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The Science of Noise

The Science of Noise

By TA News Bureau:

A specialist in tyre skid, rolling resistance, especially modelling of tyre/road interaction noise and the effect of tyre and pavement, Dr Gijsjan van Blokland is a widely known authority in this field. As a researcher, academic and member of ISO TC43 Working group, he has studied noise impact of tyres on different road surfaces to measure rolling noise levels. His research is helping engineers to design tyres to conform to the ever tightening regulations to reduce noise. In this interview to Tyre Asia, he shares his research findings and offers comments on tyre noise related issues. He was an expert member of the Dutch delegation (1995-2010) to EU Brussels (ERGA-NOISE) and UN/ECE Geneva (GRB)

To know more about the science of tyre noise, engineers turn to Dr Gijsjan van Blokland for advice and learn from his research and studies. Holding a doctorate in Physics, he has been a Senior Researcher (1986-2018) at the Netherlands-based M+P Consulting Engineers, which for the past four decades has studied and developed solutions relating to noise, vibration and air quality.
Recently he conducted a study of 30 truck tyres on four different road surfaces to measure their rolling noise levels. “We assessed the noise levels of new tyres according to the ECE R117 procedure and have compared the test results with the noise label values for these tyres according to EC/1222/2009,” he said in an interview to Tyre Asia.
“We observed a small but significant difference, with the label values being on average slightly lower. The difference, however, could be explained by the effect of temperatures during our testing and the slightly rougher test surface.”
The noise levels found on the ISO 10844 test surface (mandatory in R117) showed a limited correlation with levels found on the rougher SMA11 surface. It did correlate well with the levels found on the smooth textured TSL8 and ACSURF16 surface
The combination of traction tyre profile with the smooth ISO10844, ACSURF8 and ACSURF16 surface did generate strong tonal components in the rolling noise levels. Such tonal components are known to cause extra annoyance.
When asked whether he found any significant differences in the noise levels of new tyres vis-a-vis retreaded tyres, the noise expert said that this research has revealed some interesting aspects.
“We compared the rolling noise levels of the original tyres with the noise levels of the nearly identical retreaded versions and concluded that there was a systematic increase in the noise levels of the retreaded version with 1 dB compared to the original version.”
The cause of this shift could not be explained by the variation in tyre tread band mobility or in the hardness difference of the tread band compound.

Tread patters

Explaining his observation on test measurements of tread patterns geometry, tread rubber hardness and tread mobility spectra, Dr Blokland pointed out that the main objective of the study was to compose a reliable data base of high resolution and high quality measurement data that in the next phase of the project could be used to study the impact of noise from C3 tyres.
“The acoustic characteristics of the tyres under test were determined by the tread band mobility, the hardness of the tread compound and the geometry of the tread pattern,” he elaborated.
For all tyres, these properties are assessed together with the 1/3rd octave band spectra of the rolling noise under R117 standard test procedures.
Also for all tyres the narrowband sound spectrum is recorded at close proximity while coasting over the series of five test sections.
Commenting on the implications of the effectiveness of the current EU regulations related to tyre noise labelling and its impact, Dr Blokland said his study had covered four issues with the EU tyre noise regulation.
First, the standard procedure for C3 tyres does not include a correction for the temperature during the test. Testing under high temperatures may then lead to not representative test results.
Other studies have demonstrated that rolling noise of C3 tyres is affected by the temperature. It is recommended to include such correction in the test procedure (as is the case with C1 and C2.
Second, the properties of the road surface defined for the standardized R117 noise test (defined in ISO 10844) differ from surfaces found in Nordic countries where due to safety issues during winter conditions rougher textures are applied.
Rolling noise levels of tyres on these surface show little correlation with levels found on the smoother ISO surface.
Tightening limit values in the tyre regulation will thus not cause substantial lowering of the rolling noise levels of C3 tyres in use in these countries. For countries with smoother road textures, the tightening of limit values will have effect on the traffic noise
Third, retreaded C3 tyres at the moment are not subjected to R117 regulation. Retreading causes on average higher rolling noise levels. It is estimated that in the EU about 50% of the C3 tyres are retreaded.
Fourth, the regulatory assessment is based on overall A-weighted noise levels. The study observed string tonal components for several traction tyres that are known to cause higher annoyance than non-tonal sounds with the same strength.
On tyre retreading as a sustainable and environmentally friendly option, Dr Blokland feels that it is something that should be considered.
“My opinion is that retreading is very important for controlling the waste from worn tyres. Improved environmental friendliness can be achieved by including this category in the R117 scope.”
He said those who are interested in accessing the reports on this and other studies on truck tyre noise performed by M+P may visit https://www.mplusp.eu/search/site/truck%20tyres?f%5B0%5D=bundle%3Apublicatie

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