Sound Field Control

Noise and unwanted sounds have been proven to impair human health, well-being, and performance. Disturbing noises, for example, when talking on the phone in the car or during mobile work, impair the ability to concentrate. Undisturbed sleep and relaxing music, on the other hand, provide a good basis for high performance. A distinction can therefore be made between undesired sound fields, e.g., noise, and desired sound fields, e.g., emergency announcements or music at concert venues. Often, both undesired and desired sound fields occur simultaneously. There is therefore a need to reduce noise for the benefit of telephone conversations, music reproduction, or restful sleep.

For these reasons, researchers are working on various approaches to detect (with sensors), analyze and influence sound fields. The physical acoustic phenomena are usually considered taking into account human auditory perception.

The creation and control of sound fields requires a comprehensive understanding of their generation, propagation, and detection. Noise sound fields, such as those that occur in ventilation systems, can be compensated for by using active absorbers. Currently, there is a lack of solutions that are easy to put into operation, featuring self-monitoring and automatic recalibration.

In cars, not only disturbing vehicle, and traffic noises, but also noises from the neighboring seat (speech, music, etc.) should be suppressed. For this purpose, the various sound fields and their propagation in the car chassis and in the air must be detected by sensors, evaluated, and used as a starting point for controlling existing anti-sound measures. Special sound fields, such as alarm signals, must be handled separately.

The technical solution should initialize itself as independently as possible. Operating parameters should automatically adapt to changing system characteristics (aging, number of passengers, loading, etc.) and environmental conditions. To achieve this, algorithms must be developed that are computationally efficient, energy efficient, and robust.

Depending on the application, different methods are used to control sound fields:

• Active Noise Control (ANC)
• near-field sound reinforcement
• loudspeaker array technology for: Beamforming, Wave Field Synthesis, planar speakers
• Beamforming
• Wave Field Synthesis
• active absorbers
• metamaterials

• sensory detection of airborne and structure-borne sound fields (sound pressure, sound velocity, sound intensity) 
• sound field decomposition into single sound sources
• transfer path analysis for sound sources
• generation of static/variable sound fields by means of loudspeaker/speaker array/flat loudspeaker
• generation of focussed sound fields/spatially limited sound fields
• generation of anti-sound fields for sound reduction
• sound optimization of loudspeaker reproduction systems