Professional Engineering

Driving around Hemel Hempstead in a hybrid electric vehicle that emits a sound like a space ship is an act of puerile attention-seeking. That said, it is rather fun. School children point and laugh, pensioners back away in fear, dogs work themselves into a frenzy.

But why would anyone partake in such a ludicrous activity? Well, there is a serious point: electric vehicles are very difficult to hear and there is concern that their increasing use will lead to more accidents to pedestrians. Indeed, some countries are now considering introducing legislation to set minimum levels of noise for the quiet cars.

Acoustics expert Harman has pre-empted any such mandatory moves with the development of its Halosonic system which generates synthetic engine noise in a forward direction. The sound pitch and volume change with speed, giving the pedestrian a clue as to how close the vehicle is. A synthetic engine idle sound is also produced when the vehicle is switched on and the handbrake is released. A reversing noise can also be specified.

For the PE test drive, we chose to put a Toyota Prius fitted with the Halosonic system through its paces on the mean streets of Hemel Hempstead. Starting off in pure electric mode, with no sound on, the Prius was stealthily quiet. It glided anonymously around the McDonald’s car park, and it was clear to see how the lack of sound could put pedestrians at risk. After switching on Halosonic, though, it was a very different matter. The system offers several different engine settings, and we chose a throaty supercharged V8. Suddenly the Prius announced its arrival wherever it went.

 The space-ship setting was a bit of fun. But it did beg a serious question. If electric vehicles are to be required to produce noise, what should that noise be? Should they have to sound like an internal combustion engine?

What do you think an electric car should sound like? 

• Email PE at pe@caspianmedia.com and we will put the best suggestions up on our site