Sound Insulation and Reflection Properties of Sonic Crystal Barrier Based on Micro-Perforated Cylinders

Abstract

A sonic crystal barrier, consisting of empty micro-perforated cylindrical shells, was built on the campus at the Universitat Politècnica de València in 2011 and characterised by using a non-standardised measurement technique. In this paper, the sonic crystal barrier, upgraded with rubber crumb inside the micro-perforated cylindrical shells, was characterised by using standardised measurement techniques according to EN 1793-5 and EN 1793-6. As a result of the characterisation, sound insulation properties of the barrier were shown to be a combination of the absorptive properties of the individual building units and the reflective properties of their periodic distribution. In addition, its performance was compared with a similar barrier consisting of rigid polyvinyl chloride (PVC) cylinders, which was recently characterised using the same standardised techniques. In comparison with the barrier based on PVC cylinders, the barrier investigated here produced a broadband enhancement of the sound insulation and lower reflection indices in the targeted frequency range. It was also shown that the influence of leakage under the barrier and the width of the temporal window on sound insulation was negligible. While EN 1793-5 and 1793-6 allow a direct comparison of the performance of different noise barriers, the applicability to this new type of barriers requires further investigation.

Keywords: EN 1793-5; EN 1793-6; noise barriers; sonic crystals; sound insulation; sound reflection.

Figure A1

Influence of Adrienne temporal window width on SI measurements in two configurations. (a) Sound insulation index SI, configuration A; (b) sound insulation index SI, configuration B.

Figure A2

Influence of leakage under the barrier on SI values in the same measurement setup. The SI values are averages of the lowest three microphones (M7, M8, and M9) in the microphone grid. (a) Sound insulation index SI, configuration A. (b) Sound insulation index SI, configuration B.

Figure 1

Sonic crystal (SC) barrier sample implemented on the campus of Universitat Politècnica de València: (a) Appearance of SC barrier sample made of three rows of absorbing cylindrical units, along with experimental setup; (b) internal cross-section of a cylindrical unit, consisting of a porous core made of rubber crumb and outer micro-perforated aluminium shell.

Figure 2

(a) Attenuation spectra measured for several SC barrier samples implemented on the campus at the Universitat Politècnica de València; (b) corresponding calculated spectra simulated according to procedure described in [9].

Figure 3

Illustration of standardised EN 1793-5 and EN 1793-6 measurement methods in the presence of the SC barrier: (a) Experimental setup for SI measurement; (b) experimental setup for RI measurement.

Figure 4

Acoustic bands of a square lattice of rigid cylinders embedded in air. Dark stripes indicate complete band gaps and light grey stripes define the partial gaps. The inset plots the reciprocal lattice together with high symmetry points that define the irreducible region.

Figure 5

Attenuation spectra calculated for an acoustic barrier consisting of three rows of rigid cylinders arranged in a square configuration with a lattice constant of 22 cm and a volume filling ratio of 41%. (a) Results for incident plane waves; (b) band dispersion relation along the ΓX direction. Grey zones define band gaps along this particular direction; (c) results for impinging cylindrical waves.

Figure 6

Snapshot of total pressure maps calculated when a plane (left panels) and a cylindrical (right panels) wave interacts with acoustic barrier consisting of three rows of rigid cylinders ordered in a square configuration with lattice constant of 22 cm and volume filling ration of 41%. (a,b) Calculated maps for waves with frequency of 200 Hz; (c,d) corresponding maps for waves with frequency of 1.55 kHz. Maps are calculated by using the finite element method.

Figure 7

Attenuation spectra calculated for an acoustic barrier consisting of three rows of absorptive cylinders arranged in a square configuration with a lattice constant of 22 cm and a volume filling ratio of 41%. (a) Results for incident plane waves; (b) results for impinging cylindrical waves. Grey zones define band gaps along ΓX orientation (see Figure 4) of the barrier.

Figure 8

Positions of the microphone grid in two different configurations: (a) Configuration A, the middle column of microphones faces the centre of the cylinders; (b) configuration B, the middle column of microphone grid faces the centre of the space between two adjacent cylinders.

Figure 9

Sound insulation index sound insulation index (SI) of SC barrier with micro-perforated (MP) cylinders measured in two different configurations. Results are compared with those of standardised characterisation of SC barrier with PVC cylinders presented in Figure 6 in [24]. (a) Sound insulation index SI, configuration A; (b) sound insulation index SI, configuration B.

Figure 9

Sound insulation index sound insulation index (SI) of SC barrier with micro-perforated (MP) cylinders measured in two different configurations. Results are compared with those of standardised characterisation of SC barrier with PVC cylinders presented in Figure 6 in [24]. (a) Sound insulation index SI, configuration A; (b) sound insulation index SI, configuration B.

Figure 10

SI values measured at individual microphone positions M1–M9. Thick black curve shows the averaged SI values over all nine microphones. (a) Sound insulation index SI, configuration A; (b) sound insulation index SI, configuration B.

Figure 11

Sound reflection index reflection index (RI) of the SC barrier with MP cylinders measured in two different configurations. The results are compared with results of the standardised characterisation of SC barrier with PVC cylinders presented in Figure 7 in [24]. (a) Reflection index RI, configuration A; (b) reflection index RI, configuration B.

Figure 11

Sound reflection index reflection index (RI) of the SC barrier with MP cylinders measured in two different configurations. The results are compared with results of the standardised characterisation of SC barrier with PVC cylinders presented in Figure 7 in [24]. (a) Reflection index RI, configuration A; (b) reflection index RI, configuration B.

Figure 12

RI values measured at individual microphone positions M1–M9. Thick black curve shows the averaged RI values over all nine microphones. (a) Reflection index RI, configuration A; (b) reflection index RI, configuration B.

Figure 13

Comparison of SI experimental and finite element (FE) simulations results averaged over three microphone positions—M4, M5, and M6. (a) Sound insulation index SI, configuration A. (b) Sound insulation index SI, configuration B.

Figure 14

Comparison of RI experimental and FE simulations results averaged over three microphone positions–M4, M5 and M6. (a) Sound reflection index RI, configuration A. (b) Sound reflection index RI, configuration B.