There's a lot more to car noise than you might think. Some noises are pleasurable, some not, while some have become downright necessary for pedestrian safety. It's a subject that is now coming onto regulators' radar screens due to the potential hazards of 'silent running' with electric drive vehicles. And as Colin Peachey, a chief engineer with Lotus, tells Dave Leggett, there is also the rather ticklish issue of 'lightsaber collective consciousness' to consider when adding sound to EVs.
For the engineers at Lotus Engineering there's nothing new about Active Noise Control (ANC) technologies. ANC enables engineers to work on controlling the sound environment inside the vehicle. Engineers at Lotus have been working with it for over twenty years and a system aimed at cancelling noise in the cabin was first installed in a Nissan Bluebird, for the Japanese market, way back in 1992.
"The science behind this technology has been proven for a while," says Peachey. "We knew what we wanted to do, but what's changed radically is the capability - afforded by the advent of much more sophisticated audio systems with much greater capacity - to properly deliver without having to add weight."
That's where Harman International comes in. Lotus has teamed up with the high-end infotainment systems provider, the two bringing complimentary capabilities to the joint mission to get this technology installed in vehicles.
Under a recently signed agreement, Harman will manufacture the solutions - developed by Lotus Engineering - for the worldwide vehicle OEM market. The agreement includes all of Lotus' Active Noise Control technologies comprising Road Noise Cancellation, Engine Order Cancellation, and Electronic Sound Synthesis.
Lotus says that the Road Noise Cancellation and Engine Order Cancellation systems will provide vehicle manufacturers with the ability to greatly improve in-cabin refinement, with additional design opportunities for optimising vehicle weight reduction and fuel economy.
"The processing power in today's audio systems means there is available capacity for sophisticated sound management techniques," Peachey says. "And the market wants it."
Well, no-one actually likes road noise do they? (One possible exception, if memory serves, may be a novelty section of road in the US that was temporarily engineered with grooves on the surface that played a just about recognisable tune.)
"Road noise and continual engine drone can be a big source of discomfort and fatigue for drivers," Peachey points out. "These systems can make driving a more pleasurable experience and a safer one, too."
The Lotus noise cancelling technology works by analysing unwanted sound frequencies and adding cancelling ones. The sound environment in the cabin is monitored by an array of microphones discreetly positioned all around the cabin (in places like the headliner). Signals are also sent from the engine so that the system knows about the changing harmonics of engine speed. Vibration sensors can help with the analysis of road noise.
The information provides a feedback loop to a controller that continually adjusts noise cancellation measures to keep cabin noise at the desired or optimal level.
Can I have a throaty V8 roar, please?
In managing the sound inside the cabin, an opportunity also exists to play with the sound still further. Maybe you would like your car's engine to sound like an Aston Martin when you put your foot down, yes? But hang on, if it's a Nissan Micra you're driving, isn't that a bit daft? "Not at all," Peachey maintains. "This is about making the driver happier and enhancing the driver experience. The sound can be tweaked in many ways to achieve that. For the vehicle manufacturer there's also the opportunity to differentiate the brand or model by using acoustics creatively.
"Sound can change the perception of the product in a big way."
Peachey also conjures up an intriguing scenario in which drivers can choose different engine sounds and download them like ringtones on your cell-phone.
Things perhaps get even more interesting when you consider the sounds that a car emits externally.
Let's put aside the 'Dixie' horn mentality for a moment (and I'd imagine also that an authentic F1-style scream from your VW Polo would attract unwanted attention) and think about the particular problems presented by electric vehicles - or indeed hybrids in electric drive mode.
The problem is this: they don't make a sound do they? Well, actually, they do. There's the friction sound, AKA road noise, made by the action of the tyre on the road surface. It's a big sound and you can't miss it.
But here's the thing. That noise generally kicks in significantly only when the vehicle is travelling at a speed of over 20mph (32k/ph). At slower speeds, it's very, very quiet. The Lotus people noticed that when moving EV and hybrid prototypes around in their workshops.
A car being manoeuvred slowly from a standing start, say out of a driveway or in a car park, on a smooth surface, generates virtually no road noise. If you take out the familiar Internal Combustion Engine (ICE) engine noise that we are all used to and if you can't actually see the car, the potential dangers in EVs are obvious.
Lotus is working on external speaker solutions to deal with the problem.
External Electronic Sound Synthesis provides specified electronic sound models which can be applied to an external speaker system to improve pedestrian safety. A synthesised sound, dependent on speed, is projected from speakers at the front and rear of the vehicle, making it instantly recognisable that the vehicle is in motion.
The potential hazard posed by overly quiet electric drive is an issue that is now attracting the attention of regulators on both sides of the Atlantic.
"Just within the last few months, Europe is following the US lead and a working group is being set up in Brussels specifically to look at the problems that electric drive potentially presents for pedestrian safety," Peachey says.
And there's a balancing act to be performed to make sure that the sound in the cabin isn't radically different to that being emitted externally. "Otherwise, open the window and there will be an obvious conflict going on," Peachey says.
Modulated external sound on electric vehicles makes them noisier than they can be, but at least the resultant noise distribution is more manageable than that of ICE cars. And noise pollution is less.
"The sound from speakers is highly directional," Peachey says. "Speakers at the front, or the rear if reversing, concentrate their sound emissions in one main direction. That's not the case with the sound from the ICE, which tends to radiate in all directions, causing unwanted noise pollution."
It all certainly sounds interesting. This technology can make things better for the driver - noise cancelling in the cabin - while also potentially enabling you to have an enhanced driving experience. You can max out on the noises you like and minimise the ones you don't.
And you can have some fun on the way home from work pretending that your car, while looking like a standard econobox, is in fact a growling TVR Griffith with extreme shape-shifting tendencies.
But to get serious, this technology potentially make things safer on the streets as electric drive becomes more common. If EVs and hybrids are really going to take off, this technology offers what sounds like a helpful solution to a potentially lethal pedestrian safety issue.
Just one final nagging thought. What is an EV supposed to sound like exactly? Well, it's a kind of whirring sound isn't it?
As Peachey explains, there's a 'collective consciousness' at work that means we all have an idea of how an electric car should sound.
"It's a culturally informed thing, based on things like Sci-Fi on TV or at the cinema, but we all have an idea of how a 'futuristic' electric car should sound. Of course, that idea is not based on reality - relatively few people have actually been in an electric car."
There are things we think we all know, even if we don't - and it's a remarkably similar take that we all have. Peachey serves up a helpful illustrative example.
"This 'collective consciousness' phenomenon is also demonstrated by the perception of the lightsaber weapon in the Star Wars films. Of course, a functioning lightsaber does not actually exist, but the huge cultural impact of those films means that many people 'know' how a lightsaber looks and sounds. And if they see a movie with something in it that looks like it's supposed to be a lightsaber but it doesn't sound right, they'll instantly pick up on that. It's a little similar with electric vehicles - the challenge is to get a sound that is distinctive, but readily acceptable."
Lotus has been working with the UK's 'Guide Dogs for the Blind' association to help understand the calibration and sensitivity of guide dogs' hearing to different vehicle sounds. "The dogs are, naturally, used to hearing internal combustion engines," Peachey says. "So we bear that in mind in developing the sound for the electric vehicles. We have been able to generate sounds that produce a good result."
Doctor Who or Star Trek?
There's one more cultural nuance to bear in mind. Yes, we maybe all have a broadly shared notion of what an electric vehicle should sound like, but is that uniform across the world? No. If you grew up with Star Trek and don't even know what 'Doctor Who' is, the EV sound that you naturally plump for may sound like something out of Star Trek rather than the apparently electrically driven Dalek or K-9 from the BBC's Doctor Who TV series.
We also once had electric milk floats delivering milk to the doorstep here in Britain (they're not completely gone, but there aren't many left). This cultural stuff can be deeply embedded in the national psyche.
"But we certainly don't want the cars to sound like spaceships," notes Peachey.
Sometimes the small differences in how something sounds matter and are highly culturally determined. A sound that is attractive to a Westerner may be anything but in East Asia, and vice versa. Musical tastes differ widely across the world, for example.
Broadly speaking, this acoustics technology brings three applications: noise cancelling in ICE cars; noise management in ICE cars' cabins (eg actually changing the engine noise and cabin sound environment) and noise augmentation for electric drive cars to enhance pedestrian safety.
With respect to ICE cars, if you can customise the sound experience in a car, like you might customise the interior or tweak suspension set-ups for different markets, it's surely a step forward in better meeting customer demands across the world. Think of it as NVH treatment taken to a whole new level.
It sounds like an area of the car overdue for attention. As Peachey puts it, "This technology is actually developed, we're now 'productionising' it and that's why we are working closely with Harman International."
And EVs with added noise will also be significantly safer for pedestrians and that has to be a good thing. Wasn't it the rattling bottles that partly warned you of the advancing milk float?