The Creation of Alternative Soundproofing Using Recyclable Materials

Abstract

In today’s world, the rate of urbanization is increasingly getting faster and faster. Large cities that are heavily populated produce noise that is not only harmful to one’s hearing, but also for concentration and productivity. If constantly exposed to an environment such as the ones existing in heavily populated cities, long-term effects will take place in the health of citizens such as damage to the cochlea membrane, increased progression of hearing loss, and long-term nerve damage within the ear canal. Furthermore, there is an average of 292.4 million tons of waste being produced on average since the year 2018. Approximately 50% of materials being thrown out are materials that can be recycled or repurposed. Using recyclable materials to create an effective yet affordable soundproofing composite would be important from a health, economic and environmental standpoint. Composites created from recyclable materials (foam, cardboard, binder, soundproofing material) were constructed and their soundproofing capabilities were measured using a self-constructed low-cost impedance tube. A bluetooth speaker was used to produce a consistent frequency of sound (400 Hz) for 5 seconds into a composite. A Vernier SoundProbe was utilized to measure the sound after passing through the composite in decibels. The average amplitude (decibels) without any composite was 2.5 while with composite materials (<1.5). Percent reductions were calculated for each material (all reduced more than 15% of sound). The data supported the hypothesis in that the recyclable composites were able to reduce noise levels by 15% or more.

Introduction

In today’s world the rate of urbanization is increasingly getting faster and faster. Large cities that are heavily populated produce noise that is not only harmful to one’s hearing, but also for concentration and productivity (Carruthers, 2017). If constantly exposed to an environment such as the ones existing in heavily populated cities, long term effects will take place in the health of citizens such as damage to the cochlea membrane, increased progression of hearing loss, and long term nerve damage within the ear canal (Jarup, 2008). These effects also have their impact on the body such as increased blood sugar (diabetes) and sleep disturbance (Basner, 2011). The proportion of the population exposed to environmental noise above 65 dB has increased during the past decade from 15% to 26%. Noise exposure can cause humans to exhibit two different kinds of health effects. Auditory-hearing impairment, such as any degree of hearing loss, as well as non-auditory-stress related psychological effects, such as increased stress and cardiovascular function, and behavioral effects. (Hahad, 2019)

Due to increased urbanization, the sound being created in areas of high populations is not only more frequent, it is also louder which in turn has a greater toll on the health of the people in the area. This sound is primarily composed of vehicles passing by as well as engines of various mechanical devices being utilized (Frannsen, 2004). This amount of noise is potentially loud enough to raise one's blood pressure and heart rate, as well as cause stress, a loss of concentration, and loss of sleep (Jarup, 2008). Furthermore in these urban populations,  there is an average of 2.01 billion tons of waste being produced every year (datatopics.worldbank.org) and approximately 70% of materials being thrown out are materials that can be recycled or repurposed. (Florida Tech, 2015). This study explores affordable substitutes for soundproofing materials.

Acoustics is the study of sound, its production, transmission, and effects. The distance between each wave and its vertical height display both the frequency of the sound, as well as the pitch. A louder noise has a greater amplitude while a quieter noise has a lower amplitude.. The distance between each wave represents the frequency. Tight and compact waves indicate a higher frequency pitch whereas more spread out waves indicate a lower frequency pitch. Whether it be absorbing or reflecting, all materials have acoustical properties. Upon contact with any given surface, sound waves with higher amplitudes are more likely to be transmitted whereas those with lower amplitudes are more likely to be reflected. The behavior of sound waves are different based on the nature of the surface they come into contact with. The properties of soundproofing materials are heavily influenced by the density of the material being tested. The lower the density the easier absorption of sound waves becomes. If too low, the sound waves would be able to pass through the material. A material with high density would be able to reflect sound waves off of its surface. Soundproofing materials like Mass Loaded Vinyl (MLV), acoustic foam panels, and fiberglass insulation are widely used due to their excellent sound-absorbing properties. However, their high costs and environmental footprints necessitate the exploration of affordable, sustainable alternatives. Potential substitutes include recycled rubber, cork, hemp, flax, and cellulose. These materials are all eco-friendly, with some made from renewable resources and others from recycled products. Despite their promise, they require comprehensive testing to determine their true soundproofing capabilities and market viability. The recyclable materials tested varied in density. Some materials were less dense than others while some were more dense. Not only are these materials widely available and affordable, they also have the densities to be excellent soundproofing materials. (Tiuc et al, 2017; Starodubsteva et al, 2018)

Jun Yan et al (2014) studied the effect of polypropylene/clay composites on suppressing sound. It was found that polypropylene (PP)/clay composites dramatically increased by small quantities of clay filled in PP matrix. In this paper, different types of specimens were made at 0.9, 2.9, 4.8, 6.5, 8.2 and 9.9 wt.% of organically modified clay reinforced PP (100 gram) by solvent based techniques. A heating press and laser cutting process were used to create specimens with thickness 3 mm, diameter 29 mm and 100 mm for high and low sound frequency tests, respectively. The soundproofing property was measured by sound transmission loss (TL) through the impedance tube method. The measured results showed that about 7∼14.8 dB sound TL was increased for 29 mm diameter PP/Clay (6.5 wt.%) composite specimens compared with pure PP at 3200∼6400Hz. And about 3.3∼5.3 dB sound TL was increased for 100 mm diameter PP/Clay (6.5 wt.%) composite specimens compared with pure PP at 520∼640Hz. In addition, mechanical properties of this composite were measured, and TEM images were taken in order to observe the micro-structure for research on the relationship between soundproofing property and micromechanism. (Yun, 2014)

Kang et al (2014) evaluated the effectiveness of clay reinforced polypropylene fiber as soundproofing material. Researchers used a composite made out of clay reinforced polypropylene fiber which is a synthetic fiber that can be found in carpets and blankets due to its good heat insulating properties, and high melting point. 7 different composites were constructed that all varied in clay reinforcement weight. When compared to the control group (pure polypropylene fiber), all reinforced composite had suppressed more sound. It was observed that 6.5 wt.% clay reinforced Polypropylene composites had the best soundproofing performance in comparison with other composites for both low and high sound frequency field. In other words it was the most consistent composite for soundproofing. The set-up these researchers used to test the soundproofing capabilities of the different combinations of clay reinforced polypropylene composites was an impedance tube connected to two different amplifiers, one responsible for transmitting the sound and another for receiving the sound.

By mimicking these studies, this project aimed to find an alternative to conventional soundproofing using recyclable materials. The purpose of this experiment was to create an effective yet cost-effiicient soundproofing alternative that can reduce noise levels by 15% or more. This percent reduction was calculated by dividing 80 decibels (noise level tolerated by the human ear) by 94 decibels (average noise output in urban centers).  It was hypothesized that foam, binder and cardboard could effectively reduce noise levels by 15% or more. Cardboard should have the lowest average amplitude and the highest percent reduction of sound due to its high density relative to the other materials. The null hypothesis was that foam, binder and cardboard would have no effect on the reduction of noise levels. There will be no difference in the ability of foam, binder, and cardboard to reduce noise levels. The engineering goal of this study was to successfully construct a low cost and effective impedance tube to test the soundproofing capabilities of recyclable materials.

Methodology

Procedure:

The project was divided into two different phases. The first phase was the construction of the cost-effective impedance tube. This consisted of constructing a blue print (Figure 1) and then assembling the tube (Figure 2). The second phase was the construction and testing of the composites. All of the below protocols were completed by the authors.

Phase 1: Construction of Cost-Effective Impedance Tube

Figure 1: 2D Sketch of Low Cost Impedance Tube

(Diagram by authors,  2022)

Figure 2: Self-Constructed Low Cost Impedance Tube

(Diagram by authors, 2022)

Materials:

A 2-foot section of 3-inch diameter PVC pipe, alongside a 1-foot piece of 1.5-inch diameter PVC pipe. Two PVC end caps, one of each diameter to match the pipes, are necessary to seal the tube. You will also need two PVC flanges, both of 3-inch diameter, for attaching the pipes. A PVC converter is essential to transition between the 1.5-inch and 3-inch diameter pipes. To generate and emit sound, a MIFA speaker will be used as the sound source. You'll also need screws and bolts to secure everything together. Finally, for sound measurement, you'll require a Vernier Sound Probe and a Vernier LabQuest to accurately record and analyze the acoustic data.

The first phase was the construction of the low cost impedance tube. To reduce cost, the tube was  constructed out of standard PVC plastic pipes of different sizes. One end of the tube contained a sound source (MIFA bluetooth speaker) which was used to produce a consistent wave of broadband noise, which was the noise whose sound energy was distributed over a wide section of the audible range. A sample chamber was constructed out of 3-inch diameter PVC Tube, A PVC Converter and flanges. The sample holder played a critical role of aligning the test piece in normal position to the direction of traveling planar waves. Connecting the tubes with standard flanges reduced the cost significantly. Standard PVC flanges are readily available in the market with minimum conditioning required to be used for the desired purpose. Flanges provide an easy way to secure the sample into place and make the assembly/disassembly simpler without adding more cost to the apparatus. Flanges were used for quick release and easy access to sample in the test holder. Wing nuts and bolts were used to tighten the flanges. A Vernier Soundprobe was  placed behind the composite in a 1.5 diameter PVC Tube to measure sound pressure within the tube. The sound probe was connected to a Vernier LabQuest to receive and interpret the data.

Phase 2: Construction/Testing of Composites

Figure 3: Materials and Constructed Composites

(Diagram by authors, 2022)

The second phase was the construction and testing of composites. The five experimental groups (Figure 3) consisted of control 1 (no composite), control 2 (soundproofing material), foam, cardboard, and binder. A three inch diameter circle was cut out from each material using scissors and then placed into the constructed sample chamber. A consistent 400 Hz sound was played from the bluetooth speaker for 5 seconds. The average amplitudes of each material were graphed in decibels using a Vernier Sound probe and LabQuest 2. Tests were conducted in 5 second intervals, in a setting free of external noise to prevent any external noise being captured by the Vernier Sound Probe. Using IBM SPSS version 26 the data was analyzed by running a one way anova followed by a post hoc scheffe where p is less than 0.001. Because this was a self-constructed low cost impedance tube, there was some variation between each trial however it was minimal. The construction of this tube was overall successful in that it was able to measure the soundproofing capabilities of the recyclable materials being tested and provided reproducible results with minimal variation between trials. Average variation between trials was 0.000462 decibels (less than 5% of error).

Results

Figure 4: 400 Hertz sound wave - Control (No Material)

(Graph by authors, 2022)

Figure 5: 400 Hertz sound wave -Soundproofing Material

(Graph by authors, 2022)

Figure 6: 400 Hertz sound wave - Foam

(Graph by authors, 2022)

Figure 7: 400 Hertz sound wave - Cardboard

(Graph by authors, 2022)

Figure 8: All Materials Compared to Control (400 Hertz sound wave)

(Graph by authors, 2022)

Figure 9: Average Amplitudes of Recyclable Materials in decibels

Asterisks (***) denote significance in comparison to all groups (with the exception of SPM to Foam: One-way ANOVA followed by a post-hoc Scheffe with  p<(0.001) 

(graph by authors, 2022)

Figure 10: Percent Reduction vs. Type of Material

Asterisks (***) denote significance in comparison to all groups: One-way ANOVA followed by a post-hoc Scheffe with  p<(0.001) 

(graph by authors, 2022)

INSERT EQUATIOn

Figures 4-7 are the average amplitudes of each material as well as a control group. (Independent Variable-Time in seconds, Dependent Variable-Average Amplitude in Decibels, n=50). The peaks in the sound curve of Figure 4 plateau because the Vernier Sound Probe cannot measure sound pressures higher than 2.5 decibels. Figure 8 is Figures 4-7 compiled into one graph. Figure 9 is a bar graph comparing the average amplitudes of all the materials, whereas Figure 10 shows the percent reductions of each material. All materials had lower average amplitudes when compared to Control Group 1 and all composites were able to reduce noise levels by 15% or more, with cardboard having the highest percent reduction (87.12%). This was calculated using equation 1. As predicted, foam, binder, and cardboard composites can effectively reduce noise levels by 15% or more and cardboard had lowest average amplitude and the highest percent reduction of sound due to its high density relative to the other materials (Borlea et al 2012, Mamtaz et al 2016). The data was analyzed by running a One-way ANOVA followed by a post hoc scheffe where p is less than 0.001. Every composite material evaluated in our study showed significant differences when compared to the control. Variation between trials of each composite material was on average 0.000462 decibels (less than 5% of error) supporting the significance of the results