Originally a company specializing in precision Outdoor Microphones for permanent noise monitoring around airports, it is now one of the world’s leading companies in acoustic front-ends and transducers forming a wide range of general purpose and specialized microphones, electro-acoustic measurement devices such as ear couplers, precision calibration tools and multi-dimensional sound intensity probes. The title of his lecture is, “The Reproduction of Sound Starts at the Microphone.”

The microphones may be developed for many specific purposes: for communication, recording or precision measurements. Quality may have different meaning for different applications. Price may be a dominating factor. Carbon microphones were dominating up to the 1950s. Electret microphones have taken the place of carbon microphones with great improvement in quality and performance at low prices. The MEMS microphones are on the way.

The challenge in the high quality microphone development is to match or exceed the human ear in perception of sound for measurement purposes. Without measurements we cannot qualify our progress. We are still trying to match the frequency band, the dynamic range, the phase linearity of the human ear and to obtain very good reproducibility in all situations where humans are involved. We need microphones for development, for standardized measurements and for legal related measurements. Where are we today?