Noise measurement trailer
Noise measurement trailers (also CPX measurement trailers or near-field measurement trailers based on the close-proximity method) are used to determine the tire-road noise .
Areas of application
From a speed of approx. 30 km / h, the tire-road noise is the main source of road traffic noise . The tire-road noise depends in particular on the properties of the road surface. Noise measurement trailers are used to examine the acoustic properties of road surfaces. The measurements are carried out, for example, in the course of the new construction of cover layers before and after the construction measure in order to prove the acoustic change or improvement. In addition to quality assurance when building new roads, the measurement method is also used to assess road surfaces that have been in existence for a long time. When using noise-reducing road surfaces, so-called monitoring measurements are often carried out at intervals of one to two years in order to be able to evaluate the change in the acoustic properties of the road surface.
Structure and use of the measuring system
Noise measurement trailers corresponding to the state of the art are constructed in accordance with DIN EN ISO 11819-2: Acoustics - Measurement of the influence of road surfaces on traffic noise - Part 2: Near field measurement method . In the near field of the tire , microphones are arranged at a distance specified in the standard, which are provided with windballs. In addition to the sound pressure , the speed of the measuring vehicle and the air temperature are recorded during the measurement. Using empirical formulas , measurements at different speeds and air temperatures can be referenced to standard conditions (20 ° air temperature, 50 km / h or 80 km / h driving speed). In individual cases, the measurements are also carried out at lower or higher driving speeds if the local situation requires this. In order to largely avoid flow noises on the measurement setup and extraneous noises from the surrounding road space (e.g. from other vehicles), a hood is attached over tires and microphones. This is equipped with sound-absorbing inside in order to achieve free-field conditions in the acoustically relevant frequency range . With two measuring wheels, the sound radiation at the two tires can be coherent , which can cause interference phenomena in the sound field that falsify the measurement result. Soundproof walls between the measuring wheels can help here.
Used measuring tires
Special standard measuring tires are used so that a high level of repeatability can be achieved over the long term .
The tires are referred to as P tires (P: p assenger car) and H tires ( h eavy car). The tire P is a Uniroyal Tigerpaw 225/60 R16 Standard Reference Test Tire (SRTT). This tire is also used as a standard measuring tire in the automotive industry and is manufactured under particularly controlled conditions. The acoustic properties of the tire should correspond to those of a typical car tire, i.e. H. the tire-road noise is strongly influenced by the roughness of the road surface. The H tire is an Avon Supervan AV4 195 R14C. Compared to tire P, tire H has a significantly coarser and block-like profile. Therefore, the tire-road noise of this tire is influenced less by the roughness of the road surface and more by its sound-absorbing properties. Since the acoustic properties of the tires change over time, existing tire sets have to be regularly replaced with new tire sets. In particular, the reduction in the elasticity of the tire rubber leads to a change in the acoustic tire properties over time. Contrary to the specifications mentioned in the standard, recent studies show that the measuring tires have to be replaced annually.
Measurement results
CPX measurements are usually carried out over route sections from approx. 100 meters up to several kilometers in length. In general, network-wide surveys can also take place. The measured sound pressure levels are energetically averaged for segments of 20 meters in length . The evaluated 20 m segments are displayed as a level-location curve or georeferenced on a street using GPS .
In addition, so-called CPX indices are evaluated through arithmetic communication of the 20 m segments. The CPXP index is the mean value of the evaluated 20 m segments of the measurements with tire P, the CPXH index that of the measurements with the H tire.
Quality and comparability of the measurement results
In contrast to other tests in road construction, measurement according to the CPX method is not regulated by an approval from the testing institute, such as the "Guidelines for the Approval of Testing Centers for Building Materials and Building Material Mixtures in Road Construction" ( RAP Stra ), as the quality assurance of tests in the environmental sector has established the procedure of accreditation as a test laboratory in accordance with EN ISO / IEC 17025 and is used by practically all federal states. In order to ensure comparable measurement results, the standard for the CPX measurement procedure should therefore be in the scope of accreditation of the respective test institute.
literature
- M. Männel, S. Alber: Technical remarks on the near-field measurement method CPX . Advances in acoustics - DAGA 2010 (Berlin 2010). DPG, Bad Honnef 2010
- T. Beckenbauer: Influence of the road surface texture on the tire-road noise . Report on the research and development project 03.293 / 1995 / MRB of the Federal Ministry of Transport, Building and Housing, Bonn: Federal Ministry of Transport, Building and Housing, Department of Road Construction, Road Traffic, 2002, ISBN 3-934458-79-3
- B. Altreuther, T. Beckenbauer, M. Männel: Evaluation background for the method for characterizing the acoustic properties of open-pored road surfaces . Reports of the Federal Road Research Laboratory. In: Verkehrstechnik , issue V173, Bergisch Gladbach 2008.
Individual evidence
- ↑ muellerbbm.de
- ↑ radolfzell.de (PDF)
- ↑ mp.nl (PDF)
- ↑ gundp.ch ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF)
- ↑ dsh-v.de (PDF)
- ↑ Umwelt.sachsen.de
- ↑ lanuv.nrw.de
- ↑ lubw.baden-wuerttemberg.de ( Memento of the original from June 28, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ lfu.bayern.de (PDF)
- ↑ bmwi.de
