Focus ST Features Active Sound Symposer

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Discerning hot hatch drivers not only want their engines to sing, they want them to roar. Ford engineers made sure the new Focus ST does both, with the help of a new twist on an existing technology.

Ford engineers added a special sound tube – called a sound symposer – to amplify the throaty frequencies enthusiasts crave in performance cars. Engineers worked to naturally amplify the specific lower range of engine frequencies found between 200 and 450 Hz that are most pleasing to performance enthusiasts through the use of a composite “paddle” that vibrates with intake air pulses.

While the sound tube concept has been used on Focus XR5 in the past, the sound symposer used in Focus ST is unique because of its electronically controlled valve that opens and closes based on driver inputs – engine speed, accelerator pedal position and gear selection.
In lower gears in the Focus ST, the valve is mapped more aggressively, while in higher gears the effect is dialled back to enable quieter cruising. This is not possible with conventional, passive sound tubes.

Part of the reason Ford implemented these changes is that on Focus ST, for the first time, the symposer is attached directly to the intake manifold (as opposed to between the manifold and air intake).
Ford has engineered the symposer both to dial up the sporty sounds EcoBoost delivers under the bonnet but dial back the interior sound volumes at part throttle.

The turbo on the 2.0-litre EcoBoost engine provides plenty of power across the rev range, but it presented a special challenge to Ford engineers from a sound perspective as it absorbed much of the desired engine note. The symposer helps bring out the throaty engine sounds that drivers love.

The secret to getting this right was developing the perfect paddle to naturally amplify the ST’s great engine sound. Ford engineers tested several different paddles. Eventually, a paddle was developed with the correct stiffness that yielded the best acoustic response and ultimately, the best “flutter” and low-end frequency sound.
Work on the symposer involved an international team from suppliers of the intake manifold, battery tray, electrical hardware and software, and electrical connectors who all worked in collaboration with Ford engineers.

All in all, 30 engineers from five countries had to balance noise, vibration and harshness issues, materials, manufacturing and assembly considerations to bring the symposer to life.

The electronically controlled, active sound symposer gives the Focus ST an aural split personality. In everyday driving, the car is composed and refined. But under full throttle, the engine note is highlighted.

Among the more visible options will be the Tangerine Scream metallic colour that will be offered exclusively on Focus ST as well as race-inspired Recaro seats with matching colour accents.

Source: Ford Media