The Feasibility of Noise Insulating Materials With Variability of Frequencies and Amplitudes

The objective of this experimental investigation was to determine the effectiveness of different thermal insulating materials noise reduction properties when exposed to acoustic signals of varying frequencies and amplitudes. The experimental system incorporated two boxes separated by a thermal insulation wall. A speaker was used in one box with varied sound amplitude and frequency to test how effective the insulating material was at reducing sound transmission through a wall. The sound level was measured with a microphone in each box and the values were used to calculate the Sound Transmission Loss (STL) for each trial. Fiberglass insulation and cork insulation were the two insulation materials tested. The frequency levels of500 Hz, 1000 Hz, and 2000 Hz were tested. A three factor ANOVA analysis was completed and the null hypothesis was rejected with 95% confidence for each of the three factors. A Tukey test was conducted to determine which factor, if any, had a significant impact on the STL value. The Tukey test determined that frequency had the most significant impact on the STL value followed by the material choice with the average difference of means for comparison groups being 17.92 dB and 7.74 dB, respectively. The Tukey test also determined sound level did not have a significant impact on the STL value. The fiberglass insulation tested had the highest STL value of the two materials tested, with a maximum STL of 49.5 dB at 2000 Hz while the minimum STL was 26.2 dB at 500 Hz. The cork insulation had a maximum STL of 44.4 dB at 2000 Hz and a minimum STL of 10.5 dB of 500 Hz. At 1000 Hz however, the cork insulation had a higher STL than the fiberglass insulation with 32.6 dB and 31.6 dB respectively. This discrepancy might be due to a specific property of the cork dictating how it interacted within a specific frequency range. The test had an overall uncertainty of ±1.34 STL which was much smaller than the difference between sample groups. The ANOVA analysis also showed a strong interaction between the insulating material and the frequency as it had a much greater F-value of 869.56 as compared with the F-critical value of 2.42.