Test Report. RI Acoustic Lab. Measurement of Sound Absorption Coefficient for RockDelta NoiStop Noise Barrier. 20 Feb. 07

Transcription

1 Test Report RI Acoustic Lab Measurement of Sound Absorption Coefficient for RockDelta NoiStop Noise Barrier 20 Feb. 07

2 Title Measurement of Sound Absorption Coefficient for RockDelta NoiStop Noise Barrier Test by Date of test MLi 15 Feb. 07 Client RockDelta a/s Hovedgaden 584 DK-2640 Hedehusene Client ref. Morten Haahr Summary Laboratory measurements of the sound absorption coefficient were conducted in a reverberation room close to the guidelines in EN ISO 354:2003 and evaluated after EN :1997. Product: Thickness: Mounting depth: RockDelta NoiStop noise barriers 116 mm 0 mm The noise barrier panels were placed on the concrete floor of the reverberation room. The test results per one-third octave are shown in tabular form and graphically on the graph sheet with the single number weighting of sound absorption DL a and the absorption performance categorized in accordance with EN :1997 annex A. The reverberation room and test procedure are described in the Appendix.

3 1. Introduction Measurements of the sound absorption coefficient in a reverberation room were carried out for a noise barrier product. 2. Description of the Test Specimen Product: RockDelta NoiStop noise barrier. Density of wool 175Kg/m 3. Thickness: 116 mm Module size: 2000 mm x 900 mm 3. Mounting in the laboratory The noise barrier panels were mounted directly against a concrete floor in a frame with the size 2.70 m x 4.15 m. Pictures are shown in the Appendix. The test specimen was enclosed by a 22 mm wooden frame. The specimen was made of 3 panels on each side of a wooden post. The length of the panels on both sides of the post was of 2m. All joints between the test specimen and the frame as well as between the frame and the concrete floor were sealed with tape. The test specimen was placed so that no part of it was closer than 0.5 m to any edge of the boundary of the room. 4. Test Method The measurements were carried out close to the guidelines in EN ISO 354:2003: Measurement of Sound Absorption in a Reverberation Room. The individual sound absorption coefficients were calculated from the reverberation times measured with and without the test specimen. The measurements were made in Room1+2, RI Acoustic Lab. In the Appendix a short descriptions of the facilities are found.

4 5. Instrumentation The following instruments were used in the test: Instrument Type Modular Precision Sound Analyzer B&K 2260 Measurement Microphone B&K 4189 Omnidirectional loudspeaker B&K 4292 Power amplifier B&K 2716 Sensor for Temperature and Humidity Testo 177-H1 6. Measurement Conditions The reverberation time was measured in 6 microphone positions, placed at different heights ranging from 1.40 m to 2.1 m above the floor. The number of loudspeaker positions was two at a height of 1.5 m. In combination a total of 12 loudspeaker/microphone positions were used. The reverberation time per octave in the room without test specimen: Frequency [Hz] Reververation time T 1 [s] Temperature and relative humidity in the reverberation room during measurements: Room without test specimen: 19.1 C, 43.7% RH. Date of test: 19 Feb. 07 Room with test specimen: 18.8 C, 49.8% RH. Date of test: 15 Feb. 07

5 The correction of the absorption coefficient α s due to differences in temperature and relative humidity during measurements of T 1 (empty room reverberation time) and T 2 (reverberation time of room with specimen) was: Frequency [Hz] α s Frequency correction [Hz] α s correction 7. Test Results The test result α s per one-third octave from 100 Hz to 5000 Hz is shown in tabular form highlighted in yellow and graphically in the Appendix A. The calculated, practical sound absorption coefficient α p per octave from 125 Hz to 4000 Hz is shown together with the single-number rating of sound absorption performance DL a as well as a categorization. These values are calculated in accordance with annex A of EN1793-1: Measurement Uncertainty Measurement uncertainty (90% confidence interval) estimated from a Nordic intercomparison (Nordtest project No ) for the practical absorption coefficient α p per octave: Frequency [Hz] Uncertainty 125 ± ± ± ± ± ±0.10

6 Appendix Description of Reverberation Room The measurements are performed in a reverberation room comprised by two rooms with opening between them (Room1+2 in the RI Acoustic Lab) with walls, ceiling, and floor of concrete. The dimensions of each of the rooms in meters are: L1 W1 H1 L2 W2 H The total volume is approx. 194 m 3, and the total surface area is approx. 261 m 2. Sound diffusion is obtained with the use of acrylic sheet hanging throughout the room. A plan sketch of the two rooms is shown. Rum Rum

7 Principle Measurement of sound absorption close to the guidelines in EN ISO 354:2003 is carried out in a reverberation room. The test signal is broad band pink noise emitted by an omnidirectional loudspeaker located at two positions in the room. The reverberation time is measured at six microphone positions at different heights for each of the loudspeaker positions. For each microphone/speaker position five repeated measurements are carried out. One third octave filters are included in the analyser equipment. The reverberation time is evaluated from the averaged slope of the decay curve over a range from 5 db to 25 db below the steady state level. The average reverberation time in the reverberation room is measured with and without the test specimen mounted. From these reverberation times, the equivalent sound absorption area, A, is calculated by using Sabine s equation 55,3V A = 4Vm (1) ct V c T m is the volume, in cubic metres, of the reverberation room; is the propagation speed of sound in air, in metres per second; is the reverberation time, in seconds, of the reverberation room; is the power attenuation coefficient, in reciprocal metres, calculated according to ISO using the climatic conditions that have been present in the reverberation room during the measurement. The equivalent sound absorption of the test specimen, A T, is calculated by: A T = A 2 - A 1 (2) A 2 A 1 The equivalent sound absorption area of the reverberation room containing a test specimen The equivalent sound absorption area of the empty reverberation room In the case of a test specimen that uniformly covers a surface (a plane absorber or a specified array of test objects), the sound absorption coefficient α s is obtained by dividing A T by the treated surface area S AT α s = (3) S The attenuation coefficient of sound in air varies with relative humidity, temperature and frequency. The conditions are held as constant as possible. A correction formula is applied based on the data from ISO :1993.

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