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issue: May 2008 APPLIANCE Magazine

Simulation Software
Simulating Great Sound

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by Lisa Bonnema, Senior Editor

High-end audio manufacturer B&W uses electromagnetic simulation to ensure quality sound in its speakers while shortening design cycles.

B&W uses simulation to design most of the technology that goes into its speakers. Pictured is the Signature Diamond series, which features some of the company’s most advanced technologies, such as a Kevlar midrange/bass drive unit, a flowport, and a diamond dome tweeter.

Known as a pioneer in loudspeaker technology, West Sussex, U.K.-based Bowers & Wilkins (B&W) takes pride in designing its technology from the ground up. The manufacturer is one of the only in the industry to make many of the drive units used in its speaker systems. While this makes the company an innovation leader, it can also lengthen design cycles.

B&W knew early on that it had to use advanced methods to stay competitive. In the mid-1990s, the company tried to create its own “reverse finite element analysis” software in conjunction with the University of Brighton to calculate backward from the ideal sound characteristics to find a design solution. However, the complexity of this method led B&W to eventually purchase commercial electromagnetic design software, the Opera package from Vector Fields (Aurora, IL, U.S.).

According to Gary Geaves, head of research at B&W, the software speeds up the design cycle and helps the company incorporate design improvements. “We use the software at the start of all our loudspeaker design projects to optimize the motor systems in the loudspeaker driver, along with other simulation software, to speed and shorten the design cycle,” he tells APPLIANCE. “This typically gets us to an objective optimal design concept rapidly, as we can quickly consider up to hundreds of different variations.”

The Opera software uses a finite element method code that is optimized for electromagnetic design. Design engineers can build models within the software, or enter them from CAD files and then assign material information and drives in order to run an analysis. B&W uses the software to design what Geaves calls the “core” of the speaker drive unit—the motor. “Almost everything we do is based on our own motor components and starts life with simulation,” he says. “By doing virtual design in this manner, we are able to optimize the design for sensitivity and linearity.”

The goal is to maximize the sensitivity of the loudspeakers while minimizing the impact of nonlinearity coming from asymmetric fields in the motor’s gap. 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 achievable sensitivity. 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. “Unlike some product categories, we rely on substantial subjective testing and improvement stage as well, [because] developing good loudspeakers involves a good deal of ‘art,’” Geaves says. “We have a great interest in simulation software in general, and use PAFEC and other commercial products, as well as code of our own design, to optimize design characteristics.”

B&W uses the Vector Fields Opera package, a finite element method code that is optimized for electromagnetic design. According to software supplier Vector Fields, the package includes customized analysis tools to enable design engineers who are not necessarily familiar with the software to investigate areas of a conceptual design in a time frame that will improve the efficiency of the R&D department.

Growing with Technology

Although B&W has been using the Opera package for 12 years, the company has changed its uses and goals based on technology advancements and market needs. For example, when the software was originally purchased, it was used for design shielding for speakers that were used with CRT TVs. However, as flat TVs continue to dominate the market, this application has greatly decreased.

The company has also upgraded as new software features have been made available. “When we started, we used just a solver for static electromagnetic fields,” Geaves says. “Upgrades over time have moved us to major new capabilities in terms of simulating transient fields and eddy currents, as well as linear motion of the motor. The user interface of the package has also gone though major improvements over the years.”

Currently, the OEM is working closely with a Vector Fields engineer  to develop a software model that will help B&W 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 nonlinear and is complex to solve, and the new software model will allow B&W to quickly settle on optimum design solutions for each loudspeaker motor design. “It’s [about] cost and time,” Geaves notes. “Empirically applying conductive materials to prototype designs, and then iterating that process perhaps dozens of times, would just take too long.”

B&W is clear, however, that it will not sacrifice quality for speed. “Our loudspeakers are optimized to be as sensitive as possible and to have minimum distortion,” Geaves says. “This degree of control is one of the reasons we make our own drive units, and why we use software to optimize their characteristics.

“We simply could not achieve the same fidelity of reproduction if our products were all based on bought-in motors,” he adds. “I’m not saying that someone with audio engineering skill can’t put together a reasonable speaker using a commercial driver component, but with a flexible simulation package, we are free to liberate our imagination and search for the absolute best design solution.”



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