Measurement and Prediction of Airborne Sound Insulation Performance of Different Vertical Partition Walls in Indoor Environments: A Case Study

Abstract

This paper presents a case study in which the airborne sound insulation performance of vertical partitions is experimentally assessed and model-predicted by incorporating the indoor environment’s geometric configuration and material characteristics into the analysis. An experimental campaign was carried out to verify whether the partition actually installed in situ complies with the minimum acoustic requirements and to validate the results obtained from the predictive model, subsequently used to evaluate the acoustic performance of alternative configurations. Specifically, a case study was conducted on an existing wall separating two indoor environments at the University of Calabria (Italy), where experimental measurements revealed that the current structure fails to meet the minimum acoustic insulation requirement set by Italian regulation. To evaluate the potential improvement in acoustic performance resulting from the use of alternative structures, predictive modeling based on UNI EN ISO 12354-1 was carried out. In the simulations, the rooms were modeled according to their actual geometry, and different types of vertical partitions between the two spaces were assessed, including heavyweight masonry walls, lightweight gypsum-based systems, and drywall linings, all built using commercially available acoustic insulation materials. In addition, four other cost-effective insulated walls were evaluated, which were insulated, at most, using standard thermal insulation. In addition to acoustic performance, implementation costs were also considered. Among the acoustically insulated partitions, the highest-performing construction achieved a $R_w^{\prime }$ of 58.0 dB for €168.9/m², while a cost-effective construction based on double gypsum boards reached a $R_w^{\prime }$ equal to 51.4 dB with a cost of €65.9/m².

1. Introduction

The control of noise in indoor environments is a critical challenge in modern architecture [1], engineering [2], and urban planning [3,4]. The presence of unwanted sound, or noise pollution, can significantly affect comfort [5], productivity [6], and health [7] in various settings, including residential, office, and industrial spaces [8]. With the increasing densification of urban areas and the widespread adoption of open-plan spaces, the need for effective acoustic management has become more pressing than ever [9,10]. Consequently, the study and development of acoustic enhancement strategies are crucial for mitigating the adverse effects of noise and ensuring acceptable indoor sound quality [11].

Acoustic enhancement strategies generally fall into two categories: sound absorption and sound insulation [12]. Sound absorption involves reducing the reflection of sound waves within a space, thereby improving the overall acoustic environment [13]. This is particularly relevant for reducing reverberation times and enhancing speech intelligibility. On the other hand, sound insulation focuses on preventing the transmission of sound from one space to another, which is essential for ensuring privacy and reducing disturbances [14,15]. While significant research has been conducted on developing materials for sound absorption and insulation, challenges persist, especially in designing effective solutions that balance economic and functional constraints.

One of the most significant challenges in indoor acoustic management is the presence of partition walls that inadequately isolate noise between adjacent spaces [16]. Such partitions, commonly found in office buildings, educational institutions, and healthcare facilities, often fail to provide sufficient sound attenuation, leading to disruptive noise transfer between rooms [17]. The impact of poor acoustic insulation is well-documented, with studies indicating that excessive noise exposure in workplaces can lead to reduced cognitive performance, increased stress levels, and lower job satisfaction [18,19,20].

Numerous methods have been developed to enhance the acoustic performance of partitions, including the use of composite materials [21], decoupling techniques, and resonant absorbers. Traditional solutions, such as increasing the mass of walls or incorporating air gaps [22], remain effective but may not always be feasible due to space or weight constraints. More recently, researchers have explored the use of advanced materials, such as metamaterials and porous absorbers, which offer promising results in terms of both sound absorption and insulation [12]. Qu et al. [23] explore the design and application of lightweight partitions made of composite materials with high sound insulation properties, specifically in hotel interior spaces.

The review by Tao et al. [24] provides an overview of recent advancements in acoustic materials and noise control strategies [25,26], including the use of polyurethane foams, sandwich panels, and textile materials for sound absorption.

Caniato et al. [27,28,29] explore the energy and acoustic performance of timber in buildings, providing an overview of the potential of this material to enhance sound insulation. Additionally, they analyze the use of numerical models to predict the noise generated by service equipment in both heavyweight and lightweight timber buildings, contributing to a better understanding of sound insulation dynamics in such structures. Secchi et al. [30] present an experimental and environmental analysis of new sound-absorbing and insulating elements made from recycled cardboard, highlighting the effectiveness of low-cost sustainable materials in acoustic insulation.

Current studies primarily focus on identifying the sound insulation properties of individual materials, often through laboratory measurements. However, these approaches do not account for the fact that the real-world performance of these materials depends on the context in which they are applied, including factors such as the reverberation time of the room in which they are placed. This limitation highlights the need for research that considers both material properties and their interaction with the surrounding acoustic environment [31]. Despite the extensive research on indoor noise control, the study of the acoustic performance of building partitions still presents certain challenges, particularly in reconciling experimental validation, modeling, and economic analysis. In this context, the aim of this work is to assess the improvement in the apparent airborne sound insulation index of a vertical partition. This is achieved by experimentally evaluating the acoustic performance of an existing wall and then validating and utilizing a predictive model to compare commercial sound-insulating solutions with cost-effective insulated wall configurations. The ultimate goal is to identify constructions that meet national regulatory limits for acoustic performance while reducing costs. The innovation of this study lies in achieving regulatory acoustic insulation requirements through cost-effective solutions, specifically by proposing and evaluating wall configurations that utilize low-cost thermal insulation materials for sound insulation, instead of acoustic materials. In particular the work provides a comparative techno-economic analysis between walls insulated with purpose-designed acoustic materials and thermal insulated walls, providing a practical guide for selecting optimal wall systems based on both acoustic performance and economic viability.

The use of Echo^® software version 8.4 [32] to generate a model based on the actual spatial configuration of the rooms allows for overcoming the simplifications often adopted in theoretical studies, making the results more representative of real-world conditions. While many studies focus on innovative materials in isolation, without considering their practical application, this study evaluates the effectiveness of different constructions in a realistic scenario, including also standard sandwich-type building assemblies with air cavities and conventional porous thermal insulation (which is more cost-effective than dedicated acoustic insulation) [33]. Therefore, this work provides useful insights directly applicable to the building sector. This approach not only identifies the most effective configurations in terms of sound insulation but also assesses the economic impact of different constructions, an aspect often overlooked in scientific literature, providing a comprehensive framework for the design and optimization of building partitions. By integrating various acoustic treatment strategies, the paper seeks to provide actionable insights for architects, engineers, and policymakers aiming to design quieter and more comfortable indoor spaces.

Section 2 details the methodology, including the description of the procedures for assessing the sound insulation index using both experimental measurements and theoretical models, the case study and the presentation of improvement constructions. Section 3 presents the results obtained, including the sound pressure levels, the reverberation time, and the apparent airborne sound insulation index of the actual partition measured experimentally, as well as the theoretical acoustic outcomes of the proposed enhancements. Finally, Section 4 outlines the conclusions.

2. Materials and Method

This section describes the procedure followed to determine the improvement in the apparent airborne sound insulation index of a vertical partition, achieved through the implementation of acoustically insulated walls or cost-effective insulated partitions (insulated, at most, with typical thermal insulation materials). To this end, an experimental campaign was conducted to assess the acoustic performance of the existing partition under investigation. The results were used both to verify whether the in situ wall complies with the national regulatory limits DPCM 05/12/1997 [34], and to validate the outcomes of a predictive model. The same model was then used to evaluate the acoustic performance of the proposed alternative constructions.

2.1. Experimental Determination of the Apparent Airborne Sound Insulation Index $R_w^{\prime }$

To experimentally determine the apparent airborne sound insulation index $R_w^{\prime }$ of the vertical partition, it was necessary to measure the reverberation time in the receiving room and the sound pressure levels in both the source and receiving rooms, in accordance with UNI EN ISO 16283-1 [35].

For the latter, a dodecahedral source was used to generate pink noise in the source room, and sound pressure levels were measured at five random positions in both rooms. These measurements were performed in third-octave bands over the frequency range from 100 Hz to 3150 Hz. The measured sound pressure levels were corrected for the background noise level recorded in the receiving room with the source turned off.

For the measurement of the reverberation time in the receiving room in third-octave bands RT₆₀ an impulsive sound source was used. At this point, the apparent airborne sound insulation trend R′ in third-octave bands between the source and receiving rooms is given by:

$$R\prime =L_{p1}-\left(L_{p2}+L_{corr}\right)+10·\log \left({\displaystyle \frac{S_d·R{T}_{60}}{0.16 ·V_2}}\right)$$

(1)

where for each frequency band, L_p1 and L_p2 represent the spatial-temporal logarithmic averages of the sound pressure levels measured at the five positions in the receiving and source rooms, respectively.

Finally, by comparing the experimental curve R′ with the reference curve provided by UNI EN ISO 717-1 [36], the apparent airborne sound insulation index $R_w^{\prime }$ was determined.

This procedure, along with the processing of the experimental data, was implemented using the VibRum Plus^® software version 1.88 [37], as illustrated in Section 2.8.1.

2.2. Prediction of the Apparent Airborne Sound Insulation Index $R_w^{\prime }$

The following paragraph describes the predictive calculation method outlined in UNI EN ISO 12354-1 [38]. In particular, the apparent airborne sound insulation index of a vertical partition $R_w^{\prime }$ is equal to:

$$R_W^{\prime }=-10\log \left({10}^{\left(-{\displaystyle \frac{R_{Dd,W}}{10}} \right)}+\sum _{Df=1}^n{10}^{-{\displaystyle \frac{R_{Df,W}}{10}}} +\sum _{Fd=1}^n{10}^{-{\displaystyle \frac{R_{Fd,W}}{10}}}+\sum _{Ff=1}^n{10}^{-{\displaystyle \frac{R_{Ff,W}}{10}}}+{\displaystyle \frac{A_0}{S}}\sum _{j=1}^m{10}^{-{\displaystyle \frac{D_{n,j,W}}{10}}}\right)$$

(2)

where $A_0$ is the reference equivalent absorption area, set at 10 m²; $\mathrm{S}$ is the area of the separating partition and $D_{n,j,W}$ represents the sound transmission coefficient of any elements eventually inserted within the partition. R_ij,_w represents the sound insulation index for the sound propagation path ij, and it is calculated as:

$$R_{ij,W}={\displaystyle \frac{R_{i,W}+R_{j,W}}{2}}+∆R_{ij,W}+k_{ij}+10\log \left({\displaystyle \frac{S}{l_{ij}}}\right)$$

(3)

$R_{i,W}$ and $R_{j,W}$ are the sound reduction indices of the individual building components involved in the propagation path; $∆R_{ij,W}$ accounts for any increase in sound reduction due to the presence of additional layers along the propagation path; $k_{ij}$ is the vibration reduction index through the junction between elements, which depends on the junction type and the surface mass of the involved partitions and $l_{ij}$ is the length of the junction.

As detailed in Section 2.8.2, the predictive calculation was implemented using the Echo^® software.

2.3. Case Study

The acoustic in situ analysis was carried out with reference to the vertical partition wall separating two adjacent indoor environments at the University of Calabria, Rende (Italy). The first room, identified as the source room, is a technical space with a volume of 172 m³, while the adjacent room, designated for office use, represents the receiving room with a volume of 183 m³. Figure 1 highlights in red the vertical partition under investigation, which consists of 2 cm thick plywood panels enclosing an unventilated air cavity of 6 cm thickness. The stratigraphy of the remaining building elements is described in detail in Section 2.8.2.

Figure 2 and Figure 3 show the plan and sectional views, along with their geometric dimensions in meters, of the receiving and source room, respectively. As shown in the figures, a suspended ceiling is present, consisting of an unventilated air gap and a layer of polystyrene.

2.4. Measurement Equipment

The measurements were carried out using a Svantek 979 (Svantek Italy, Milan, Italy) integrating sound level meter, equipped with a condenser microphone and calibrated with a certified Class 1 acoustic calibrator. The noise was generated using a “12-dodicifacce” DF02AD dodecahedral loudspeaker (Safe, Padova, Italy) (see Figure 4).

Signal sampling was carried out without any weighting (Z-weighting mode) at a sampling frequency of 48 kHz. All data acquisitions were performed in third-octave bands, as required by the regulation. The integration interval and measurement duration were set to 1 s (Slow time constant) and 15 s, respectively. Regarding the measurement of the reverberation time in the receiving room, the integration interval and duration were set to 0.125 s (Fast time constant) and 1 s, respectively.

2.5. Acoustically Insulated Wall Configurations

Several wall assemblies were evaluated and compared, each built using commercially available sound-insulating materials produced by three different companies operating in the acoustics sector (Isolmant, FIBRAN and Fermacell).

With regard to Isolmant (Tecnasfalti, Milan, Italy), the acoustic performance of the walls is improved through the use of a panel made of recycled polyester-based technical textile fiber (see Figure 5). The wall configurations analyzed are as follows:

• Perfetto Special 1 features a total thickness of 30 cm and consists of a 15 cm thick masonry block layer, a 5 cm air cavity containing 3 cm of insulating material, and a second masonry layer of 10 cm. Additionally, an elastic joint between the wall and the floor is provided by means of a perimeter acoustic decoupling strip, in order to reduce flanking sound transmission.
• Perfetto Special 2 has an overall thickness of 26 cm and is composed of a 12 cm thick masonry block layer, a 4 cm cavity with 3 cm of insulation, and a 10 cm thick masonry block layer.
• Perfetto Special CG comprises a 2 cm plaster layer, 8 cm of hollow clay brick, a 2 cm base coat, and a 7.5 cm metal frame filled with 4.5 cm of insulation and covered with a double 2.5 cm gypsum board. The geometrical configuration of the metal support frame is illustrated in Figure 6.

The main characteristics used for the determination of the apparent airborne sound insulation index $R_w^{\prime }$ of the Isolmant analyzed wall configurations are reported in

Table 1. Main characteristics of the wall configurations using Isolmant materials.

Wall Type	Thickness (m)	Insulation Thickness (m)	Superficial Mass (kg/m2)	Total Area (m2)	Rw (dB)
Perfetto Special 1	0.30	0.030	170	29.5	67
Perfetto Special 2	0.26	0.030	160	29.5	63
Perfetto CG	0.22	0.045	122	29.5	55

[39].

FIBRAN (Fibran, Genova, Italy) proposes lightweight and less invasive solutions compared to those developed by Isolmant, employing gypsum plasterboard panels and rockwool as the insulating material. Specifically:

• The FIBRAN B-040/A13—1 wall system has a total thickness of 10 cm and consists of two FIBRANgyps A13 plasterboards, each 1.3 cm thick, a 4 cm layer of FIBRANgeo B-040 rockwool, a 1 cm air cavity, and other two plasterboards, also 1.3 cm thick.
• The FIBRAN B-050/SUPER13 configuration follows the same stratigraphy as the previous one, while featuring two FIBRANgyps SUPER13 plasterboards, a 5 cm thick layer of FIBRANgeo B-050 rockwool, and a 2.5 cm air cavity.
• The FIBRAN B-040/A13—2 wall features the same materials as the first configuration, with a 5 cm thick air cavity, bordered this time by two layers of FIBRANgeo B-040 rockwool, each 4 cm thick.

The main characteristics used for the determination of the apparent airborne sound insulation index $R_w^{\prime }$ of the FIBRAN analyzed wall configurations are reported in

Table 2. Main characteristics of the wall configurations using FIBRAN materials.

Wall Type	Thickness (m)	Insulation Thickness (m)	Superficial Mass (kg/m2)	Total Area (m2)	Rw (dB)
FIBRAN B-040/A13—1	0.10	0.04	38.6	29.5	51
FIBRAN B-050/SUPER13	0.13	0.05	53.3	29.5	59
FIBRAN B-040/A13—2	0.18	0.08	40.3	29.5	62

[40].

To avoid the demolition of the existing wall and the construction of a new partition, Fermacell (James Hardie Europe GmbH, Dusseldorf, Germany) offers the possibility of improving acoustic performance through the installation of an additional acoustic partition, consisting of a 1 cm thick gypsum-fiber board and a 5 cm rock wool panel placed in the air cavity [41], as shown in Figure 7. In the predictive calculations, it was assumed that this additional partition is applied to both sides of the existing wall.

2.6. Cost-Effective Insulated Walls

This section presents and analyses structural proposals aimed at improving the apparent airborne sound insulation index $R_w^{\prime }$ to meet regulatory requirements, while maintaining cost-effectiveness through the use of, at most, typical thermal insulation material. Specifically, four different types of walls were studied, as described below:

• Type A: masonry wall consisting of a 2 cm thick plaster layer, 8 cm thick hollow brick wall, and another 2 cm thick plaster layer.
• Type B: masonry wall of Type A with an additional partition on the side of the receiving room, consisting of 1.3 cm thick drywall layer, 5 cm thick layer of sintered expanded polystyrene, and 2 cm thick non-ventilated air cavity.
• Type C: partition wall consisting of two plasterboard layers, each 2.6 cm thick, enclosing a 5 cm thick rock wool panel and a 5 cm thick non-ventilated air cavity, and employing double metal studs for acoustic decoupling.
• Type D: metal stud partition wall consisting of two plywood layers, each 3 cm thick, enclosing a 5 cm thick rock wool panel and a 5 cm thick non-ventilated air cavity, and employing double metal studs for acoustic decoupling.

The main characteristics for determining the $R_w^{\prime }$ index of the four analyzed walls are shown in

Table 3. Main characteristics of the novel configurations.

Wall Type	Thickness (m)	Insulation Thickness (m)	Superficial Mass (kg/m2)	Total Area (m2)	Rw (dB)
A	0.12	0.00	118.0	29.5	41.4
B	0.20	0.05	130.7	29.5	41.4
C	0.15	0.05	51.8	29.5	59.3
D	0.16	0.05	67.0	29.5	61.5

.

2.7. Cost Analysis

Based on manufacturer catalogs [42,43,44,45] and a market analysis of 10 different manufacturers in the sector, the cost per square meter was estimated for each of the proposed constructions. The values reported in

Table 4. Costs per square meter for the analyzed partition walls.

Wall Type	Cost (€/m2)
Perfetto Special 1	168.9
Perfetto Special 2	147.5
Perfetto CG	111.7
FIBRAN B-040/A13—1	115.6
FIBRAN B-050/SUPER13	147.15
FIBRAN B-040/A13—2	122.92
Fermacell	54.2
A	51.81
B	94.2
C	65.9
D	142.6

refer to the complete system, including ancillary components, plasterboard panels, masonry elements, metal framework, and labor costs.

2.8. Software

2.8.1. On-Site Measurements Processing Software

For processing the measurements, the VibRum Plus^® software was used, which implements the reference standard UNI EN ISO 16283-1:2014 in order to determine the apparent airborne sound insulation index $R_w^{\prime }$. To this end, the software compares the sound insulation trend R′ obtained from the processing of the experimental measurements, with the limiting curve from the UNI EN ISO 717-1 standard. The software requires both the volume of the rooms and the surfaces of the building components.

2.8.2. Predictive Calculations Software

The predictive calculations of the sound insulation indices for the proposed vertical partitions were conducted using the ECHO^® software, in which the volumes and surfaces defining the emitting and receiving rooms were reconstructed. Furthermore, the physical and geometrical description of the layers constituting the wall, surface mass, and sound insulation performance R_w of each building components were specified. Figure 8 containsthe characteristics of the vertical partition (shown in red) and the building components of the two rooms (shown in yellow), as actually installed in situ.

After verifying that the apparent airborne sound insulation $R_w^{\prime }$ index of the partition currently installed in situ, obtained using the Echo^® software, is in good agreement with the value measured experimentally (as shown in Section 3.2), the characteristics of the vertical partition were modified according to the proposed and analyzed construction typologies and, for each of them, the software computed the corresponding $R_w^{\prime }$ index.

Figure 9 shows the sound propagation paths between the two rooms, relative to the considered construction joint shown in red, with the relevant path i-j indicated by the blue arrow. As indicated in Equation (3), to evaluate the term Rij along this path, it is necessary to define the type and length of the joints.

3. Results

This section presents the results obtained from the experimental campaign and processed using the VibRum Plus^® software, with the aim of evaluating the apparent airborne sound insulation index $R_w^{\prime }$ of the actual vertical partition. Subsequently, the result of the predictive calculation is shown in order to assess whether the $R_w^{\prime }$ value obtained with the Echo^® software is consistent with the experimentally measured outcome. Finally, the apparent airborne sound insulation indices obtained either through the use of acoustically insulated walls with commercially available insulating materials, or through the cost-effective insulated walls proposed in this study, are presented along with the corresponding cost estimates.

3.1. Experimental Measurement Results

With reference to the partition currently installed in situ, Figure 10, Figure 11 and Figure 12 present the frequency-domain spectral analysis of the equivalent sound pressure levels, obtained from the spatial average of five measurements taken in the source room, the receiving room, and the background noise in the receiving room, respectively. The last bar in each graph represents the total equivalent sound pressure level. Both at the total and spectral levels (with the exception of the low frequency bands), a reduction in sound pressure levels is observed between the source and receiving rooms, as a result of the presence of the vertical partition separating the two environments.

Figure 13 shows the frequency analysis in the time domain of the sound pressure levels prior to integration, measured in one-third octave bands in the receiving room. For the experimental measurement of RT, the sound pressure level drops of 10 dB, 20 dB and 30 dB were considered and, for each of them, the time corresponding to a 60 dB decay was obtained through linear extrapolation (EDT, RT₂₀ and RT₃₀, respectively). The RT value corresponds to the extrapolated time associated with the highest drop achievable.

Table 5. Reverberation time measurements.

Frequency (Hz)	EDT (s)	RT20 (s)	RT30 (s)	RT (s)
100	0.801	0.637	-	0.637
125	1.218	0.606	0.511	0.511
160	1.009	0.782	0.797	0.797
200	0.458	0.796	0.685	0.685
250	0.843	0.759	0.713	0.713
315	0.620	0.636	0.708	0.708
400	0.482	0.582	0.592	0.592
500	0.485	0.640	0.679	0.679
630	0.577	0.434	0.526	0.526
800	0.394	0.482	0.561	0.561
1000	0.410	0.466	0.492	0.492
1250	0.459	0.461	0.466	0.466
1600	0.415	0.427	0.416	0.416
2000	0.414	0.418	0.436	0.436
2500	0.460	0.443	0.493	0.493
3150	0.391	0.491	0.490	0.490

reports the reverberation time RT as a function of frequency.

Using the VibRum Plus^® software, the acquisitions were processed, and the UNI EN ISO 717-1 standard was implemented to determine the value of the index $R_w^{\prime }$. Figure 14 shows the trend of the apparent airborne sound insulation trend R′ in black, and the limiting curve provided by the standard in red. At high frequencies, the figure shows that the critical coincidence frequency occurs at 1600 Hz, where a reduction in sound insulation performance is observed, followed by an attenuated increase. The $R_w^{\prime }$ value is provided alongside the C and C_tr values, defined by the standard as the spectral adaptation terms for high and medium-low frequencies, respectively.

The value of $R_w^{\prime }$ obtained from the experimental measurements is 28 dB, and since the Italian regulations on passive acoustic performance for buildings [34] prescribe a value greater than 50 dB, the result shows that the actual partition does not meet the acoustic insulation requirements.

3.2. Predictive Calculation Results

Using the Echo^® software, the predictive calculation was conducted considering the vertical partition currently installed between the two rooms. Figure 15 presents the results of the term R_ij as a function of the sound propagation path.

The predicted value of the apparent airborne sound insulation index $R_w^{\prime }$ for the vertical partition currently used to separate the two rooms was found to be 32.1 dB, which shows good agreement with the experimentally determined value of 28 dB. This confirms that the software can be effectively used to evaluate the performance of the vertical partitions under investigation.

3.3. Acoustically Insulated Wall Configurations

Table 6. Predicted apparent airborne sound insulation index and total cost for each commercial wall configuration.

Wall Type	${\mathit{R}}_{\mathit{w}}^{\prime }$ (dB)	Total Cost (€)
Perfetto Special 1	58.0	5068.0
Perfetto Special 2	56.8	4424.6
Perfetto CG	52.5	3350.8
FIBRAN B-040/A13—1	47.9	3468.3
FIBRAN B-050/SUPER13	51.4	4414.5
FIBRAN B-040/A13—2	50.9	3687.6
Fermacell	47.3	3250.6

presents the $R_w^{\prime }$ index obtained from the predictive calculations along with the total cost associated with each type of analyzed vertical partition. Figure 16 shows the breakdown of the total cost into its individual contributions for each commercial construction.

As shown, the most expensive construction is the Perfetto Special 1, mainly due to the significant cost contributions of both the masonry and the insulation layer, which also provides the best acoustic performance. Conversely, the most cost-effective construction is the Fermacell partition, which, however, fails to meet the regulatory requirements and exhibits the lowest sound insulation performance. Similarly, the FIBRAN B-040/A13—1 system does not comply with the national standard and is also more expensive than the Perfetto CG, which is the most economical among the configurations that meet regulatory limits, with an index $R_w^{\prime }$ of 52.5 dB. In the case of FIBRAN B-040/A13—2, which includes a double insulating layer and results in a slightly higher cost, the regulatory threshold is met, and the $R_w^{\prime }$ value is only 0.5 dB lower than that of the FIBRAN B-050/SUPER13 configuration. However, the cost of the latter is comparable to that of the Perfetto Special 2, while its acoustic performance is 5.4 dB lower. The Perfetto Special 2 construction, which achieves an $R_w^{\prime }$ value only 1.2 dB lower than the Perfetto Special 1, is less expensive due to the use of 12 cm thick concrete blocks instead of 15 cm.

3.4. Cost-Effective Insulated Walls

Similarly, for the proposed cost-effective insulated walls,

Table 7. Predicted apparent airborne sound insulation index and total cost for the proposed cost-effective insulated walls.

Wall Type	${\mathit{R}}_{\mathit{w}}^{\prime }$ (dB)	Total Cost (€)
A	41.2	1554.3
B	53.8	2826.4
C	51.4	1977.7
D	52.7	4276.7

reports the results of the predicted apparent sound insulation index $R_w^{\prime }$ and the corresponding total cost for each construction. Figure 17 illustrates the cost breakdown for each wall type.

The results indicate that, compared to the currently installed wall, which provides a predicted index $R_w^{\prime }$ of 32.1 dB (with an experimentally measured value of 28 dB), the use of Wall Type A, consisting of standard uninsulated masonry, yields an acoustic performance improvement. However, it still fails to meet the regulatory requirement, achieving an index of 41.2 dB. The other three wall types exceed the minimum required value. In particular, Wall Type B, a masonry wall combined with a lining, provides the highest airborne sound insulation performance, equal to 53.8 dB. Among the configurations with an index greater than 50 dB, the most cost-effective is Wall Type C, a plasterboard partition. Wall Type D, which incorporates plywood panels, delivers a slightly higher performance of 52.7 dB, only 1.3 dB more than Wall Type C, it is the most expensive construction due to the high cost of plywood. In contrast, Wall Type C allows for a 30% cost saving relative to Wall Type B, with only a 2.4 dB reduction in the performance index. Furthermore, Wall Type C is the lightest among the proposed alternatives, with a surface mass of 51.8 kg/m², and features a compact thickness of just 15 cm.

4. Conclusions

This study investigated the improvement in the apparent sound insulation index $R_w^{\prime }$ for airborne noise as a function of the wall system used to separate two indoor environments at the University of Calabria. An experimental campaign was conducted to assess the acoustic performance of the existing wall and to validate the theoretical prediction model used for evaluating alternative structural solutions. The experimental study was carried out using a Svantek 979 sound level meter (Svantek Italy, Milan, Italy) equipped with a condenser microphone and a Svantek SI 312 dodecahedral sound source. Data processing was performed using VibRum Plus^® software.

The results showed that the existing wall does not comply with the minimum regulatory requirement of 50 dB, exhibiting an $R_w^{\prime }$ value of 28 dB. This was compared with the predicted results obtained via the Echo^® software, showing good agreement. This software was subsequently used to evaluate theoretical improvements in acoustic performance achievable through the use of acoustically insulated walls with commercially available insulating materials or cost-effective insulated walls proposed in this study. For each option, a cost analysis was also carried out to identify a cost-effective construction that meets the regulatory minimum of 50 dB.

Regarding commercial systems, the best acoustic performance was associated with the Perfetto Special 1 system, which also exhibits the highest cost. Conversely, although the use of a Fermacell lining is easy to install and inexpensive, its performance index of 47.3 dB does not satisfy the regulatory limit. The Perfetto CG system achieves an index of 52.5 dB with only a 3.08% cost increase compared to the Fermacell construction.

In terms of the cost-effective insulated constructions, replacing the existing wall with Wall Type A (hollow brick masonry without acoustic insulation) represents the most economical intervention and improves the sound reduction index to 41.2 dB. However, this remains below the threshold. The remaining three wall types met the regulatory limit, with a maximum difference of 2.4 dB between Wall Type B (53.8 dB) and Wall Type C (51.4 dB). Wall Type B, a masonry construction, shows a 42.9% higher cost compared to Wall Type C, which is a plasterboard partition. Moreover, Wall Type C has the lowest surface mass among the proposed constructions. Wall Type D is the least economical due to the use of plywood panels, with a cost approximately double that of Wall Type C, offering only a 1.3 dB improvement. Comparing the commercial construction Perfetto CG with the cost-effective insulated Wall Type C reveals a marginal advantage of 1.1 dB in favor of the former, which comes at a 69.4% higher cost. In terms of weight and thickness, Wall Type C exhibits a surface mass of 51.8 kg/m² and a thickness of 15 cm, whereas the commercial masonry system has significantly higher values of 122 kg/m² and 22 cm, respectively.

A limitation of this study lies in the uncertainty associated with the predictive calculation model, which, despite validation against the existing wall, still requires experimental verification through real-world implementation of the proposed constructions. However, such an approach is impractical in the context of retrofitting existing environments or designing new constructions. Therefore, the presented results are of significant value in the field of building acoustics, providing technical and economic guidance for the selection of effective wall systems capable of achieving regulatory sound insulation requirements at minimized cost. Future work will involve the demolition of the current wall and the construction of the Wall Type C to evaluate its in situ performance.