Investigation of Acoustic Efficiency of Wood Charcoal in Impedance Tube for Usage in Sound-Reflective Devices

Round 1

Reviewer 1 Report

Line 21- “The sound reflection coefficient increases with density increases” should be written as “The sound reflection coefficient increases with the increase in density”. In line 22 instead of creation, it is better to use “prepared”.

Line 29: the sentence should be re-written and it is not possible to understand what the authors are trying to convey.

Line 38: it should be “by analysing” rather than by analysed.

Line 63 to 65, the structure of the sentences should be modified.

Line 90: It should be “such as thickness and bulk density”

Line 91 to 94 should be re-written.

The introduction as a whole has lot of information, but a major detail about experimental studies by making use of impedance tube is missing. The authors can also include similar literature where carbon usage in the form of bulk material or powdered or any other form can be included. A thorough grammar check should be done since in many places the sentence formation is very poor and is not constructed in a way to be included in any original research work.

Line 96-104 should be re phrased properly.  How were the bulk density measurements done? This detail is missing and should be included.

Since the formulae used in equation no 1 to 8 are not derived by the authors, they should quote the reference from where it was taken.

A major detail about Impedance tube set up, the make and the model is missing.

In the results and discussions section, a detail about the proposed diffuser is missing and a better drawing could be made. It is not clear about how the authors intent to include charcoal in perforated boards and what is the size of the proposed diffusers and the percentage concentration of charcoal in the perforated boards is also not clear. When the authors call it an invention, this should be something new and novel and they should give proof of the novelty of the proposed design. Also, since this is only a proposal, how efficient this is in comparison with the existing ones is also nor clear. Authors should address these appropriately.

Author Response

Response to Reviewer 1 Comments

Thank you for considering publishing our manuscript on the topic of the Investigation of acoustic efficiency of wood charcoal in impedance tubes for the usage of sound reflective constructions. The manuscript was changed according to your comments.

Point 1:

Line 21- “The sound reflection coefficient increases with density increases” should be written as “The sound reflection coefficient increases with the increase in density”. In line 22 instead of creation, it is better to use “prepared”.

Response 1: Line 21

Corrected. “The sound reflection coefficient increases with density increases” written in the manuscript as “The sound reflection coefficient increases with the increase in density” In line 22 revised “prepared”.

Point 2:

Line 29:- “the sentence should be re-written and it is not possible to understand what the authors are trying to convey.

Response 2:

Line 29:  Corrected - “the sentence re-written as Charcoal is a rigid naturally porous material that has high sound reflection properties. The factors that influence the sound reflection properties: are pore type, bulk density and thickness.

Point 3:

Line 38: it should be “by analysing” rather than by analysed.

Response 3: 

Line 38: Corrected

Point 4:

Line 63 to 65, the structure of the sentences should be modified

The sound absorption coefficient (SAC) characterizes sound propagation in charcoal little is absorbed. SAC is also helpful for the optimization and design of noise control devices. The structure of charcoal, as it was revealed, had its microstructure.

Response 4: 

Line 63 to 65 Corrected. According to studies, charcoal has smaller absorption properties compared with other sound absorption materials. The sound absorption coefficient (SAC) lets us know the acoustic effectiveness of charcoal.

Point 5:

Line 90: It should be “such as thickness and bulk density”

Response 5:

Line 90 Corrected

Point 6:

Line 91 to 94 should be re-written. 

Response 6 :

Line 91 to 94 Corrected

The aim of this study is to investigate the acoustic efficiency of charcoal and to study the influence of sound absorptive factors such as thickness and bulk density of charcoal material. Simultaneously, it's important to investigate the usage of charcoal reflective property on the prepared construction example. Sound diffusing construction has been manufactured for this goal. An acoustic diffuser helps to improve the acoustics of the room and eliminate negative effects such as echo. 

Point 7:

The introduction as a whole has a lot of information, but a major detail about experimental studies by make use of impedance tubes is missing. The authors can also include similar literature where carbon usage in the form of bulk material or powdered or any other form can be included. A thorough grammar check should be done since in many places the sentence formation is very poor and is not constructed in a way to be included in any original research work.

Response 7:

Corrected

The research on the sound absorption coefficients (α) of charcoal conducts the transfer function method of two microphones in an impedance tube (ISO 10534-2 and ASTM E1050). Studies using the impedance tube measurement of sound absorption coefficients by activated carbon fibre nonwoven were reached. The composite with the surface layer of cotton fibre nonwoven possessed a higher fabric density and therefore showed better sound insulation than the composites with glass fibre and ACF.

Jiang, N.; Chen, J.; Parikh, D. Acoustical Evaluation of Carbonized and Activated Cotton Nonwovens. Bioresource technology 2009, 100 (24), 6533–6536.

Astrauskas, T.; Januševicius, T.; Grubliauskas, R. Acoustic Panels Made of Paper Sludge and Clay Composites. Sustainability 2021, 13, 637. 2021.

ISO, U. 10534-2. Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes. Part 2: Transfer-Function Method. International Organization for Standardization. Genève 1998.

Novak, C.; Ule, H.; Cert, J. K. I. B. Comparative Study of the ASTM E1050 Standard for Different Impedance Tube Lengths; Institute of Noise Control Engineering, 2011; Vol. 1, pp 815–822.

After reviewing the manuscript, language editing services for improving writing and re-written lines and phrases were used.

Point 8:

Line 96-104 should be re-phrased properly. 

Charcoal for research was manufactured from three types of wood birch Betula pendula, pine Pinus sylvestris, and oak (Quercus robur). The wood was collected from the Lithuanian forest; it is a widespread tree in the region. The samples of charcoal were prepared of 10, 18, 25, and 50 mm thicknesses and a diameter of 30 mm.

The charcoal was manufactured by partial combustion in a carbonization system muffle furnace E5CK-T with a heating rate of 10 °C/min, burning time was 1 h, under oxygen-limited conditions, and under atmospheric pressure. The pyrolysis was performed at a peak temperature of 330 C°. Prepared samples of charcoal were homogeneous solid and isotropic, shown in Figure 1.

How were the bulk density measurements done? This detail is missing and should be included.

Response 8:

Corrected

The bulk densities of charcoal were measured according to the formula:

D = M / V

M - the mass of soil, g

V - volume as a whole, cm³

Point 9:

Since the formulae used in equations no 1 to 8 are not derived by the authors, they should quote the reference from where it was taken.

Response 9:

Corrected

 Schröder, M. R. Diffuse Sound Reflection by Maximum− Length Sequences. The Journal of the Acoustical Society of America 1975, 57 (1), 149–150.

Schroeder, M. R. Binaural Dissimilarity and Optimum Ceilings for Concert Halls: More Lateral Sound Diffusion. The Journal of the Acoustical Society of America 1979, 65 (4), 958–963.

Point 10:

A major detail about the Impedance tube set up, the make and the model is missing.

Response 10:

 Information Impedance tube set-up added to the article

Impedance tube method. The research was carried out using the impedance tube technique determination of the sound absorption coefficient according to DIN EN ISO 10534-2. AcoustiTube, type III, inner diameter: 30 mm, frequency range: 150 Hz – 6.600 Hz. The measurement system AED 1000 is supported by the analysis software AED 1001. The measuring results allow the direct computation of the rated sound absorption coefficient of the material according to DIN EN ISO 11654 (ISO 11654). The impedance tube for research is shown in figure 2. Matlab was used for the calculation of the sound absorption coefficient. Added some detail to equations.

Point 11:

In the results and discussions section, a detail about the proposed diffuser is missing and a better drawing could be made. It is not clear how the authors intend to include charcoal in perforated boards and what is the size of the proposed diffusers and the percentage concentration of charcoal in the perforated boards are also not clear.

When the authors call it an invention, this should be something new and novel and they should give proof of the novelty of the proposed design. Also, since this is only a proposal, how efficient this is in comparison with the existing ones is also not clear. Authors should address these appropriately.

Response 11:

Corrected drawing

In the triangle plywood (wood) diffusor drilled out the perforations. For the reason that choosing perforations sizes diameter 20 mm, pitch 30 mm, thickness 10 mm. The charcoal is prepared in a muffle furnace. In the perforation in a wood acoustic diffuser, the charcoal elements intend and fastened with perforations with a binder. The calculation formula of the square hole of acoustic diffuser arrangement such as perforation rate type added to the manuscript.

The developed triangular, theoretical acoustic diffuser calculation for the research diffuser has a design frequency of 550 (on which dispersion is most effective). These values correspond to most of the mid frequencies, which significantly affect the naturalness of the sound reproduction. shown in table 2.

Table 2 - Cell depth calculation results

The total frequency range of the acoustic diffuser is from 412.5 to 2007.3 Hz. Estimated well width 8.7 cm diffuser size seven front planes with a total construction width of 63 cm, the height of 120 cm. The percentage concentration of charcoal in the perforated boards is 35 %.

Scientific Novelty. Charcoal has not been researched for the production of sound diffusion constructions and has never been used to create acoustic diffusers. The current literature has not explored the acoustic and non-acoustic properties of charcoal construction that can effectively improve room acoustics. The existing acoustic diffuser is wedge-shaped, rectangular planes dissipate sound less efficiently than other forms. Invented diffuser from wooden triangular perforated planes filled with charcoal cylinder elements. Triangular-shaped planes distribute the reflected sound well at different positions from the source and increase the diffuseness of the sound field in the room. The materials from which this design is developed are environmentally friendly. The scattering properties of triangle plywood (wood) diffusor are the subject of future research.

The manuscript was submitted for review in language editing services. Linguistic corrections are indicated in the manuscript.

Reviewer 2 Report

The manuscript lacks coherence. It is poorly written and very difficult to understand clearly the point of view of the authors. In my opinion it is not fit for the journal and his rejected.

Author Response

Thank you for considering publishing our manuscript on the topic of the Investigation of acoustic efficiency of wood charcoal in impedance tubes for the usage of sound reflective constructions. The manuscript was changed according to your comments.

Point 1:

The manuscript lacks coherence. It is poorly written and very difficult to understand clearly the point of view of the authors. In my opinion, it is not fit for the journal and is rejected.

Response 1

In our opinion, it is fit for the journal. The manuscript has been revised to make it more understandable for readers. The reviewed manuscript was submitted to language editing services. Linguistic corrections in the manuscript are indicated.

Reviewer 3 Report

- the formatting of the units should be corrected (kg/m3 -> kg/m³)

- imprecise citations:, line 357 "28. Khrystoslavenko, O.; Grubliauskas, R. Theoretical predictions of sound scattering coefficient and sound diffusion 357 coefficient from quadratic residue diffusers; 2020", line 359, "Jung, S. S.; Kim, H. C.; Kim, Y. T.; Seo, J. T. Sound Absorption Characteristics of a Pine Wood Charcoal and with Artificially 359 Drilled Charcoal." (sources seems to be missing)

- linguistic corrections indicated (e.g. line 75 "Charcoal is a homogeneous rigid porous material most of the sound wave is reflected." -> "Charcoal is a homogeneous rigid porous material in which most of the sound wave is reflected.")

Author Response

Response to Reviewer 3 Comments

Thank you for considering publishing our manuscript on the topic of the Investigation of acoustic efficiency of wood charcoal in impedance tubes for the usage of sound reflective constructions. The manuscript was changed according to your comments.

Point 1:

- the formatting of the units should be corrected (kg/m3 -> kg/m3)

Response 1

Corrected

Point 2:

- imprecise citations: line 357 "28. Khrystoslavenko, O.; Grubliauskas, R. Theoretical predictions of sound scattering coefficient and sound diffusion 357 coefficient from quadratic residue diffusers; 2020", line 359, "Jung, S. S.; Kim, H. C.; Kim, Y. T.; Seo, J. T. Sound Absorption Characteristics of a Pine Wood Charcoal and with Artificially 359 Drilled Charcoal." (sources seems to be missing)

Response 2 

Line 357  Corrected. Krystoslavenko O.; Grubliauskas R.; Theoretical predictions of sound scattering and sound diffusion coefficient from quadratic residue diffusers. Proceedings of the 22nd Conference for Junior Researchers Environment Protection Engineering “, Vilnius, Lithuania, 20 April 2019; pp. 80–87.

The source was missing. Revised source: Suh, J. G.; Kim, Y. T.; Jung, S. S. Measurement and Calculation of the Sound Absorption Coefficient of Pine Wood Charcoal. Journal of the Korean Physical Society 2013, 63 (8), 1576–1582.

Point 3:

- linguistic corrections indicated (e.g. line 75 "Charcoal is a homogeneous rigid porous material most of the sound wave is reflected." -> "Charcoal is a homogeneous rigid porous material in which most of the sound wave is reflected.").

Response 3

Charcoal is a homogeneous rigid porous material most of the sound wave is reflected." formatted in the manuscript: "Charcoal is a homogeneous rigid porous material in which most of the sound wave is reflected."

The manuscript was submitted for review in language editing services. Linguistic corrections are indicated in the manuscript.

Round 2

Reviewer 1 Report

Dear authors I have gone through the revisions and all the points have been addressed properly.

Author Response

Response:

Thank the reviewer for their time and comments.

Reviewer 2 Report

Reviewer comments: 

 “Investigation of acoustic efficiency of wood charcoal in impedance tube for the usage of sound reflective constructions.”

Abstract contains sufficient basic components; literature review can be improved by incorporating below given references related to sustainability and porosity of materials in accordance with manuscript. This will the enrich the contents of the manuscript.

1.     Ayaz Ahmed, Adnan Qayoum, Fasil Qayoom Mir, Investigation of the thermal behavior of the natural insulation materials for low temperature regions, Journal of Building Engineering, Volume 26, November 2019, 100849, https://doi.org/10.1016/j.jobe.2019.100849

2.     Ayaz Ahmed, Adnan Qayoum, Fasil Qayoom Mir, Spectroscopic studies of renewable insulation materials for energy saving in building sector, Journal of Building Engineering, Volume 44, December 2021, 103300, https://doi.org/10.1016/j.jobe.2021.103300

3.     Investigation on the thermal degradation, moisture absorption characteristics and antibacterial behavior of natural insulation materials, Materials for Renewable and Sustainable Energy volume 10, Article number: 4 (2021), https://doi.org/10.1007/s40243-021-00188-8

All the suggested changes have been incorporated in the manuscript. As such theoretical formulation and methodology seems to be good. In addition, results and discussion has become quite elaborate now.

Author Response

Corrected

Building insulation natural materials like sheep wool, goat wool and horse mane are one of the best procedures that reduce greenhouse gases and provide better thermal comfort. Due to their porous structure and low density (goat wool density 269.874 kg/m³), this natural material has good acoustic properties too. Ayaz et al. show that natural materials have better environmental aspects and efficiency than conventional materials. Natural materials allow for a move toward a completely sustainable energy strategy.

Thank the reviewer for their time and comments.