Vehicle noise is a very complex problem for car manufacturers. Most enthusiasts enjoy the sound of a sporty engine, but strict drive-by noise limits and complaining neighbors ensure engine sound levels are relatively tame these days.
To overcome these problems, Ford engineers have made sure the new Focus ST will appeal to the sporty driver with the help of a new twist on existing technology.
The boffins added a special sound tube – called a sound symposer – to amplify the frequencies most enthusiasts enjoy. They worked to naturally amplify the specific low range of frequencies between 200 and 450Hz that are most pleasing to performance drivers. And it’s achieved with a composite “paddle” that vibrates with intake air pulses.
Although the sound tube concept was used on previous Mustangs, the Focus ST is unique because its valve is electronically controlled to open and close according to driver input – engine speed, accelerator position and gear selection.
Therefore, in lower gears the valve is more aggressive, while the effect is reduced in higher gears to enable quieter cruising. Apparently, this wouldn’t be possible with conventional sound tubes.
Part of the reason Ford made these changes is that on Focus ST the symposer is attached to the intake manifold (as opposed to between the manifold and air intake).
The secret was developing the perfect paddle to naturally amplify the ST’s engine sound. Ford engineers tested several paddles until they discovered the correct stiffness that yielded the best acoustic response.
An international team of suppliers came together with Ford to accelerate development of the symposer. All in all, 30 engineers from five countries had to balance NVH, materials, manufacturing and assembly to bring the symposer to life.