Breaking the Silence: Halosonic


Discussing the practicalities of electric cars is a can of worms, and one that many are reluctant to open. One particular practicality, however, doesn’t concern range anxiety, battery costs, charge time or anything like that. It concerns sound.

Sound, in general terms, is already a hot topic with electric cars – Nissan’s latest Leaf employs a BOSE sound system that uses half the energy of the previous system and Audi invested a lot of time developing an electronic engine roar for the stillborn R8 e-Tron. These energy-saving sound systems are another story, however. Halosonic - a collaboration between Harman and Lotus – focuses on the sound itself and how it can influence virtually everything inside and around a car.

Legislation will soon demand that electric cars emit a sound for the benfit of pedestrians

Silence is considered one of key constituents of luxury. It’s why the cabin of a Rolls-Royce Phantom is eerily quiet, and until now it’s been one of key selling points for hybrid cars like the Toyota Prius as well as pure EVs. This will all change when legislation demanding silent cars produce a synthesized sound comes into force first in the USA and later in Europe.

Why? To stop everybody getting run over, which is a goal one and all can agree on. The ability to hear vehicles approaching is clearly of even greater importance to elderly or visually impaired pedestrians, too. The volume of the sound car produce will of course be mandated, but interestingly the type of sound won’t. Some people are going to have a lot of fun, you’d imagine, but the reality is that people driving a hybrid GMC in rural Colorado are going to need a different sound to their electric Corvette-driving counterparts in Beverley Hills.

This is where Halosonic comes in, and it’s taking automotive sound synthesis a step further with aural expertise from Steve Levine. Levine, famous for producing records for both Culture Club and the Beach Boys, isn’t an automotive person per se, but an ownership history that includes machines as raw as a classic TVR and 911 3.2 says otherwise. He is, in other words, the man for the job, and explains the technology with a frank simplicity that is greatly appreciated.    

External speaker is mounted behind the front bumper. Note accelerometres on front axle

Halosonic technology can be roughly split into two parts: what pedestrians outside the vehicle hear and what occupants inside the vehicle hear and, importantly, how they perceive it.   

Creating an external sound is fairly straightforward. A speaker is mounted behind the front bumper, slightly offset, and projects a given sound ahead. To date, the most popular ideas have been futuristic humming sounds, but the unit also has to be hardy enough to handle freezing, and equally very high, temperatures as well as water ingress. These can all be accommodated for. Noise pollution is of course a serious issue, but with the direction of sound accurately controlled and no exhaust noise at the rear, Halosonic-equipped cars have proven more easily heard on approach but quieter after passing as the sound decay is quicker (see graph below). Above 50mph the external speaker switches off, as wind noise and tyre roar take over. So far so good, but it’s on the inside where things get interesting.

So would you like your electric car to sound like a Pagani? The SS Enterprise? Or perhaps a Ford Transit (it’s been done)?

Halosonic will let you do this, and it will let you do this convincingly. Lotus have contributed to the project by sharing their knowledge of the individual algorithms that track inputs such as pedal depression, steering input and gear changes. They use this knowledge to make the right decisions regarding tyre wear, fuel-air mix and engine mapping and so on for their F1 cars. When applied to in-car acoustics same the technology allows for the production of sounds in real time. So if you accelerate, the sound precisely matches your inputs in terms of both tone and volume, and likewise for braking. Levine stresses that the system is fully integrated, and not simply a prerecorded track, and the end result is that you get a driving experience that’s perfectly aligned to what you would expect in a petrol or diesel car. It’s easy to underestimate the sensory effect sound has on us when we drive. The system also means that the tactile feedback absent in electric cars – namely the feelings of engine braking and judging distances – can be put back into driving. Of course, dipping the throttle on a docile Prius and hearing the sound of a red-blooded V12 is a somewhat incongruous experience, but it highlights the possibilities.

Sound from the Halosonic car is more focused and less polluting once the car has passed

This kind of experiential manipulation can also be used to more machiavellian ends. We all like what is familiar to us, particularly with costly products such as cars, but manufacturers could recreate an accustomed sound even though the car itself – its drivetrain – uses less familiar tech. The level of detail is immense and alternator whine, spark plugs and induction noise can all be sonically recreated. One potential use is to make diesel-engined cars sound like they have a petrol engine, which would encourage uptake in the diesel-skeptic USA. A development car fitted with this exact specification already exists.

Another aspect of Halosonic is noise cancellation. The system can pick up on road, tyre and engine noise and play a cancelling frequency back through the car. Sounds simple, but as always it’s absurdly complicated, although the benefits of removing heavy NVH (noise, vibration, harshness) materials are plain to see. The end result is that your car is quieter and more efficient, and wasn’t that one of the original draws of electric cars in the first place?

There’s never been any doubt that sound is an integral part of the driving experience, but so far it’s been an entirely hedonistic affair. Now, technology is allowing companies like Harmon to use sound to make cars safer, more efficient, and also fun. Halosonic is due in electric production cars this year, and although its creator is tight-lipped on the exact clients, they’ve confirmed that it’s a Europen OEM. BMW i3, anyone? We’ll have to wait and see.

Now, try to imagine that V8 twin-turbo Tesla again.  

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