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Reduce the pressure, go for particle velocity

Noise reduction on a high performance two-wheeler

Nowadays for events, as for example motor races, very strict noise regulations apply. Currently noise levels are frequently exceeding regulations. Creating a need for solutions helping to reduce noise from the two-wheelers. The challenging task to do this for a superbike, a high performance two-wheeler, is to achieve this without altering its performance.


  • Reduce maximum overall level at a defined distance from the racetrack produced as a total by all superbikes on the racetrack
  • Reduce the SPL at 1 meter for an individual superbike
  • Find a solution that has negligible impact on performance e.g. horse power and torque

Achieved Goals

  • Noise reduction achieved of 11.6 dBA
    • Baseline two-wheeler 109.4 dBA
    • Modified two-wheeler 97.8 dBA
  • Static and dynamic test results show no performance difference between baseline and modified two-wheeler


The acoustic signals of the sound field are acquired by manually moving a PU probe across a measurement plane whilst filming the event with a camera. At post-processing stage, the sensor position is extracted by applying automatic colour detection to each frame of the video. The results are finally combined with a background picture of the measured environment to obtain a visual representation which allows us to “see” the sound pressure, particle velocity or sound intensity spatial distribution.

Ranking of areas

The whole superbike was measured and scanned using Scan&Paint 2D This will help to rank the dominant noise areas and components as well as give inside at what frequencies most sound is emitted Two dominant areas were found:

  1. Exhaust System (highest overall level)
  2. Intake System (2nd highest overall level)

During the static measurement a harmonic peak of 114.7 dB PVL was found at 515Hz in the overall averaged spectrum for the exhaust system. In the measured plane, very near the exhaust surface, even overall values over 120 dB PVL are measured.

Designing a solution

To achieve the desired noise reduction a resonator will be designed for the exhaust. In order to design a good resonator, besides the frequency the speed of sound has to be taken in account, which varies depending on the temperature. For this reason the temperature was measured at the exhaust during operation. The temperature measured during static testing at the exhaust is between 500-600 degrees Celsius. A prototype branch resonator with adjustable length between 29-31cm was build for testing. After extensive measurements at different length it showed that the optimal length would be 29cm.


To get one step closer in the process to a final product, a second prototype was designed for the optimal size of 29 cm. Static tests proven again the same noise reduction and no decrease in terms of performance. A final proof was a dynamic test on a circuit with this branch resonator installed on an actual superbike. During a race weekend on the TT cicuit in Assen a final dynamic measurement took place.The starting point , as the outcome of the base line measurement at the beginning of the project, with the original superbike was a level of 109.4 dB(A). The maximum level prescribed by the regulations for this weekend was 102 dB(A). During the measurements with the modified superbike including an Arrow Endurance exhaust with a branch resonator the measured level was only 97.8 dB(A). The noise level of the superbike was now reduced by 11.6 dB(A) overall and therefore no longer exceeding regulations but within 4.2 dB(A) margin of the max level. So a big success!

Reduce the pressure, go for particle velocity


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