## 2 Materials and Methods
### Transmission Loss Measurements  
The studies were conducted in the reverberation rooms of the Institute of Power Engineering, OTC-Thermal Technology Branch,ITC\" in Lodz (Warsaw, Poland). Panels were tested by mounting an aperture between two reverberant test chambers. The measurement was performed by the current ISO standard: _10140-2:2021 Acoustics--Laboratory Measurement of Sound Insulation of Building Elements--Part 2: Measurement of Airborne Sound Insulation_ and _10140-4:2021 Acoustics--Laboratory measurement of sound insulation of building elements--art 4: Measurement procedures and requirements_. Both the source and receiving  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Panel**} & **Panel** & **Commercial** & **Young’s** & **Poisson’s** & **Cross-Sectional** \\  & **Thickness mm** & **Mark** & **Modulus GPa** & **Ratio** & **Panel Height mm** \\ \hline  & **h** & & **E** & **v** & **Z** \\ \hline GW270 & 3.5 & light & 2.4 & 0.4 & 0.150 \\ \hline GW300 & 5.5 & light & 2.4 & 0.4 & 0.115 \\ \hline GW580 & 7.0 & Z-type & 2.4 & 0.4 & 0.240 \\ \hline GW700 & 9.0 &
\begin{tabular}{c} Z-type \\ Strengthened * \\ \end{tabular} & 2.4 & 0.4 & 0.250 \\ \hline GW610 & 9.0 & \(\Omega\)-type & 2.4 & 0.4 & 0.230 \\ \hline GW448 & 12.0 & Z type & 2.4 & 0.4 & 0.254 \\ \hline \hline \end{tabular}  
* undisclosed trade information.  
\end{table}
Table 1: The parameters of studied fluted PVC panels.  
Figure 3: Panel profiles were studied in this work.  
rooms were constructed to give a reverberant sound field with volumes of V = 237 m\({}^{3}\) and an area of 231.5 m\({}^{2}\) for each.  
The tested PVC panels (size 1.0 m \(\times\) 1.0 m) in a frame were fixed to an aperture opening between the two reverberation rooms. Panels had to be cut down to fit the aperture opening dimension. Edges of each specimen were sealed tightly using soundproof silicone sealant.  
White noise was produced using an all-in-one DO 203 omnidirectional noise source, including a dodecahedron loudspeaker with a power amplifier and a noise generator. Measured parameters were sound pressure level in both rooms and reverberation time (T\({}_{60}\)) in the receiver room. T\({}_{60}\) is defined as the time required for the sound source to reduce to a level of 60 dB when it is turned off in a closed room. Reverberation times were measured in the frequency range of 50 Hz to 10,000 Hz. Sound pressure levels in the rooms were sampled using two sets of 1/2-inch microphones, each coupled with a pre-amplifier and fed to a SVAN 958 analyzer for 1/3 octave band spectrum analysis. The background level was measured and calibrated using the Bruel & Kjaer 4231 calibrator before and after the measurement procedure. The environmental conditions were also monitored by recording the temperature, relative humidity, and atmospheric pressure.  
Transmission loss was obtained using the equation for the transmission of sound between two reverberant spaces:  
\[TL=\overline{L_{s}}-\overline{L_{r}}+10 log\bigg{(}\frac{S}{A}\bigg{)}\ (dB) \tag{21}\]  
where:  
\(\overline{L_{s}}\)--spatial average sound pressure level in the source room, dB  
\(\overline{L_{r}}\)--spatial average sound pressure level in the receiver room, dB  
\(TL\)--reverberant field transmission loss, dB  
\(S\)--the area of the transmitting surface, m\({}^{2}\)  
\(A\)--room constant in the receiver room, using the Sabine equation: A = 0.16 \(\times\) (V/T\({}_{60}\)), m\({}^{2}\)