Utility noise modeling can help project teams compare barrier materials before committing to a substation, transformer, or power-facility noise control plan. In this preliminary Sound Fighter Systems study, a point source was modeled inside a four-sided 24′ x 24′ x 24′ enclosure to compare an absorptive Sound Fighter® barrier condition with two reflective concrete barrier conditions.
The model showed a clear difference between absorptive and reflective barrier performance. In this scenario, the absorptive barrier provided about 4–6 dB more attenuation than reflective concrete in key receiver areas, with greater modeled gains at some longer-distance and higher-elevation points.
That difference matters during early project planning. A reflective wall may need several additional feet of height to reach the same modeled reduction, which can affect material use, visual impact, and site layout. Because this was a controlled preliminary model, each utility site should still be reviewed against its own equipment, source levels, terrain, receiver locations, and local noise limits.
Model and Methodology
Our findings are based on a SoundPLAN model of a simple point source located inside a four-sided enclosure on level terrain.
The dimensions of the enclosure were 24’ x 24’ x 24’ which approximates the source-to-barrier distance and the barrier height of the Dominion Power Substation provided by Sound Fighter®.
The model focused on the relative performance of an absorptive noise barrier and two reflective barriers. The absorptive barrier was based on the Acoustic Systems laboratory report dated May 1, 1996, for Sound Fighter®’s System.
The absorption coefficients used in the reflective barrier conditions were based on typical noise reduction coefficients (NRC) for concrete with NRC 0.05 and NRC 0.15.
The associated one-third octave band data used for both reflective concrete sound wall was based on the Federal Highway Administration’s (FHWA) Traffic Noise Model (TNM) coefficients.
Results and Discussion
Predicted absolute sound pressure levels for each condition are not of particular interest because this study investigated a theoretical source, path, and receiver.
However, a comparison of resulting levels between conditions provides insight into the difference in effectiveness between noise barriers, and these findings are presented in Figures 1-3.
Each figure shows the difference in average sound pressure level across frequencies using the day/night sound level (Ldn) calculation.
Figure 1 provides a comparison between the two reflective barriers, NRC 0.05 and NRC 0.15. This comparison shows the NRC 0.15 barrier provides minimal improvement in sound attenuation panels (2 dB or less in the entire plan view) over the NRC 0.05 barrier.
Figure 2 and Figure 3 presents the difference in predicted sound pressure level between the NRC 1.05 (barrier system) and each reflective barrier—NRC 0.05 and NRC 0.15, respectively.
The direct comparisons show the predicted increase in sound attenuation by the absorptive system over the reflective concrete noise barrier.
Figure 2 shows a 4-6 dB increase in attenuation beginning within the first 35 feet from the barrier, and Figure 3 shows similar results starting within the first 85 feet of the barrier.
At greater distances from the barrier and at higher elevations above ground, the absorptive barrier’s advantage in attenuation over a reflective barrier increases to more than 6 dB.
The significance of the increase attenuation at higher elevations can become relevant in situations with changing topography.
Generally speaking, a change in sound level of about 6 dB is considered a perceivable and significant difference in sound pressure level. Changing a reflective barrier to an absorptive barrier can provide enough of a change in level that a person could identify a noticeable decrease in the noise produced by a source.
The FHWA states that effective noise barriers typically reduce levels by 5-10 dB. Based on a typical barrier and our preliminary findings, the improved attenuation of an absorptive barrier can be significant —potentially improving a barrier’s typical attenuation to 7-16 dB.
Another way to consider the difference in absorptive and diffusive barriers is to consider the effective height of a barrier to achieve a sound level at a particular receiver location.
The FHWA states that once the line-of-sight is blocked by a barrier, each additional meter in barrier height provides approximately 1.5 dB of additional attenuation.
For example, a reflective barrier would have to be 1-4 meters (approximately 3’ to 13’) higher to provide the additional attenuation achieved by the absorptive barriers shown in Figure 2. Such a change in barrier height can significantly add to the material costs of the barrier.
Conversely, an absorptive barrier could be used in place of a reflective barrier and be 1-4 meters shorter making an absorptive barrier more efficient per square foot of material when compared to a reflective barrier.
The preliminary study has shown that absorptive barriers can have a significant advantage over reflective barriers through a reduction in perceived sound level and an improved efficiency when considering attenuation per square foot of barrier material.
Figure 1: The difference in predicted sound pressure levels between the two reflective barriers—NRC 0.05 and NRC 0.15 barrier. The range of levels is divided by 2 dB increments as indicated on the right.
Three views of the difference in level are shown—a plan view and two cross-section views. Grid spacing is 10 ft by 10 ft.
Figure 2: The difference in predicted sound pressure levels between the NRC 1.05 (LSE® System) and the NRC 0.05 barrier. The range of levels is divided by 2 dB increments as indicated on the right.
Three views of the difference in level are shown—a plan view and two cross-section views. Grid spacing is 10 ft by 10 ft.
Figure 3: The difference in predicted sound pressure levels between the NRC 1.05 (LSE® System) and the NRC 0.15 barrier. The range of levels is divided by 2 dB increments as indicated on the right.
Three views of the difference in level are shown—a plan view and two cross-section views. Grid spacing is 10 ft by 10 ft.
FAQ
What did the utility noise modeling study show about absorptive barriers?
The preliminary model showed that the absorptive Sound Fighter® barrier condition provided about 4–6 dB more attenuation than reflective concrete barrier conditions in key receiver areas. In some longer-distance and higher-elevation areas, the modeled advantage increased to more than 6 dB.
The study also suggests that an absorptive barrier may reach similar noise-reduction goals with less wall height than a reflective barrier. In the modeled comparison, that difference was roughly 3 to 13 feet, depending on the receiver location and design assumptions.
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