Electromagnetic simulation helps loudspeaker technology pioneer maintain its edge

B&W makes some of the world’s highest-fidelity loudspeakers, and as global competition increases, the company sees an increasing role for electromagnetic simulation to improve design characteristics and shorten design cycles.

B&W targets the very high end of the audio reproduction market, and has a track history of innovation. Its speakers are widely used in recording studios, and it also serves the consumer market with innovations such as hi-fi speakers for MP3 players, and flat hi-fi speakers to go with plasma TVs.

The company has been using electromagnetic design software for well over a decade. Its first major foray into this area started in the mid 1990s, when the company tried to create its own ‘reverse finite element analysis’ software in conjunction with the University of Brighton — to calculate backwards from the ideal sound characteristics to find a design solution. The huge complexity of this problem meant that the work petered out, but it made B&W purchase its first professional electromagnetic design software, the Vector Fields Opera package.

The Opera software plays a major role today at the start of design cycles to try and optimize the magnetic characteristics of the speaker motor to achieve as high and as linear a field as possible, to maximize speaker sensitivity.

This is a particular issue for the high-frequency tweeter elements of a sound system. One of the major limitations affecting tweeter speakers is behind the speaker, in the tube or space that absorbs the sound emanating from the rear of the diaphragm. Good acoustic performance demands an air hole in the motor system, which inevitably leads to a compromise in the maximum flux levels and sensitivity achievable, and the Opera tool helps B&W to optimize the magnetic performance of the motor design early in the design cycle. Once initial design concepts are produced, B&W still relies greatly on real-world listening tests to prove and optimize a design.

The company is also using Opera to find solutions to more complex dynamic problems. In development currently — in conjunction with a Vector Fields applications engineer — is a generic model that will help B&W to overcome the problems caused by the dynamically changing impedance of the voice coil as it moves in the air gap — and gets nearer or farther to the steel magnetic material. This changing impedance gives rise to distortion, typically heard as a roughness of voice. In the past, B&W has solved this issue empirically, by the application of conductive material to reduce the change. However, the problem is non-linear and is complex to solve, and the new model will allow B&W to quickly settle on optimum design solutions for each loudspeaker motor design.