The Effectiveness Of Different Sound Absorbing Materials On The Transmission Of Sound At 3000 Hz

The Effectiveness Of Different Sound Absorbing Materials On The Transmission Of Sound At 3000 Hz

Eelan Al Zuhairi – Lurnea High School

Abstract

This investigation aimed to determine which sound absorbing material (concrete sheets, plaster sheets, acoustic pinboard and Abelflex Expansion Joint Filler) prevents transmission of sound when tested at a frequency of 3000 Hz. The investigation was conducted by using concrete mix, plaster mix, acoustic pinboard and joint filler, gauging trowel was also used to mix the concrete and the plaster mixture, 4x of empty boxes were used to test each different material. Small speak was used and connected to the laptop to examine the frequency on each sound absorbing material. It was revealed that acoustic pinboard results were the best sound absorbing material as it had the best quality of preventing the transmission of sound. It can be concluded that acoustic pinboard was the most efficient material. For these results to be considered accurate and reliable further investigation needs to be carried out with four different materials and more repetition of the pressure.

Literature review

The latest population growth and urbanization have substantially increased use of modern instruments in houses. As an efflux in construction and production noise problems have escalated rapidly. This comes to a conclusion where acoustical soundproofing materials are essential as they are used in two crucial ways; Soundproofing: which basically reduces the sound pressure with respect to a specified sound source and receptor. Sound absorbing: is the amount of energy removed from the sound wave as the wave passes through a given thickness of material. Sound is a wave, a motif or compound. Sound is processed through vibrations of objects. The vibrations push and pull-on air molecules. The exert force generates a certain compression of the air (escalation in pressure), and the pull generates a rarefaction of the air (lessening in pressure). Since the air particles are already in a constant motion, the rarefactions and compressions established at the starting origin are rapidly imparted by the air as an expanding wave. the frequency range of everyday sound from 250-6000. The sound transformation occurs as a result of flying noises (voices, music, etc). The airborne sound wave hits the wall, and the pressure variations generate the wall to vibrate. This vibrational energy is transferred via the wall and emitted as airborne sound on the other side. Sound is conducted through solid by oscillation, therefore through a wall. How much acoustic power breaks through the wall relies on the thickness of the wall and its material. In the case of the wall, there are more layers of material, meaning more radiation steps, and more energy loss. The sound going through the wall will be more weakened/reduced than the sound going through a single pane of glass.

Another crucial point is that the wall and the window, being made of different materials, probably have very different natural frequencies. The way each lessened sound will be different for this reason too. In this experiment sound absorbing materials will be used such as Concrete sheets, Plaster sheets, Acoustic Pinboard, Acoustic foam to measure the sound transmission frequency so that it indicates which material is the most effective for absorbing sound. The reason why this experiment was conducted is because Certain sounds are extremely annoying to all of us collectively, however people with autism find it 10x times more annoying than a normal individual as it feels really painful to them and causes unwanted actions or reactions. People with autism may either overreact and exaggerate or totally ignore many ordinary sensations such as smells, sights and sounds. For instance, they might not filter out noises that are irrelevant and unnecessary, or might find that certain sounds can be very uncomfortable and distracting. There are various different types of noise sensitivities autistic people may experience, including: phonophobia is an uncommon and constant fear of either particular or general environmental sounds. People with autism may try to avoid exposing themselves to the sounds they are scared of, and most of them could end up being housebound due to their anxiety. Usually led by tinnitus, hyperacusis is an intolerance of everyday generalized environmental noise. When autistic people suffer from this it’s more likely that they are able to handle most sounds, as long as they’re at a consistent level. Yet, this changes when the noises change frequency, specially when they rise above 70 decibels for e.g., hearing a vacuum cleaner running. And lastly mysophobia This is specified by an emotional reaction, such as rage or having a temper, to certain sounds. The core trigger for this is mainly a soft sound that’s usually related to breathing or eating, and can be connected to people who are close to them. Sound absorbent materials can be used to make a suitable acoustic environment within a space by lessening the prolongation of a sound. Reverberation affects the way a space 'sounds'. A long reverberation time can make a room sound loud and noisy and causes speech to sound muffled and echoey. The topic was chosen from an online article on “Acoustical properties of particleboards made from betung bamboo (Dendrocalamus asper) as building Construction materials”. The purpose of their study was to determine the acoustical properties of particleboard made from Betung bamboo (Dendrocalamus asper). As the materials used in their experiment were 3 different sizes of betung bamboo (fine, wool and medium) In this investigation it was extended on this article but testing out different types of materials leading to the inspiration to produce his inquiry question on “ Which sound absorbing material…... prevents transmission of sound when…. (low, medium and high)?”. The hypothesis of this experimental research was: When the concrete sheets are tested on the box, they will block more sound transmission than other materials, that’s because concrete works to reflect and absorb sound waves. Hence, it provides a very effective barrier for noise transmission. concrete is also very dense and thick which makes it an excellent insulator against airborne or impact noises. Since concrete is heavier than gypsum, it is harder for sound to move through it. Regardless, the noise might still be heard but with a lower bass sound since a heavy wall vibrates like any other. As the concrete sheets were designed to reflect noise towards the source and absorb some of the energy from the sound wave. This experimental research was assigned as a simulation setting of a real life.

Research Question

Which sound absorbing material (concrete sheets, plaster sheets, acoustic pinboard and Abelflex Expansion Joint Filler) prevents transmission of sound when tested at three distinct frequency levels (low, medium and high)?

Hypothesis

When the concrete sheets are tested on the box, they will block more sound transmission than other materials, that’s because concrete works to reflect and absorb sound waves. Hence, it provides a very effective barrier for noise transmission. concrete is also very dense and thick which makes it an excellent insulator against airborne or impact noises. Since concrete is heavier than gypsum, it is harder for sound to move through it. Regardless, the noise might still be heard but with a lower bass sound since a heavy wall vibrates like any other. As the concrete sheets were designed to reflect noise towards the source and absorb some of the energy from the sound wave.

Methodology

Diagram of the experiment

Preparation of sound – absorbing materials for testing

The following materials and equipment were purchased from Bunnings Australia : x1 Dingo 10kg concrete mix, x2 Dingo 2.5kg Plaster Of Paris, x4 10L Clear Modular Storage Container, x1 Craftright 175mm Gauging Trowel, x1 Small speaker, x1 Computer or laptop, x1 Ormonoid 10 x 150mm 6m Abelflex Expansion Joint Filler, x1 ForestOne 1200 x 800mm 9mm white acoustic pinboard. (note: same thickness is important).

All the statistical analysis was carried out using microsoft excel version 2206. A thorough internet search on tone generator, frequency generator and sound frequency generator was carried out to download. A suitable frequency range of 3000 Hz was selected and downloaded to test. The bluetooth speakers were connected to a laptop. Sound meter app was downloaded from the apple store to measure the frequency of each trial. The selected frequency of 3000 Hz was tested on an empty box container x10 times for reliability then the records were written on a table for the empty box. Water was added to the cement mixture to turn it into liquid then a trowel was utilized to stick it on each side of the container and let it harden. After the concrete was ready to be tested, bluetooth speakers were placed inside the container. The speaker volume was adjusted to get a constant sound pressure on the sound level meter app at a fixed distance from the speaker. The selected frequency level of 3000 Hz was tested and measured using the “Decibel X” app. The experiment with the concrete sheets was repeated 10x for reliability. Another empty container was out to test the plaster sheets. The plaster mixture was prepared and placed on each side of the container box. Same steps were repeated with the plaster sheets. Third container was also out to examine the acoustic pinboard. The acoustic pinboard was cut out into the same sizes of the container sides, then the same testing steps were repeated with the acoustic pinboard. Finally, the last container was used to examine the Abelflex Expansion Joint Filler and the same steps were also repeated with the Abelflex expansion joint filler. All absorbance data was well processed and organized. an approbating table was made to record the data. Then a column graph was sketched to demonstrate the average results from post and pre tests for each different sound absorbing material was used. A risk analysis was carried out using the RiskAssess software program to find the risks behind conducting this experiment and the risks were such as spill of water, can cause serious injury such as cuts or back, leg injury. In order to prevent this risk, cleaning the area using a mop is required. Loud sounds can cause hearing damage, in order to prevent this issue wear an earplug or keep the speaker volume at a reasonable level.

Results

Pre-Test (no box) → Abelflex Expansion Joint Filter box

Post -Test (Box presence) dB → Ablelflex Expansion Joint Filler box

Pre – Test (no box) dB → concrete box

Post – Test (Box presence) dB → concrete box

Pre – Test (no box) dB → plaster box

Post – Test Post (Box presence) dB → concrete

Pre – Test (no box) → acoustic pinboard box

Post – Test Post (Box presence) dB → acoustic pinboard box

Pre – Test (no box) dB → empty box

Post – Test (Box presence) dB → acoustic pinboard box

This column graph shows the differences of each sound absorbing materials in order such as ( Acoustic pinboard = blue, Abelflex expansion joint filler = yellow, concrete = red, empty box = purple, and plaster = green). The vertical error bars indicate the standard deviation of each material which was found by the pre-post test averages through using microsoft excel.

The highest standard deviation was 6.431209 with the material acoustic pinboard. Whereas the lowest standard deviation was 3.964509 with the material Abelflex Expansion Joint Filler. As seen in the graph above.

Null hypothesis

For the student's ‘t’ test the null hypothesis stated that there was no difference between the means of the sounds absorption carried out by the materials used. The alternative hypothesis on the other hand stated that the means of the sound absorption carried out by the materials used was not the same. Two sided ‘t’ test was performed with the results shown below:

This t test table shows the p value difference of each sound absorption material versus empty box to determine the effectiveness of the material. The plaster table shows the P value of 0.4 is greater than the alpha value of 0.05 which means that there is no statistical difference between the exposure of plaster and empty box. The second column table of Abelflex vs empty box shows the P value of 2.7….4E means its highly statistically significant result as alpha value of (0.05) is greater than the p-value. Therefore, the null hypothesis is rejected and hence that homoscedasticity cannot be assumed. Last but not least concrete vs empty box column tables show the P value of 0.1 which is technically greater than the alpha value of 0.05 which means there is no significant difference between the concrete and the empty box. Lastly, acoustic pinboard vs empty box also showed the P value

1.1….4E means its highly statistically significant result as alpha value of (0.05) is greater than the p-value. Therefore, the null hypothesis is rejected and hence that homoscedasticity cannot be assumed.

Table 1-5 demonstrates the sound transmission capabilities of the relevant materials

(concrete sheets, plaster sheets, acoustic pinboard and Abelflex Expansion Joint Filler) at the selected frequency level of 3000 hz. The baseline data of sound transmission was obtained through the absence of the box covered with the relevant material which is shown by the pre test column. The post test column indicates the sound transmission in the presence of the relevant sound absorbing material. The post test data was subtracted from the post test date to find the accurate average transmission capability of the materials used. There were 10 trials carried out with each material and average of the pre test and post test data were taken per material used in the investigation. (the higher the average result the better sound absorbing material is).

The order of the best sound absorbing materials was ( acoustic pinboard, Abelflex Expansion Joint Filler, concrete sheets, empty box, plaster sheets).

Table 1. Measurement of sound transmittance with the plaster box at 3000 Hz

Table 2. Measurement of sound transmittance with the Abelflex Expansion Joint Filler box at 3000 Hz

Table 3. Measurement of sound transmittance with the white acoustic pinboard box at 3000 Hz

Table 4. Measurement of sound transmittance with the concrete box at 3000 Hz

Table 5. Measurement of sound transmittance with the empty box at 3000 Hz

Table 6. The descriptive statistical analysis of the experimental findings

Discussion

The following results are presented in the tables to compare the pre test and post test results. The use of the tables and graphs above demonstrates the effectiveness level of each different sound absorption material. The outcome of this experiment reveals that acoustic pinboard was the most effective sound absorption material as it had 31.44 dB average amount of sound prevented from the transmission. Hence the higher result indicates the better sound absorbing material is. The second effective sound absorption material was concrete as it had an average of 20.48 dB. Third highest was Abelflex expansion joint filler as the average was 11.18 dB. Last but not least, the empty box had an average of 7.25 dB and lastly, the plaster had an average of 5.53 dB which means it is the least effective sound transmission material. According to the background research and the literature review the results seemed accurate but the standard deviation shows otherwise. As the acoustic pinboard had a standard deviation of 6.431209 which resulted to be the highest but that means the data is more spread out. Meanwhile the plaster had the lowest standard deviation of 3.949698 and that means the data is clustered around the mean. As an overall the standard deviation in this experiment was high which indicates that the values are spread out over a wider range. Although the t tests comparing concrete and empty box, plaster and empty box revealed that there was no difference between the high frequency exposed to them. This result needs to be confirmed through further investigations since it is apparent, from literature, that concrete is very dense and thick which makes it an excellent insulator against airborne or impact noises and should work to reflect and absorb sound waves. According to the journal article of “Sound-Absorbing Composites with Rubber Crumb from Used Tires” in their discussion it mentions that “ they have used gypsum and rubber crumb as their sound absorbing material. One can conclude that the most effective in terms of sound absorbing properties is the composition of concrete using only rubber crumb as an aggregate. The result was the composition of concrete using only rubber crumb as an aggregate. The result was achieved due to the addition of the fractioned rubber crumb of fractions from 5 to 2.5 mm in a quantity of 6%; fractions from 2.5 to 1.25 in a quantity of 29%; fractions from 1.25 to 0.63 in a quantity of 29%; fractions from 0.63 from 0.315 to 0.16 mm in a quantity of 7%. The use of fractioned rubber crumb enables us to obtain the necessary sound absorption since the large specific surface area of open pore walls contributes to the active conversion of sound vibration energy into thermal energy due to friction losses. The use of rubber crumb with larger grains significantly reduces the compressive strength of the developed material. The proposed grain composition of the rubber crumb was stated as a result of evaluating the strength and sound absorption properties of the material. The proposed composite is made from secondary resources, which contributes to the development of resource-and energy-saving technologies. The proposed gypsum–cement–pozzolan composition allows us to increase the sound absorption coefficient, which rises from values of 0.31–0.48 to values of 0.46–0.70 in the studied frequency range in comparison with the composition without rubber crumbs. These results confirm the published data in [43], in which it was shown that the sound absorption coefficient of cement concrete with rubber crumbs increases at high frequencies. Summarizing the results obtained and the previously published data of other authors one can conclude that the sound absorption coefficient of gypsum and cement composites rises significantly with the increase in amount of rubber crumb from used car tires and it depends less on the properties of this rubber crumb. The mechanical properties of gypsum and cement composites significantly depend on both the amount and the properties of the rubber crumb.” Thus in their experimental research the conclusion was “ The use of fractionated rubber crumb allows us to obtain the necessary sound absorption with a less pronounced decrease in strength characteristics. The proposed grain composition of the rubber crumb was determined as a result of evaluating the strength and sound-absorbing properties of the material. Meanwhile in this experiment the most efficient sound absorption material was the acoustic pinboard. As the acoustic pinboard contains an oven polyester board with a gray finish. It is most likely to be very durable, and absorbs noise with impressive acoustic properties and hence it is an effective pinboard. Therefore the experiment was not accurate nor precise. The experiment requires a lower standard deviation which indicates that the values tend to be close to the mean of the set to be more accurate. This resulted to be one of the limitations in this experiment. The materials used had high SD which affected the precision and consistency of the experiment. When a SD is high, it indicates the precision of the measurement is low which affects the accuracy of the measurement as well. This could be due to the limitation of the methodology used to prevent this more advanced measurement techniques should be used. To improve the low precision it has to be conducted with more trials. For feature direction for scientific research more background research on sound, sound-blocking materials, and sound-blocking construction techniques is required. Then a hypothesis is needed about which materials might be better at attenuating low frequencies, and which materials might be better at attenuating high frequencies. In order to test the hypothesis, it is important to obtain pieces of each of the different materials that are needed to be tested. audio test files also needed and a sound level meter. The audio test files will have a series of pure tones at low, medium, and high frequencies. different tones needed to be examined and the sound level meter to test how well the different materials attenuate different frequencies. There were no random mistakes, the results were nearly identical and reflect the true value.

Conclusion

The amount of sound that materials can absorb depends on the frequency of the sound that has been tested. Acoustic pinboard and Abelflex Expansion Joint Filler are lightweight materials and are able to absorb middle and high frequency sounds. As it was hypothesized that when the concrete sheets are tested on the box, they will block more sound transmission than other materials. Hence, acoustic pinboards have polyester which absorbs an impressive amount of sound transmission. Ableflex Expansion Jointing is made from Polyethylene Foam which also absorbs a decent amount of sound. This makes them useful products for controlling sound levels for environments like offices or sound rooms. The use of acoustic pinboard helps to reduce the room’s background sounds, reverberation, echo also it comes in handy on various occasions, including professional recording studios. Soundabsorbing materials are often used in multiple layers to provide compounding effects. The results suggest that these lightweight materials will not work well to control higher energy, low-frequency bass waves. Therefore the performance of the soundproof foam depends on the type of foam used and its efficiency in absorbing and dissipating the sound energy into heat energy. Future investigations need to confirm the findings from this study.

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