Noise barriers

Adrienne project (1995-97)

Background

When drafting the related EN 1793 standards, the CEN/TC 226/WG 6 met problems with the existing methods. These methods had been designed for acoustic products to be used inside buildings, while WG 6 deals with noise reducing devices along roads, i.e. outside buildings. The need to have an appropriate method, relevant for specific angles of incidence and able to investigate flat and non flat products, was evident.

Objectives

The new method should preferably use the same principles and equipment for measuring sound absorption and airborne sound insulation. The new method must work for flat and non flat products, giving values for absorption and insulation which can be considered realistic for the intended use (road traffic noise). All of that with a lowest frequency limit which should be as close as possible to 100 Hz (one-third octave band). Expressing results in conformity to already existing EN 1793 standards, the accuracy of single number ratings should be as close as possible to +/- 1 dB.

Partners list

Work program

Work Package 1: Selection of the method. Seven methods have been compared in order to choose the most appropriate one for starting the research; the MLS method has been kept.
Work Package 2: Development of the method. Definition of quantities to be measured (reflection loss for sound absorption/reflection/scattering and transmission loss for airborne sound insulation), equipment, signal and signal analysis, location of the sensors. About hundred tests have been carried out. A close look has been taken to external effects (sensitivity to temperature changes, wind, etc.). The MLS signal and sample rate have been fixed, as well as the time window for signal processing (Adrienne window). A subtraction technique has been chosen, implying the construction of a new sound source/microphone unit.
Work Package 3: Application and check of the method. Extensive and systematic tests have been carried out in a "blind" way by eight laboratories on the same samples assembled in a huge test wall of 20x4 m (LxH). Six samples for sound absorption and three samples in three different configurations for airborne sound insulation have been tested.
Work Package 4: Final analysis and report. Comparison of the results from WP3 in order to understand the power of the new method , its accuracy, its advantages and drawbacks; drafting of new proposals for improving the method, which is going to be proposed for a new standard (EN 1793-5).

Results

The new method uses a repeatable MLS signal fed to a specific loudspeaker/microphone unit. It is easy to use and affordable, it has shown the best background noise immunity ever, it is representative and adequate for its intended use alog highways. In the final "blind" test done by eight different laboratories, the single number rating values shown an encouraging good repeatability (+/- 1 dB for absorption, +/- 2 dB for airborne sound insulation). The main remaining problem is still imposed by physics: the lowest reliable frequency limit has been reduced from 400 Hz to 200 Hz (using the subtraction technique); further improvements are requested to reach 100 Hz. A final true Round Robin test should be carried out after having applied the proposed improvements, in order to draft the definitive new standard. It is worth noting that the new method can equally be applied for road noise and railway noise reducing devices; moreover, a similar, more simplified, procedure is under consideration by ISO for characterizing the sound absorption of road surfaces (ISO 13472-1).

RL measurement - Altuglas    RL measurement - MICE    RL measurement - Beton Bois

Grenoble test site (1997): Reflection Loss measurements in front of the Altuglas sample (left), MICE sample (center) and Beton Bois sample (right). Photos by M. Garai (C) 1997-2000.

RL measurement - Reflecting zigzag    RL measurement - Half-absorbing zigzag    RL measurement - Absorbing zigzag

Grenoble test site (1997): Reflection Loss measurements in front of the zigzag sample: reflecting (left), half-absorbing (center) and absorbing (right). Photos by M. Garai (C) 1997-2000.

RL measurement - Altuglas

Grenoble test site (1997): Reflection Loss measurement results for the Altuglas sample.

RL measurement - MICE

Grenoble test site (1997): Reflection Loss measurement results for the MICE sample.

RL measurement - Beton Bois

Grenoble test site (1997): Reflection Loss measurement results for the Beton Bois sample.

RL measurement - Reflecting zigzag

Grenoble test site (1997): Reflection Loss measurement results for the reflecting zigzag sample.

RL measurement - Half-absorbing zigzag

Grenoble test site (1997): Reflection Loss measurement results for the half-absorbing zigzag sample.

RL measurement - Absorbing zigzag

Grenoble test site (1997): Reflection Loss measurement results for the absorbing zigzag sample.

TL measurement - Element - Altuglas    TL measurement - Element - MICE    TL measurement - Element - Composite   

Grenoble test site (1997): Transmission Loss measurements in front of the Altuglas sample (left), MICE sample (center) and composite wall sample (right). Photos by M. Garai (C) 1997-2000.

TL measurement - Element - Altuglas

Grenoble test site (1997): Transmission Loss results for the Altuglas sample. Element measurements.

TL measurement - Post - Altuglas

Grenoble test site (1997): Transmission Loss results for the Altuglas sample. Post measurements.

TL measurement - Element - MICE

Grenoble test site (1997): Transmission Loss results for the MICE sample. Element measurements.

TL measurement - Post - MICE

Grenoble test site (1997): Transmission Loss results for the MICE sample. Post measurements.

TL measurement - Element - Composite

Grenoble test site (1997): Transmission Loss results for the Composite sample. Element measurements.

TL measurement - Post - Composite

Grenoble test site (1997): Transmission Loss results for the Composite sample. Post measurements.

Acknowledgment

The Adrienne research was funded by the European Commission, through the Standards, Measurement and Testing (SMT) program (contract MAT1-CT94049).

Basic references

  1. AFNOR S 31-089 (1990) Code d’essai pour la détermination de caractéristiques acoustiques d’écrans installés en champ libre, AFNOR, Paris.
  2. ANFOSSO-LEDEE F. (1997) Evaluation des qualités d'absorption des écrans antibruit non plans, Proc. 4th Congrès Français d'Acoustique, Marseille.
  3. ANFOSSO-LEDEE F., GARAI M., CLAIRBOIS J.-P. (2000) "Adrienne: une méthode européenne pour la qualification sur site des écrans antibruit", Bulletin des Laboratories des Ponts et Chausées, 225, 89-104. (PDF, 821 KB)
  4. COBO P., GARAI M. & SANTIAGO S. (1997) Reflection loss measurements on flat and non flat samples using the MLS method with the signal subtraction technique, Proc. XXVIII Jornadas Nacionales de Acustica (Tecniacustica '97), Oviedo.
  5. CLAIRBOIS J.-P., BEAUMONT J., GARAI M., SCHUPP G. (1998) A new in-situ method for the acoustic performance of road traffic noise reducing devices, Proc. 16th I.C.A. and 135th A.S.A. meeting (invited paper), Seattle, U.S.A. (1998) and J. Acoust. Soc. Am., 103(5), Pt. 2, 2801 (1998). (PDF, 150 KB)
  6. CLAIRBOIS J.-P., BEAUMONT J., GARAI M., SCHUPP G. (1998) A new in-situ method for the acoustic performance of road traffic noise reducing devices, Proc. Euro-Noise '98, Munich.
  7. GARAI M. (1993) "Measurement of the sound-absorption coefficient in situ: the reflection method using periodic pseudorandom sequences of maximum-length", Appl. Acoust., 39, 119-39.
  8. GARAI M., COCCHI A. (1996) On the measurement of sound absorption of non-flat barriers, Proc. Inter-Noise '96, Liverpool.
  9. GARAI M., GUIDORZI P. (1998) Caratterizzazione in situ delle proprietà riflettenti di barriere acustiche non piatte, Atti XXVI Convegno Nazionale AIA, Torino. (PDF, 35 KB)
  10. GARAI M., GUIDORZI P. (1999) Caratterizzazione in situ delle proprietà fonoisolanti di barriere acustiche, Atti XXVII Convegno Nazionale AIA, Genova. (PDF, 35 KB)
  11. GARAI M., BERENGIER M., GUIDORZI P., L'HERMITE PH. (1998) Procedure for measuring the sound absorption of road surfaces in situ, Proc. Euro-Noise '98 (invited paper), Munich. (PDF, 35 KB)
  12. MOMMERTZ E. (1995) "Angle-dependent in-situ measurements of reflection coefficients using a subtraction technique", Appl. Acoust., 46, 251-263.
  13. WILMS U., HEINZ R. (1991) "In-situ Messung komplexer Reflexionfaktoren von Wandflächen", Acustica, 75, 28-39.