Benefits of Acoustic FE/BE Analysis in Loudspeaker Design

Analytical tools such as the finite and boundary element methods can be used to assist in the design process. These techniques can potentially permit consideration of very radical changes using non-standard components, which would be very expensive to construct on a one-off basis, thus accelerating the design cycle. They also have a role to play in helping the engineer comprehend the phenomena and hence make more efficient design changes.

Elliptical cone (pistonic)

Elliptical cone (breakup)

A common performance indicator for a loudspeaker box is the pressure against frequency response at some point on axis in front of it. Ideally this should be fairly flat for a constant electrical input against frequency. However there are many phenomena which affect the final result, e.g.

• The cone may be vibrating rigidly if it is stiff or at low frequency.
• Under other conditions cone breakup can occur, influencing the radiation efficiency.
• The loading on the cone due to air inside the box is generally small compared to the excitation from the voice coil, but under some conditions there can be a cavity resonance effect.
• The loading of air in front of the cone may have an added mass effect at low frequencies, particularly if the cone is light.
• The sound at a measurement point is affected by diffraction from the edges of the box and reflections off walls, ceiling, floor and furniture.

If the designer does not understand why a particular system is producing its response then new models can only change at an evolutionary pace. To acquire this comprehension it is useful to isolate different phenomena. Sometimes this can be done experimentally, e.g. using an anechoic chamber to eliminate reflections, or using an anechoic half chamber (i.e. with one rigid wall) to remove diffraction by edges. With an analytical approach it is possible to visualise the complete pressure field and the structural deformed shape. It is also possible to investigate design changes, even those which are impossible experimentally, e.g. eliminating air behind the cone, which improves the understanding of why a system works as it does.