Measuring and managing engine noise emissions through NVH testing

Volvo Penta engines power a wide variety of vessels, vehicles and machines, in many different industries. Because they are subject to regulatory demands on noise emissions, we test our engines in test cells and at sea. That way, we can ensure that they are in compliance with certification standards and international legislation.

NVH – a standardized method for identifying noise and vibration levels

NVH, which stands for “noise, vibration and harshness”, is the study and modification of noise and vibration characteristics. Harshness is mostly applicable in the cases of sound quality testing. NVH studies can be conducted in vessels, outdoors or in specially designed test cells free of additional noise pollution and sound reflections from the walls. In the test cell, the standardized noise tests are conducted by skilled test cell technicians. Ten microphones are arranged in a sphere around the engine, according to the ISO standard. The purpose of this is to calculate the sound power levels emitted from the engine.

Pass-by measurements record marine engine noise in their typical environment

We measure boat engine noise emissions by means of pass-by measurement. Volvo Penta can conduct these tests at our facility for product development and testing at Krossholmen in the Gothenburg archipelago. We set up the measuring equipment – a microphone and a sound analyzer – at a defined position. In our case, on an island close to the test facility. The test boat is then driven past the measuring equipment, which in turn records the noise emitted by the boat with its engine running at maximum speed. The distance between the boat and the measuring equipment is 25 meters.

Noise measurements as a diagnostic tool

The sound emissions of an engine and its drive may also need to be measured, and possibly adjusted. By conducting a synchronized measurement of the sound and engine speed (rpm) signal, the sound can be broken down into different components. By establishing the relationship between frequency and speed, these sound components can be sorted out. It is thereby usually possible to pinpoint a certain component; a gear mesh, bearings, propeller blades, cardan shaft, et cetera. So, if one of these components gives off an unusually high level of noise, it may indicate that some part is broken, worn out, poorly aligned or imbalanced.

Photographing “noise” with an acoustic camera

Using an acoustic camera is often highly beneficial in order to localize the source of specific components in the sound. The camera consists of a stand/tripod, with approximately forty microphones placed in the shape of an antenna or sphere. The microphones measure the sound, and can – by means of advanced signal processing – transform the sound into a graphic image. It is then possible,  to overlay the image on to a video, or a photograph of an engine (for example). This method is often useful when one wants to find the origin of prominent or disturbing components in a certain noise.

The innovative challenges and potentials of new noise emission directives

It is highly likely that new technologies of power generation will partly or completely replace combustion engines in the future. More silent replacements will make other noises more dominant, namely those previously drowned out by the sound of the engine itself. Identifying and adjusting those noise sources calls for potentially new methods and challenges in the field of NVH.

The pass-by measurements conducted today provide us with data on above-surface noise emissions, but in the future we will most likely have to look – or, rather, listen – more closely below the surface as well. Scientists and various government agencies, such as the Swedish Agency for Marine and Water Management, devote increasing amounts of time and resources to the studying of underwater environments. The impact on animal life caused by underwater noise pollution is a key aspect of this research. Volvo Penta is watching this development closely in order to remain at the forefront of sustainable marine solutions.

Do you want to know more about our solutions and products, for leisure boats as well as commercial craft? Visit our website, stay up to date by reading our Volvo Penta Professional Power Blog, and feel free to contact me if you have any questions.

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