Hyundai develops advanced anti-noise technology
Road noise is something that the motorist hears, writes Iain Robertson, which can be exceptionally distracting, repetitively annoying and ultimately disturbing; a good reason for one carmaker to invest in next step technology to eradicate it.
Within the next two years, the EU will have finalised its in-car drowsiness legislation. Research into the phenomenon, which, in its most disturbing form, can lead to ‘microsleep’, by which the driver’s motor functions may appear to be operating ‘as normal’, even though he may be sound asleep, has been intense enough to warrant a change in the law.
The biggest problem arises from a repetitive soundwave known as a heterodyne. It may not be immediately obvious, because it is at such a low level of intrusion that it can be ignored and even balanced by other sounds, including the in-car entertainment system. However, its penetrative and repetitive impact can be such that it lulls not only the driver but also the passengers into a mildly sonorous and relaxed state, even sleep.
We have all heard about the frustrated parental babysitter, who resorts to taking a child out in the car, even at the dead of night, to stop it crying. It is the gentle mechanical buzz that has the desired soporific effect. Heterodyning is caused by pattern noises; these include tyre treads, linear spring motion, damper action, engine tones and even wind noise. However, even they can be disturbed by the irregularity of road surfaces. If you want to sample heterodyning, drive at speeds of up to 60mph, open just one window by around an inch and, to accentuate it, crack open a window on the opposite side of the car. The resultant roar will become unbearable very quickly.
When Ford launched its Puma (Fiesta-based) compact coupe model, it also introduced the sonic feedback tube. Closely akin to an open stethoscope attached to its engine’s cylinder-head, in reality it was a simple feedback plastic pipe running from engine bay to the car’s interior. The idea was to introduce engine intake ‘roar’, in order to enliven the cabin driving experience, without breaching exterior noise legislation. It worked for some people (many others requested it be removed).
Just a few years later, Renault went a step further by developing the sound symposer for its sportier models. Using the R-Line touchscreen, the driver could reach a page that listed everything from a Clio rallycar to a Bultaco trials bike; a choice of around ten different sounds connected by a not dissimilar sonic tube to Ford’s set-up, with the ‘advantage’ of introducing several alien soundtracks. Once the initial novelty had worn off, it was readily ignored, although it was always amusing to dial-in a specific sound, if you knew the next driver of the vehicle would be unable to switch it off!
While tuning firms will replace entire vehicle exhaust systems (some of which are illegal for road use) with the intention of producing a racier soundtrack on all manner of customers’ vehicles, from a hopped-up Corsa, to a race replica Nissan Skyline, or Subaru Impreza, very little can disguise the extraneous noise phenomenon known as road roar (transmitted from tyres and suspension systems), which may even include wind roar (caused by wiper blades, door mirrors and roof rails). In its least intrusive form, it can be little more than a gentle rustling sound; in its worst form, it can become a heterodyning racket to drive you slightly insane.
Hyundai has developed RANC, which builds on its current Active Noise Control (ANC) technology, by reducing noise actively, emitting soundwaves inverted to counteract incoming noise. It is a software-driven technology that analyses the in-cabin sound to decrease engine and road noise, rather than the passive method of blocking noise through sound insulation, which adds weight but fails to block the buzzing infrasound completely. In contrast, ANC utilises lighter parts like microphones and controllers to reduce infrasound more efficiently.
Hyundai has monitored that it takes about 0.009s for road, or engine, noise to reach cabin occupants’ ears. With RANC technology, Hyundai can improve in-cabin quietness significantly. The new system analyses various types of noise in real-time and produces inverted soundwaves in just 0.002s, which it plays back into the cabin. Resonant sounds created between tyres and wheels, or rumbling from the road surface, can be removed effectively. As these extraneous noises are even more obvious on EVs, where there is no engine noise to contend with, cabin serenity becomes even more important.
To be fair, some noises are quite vital to ensuring that the driver is aware of a necessary link to an operating vehicle and its connection with the road. To eradicate some extraneous noises may be perceived as important in terms of judged levels of refinement but we need to feel alive at times and too much refinement could have antipathetic and unproductive implications. Vehicle aerodynamics also have a major role to play in reducing some of the nastier implications of noises. Extensive work has been carried out by various carmakers to reduce air swirl patterns around door mirrors and roof rails, by introducing spoilers that upset the airflow but also help to remove the build-up of condensation, moisture and air pressure.
However, it is a constant battle that can lead to conflicting end solutions. The Hyundai system of wave inversion is an intriguing one but it still requires an anti-noise sound generation and playback medium, which is ironic, when you think about it.
Conclusion: Some natural in-car sounds can lead to occupant drowsiness and, within the next two years, fresh EU legislation is going to lead to a broad mix of anti-drowsiness alert systems being fitted to all vehicles. Hyundai has simply got there first, with its technology.