# A case study on room acoustic solutions for social gathering places

Yue Li, Julie Meyer, Timur Mukhametkaliyev, Zhang Ze

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## To cite this version:

Yue Li, Julie Meyer, Timur Mukhametkaliyev, Zhang Ze. A case study on room acoustic solutions for social gathering places. Forum Acusticum, Dec 2020, Lyon, France. pp.2597-2597, 2020, 10.48465/fa.2020.0220. hal-03242417

HAL Id: hal-03242417

https://hal.science/hal-03242417

Submitted on 17 Feb 2023

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# A case study on room acoustic solutions for social gathering places

Yue Li<sup>a,b</sup>, Julie Meyer<sup>c</sup>, Timur Mukhametkaliyev<sup>d</sup> and Ze Zhang<sup>b,e</sup>,

<sup>a</sup> Siemens Digital Industries Software, Belgium

<sup>b</sup> KU Leuven, Belgium

<sup>c</sup> Aalto University, Finland

<sup>d</sup> Materialise HQ, Belgium

<sup>e</sup> DMMS lab, Flanders Make, Belgium

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## Introduction

This project proposes a comprehensive engineering approach involving the metamaterial design, simulations, and manufacture of new metamaterial lamps for improving sound absorption and reducing reverberation time in social gathering places. The case presented is a real restaurant in the Netherlands. The chosen space has dimensions 8 m x 3.5 m x 3 m and can accommodate 12-16 persons.

<figure><img src="image_6.png" /><figcaption>Fig. 1 Photo of the interior of the chosen space (left), $T_{20}$ from the measurements and numerical model (right).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 2 Diagram of the case study.</figcaption></figure>

## Simulation: model calibration

The f-FMBEM and FDTD solvers are compared in both time-domain and frequency-domain on several cases to ensure the correctness of the solutions given by the two numerical solvers.

<figure><img src="image_8.png" /><figcaption>Fig. 3 Comparison of f-FMBEM and FDTD in frequency-domain.</figcaption></figure>

FDTD simulations are used to calibrate the material properties of the model according to the measured $T_{20}$ and create the Digital Twin. The acoustic parameters, such as frequency band, surface area, location and impedance for the new treatment are then provided for the metamaterial design to achieve the desired reduction of $T_{20}$.

## Metamaterial design & Manufacture

### Prototype description:

Multiple ducts combined to create multiple absorption peaks.

<figure><img src="image_9.png" /><figcaption>Fig. 4 Description of the prototype design.</figcaption></figure>

## Analytical model:

Numerical model derived for the design; a good match observed with simulation results

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<figure><img src="image_11.png" /><figcaption>Fig. 5 Validation cases, top: 4 ducts design; bottom: 10 ducts design</figcaption></figure>

## Optimization & result:

Optimization performed on the geometry to maximize the absorption; a set of duct geometries obtained.

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* **Maximized:** absorption from 500 Hz to 1000 Hz

* **Variables:** Dimensions of ducts

* **Patch size:** 30 cm*30 cm

* **Nr. Of ducts:** 15

<figure><img src="image_13.png" /><figcaption>Fig. 6 Absorption coefficient of the optimized structure</figcaption></figure>

## Lamp design & Manufacture:

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<figure><img src="image_15.png" /><figcaption>Fig. 7 Design of the acoustic metamaterial lamp with different positioning of ducts inside of the volume.</figcaption></figure>

## Simulation: verification of the design

The metamaterial lamps are evaluated in the digital room. f-FMBEM analyzes the room modes and computes the sound pressure level (SPL) over the target frequency band. The reverberation times are extracted to evaluate the improvement of the design. The analysis can also provide insights to the spatial arrangement of the lamps.

<figure><img src="image_16.png" /><figcaption>Fig. 8 Average SPL comparison at 1.2 m height horizontal plane, new treatment shows 16 dB maximum reduction, and 2 dB average reduction</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. 9 Top view of frequency response at 850 Hz: original room (top) and room with metamaterial lamps (bottom)</figcaption></figure>

<table><caption>Table. 1 Reverberation time comparison</caption><thead><tr><td>1/3 octave band</td><td>Original room</td><td>Room with new treatment</td></tr></thead><tbody><tr><td>500</td><td>1.32 s</td><td>0.62 s</td></tr><tr><td>630</td><td>1.28 s</td><td>0.58 s</td></tr><tr><td>800</td><td>1.19 s</td><td>0.61 s</td></tr><tr><td>1000</td><td>1.29 s</td><td>0.76 s</td></tr></tbody></table>

The numerical study verifies that the new metamaterial lamps can mitigate many of the high modes in the room over the target frequency band and significantly reduce the reverberation time of the original room.

This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 721536.

<footnote>[1] Saarelma, J. (2013). Finite-difference time-domain solver for room acoustics using graphics processing units. Master's thesis, Aalto University, Finland.</footnote>