Martin Spang in Volvo's acoustic lab

Volvo's acoustic lab, inaugurated in 2009, is one of the most modern in the automotive industry. The sound level of a normal conversation is 60-70dB, but Volvo acoustic engineer Martin Spång (above) says the background noise level inside the acoustic lab is just 17dB: "This is such a quiet noise level that you'd be able to hear someone's tummy rumble from the other side of the chamber."

The 2500 square metre concrete chamber is entirely insulated from the rest of the building to prevent any background sound from seeping through, and the walls and ceiling are lined with sound-absorbing wedges to damp reflecting sound. The floor is hard and smooth so that it reflects sound in the same way as a road surface. Test cars can be driven on rollers with various surface treatments to simulate different road types.

The soundscape of a hybrid car is very different to a conventional vehicle, says Spång: "The combustion engine sound is instinctively connected to our perception of driving a car. It works as an acoustic mat that blankets other sounds. When that mat is lifted off, you suddenly become aware of a number of other sounds."

Tyre noise and wind noise become more obvious to the driver, along with noises from pumps, fans and relays, and even the splashing of fuel in the tank.

"What's important here is to strike the right balance between traditional and new sources of noise," says Spång. "Some sounds can be isolated and removed. In other cases it is up to our suppliers to develop quieter components together with us."

But the wider adoption of hybrid powertrains will lead to a change in perception of vehicle noise, he adds. "Customers will get used to the fact that electric cars sound somewhat different," says Spång. "This will become part of these cars' personality - their attraction and their trademark."