A Simple Method to Estimate the In Situ Performance of Noise Barriers

Round 1

Reviewer 1 Report

The article addresses the important issue of estimating the effect of noise barriers on noise reduction in protected areas. The authors propose to simplify the estimation of the noise reduction effect by combining the effects of a numerical simulation taking into account the real positioning of barriers, noise sources and protected areas and an idealised barrier model and then modifying the results to take into account the non-ideal absorption and reflection properties of the barrier. The idea seems attractive and the presented simulation results seem to confirm the correctness of the reasoning. 

Unfortunately, the authors, apart from the figures, do not provide tables with objective values of similarity measures and uncertainties between existing methods and their proposed methods. Specific details of the numerical simulations carried out are also missing. Apart from giving general names of the methods, no specific equations are presented. Also, in the era of modern achievements in describing acoustic fields, the use of idealized acoustic source models (ideal plane or spherical wave) requires at least a comment on where they can be used and what the limitations are. 

The authors show an example of a modern sonic cristal barrier (Fig.6.). It is a pity that, as part of the research presented in this article, they did not present at least an attempt to compare the simulation results with the actual measurements, and after all, in-situ is in the title.

I look forward to completing the article in the aspects given above.

Author Response

The authors would like to thank the referee for his detailed review. A detailed list of responses (in red) to his/her comments can be found below.

 

The article addresses the important issue of estimating the effect of noise barriers on noise reduction in protected areas. The authors propose to simplify the estimation of the noise reduction effect by combining the effects of a numerical simulation taking into account the real positioning of barriers, noise sources and protected areas and an idealised barrier model and then modifying the results to take into account the non-ideal absorption and reflection properties of the barrier. The idea seems attractive and the presented simulation results seem to confirm the correctness of the reasoning. 

Unfortunately, the authors, apart from the figures, do not provide tables with objective values of similarity measures and uncertainties between existing methods and their proposed methods.

We have included a table with numerical data in order to show the accuracy of the proposed method

Specific details of the numerical simulations carried out are also missing. Apart from giving general names of the methods, no specific equations are presented.

The authors agree with the referee in that some more information should be given. About the numerical method. Although the boundary conditions were already indicated in the paper, some additional explanation and the fundamentals of the method have now been introduced in the paper. A detailed description of the implemented method can be found in the reference (listed in the paper’s reference list):

1. Redondo, R. Picó, B. Roig, M.R. Avis. Time domain simulation of sound diffusers using finite-difference schemes. Acta Acustica united with Acustica 93(4) July 2007

Also, in the era of modern achievements in describing acoustic fields, the use of idealized acoustic source models (ideal plane or spherical wave) requires at least a comment on where they can be used and what the limitations are. 

We assume in the paper that the incident field is a plane wave. This only corresponds to the case of large distance from the source to the screen. Nevertheless, we have checked the validity of the model for shorter source-screen distances. These results are not included in the paper for the sake of brevity. Additionally, we prefer to illustrate only the case of a plane wave in the paper because it is easier to discuss the Huygens–Fresnel-Kirchhoff principle.

The authors show an example of a modern sonic cristal barrier (Fig.6.). It is a pity that, as part of the research presented in this article, they did not present at least an attempt to compare the simulation results with the actual measurements, and after all, in-situ is in the title.

Figure 6 corresponds to a small prototype of a sonic crystal barrier with a width of 2 m that makes it almost impossible to measure the isolation due to the side-edge effect. The width has to be much higher than the height that in this case is about 3 m.

I look forward to completing the article in the aspects given above.

 

Thanks again for you detailed revision of the paper. We hope that the changes made to the article will be satisfactory to you.

Yours sincerely

 

Author Response File: Author Response.docx

Reviewer 2 Report

The topic is a timely and an up to date problem which is significantly required to be solved. Traffic noises and generally noise pollution make an annoying life for people, particularly those who live in crowded cities. From this reviewer’s point of view, this paper is worthy of investigation. The paper is well-organized and the English is well-written. The quality of the presentations and figures look good. I recommend the paper for publication in Applied Sciences after a minor revision based on the following comments,

-It is suggested to add some references to the mathematical equations used in the paper from other references. This makes the formulas more reliable.

-Instead of using larger numbers in the horizontal axis of Figure 2, it is suggested to add e+3 beside the f(Hz) and write the numbers in the shorter amounts as (0.125, 0.25, 0.5, 1, 2, and 4).

-The conclusion section is not perfect. It is recommended to expand it by adding further details to the paper and explaining the most interesting achievements of the performed work.

-Reference format is not the same for all the references. There should be unity among them.

-What is the fundamental idea of Eq. (5)? How and based on what concepts is it derived? These shall be discussed.

Author Response

The authors would like to thank the referee for his detailed review. A detailed list of responses (in red) to his/her comments can be found below.

 

The topic is a timely and an up to date problem which is significantly required to be solved. Traffic noises and generally noise pollution make an annoying life for people, particularly those who live in crowded cities. From this reviewer’s point of view, this paper is worthy of investigation. The paper is well-organized and the English is well-written. The quality of the presentations and figures look good. I recommend the paper for publication in Applied Sciences after a minor revision based on the following comments,

-It is suggested to add some references to the mathematical equations used in the paper from other references. This makes the formulas more reliable.

We have carefully checked the references to the equations in the paper. We can divide equations in 3 parts. First one is the definitions of the parameters proposed in the standards to quantify the performance of noise barrier (that include the references to the standards). Secondly, we derive some expressions that allow the calculation of the insertion loss from the combination of a rigid barrier case with the isolation of the barrier. This part is a novelty and as a result no references can be added. The final set of equations corresponds to previous proposals and are as well correctly linked with their respective references.

-Instead of using larger numbers in the horizontal axis of Figure 2, it is suggested to add e+3 beside the f(Hz) and write the numbers in the shorter amounts as (0.125, 0.25, 0.5, 1, 2, and 4).

Sorry for that. We have changed to a standard way of representing the octave bands central frequencies, i.e., 1k, 2k, 4k

-The conclusion section is not perfect. It is recommended to expand it by adding further details to the paper and explaining the most interesting achievements of the performed work.

The authors recognize that the work conclusions should be improved and thank the reviewer for the opportunity and suggestion. Therefore, the Conclusions section has been revised, details regarding the paper and performed work have been introduced, and the main achievements have been highlighted and explained. 

-Reference format is not the same for all the references. There should be unity among them.

The format of the References has been revised in order to unify all of them. Thanks for your observation.

-What is the fundamental idea of Eq. (5)? How and based on what concepts is it derived? These shall be discussed.

The idea of Eq. (5) is already explain in the paragraph above it. It is just a particularization of the Huygens–Fresnel-Kirchhoff principle, i.e. the acoustic field on the receivers is the sum of the interfered (by the noise barrier) and not interfered components. In other words, the in-situ transmission coefficient can be written as

see attached file

Where the first term is the interfered component and the second one is the non-interfered component. Equation (5) is just a logarithmic version of this equation.

 

Thanks again for you detailed revision of the paper. We hope that the changes made to the article will be satisfactory to you.

Yours sincerely

 

Author Response File: Author Response.docx

Reviewer 3 Report

The authors discuss the calculation of the sound attenuation of a barrier.

The topic is not new, therefore the authors should explain the novelty element and their contribution to the development of the sector.

Paragraph 2, how you calculated the "ε" parameter.

you should better explain the procedure and give some numerical examples.

When using the FDTD model is it software that you wrote yourself or is it commercial? what are the limits, the boundary conditions that you have inserted into the model?

When you talk about sonic crystal barriers, see also the paper by Iannace et al. see the results of the measurements.

Also in the procedure you describe you should make explicit that how you apply the formulas from (8) to (11).

How do you calculate the values you enter in the formula (7).

Increase the conclusions paragraph.

Thanks for your attention.

Author Response

The authors would like to thank the referee for his detailed review. A detailed list of responses (in red) to his/her comments can be found below.

 

The authors discuss the calculation of the sound attenuation of a barrier.

The topic is not new, therefore the authors should explain the novelty element and their contribution to the development of the sector.

We believe that the novelty and scientific contribution is indicated on several occasions throughout the paper, in particular at the end of the abstract, in the last paragraph of the introduction and as well in the conclusions.

Paragraph 2, how you calculated the "ε" parameter. You should better explain the procedure and give some numerical examples.

We have included a step by step explanation of how to obtain this parameter (see equations 7 and 8). It can be obtained from the simulation of the limiting case in which the noise barrier is consider completely stiff and reflective.

Figure 4 includes the R=infinity case that is the one that should be consider for the calculation of e.

When using the FDTD model is it software that you wrote yourself or is it commercial? what are the limits, the boundary conditions that you have inserted into the model?

Indeed, the used numerical code has been implemented by the authors and is not a commercial code. Although the boundary conditions were already indicated in the paper, some additional explanation and the fundamentals of the method have now been introduced in the paper. All details of the implemented method can be found in the reference (listed in the paper’s reference list):

1. Redondo, R. Picó, B. Roig, M.R. Avis. Time domain simulation of sound diffusers using finite-difference schemes. Acta Acustica united with Acustica 93(4) July 2007

 

When you talk about sonic crystal barriers, see also the paper by Iannace et al. see the results of the measurements.

There are several articles in which measurements of sound insulation of sonic crystals are made. We have chosen to include only the first of these papers (reference 21 in the new version of the article) since in general it can be said that edge diffraction effects greatly mask the results.

In the particular case of the article proposed by the referee, the first bandgap is not even accurately visible.

 

Also in the procedure you describe you should make explicit that how you apply the formulas from (8) to (11).

How do you calculate the values you enter in the formula (7).

These equations come from other papers (references 23&24 in the new version of the paper). We have only modified the nomenclature for better comparison with our proposal. The process to obtain the values in equation 7 are explain in our paper but as well in the cited references.

 

Increase the conclusions paragraph.

The authors recognize that the work conclusions should be improved and thank the reviewer for the opportunity and suggestion. Therefore, the Conclusions section has been revised, details regarding the paper and performed work have been introduced, and the main achievements have been highlighted and explained. 

Thanks for your attention.

Thanks again for you detailed revision of the paper. We hope that the changes made to the article will be satisfactory to you.

Yours sincerely

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

In table 1 units dBA instead of dbA. I'm also thinking about result precission presentation. If 1dB is JND, so 0.1dB is sufficient precission  for results presentation.

Author Response

Referee 1

 

The authors would like to thank the referee for his/her suggestion. A detailed list of responses (in red) to his/her comments can be found below.

 

In table 1 units dBA instead of dbA. I'm also thinking about result precission presentation. If 1dB is JND, so 0.1dB is sufficient precission  for results presentation.

 

We have corrected the mistake. Concerning the precision we have change to 0.1dB

Author Response File: Author Response.docx

Reviewer 3 Report

improve quality of graphs

Author Response

Referee 3

 

The authors would like to thank the referee for his/her suggestion. A detailed list of responses (in red) to his/her comments can be found below.

 

improve quality of graphs

 

We would like to solve the problem detected by the referee but we do not know which of the graphs he is referring to, simulation schemes, results, picture of a screen...

As this kind of issue is usually solved by the editorial board, we are waiting for the specifications on this matter.

Author Response File: Author Response.docx