GOTHENBURG, SWEDEN - Acoustic design for cars is becoming increasingly important. With a brand-new acoustic laboratory, Volvo Cars' sound experts can make further progress in the area of engine noise. Volvo cars are to have a unique Scandinavian sound.

The new acoustic laboratory is located in new premises in the very heart of the Volvo Cars production complex in Torslanda, Sweden. The chamber has a network of sound-absorbing protrusions embedded in the walls and ceiling to give optimal preconditions for testing engine noise. No background noise penetrates, no standing sound waves occur to disrupt the tests.

On the other hand, the acoustic lab's hard floor is a very realistic representation of the surfaces on which cars operate. It recreates the same sound effects as when driving on tarmac.

"With our new test chamber we can test four-wheel drive cars in an entirely different environment than we could previously," says Eva Lahti, acoustic engineer at Volvo Cars.

The new test chamber is part of the NVH (Noise, Vibration and Harshness) Centre at Volvo Cars where more than 60 people work to create the right sound pattern for Volvo's cars.

"Most of our work relates to creating the foundation for the best acoustic comfort from the customer's viewpoint. Customers who purchase a premium car expect that," says Johan Stenson, manager of the NVH Centre.

Work on designing a car's sound is divided into three parts:
1. Sounds that irritate - for example squeaks and rattles, road rumble and wind roar.
2. Sounds that inform - for example engine noise and the "click" of various controls.
3. Sounds that impress - for example engine note and the sound of a door shutting.

It's all about eliminating sounds from the first category so that the others are heard as intended. Acoustic design has developed into something of a science among premium car manufacturers today. Having said that, it is a relatively new science.

"There's no long tradition in the sphere of acoustic design, but it is gaining in importance. Our challenge is to create an experience that delivers the right 'Volvo sound'," says Johan Stenson.

The aim is to create typical "Scandinavian sound comfort" and an acoustic palette that matches the aura of the brand in terms of its core values of the environment, safety and design.

Eva Lahti explains what is meant by Scandinavian sound comfort: "Here in Sweden and Scandinavia we have large, quiet spaces. The acoustic environment is open and free, not densely packed. And that's how our customers expect a Volvo to sound."

When it comes specifically to work on engine noise - the work that is done in the new noise lab - the focus is on two criteria: sound that informs and sound that impresses.

For engine noise that provides information, the experts aim for the optimal balance - the car's driving properties, road noise, steering feel and engine note should all create a single cohesive pattern.

"If I cruise at a steady speed, the engine should produce a pleasant, relaxing note. But if I accelerate from low speed under full throttle, the difference should be heard in the sound the engine produces. It should give me feedback to verify what I am doing so I do not lose my intuitive link with the car," explains Eva Lahti.

Johan Stenson feels that the science of developing impressive engine sound can become an important competitive tool for securing customers.

"For impressive engine sound, we have so far achieved the most striking results with our high-end products. The first car we worked on was the V8-powered Volvo XC90. We aimed to create a sophisticated V8 sound with a typical European note," says Johan Stenson.

And in fact it is that V8 engine note that became Eva Lahti's absolute favourite. She was involved in a test in which the car was first driven very carefully. The engine whispered discreetly, it sounded like a purring cat.

"Then we switched test drivers. The new driver floored it immediately. Wow! I was stunned - the engine showed a totally different side to its personality depending on how it was driven. Fantastic!

In the near future there are some exciting challenges facing the acoustic experts at the NVH Centre. In 2012, Volvo Cars will start marketing plug-in hybrids featuring a mixture of electric and/or diesel power. When the car is powered by electricity, progress is virtually silent. This means that other, more irritating, sounds will become more noticeable. This makes acoustic design very important. And things will be equally important from the traffic-safety viewpoint - it must be possible to hear an approaching car.

Legal requirements will probably be implemented in most countries, and in fact some US states already apply such legislation. In Europe, there are discussions on just how quiet a car is allowed to be.
"So just how should our plug-in hybrid sound? So far we have no bank of experience from which to obtain data. We'll have to start examining this issue fairly soon," says Johan Stenson.

Facts about the new semi-acoustic test chamber at the NVH Centre:

• The facility entered full operation in the first half of 2009.

• The building is insulated from vibration so as to avoid all outside interference.

• The three-storey building has three vibration zones.

• The test chamber is made of concrete; it measures 22x15.9x6.75 metres.

• The sound-insulated protrusions that cover the walls and ceiling measure 1.5 metres from the underlying concrete surface to the tip.

• The measurement equipment is designed for use with both four-wheel drive and two-wheel drive cars.

• Maximum output is 300 kW from 90 to 250 kilometres per hour for high-performance testing.