## 1 Introduction  
According to the World Health Organization (WHO), high levels of noise are associated with long-term health problems [1] such as hypertension, hearing loss, sleep disturbance, child development, dementia, and psychological disorders. Considering these negative consequences of noise pollution, it is imperative that environmental noise pollution be kept below 60 dB as dictated by the UK's Environmental Protection Act of 1997 and the WHO's environmental noise prevention act [1]. This may also mean working within the context of the 2030 United Nations Sustainable Development Goals (SDGs)--targeting good health and well-being of the human population [Goal 3], sustainable cities and communities [Goal 11] and climate action [Goal 13]. Soundproofing devices ranging from natural (wool, asbestos, hemp, flax, etc.) to man-made (polyurethane, polyester, melamine, polyethylene, etc.) materials have already been prescribed [2; 3; 4; 5; 6; 7; 8; 9], however, potential excellent candidate materials should be capable of withstanding high temperatures, high pressures, and impact loads, as well as stand the test of time. As a result, manipulation of macroporous material pore networks, shapes, and sizes could lead to the development of optimum vibroacoustic systems capable of significantly reducing excessive noise along with the advantages of being ultra-light, fixed morphologies, with high Young modulus, environmentally friendly materials, as well as recyclable. The term soundproofing material has always been used to describe those materials that have been either used in their naturally occurring phenomena or artificially replicated to provide optimum pressure wave penetration and absorption. [PERSON] et al. [10] conducted an experimental study on the sound absorption performance of Alporas foams that suggested the use of cellular metallic components as a potential barrier to noise and vibration control. Their research revealed that compression force and mechanical holes--the drilling of these foams affects their relative densities and pore-structure-related information, and the result is a shift in sound absorption spectra to either frequency minima or maxima. In the absence of a back cavity (air-gap), [PERSON] et al. [11] found that aluminium foams with relatively small mean pore sizes (500 \(\upmu\)m) exhibited the highest quarter-wavelength layer peak in resonant when compared to structures with larger pore sizes. [PERSON] and [PERSON] [12] concluded that soundproofing metal foam has a higher sound absorption coefficient in the presence of a back cavity and, by extension, when the material is thicker. According to experimental measurements over negatively-infiltration processed aluminium foams, airflow resistance (ratio of fluid dynamic viscosity to the permeability of the porous structure) accounted for the major influence on the shift in their absorption spectra [3]. Studying the sound absorption spectra over Recemat NCX2733 revealed that this material performed poorly in comparison to several other soundproofing materials, such as bottleneck-type aluminium foam (ALF) [3; 13; 14], polyhedral ceramic foam (PCF) [14; 15; 16], sintered fibre metal (SFM) [6] and glass wool fibre (GWF) [7]. Figure 1 displays such plots of the experimentally determined and numerically simulated (to be discussed later) normal incidence sound absorption spectra against resonance frequency for these materials. Recemat NCX2733's poor performance was attributable to the combination of excessive pore openings, pore volume, and reduced ligament orientations, which had the effect of reducing successive back cavities [13; 17] that could potentially affect sound absorption within the material. Thus, it is likely that technological variability and operating conditions used for the processing of porous metallic components will affect their application as soundproofing devices.