Creating the perfect truck sound
Truck noise is often taken for granted. It is simply there. However, a team at Volvo is dedicated to increasing safety and comfort by optimising the interior and exterior sounds made by trucks.
Vital sound spots that make the difference
The beating heart of the truck, engine sounds are vital in communicating information to the driver.
The truck’s transmission makes noises on being engaged, sounds that are important to sync with the rest of the vehicle.
The intake channel is a direct sound link between the engine cylinders and the surroundings, and communicates information to the driver about the engine’s working condition.
The air conditioning system in a truck should not only work well. It should also not create sounds that disturb the driver.
The contact force between the road and the tyres generates noise. An experienced truck driver uses changes in the tyre noise as a warning for slippery road conditions.
High torque is transferred from the gearbox to the tyres via the rear axle transmission. The gear inside the rear axle needs to be optimised in order not to generate unnecessary noise.
There are many elements that go into making a truck the safest and most comfortable vehicle it can possibly be. State-of-the-art engineering, automated driving systems and revolutionary design all contribute to the development of the trucks of the future. One aspect that is often easy to underestimate is how much the noise created by various areas of a truck can affect the driving experience.
In fact, Volvo Trucks has been dedicated to noise optimisation for several decades. The first Volvo noise chamber was set up in Gothenburg, Sweden in 1982. Sound modification in Volvo truck models has been ongoing ever since, and a team of Noise and Vibration Test Engineers in Gothenburg are constantly working to keep Volvo Trucks ahead of the competition in this area.
The Noise & Vibration Laboratory is a hive of quiet activity. Interesting looking machines emit red lights and a vast, hushed studio with a collage of sound-absorbing material on the walls has a Volvo FH testing truck at its centre. Here we meet three NVH (Noise, Vibration & Harshness) Engineers, who have many years combined experience working in the specialised branch. Theresia Manns, Geir Andresen and Torbjörn Ågren work closely within a team of around ten engineers, mainly at this location but also at Volvo Trucks’ Proving Ground at Hällered, just outside Gothenburg.
“We are working to optimise the interior and exterior noise produced by the trucks,” says Theresia Manns. “There is often a perception that we just want to lower the noise level, but it is also the quality of the sound that is important. Our goal is to achieve the best sound quality and to improve the driver’s experience, both from a safety and from a comfort point-of-view.”
The importance of working together with other branches of the organisation to achieve better results is acknowledged by Torbjörn Ågren. “Each truck feature has one dedicated Feature Leader. They are responsible for the development of this particular feature. In this respect, our feature is the complete vehicle noise. We have regular contact with those responsible for components and the project programme. Legal requirements are obviously vital to keep informed about and ahead of. The department of product planning sets the high level requirements and we work together to establish exactly what the customer wants in terms of optimised sound. It is also important to consider what our competitors are doing in this field.”
The NVH Engineers’ daily work centres around development and testing of the various Volvo truck models for sources of noise, and facilitating improvements in these areas. According to legal requirements, verified truck noise testing must be carried out outside. “At the moment, indoor testing is not legally recognised by the authorities,” says Geir Andresen. “However it may become properly certified in the future. The ISO test track at Volvo Trucks’ proving ground is therefore vital to our work for noise verification. It is hard to simulate real conditions indoors, and therefore we do our verified legal testing outdoors.”
Noise levels created by trucks are subject to strict legislation worldwide. The European market and some markets elsewhere are following the ECE regulations, but the noise legislation varies depending on the market. In addition, local noise requirements must be considered.
The intricacies involved in working with sound are reflected by the huge array of monitoring equipment at the Noise & Vibration Laboratory. One of the most distinctive looking contraptions is a 3D acoustic camera, which resembles a large disco ball and is fitted with many small microphones. The camera is used as a sound source localiser, and it scans the cab interior for sources of sound. Noise is calculated via algorithms to create a sound level picture. Higher levels of noise from certain areas are represented by bright colour zones in the picture. In this way, the team can isolate particular sound spots and work to phase them into the truck’s desired overall sound picture.
Thinking about how drivers receive information from truck sounds is another important factor in the team’s work. “The truck’s response when inside the cab is mostly heard rather than seen,” says Theresia Manns. “Noise carries information which the driver reacts to. Also, people often don’t actually notice uncomfortable noise until it is gone.”
Measuring the total noise level of trucks involves meeting a series of targets. “Sometimes decreasing the noise contribution of one area of the vehicle can mean that another previously inaudible sound is suddenly noticeable,” continues Geir Andresen. “We are dealing with the complete truck. Noise feedback can sometimes transfer to the cab interior from other areas, for example. Sound insulation and structural development work is therefore very important.”
The safety aspect of in-cab noise is highlighted by the work carried out in optimising the noise frequency content. “Drivers become tired from low frequency noise,” says Theresia Manns. “It is all about not noticing unpleasant noise and experiencing good sound quality. We work to deliver an environment where a driver can spend a lot of time without becoming adversely affected by monotonous noise, even if the level is low. ”
Isolating a particular truck sound can be painstaking work for the Test Engineers at the laboratory. ‘The Encapsulated Truck’ involves a time-consuming process where the vehicle is completely clad in order to expose one particular noise source for a detailed examination. Less time consuming methods are also used, both in the test cell and at the test track. “We are busiest when verification has to be conducted outside and weather is beneficial,” says Torbjörn Ågren. “There is a lot of pre-work to take care of. The run-up to the introduction of new legislation is also a very active period, as are certain periods within a particular project.”
As we leave the team, they are about to get busy again setting up the 3D acoustic camera for more testing. Torbjörn Ågren concludes by stating that their work is all about finding the right balance, both literally and metaphorically. “We are looking to make modifications that contribute positively to the driving experience. It is about improving in steps. At the end of the day, we want the truck to sound like a Volvo.”