Horn Use Patterns and Acoustic Characteristics in Congested Urban Traffic: A Case Study of Ho Chi Minh City

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper investigates the usage patterns and acoustic characteristics of motorcycle horns in Vietnam. Through laboratory measurements, the authors clarify that the noise levels are extremely high and that differences of up to 17 dB exist depending on the honking pattern. Understanding source characteristics is crucial for effective noise control, and the paper provides valuable data in this regard. However, there are several points where improvements could be made, particularly in how data are presented in the figures and in the discussion section. These are outlined below for the authors’ reference.

Comments on Content

• Title and Content Misalignment:
  There appears to be a slight discrepancy between the title and the actual content of the paper. While the study provides detailed laboratory-based analyses of the acoustic characteristics of motorcycle horns as sound sources, the title suggests an evaluation of their impact in urban traffic. This might lead readers to expect an empirical investigation of the presence or absence of horns in traffic scenarios, or a quantitative evaluation based on traffic volume and noise level estimation.

• Section 3.1 Power Spectrum:
  Are the acoustic characteristics described here based on sound pressure levels at a receiving point, or are they calculated sound power levels that take into account distance attenuation in a semi-free field with a floor surface? Please clarify.
  Also, the section titles—3.1 Power Spectrum and 3.2 Frequency Characteristics—appear to differentiate between narrowband FFT analysis and 1/3 octave band analysis. However, this distinction is not immediately clear or standard, and should be explained or reconsidered.

• Figure 5 – A-Weighted Spectrum via FFT:
  The FFT-based narrowband analysis shown here will vary depending on the number of FFT points, affecting both frequency resolution and spectral values. Please either convert the levels to dB/Hz or clearly specify the frequency resolution used.

• Figures 6 and Onward – 1/3 Octave Band Spectrum:
  The horizontal axis currently uses value labels every 2/3 octave and minor ticks every 1/6 octave, which is not a common convention. Please revise to use either labeled major ticks for each 1/3 octave band or, alternatively, label only the center frequencies used in 1/1 octave band analysis. A more appropriate label for the x-axis might be “1/3 Octave Band Center Frequency.”

• Figure 8 – Peak Normalization of Pattern P1:
  It seems the spectrum for Pattern P1 has been shifted upwards to align peaks with others. If this is the case, P1 should no longer be listed as 87 dB. Please revise the level accordingly.

• Section 3.3 – Directionality:
  While a diaphragm alone would typically exhibit omnidirectional characteristics, how do you expect this to change when the horn is mounted on a motorcycle? If any information or assumptions are available, please include them.

• Figure 14 – Polar Plot Grid:
  Please add concentric circular grids every 10 dB and radial lines every 45 degrees to make the plot easier to interpret.

• Section 3.4 – Electric Horn Sound:
  The electric horn shows higher energy in the 630 Hz to 1 kHz range than the mechanical horn. Does this affect the overall sound level or timbre? Please discuss any possible causes or implications.

• Section 4 – Discussion:
  The second line refers to Japanese safety standards. Please describe the specific content (e.g., the requirement that the sound must exceed XX dB at a specified measurement point).
  Also, the statement about a 17 dB increase around line 5 would be more convincing if a summary table listing sound levels was included in the results section.

• Comparison with Other Noise Sources:
  In order to evaluate the impact of horns, it would be useful to quantitatively compare them with other traffic noise sources such as powertrains or tire–road interaction noise. Do the authors have any relevant data or references to include?

• Section 5 – Conclusions:
  In line 14, the authors suggest lowering the sound levels of motorcycle horns. How many decibels should they be reduced by? Please provide a specific target or range if possible.

Minor Revisions

• The line break at lines 17–18 in the Introduction appears to be erroneous.

• In the last line of page 1, the notation Lden should be italicized (L). Also, ensure that all instances of LAeq,T in the text and figures follow ISO notation standards.

• dB represents a level, but dBA is not a correct unit. Please revise accordingly.

• In Figures from 5 onward, the small subfigures showing horn time patterns are informative, but the text is too small to read easily. Please enlarge the text.

• In Figure 17, the plot labeled M = 0.5 sec uses a mix of dots and dashed lines, which might give the impression of a connected line. Please consider an alternative representation.
  Also, Figure 18 and its caption do not match. If they convey the same information, please unify them for consistency.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. "Medium-sized Vietnamese cities [4,5] confirmed consistently high exposure to road traffic noise" contains an error – part of the sentence has been incorrectly moved to the next paragraph, whereas it should remain in the previous one.

2. What is the purpose of the studies described in section 2, given that they are not referred to later? Do these studies contribute anything to the article? There is no mention of the results.

3. Regarding section 2 – the description of the methodology is very weak. Please specify what type of sound level meter was used. Was it a Class 1 or Class 2 meter? Were the measurements taken with or without weighting correction? What was the time constant set on the meter? How many meters away from the noise source was the meter placed? How long did the measurements last, and during what times of day?

4. In section 2.2 – the reference should be to Figure 3, not "drawing no. 3."

5. I suggest modifying the description – the text refers to two types of noise events, but then lists six (P1–P6). It may be more appropriate to indicate that there are two main types of events, each subdivided into three subcategories or classes.

6. In section 2.3, the sound level meter is described again. Is this the same meter as in section 2.1?

7. Section 2.3 mentions only the height of the meter placement, not its distance from the noise source. Figure 4 includes complete information, so I recommend integrating that full information into the text.

8. Figure 5 – why are the results presented only in the range of 300 Hz to 10 kHz, even though the human ear perceives sounds from 20 Hz to 20 kHz? The text also indicates that the measurement range extends to 20 kHz. Why, then, are the results limited? Why is the spectral data presented only for P1? A detailed comparison for the other events may be valuable.

9. Section 3.2 – “The overall Laeq, T for [P1] is measured at 87 dBA as illustrated in the pattern [P1]” – does this refer to a single sample? A single measurement?

10. Figures 6–13 – The ternary plots are incorrectly visualized. I recommend using bar plots ("bands") instead of curve plots, as the latter may mislead the reader.

11. Section 3.3 – “The sound level meter was situated three meters away from the horn” – this does not align with the description provided in Figure 4.

12. “The data illustrates relatively constant sound pressure levels in all directions, suggesting that the horn sound is uniformly distributed around the horn's location.” – If the measurement was taken in a reverberation chamber, this conclusion is obvious.

13. Figure 15 – again, why is the frequency range limited to 10 kHz?

14. Section 4 – It may be worthwhile to consider suggesting changes or the introduction of legal regulations, based on the specific acoustic characteristics of the studied area.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for your thorough revisions. All of the previously raised concerns have been properly addressed, and I find the manuscript acceptable in its current form.
One minor issue remains: the numerical values on the x-axis of Figure 6 are missing and should be added for clarity.

Author Response

Comments and Suggestions for Authors

Thank you for your thorough revisions. All of the previously raised concerns have been properly addressed, and I find the manuscript acceptable in its current form.
One minor issue remains: the numerical values on the x-axis of Figure 6 are missing and should be added for clarity.

Response to Reviewer’s Comment:

We sincerely thank the reviewer for the positive feedback and for recognizing our revisions. Regarding the minor issue raised, we have now added the missing numerical values on the x-axis of Figure 6 to improve clarity. The revised figure is included in the updated manuscript.

Thank you once again for your helpful comments and support.

Reviewer 2 Report

Comments and Suggestions for Authors

1. The results in Figure 15 should be presented across the full audible frequency range.
2. Out of the 14 cited references, 8 are self-citations. The authors should conduct a significantly broader review of the literature.

Author Response

Comment 1: The results in Figure 15 should be presented across the full audible frequency range.

Response to Reviewer’s Comment 1:

Thank you for pointing this out. We agree that presenting the results across the full audible frequency range will provide a more comprehensive understanding. We have updated Figure 15 to display the results across the full audible frequency range (20 Hz to 20 kHz)

Comment 2: Out of the 14 cited references, 8 are self-citations. The authors should conduct a significantly broader review of the literature.

Response to Reviewer’s Comment 2:

We appreciate the reviewer’s advice regarding the balance of cited literature. In response, we have conducted an extensive review of relevant and recent studies in the field and expanded our reference list accordingly. In the revised manuscript, several self-citations have been removed, and additional works by other researchers have been incorporated to provide a broader scientific context and reduce the proportion of self-citations. These newly added references are discussed in the Introduction section to better situate our work within the wider body of existing research.