###### Abstract  
With the rapid increase in automobiles, the importance of reducing low-frequency noise is being emphasized for a comfortable urban environment. Helmholtz resonators are widely used to attenuate low-frequency noise over a narrow range. In this study, a slit-type soundproof panel is designed to achieve low-frequency noise attenuation in the range of 500 Hz to 1000 Hz with the characteristics of a Helmholtz resonator and the ability to pass air through the slits on the panel surface for reducing wind load. The basic dimension of the soundproof panel is determined using the classical formula and numerical analysis using a commercial program, COMSOL Multiphysics, for transmission loss prediction. From the numerical study, it is identified that the transmission loss performance is improved compared to the basic design according to the shape change and configuration method of the Helmholtz resonator. Although the correlation according to the shape change and configuration method cannot be derived, it is confirmed that it can be used as an effective method for deriving a soundproof panel design that satisfies the basic performance. Helmholtz resonator; low-frequency noise; slit-type; sound attenuation; soundproof panel; transmission loss +
Footnote †: journal: Applied Sciences  
mass end correction for three of the simplest cases of a concentric aperture in a circular tube, a circular aperture in a circular tube, and a square aperture in a square tube [1]. [PERSON] and [PERSON] investigated a Helmholtz resonator with a neck to reduce combustion instability related to acoustic modes in a rocket engine. They developed a generalized formulation and applied it to a quarter-wave tube and a Helmholtz resonator with different neck lengths [2]. [PERSON] also analyzed the effects of geometry on the resonance frequency of an HR. The results from the Rayleigh equation and a transcendental equation were compared under the extreme conditions of the geometry of a cavity and an orifice, such as depth, length, and width. [PERSON] concluded that those classical equations had limited validity when extremes of geometry were encountered, and a computer program should be used to calculate the resonance frequency due to the complex interplay of numerical quantities [3]. [PERSON] and [PERSON] investigated the effect of the volume length-to-diameter ratio on the resonance frequency and transmission loss of a concentric, cylindrical HR. Their results showed that volume dimensions neglected on the classical theory could significantly affect the resonance frequency and transmission and concluded that multi-dimensional computation would achieve a closer result compared to the experiments [4]. [PERSON] and [PERSON] presented the effect of an extended neck of a concentric circular Helmholtz resonator with the theoretical, numerical, and experimental methods. Their result showed that the resonance frequency could be controlled by the change in length, shape, and perforation porosity of the extended neck without volume change [5]. [PERSON] et al. investigated the nature of Helmholtz resonators related to structural parameters and boundary conditions with the Finite Element Method (FEM). They also compared results from FEM to those of the impedance tube test, and concluded that the numerical analysis yielded reliable results compensating many restrictions from the theoretical formula [6]. [PERSON] and [PERSON] proposed the noise attenuation capacity index, the integral of transmission loss over the frequency domain, to evaluate the noise attenuation performance of a Helmholtz resonator. They derived that index from the theoretical formula and then validated it with FEM simulation. Their results presented that the noise attenuation capacity index was only related to the geometries of the neck and the cross-sectional area of the duct [7]. Along with the studies related to geometric features of an HR, many researchers have also attempted to broaden the attenuation band because a single HR has a narrow noise attenuation band. [PERSON] et al.