1 Introduction

Airborne sound insulation of multilayered sandwich constructions has been always a grey area of research amongst the building manufacturers and researchers for developing sandwich configurations providing enhanced acoustic performance. The prime considerations for design of sound insulative material are the building elements, viz. the walls, windows, roof, ceilings and exterior facade. Thus, a proper treatment of the building elements would considerably reduce the outside noise exposure and protect the residents from hazards of noise pollution. Also, the development of highly insulative doors, noise barriers and machinery noise enclosures can be very instrumental in noise control solutions. The dry wall technology that has emerged in past two decades has numerous advantages compared to the masonry constructions as: speed of installation is much faster than masonry constructions; lighter in weight, higher sound insulation and fire resistance, and less heat convection. The sound insulation provided by the drywall constructions can also be significantly enhanced by combination with masonry constructions for its suitability for building facades [1]. However, the dry wall constructions sometimes suffer from poor low frequency sound insulation which can be compensated by sandwich construction involving sound absorbing materials, using double stud walls or resilient channels, etc. [2]. The airborne sound insulation is measured in Reverberation Chambers by ascertaining the difference of sound pressure level in the source and the receiving room. There are varied single-number ratings, viz. Sound Transmission Class (STC), Weighted sound reduction index (Rw) and spectrum adaptation terms C, Ctr used for describing the sound insulation properties of partition wall panels. The STC value is defined as sound transmission loss value where the STC contour intersects the 500 Hz line [3, 4]. The better the STC of materials, higher the sound insulation it provides. Similarly, the weighted sound reduction index, Rw is used to facilitate the comparison of sound insulation performance of different materials in European continent [5]. There had been various studies reported on enhancing the STC/Rw of sandwich constructions. Also, analytical models facilitate the prediction of single-number ratings in many cases [6,7,8,9].

The light weight dry wall partition systems are used widely consists of GI steel frame, encased with gypsum plasterboards on either side attached through self-drilling drywall screws [10]. Structurally decoupling the drywall panels from each other (by using resilient channel, steel studs, a staggered-stud wall, or a double stud wall) can yield modest improvements in STC as revealed in some previous studies [11,12,13,14,15,16,17].

This present paper presents the sound insulation characteristics of various types of sandwich constructions available commercially. Such a comprehensive study focused on analyzing the sound insulation characteristics at 1/3rd octave band frequencies of various materials has been rarely reported. Also, the use of some materials like Tecsound sheets embedded in sandwich constructions, damping materials, vapor barriers, etc., in developing sandwich constructions of higher sound insulation had been not much reported. The sound insulation of various dry wall systems utilizing vapor barriers, GI blocks, Tecsound sheets, Asbestos and non-Asbestos sheets, Stainless, Aluminum, Plastic and transparent sheets and various damping materials and double galzing’s is reported in the study that can be helpful in the development of multi-layered sandwich constructions of enhanced acoustic performance accomplishing the desired noise level reductions. Such multi-layered constructions can be used in doors, noise barriers or enclosures for traffic and machinery noise control [18, 19]. The study also presents the calculation of measurement uncertainty in sound transmission loss evaluation of acoustical materials in frequency range of 100 Hz to 5 kHz.

2 Airborne Sound Insulation Measurements and Uncertainty

Sound transmission loss measurements were carried out by means of placing sample in a window opening between two reverberation rooms and calculating sound pressure levels in 1/3rd octave band at 125–4000 Hz frequency range. In this method, one measurement microphone is placed in source room and other microphone is placed in receiving room. When sound generates by the reference source and incident on building material mounted on the wall with specific dimensions, it gets reflected, absorbed and transmitted. The measured microphones present in source room and receiving room are used to record the sound pressure levels within the rooms. The various instruments used for airborne sound insulation measurements are the Reference Omnipower Sound Source Type 4292-L Optimum, B&K Power Amplifier Type 2734, Sound level analyzer Type 2270, AKG PT 470 Wireless Bodypack Transmitter and Measurement Microphone Type 4189 traceable to the national measurement standards of sound pressure level are shown in Fig. 1. The Reverberation Chambers dimensions are: 6 m × 6.5 m × 7 m, cut-off frequency: 100 Hz with source room volume: 257 m3 and receiving room volume: 271 m3 as shown in Fig. 2. The dimensions of the wall specimen window are 930 mm × 630 mm. The diffusivity of the room is prior checked so to ensure the standard deviation of sound pressure level at different positions in the room is less than ± 1.0 dB. These sound pressure levels in source room and receiving room are used to calculate the Sound Transmission Loss (STL) at 16 different frequencies in range 100 Hz to 4 kHz as [3]:

$$ {\text{STL}} = L_{{{\text{p1}}}} {-}L_{{{\text{p2}}}} + \, 10 \times \log \left( {\frac{{RT_{{\text{R}}} \times A_{{\text{S}}} }}{0.161V}} \right) $$
(1)

where LP1: Sound Pressure level in source room; LP2: Sound Pressure level in receiving room; RTR: Reverberation time in receiving room; AS: Sample Area; V: Source room volume. Sound Transmission Class is derived from Sound transmission loss values in 1/3rd octave band from 125 to 4000 Hz at 16 standard frequencies. These values are plotted with a standard reference contour provided by ASTM E413-87 and adjusting the standard contour on measured curve at 500 Hz to determine the Sound Transmission Class (STC) value at contour intercept at 500 Hz [4]. The weighted sound reduction index, Rw and spectrum adaptation terms are calculated as per ISO 717-1 [5]. Table 1 shows the factors affecting the measurement uncertainty in sound transmission loss measurements with a coverage factor of k = 2 as per the Guide to the Expression of Uncertainty in Measurement [20]. The sensitivity coefficient of unity is assumed for each component contributing to the uncertainty of measurement in sensitivity determination. The evaluated expanded measurement uncertainty in sound transmission loss measurements ranges between ± 1.5 to 2.0 dB in frequency range 100–4000 Hz, which is at a coverage factor k = 2 and which corresponds to a coverage probability of approximately 95% for normal distribution

Fig. 1
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Set-up of airborne sound insulation measurements in reverberation chambers

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Fig. 2
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Pictorial view of reverberation chambers used for airborne sound insulation measurements and diffusers installed for ensuring sound diffusivity at CSIR-National Physical Laboratory, New Delhi

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Table 1 Measurement uncertainty in sound transmission loss measurements in reverberation chambers
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3 Results and Discussion

The typical sound insulation of a material can be broadly classified in different regions: stiffness and damping controlled; mass controlled region and co-incidence effect region [21]. At lower frequencies, the stiffness of the panel of the panel resonances affects the sound insulation of the material. At lower frequencies, stiffer the material, the better is the transmission loss [22]. The middle frequency range shows the linear dependence of sound transmission loss on the mass of the construction and as such the sound transmission loss increases with the frequency at the rate of 6 dB/octave. In the higher frequency range, co-incidence dip is observed at the critical frequency that occurs when the wavelength of the sound in air coincides with the structural wavelength [2, 21,22,23,24,25,26,27,28]. Above the critical frequency, the insulation curves exhibit slopes with an inclination close to 9 dB/octave [26]. The sound reduction index for the plane waves assuming grazing incidence follows the mass law [27] described as:

$$ R = { 2}0\,{\text{Log }}\left( {Mf} \right){-}{47}\,{\text{dB}} $$
(2)

where M is the mass per unit area of panel in kg/m2 and f is frequency in Hz. This equation predicts an increase in the sound reduction index of about 6 dB for each doubling of the mass per unit area [27]. The sound insulation of various dry wall systems utilizing vapor barriers, GI blocks, Tecsound sheets, Asbestos and non-Asbestos sheets, Stainless, Aluminum, Plastic and transparent sheets and various damping materials and double Galzing’s is discussed.

3.1 Polycarbonate Sheets

Polycarbonate sheets are environmental friendly and used widely as noise barriers and enclosures as they possess higher stiffness, UV protection, thermal insulation and are light-weight. Figure 3 shows the sound transmission loss characteristics of the various polycarbonate sheets tested in the Reverberation chambers. It can be observed that these sheets encounter low frequency dip in frequency range of 160–315 Hz and higher frequency coincidence dip at 2 kHz. Table 2 shows the details and measured STC and Rw(C, Ctr) of different Polycarbonate Sheet. It can observed that the STC/Rw values lies between 19 and 21 which suggests the need of exploring the suitability of sandwich polycarbonate sheets can provide better sound insulation rather than single sheets.

Fig. 3
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Sound transmission loss of different polycarbonate sheets

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Table 2 Details and measured STC and Rw(C, Ctr) of different polycarbonate sheet
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3.2 Sandwich GI Metal Stud Dry Wall System with Vapor Barrier

A vapor barrier is generally a plastic or foil sheet that provides damp proofing and resists the diffusion of moisture through the partition wall. Table 3 shows the details and measured STC and Rw(C, Ctr) of different sandwich GI Metal stud dry wall system with vapor barrier. Figure 4 shows the sound transmission loss characteristics of the various sandwich GI Metal stud dry wall system with vapor barrier tested in the Reverberation chambers.

Table 3 Details and measured STC and Rw(C,Ctr) of different Sandwich GI Metal stud dry wall system with vapor barrier
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Fig. 4
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Sound transmission loss of different sandwich GI metal stud dry wall system with vapor barrier

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3.3 Gypsum Sandwich Partition Panels

The various sandwich gypsum constructions tested in the Reverberation chambers are tabulated in Table 4. Figure 5 shows the sound transmission loss characteristics of the various sandwich gypsum partition panels tested in the Reverberation chambers. The weighted sound reduction index, Rw of sandwich gypsum constructions lies between 40 and 48, while the Rw + Ctr values lie between 31 to 39 dB. The addition of steel studs with gypsum boards each side interestingly enhances the low frequency sound insulation characteristics, but at higher frequencies (> 2 kHz) a coincidence dip is observed.

Table 4 Details and measured STC and Rw(C, Ctr) of different Gypsum sandwich partition panels
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Fig. 5
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Sound transmission loss of different gypsum sandwich partition panels

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3.4 Autoclaved Aerated Concrete (AAC) Blocks

The various AAC block constructions tested in the Reverberation chambers are tabulated in Table 5. Figure 6 shows the sound transmission loss characteristics of the various AAC block constructions tested in the Reverberation chambers. The Rw/STC of AAC block constructions varied in range of 32–48, while the Rw + Ctr values lie between 26 and 42 dB. AAC blocks suffer from low frequencies dip in range 160–315 Hz and higher frequency dip at 2 kHz. It can be observed that a widely used 200 mm thick AAC Block with 12 mm plaster on both sides shows a low frequency resonance dip at 250 Hz and a high frequency coincidence dip at 3.15 kHz and shows an Rw + Ctr value of 38 dB. A 230 mm thick AAC Block has fairly high sound insulation in the entire frequency range and shows an Rw + Ctr value of 42 dB.

Table 5 Details and measured STC and Rw(C, Ctr) of different AAC blocks
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Fig. 6
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Sound transmission loss of AAC blocks

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3.5 GI Blocks

The various GI blocks constructions tested in the Reverberation chambers are tabulated in Table 6. Figure 7 shows the sound transmission loss characteristics of the various GI blocks constructions tested in the Reverberation chambers. The Rw/STC of GI blocks constructions varied in range of 31–40, while the Rw + Ctr values lie between 26 and 34 dB.

Table 6 Details and measured STC and Rw(C, Ctr) of different GI blocks
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Fig. 7
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Sound transmission loss of different GI blocks

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3.6 Tecsound Sheets

Tecsound sheets are polymer based, asphalt free, high density synthetic sound proofing membrane sheet included with a self-adhesive layer embedded in sandwich constructions. The various Tecsound sheet constructions tested in the Reverberation chambers is tabulated in Table 7. Figure 8 shows the sound transmission loss characteristics of the various Tecsound sheet constructions tested in the Reverberation chambers. The Rw/STC of Tecsound sheet constructions varied in range of 35–48, while the Rw + Ctr values lie between 29 and 39 dB. The low frequency dips are significantly controlled using these sheets, while coincidence dip at higher frequencies in observed in some cases.

Table 7 Details and measured STC and Rw(C, Ctr) of different Tecsound (polymer-based, asphalt-free, high density synthetic soundproofing membrane) sheet embedded in sandwich constructions
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Fig. 8
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Sound transmission loss of Tecsound sheets embedded in sandwich constructions

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3.7 Green Materials

The various Green material constructions tested in the Reverberation chambers were the agri-bio panels made of natural agri-residue sugarcane bagasse, bamboo composites, teak wood, ply board and sandwich type composite sound reducing door panel (Table 8). Figure 9 shows the sound transmission loss characteristics of the various Green material constructions tested in the Reverberation chambers. The Rw/STC of Green material constructions varied in range of 29–37, while the Rw + Ctr values lie between 24 and 32 dB.

Table 8 Details and measured STC and Rw(C, Ctr) of different Green materials
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Fig. 9
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Sound transmission loss of green material partition panels

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3.8 Asbestos and Non-asbestos Sheets

The various Asbestos and Non-Asbestos sheet constructions tested in the Reverberation chambers are tabulated in Table 9. Figure 10 shows the sound transmission loss characteristics of the various Asbestos and Non-Asbestos sheet constructions tested in the Reverberation chambers. The Rw/STC of Asbestos and Non-Asbestos sheet constructions varied in range of 36–44, while the Rw + Ctr values lie between 32 and 38 dB. A 75 mm thick Asbestos sheet construction shows the dip at various frequencies in the entire measurement frequency range, while a 100 mm thick non asbestos sandwich construction shows enhanced sound insulation characteristics registering a dip at 160 Hz and 4 kHz.

Table 9 Details and measured STC and Rw(C, Ctr) of different asbestos and non-asbestos sheets
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Fig. 10
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Sound transmission loss of different asbestos and non-asbestos sheets

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3.9 Stainless, Aluminium, Plastic and Transparent Sheets

The various Stainless, Aluminium, Plastic and Transparent Sheet constructions tested in the Reverberation chambers are tabulated in Table 10. Figure 11 shows the sound transmission loss characteristics of the various Stainless, Aluminium, Plastic and Transparent Sheets constructions tested in the Reverberation chambers. The Rw/STC of Stainless, Aluminium, Plastic and Transparent sheet constructions was observed to vary in range of 19–50, while the Rw + Ctr values was observed in range of 16–33 dB. It can be observed that in case of 3 mm thick Aluminum Composite Panel (ACP) sheet widely used, the low frequency dip at 250 Hz and at high frequency dip at 4 kHz are observed.

Table 10 Details and measured STC and Rw(C, Ctr) of different stainless, aluminium, plastic and transparent sheets
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Fig. 11
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Sound transmission loss of stainless, aluminium, plastic and transparent sheets

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3.10 Partition Panels of Various Damping Materials and Other Sandwich Constructions

The details of the partition panels of various damping materials and other sandwich constructions tested in the Reverberation chambers are tabulated in Table 11. These constructions involve the sheets made of Butyl rubber dampener, vinyl barrier, calcium silicate based tiles, Fibre Cement boards. The sandwich constructions employing the cold rolled closed annealed steel sheet suffers from low frequency dip at 160 Hz and coincidence dip at 2 kHz. Also, the Light Gauge Steel Frame (LGSF) suffers from low frequency sound insulation dip observed at 160 Hz. Figure 12 shows the sound transmission loss characteristics of the various damping and other sandwich constructions tested in the Reverberation chambers. It was observed that the Rw/STC of these constructions varied in range of 30–40, while the Rw + Ctr values lie between 27 and 37 dB.

Table 11 Details and measured STC and Rw(C, Ctr) of different partition panels of various damping materials and other sandwich constructions
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Fig. 12
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Sound transmission loss of different partition panels of various damping materials

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3.10.1 Double Glazed Windows

The details of the double glazed windows tested in the Reverberation chambers are tabulated in Table 12. These constructions involve the 10 mm and 12 mm toughened glass. Figure 13 shows the sound transmission loss characteristics of the double glazed windows. It can be observed that the Rw varied from 36 to 40 for the double glazed windows. The 10(62)12 mm double glazed window shows a dip at 1.25 kHz, while the 12(62)10 mm double glazed window shows dip at 1 kHz and 1.25 kHz. It can be also observed that the back panel thickness has major role as compared to the front panel thickness as in case of 12(62)10 mm double glazed window, the Rw/STC is higher than 10(62)12 mm double glazed window. This may be attributed to the reduction in the co-incidence dip due to increased back pane thickness [29,30,31]. The co-incidence dip has been observed to shift to the lower frequencies as the back pane thickness is increased [25].

Table 12 Details and measured STC and Rw(C, Ctr) of double glazed windows
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Fig. 13
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Sound transmission loss of double glazed windows

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4 Conclusions

The paper reports the airborne sound insulation characteristics of sixty three sandwich partition panels and masonry constructions tested in Reverberation chambers for their applications as doors, noise barriers or enclosures for traffic and machinery noise control and for developing the canopies for Diesel Generator Sets used widely in industries and commercial zones in Indian scenario and also for window glazing’s. The study presents the rarely reported sound insulation characteristics of various types of sandwich constructions available commercially. The sound insulation of various dry wall systems utilizing vapor barriers, GI blocks, Tecsound sheets, Asbestos and non-Asbestos sheets, Stainless, Aluminium, Plastic and transparent sheets and various damping materials and double glazing’s is reported in the study. The following conclusions are derived from the present study as follows:

  1. 1.

    The expanded measurement uncertainty in sound transmission loss measurement ranges between ± 1.5 an 2.0 dB in frequency range 100–4000 Hz, which is at a coverage factor k = 2 and which corresponds to a coverage probability of approximately 95% for normal distribution

  2. 2.

    The study suggests that sandwich constructions utilizing the various Gypsum and Tecsound sheets can provide enhanced acoustic performance comparable to the masonry constructions. The weighted sound reduction index, Rw of sandwich gypsum constructions lies between 40 and 48, while the Rw + Ctr values lie between 31 and 39 dB. The weighted sound reduction index, Rw of sandwich Tecsound constructions lies between 34 and 47, while the Rw + Ctr values lie between 29 and 39 dB.

  3. 3.

    The weighted sound reduction index, Rw of masonry constructions, AAC blocks tested lies between 31 and 48, while the Rw + Ctr values lie between 26 and 42 dB. AAC blocks suffer from low frequencies dip in range 160–315 Hz and higher frequency dip at 2 kHz.

  4. 4.

    The experimental results suggest that the polycarbonate sheets offer less sound insulation as the weighted sound reduction index, Rw lies between 19 and 21, while the Rw + Ctr values lie between 14 and 17 dB. These sheets suffer from poor low frequency sound insulation as low frequency dips are observed in lower frequencies from 160 to 250 Hz. Thus, sandwich constructions for polycarbonate sheets can be considered for accomplishing the desired noise level attenuation.

  5. 5.

    The Rw/STC value of double glazed windows tested in Reverberation chambers is observed to be enhanced with increasing the back pane thickness attributed to the reduced co-incidence dip.

Thus, the present study can be helpful in the development of optimal sandwich constructions of enhanced acoustic performance accomplishing the desired noise level reductions. Future efforts shall focused on developing sandwich constructions involving gypsum board, Tecsound sheets and fiber cement boards for developing sandwich constructions of enhanced acoustic insulation. Future efforts are also targeted in enhancing the low frequency diffusion characteristics in Reverberation chambers for evaluating the sound transmission loss characteristics in the measurement frequency range below 100 Hz.