Effect of Compaction on the Sound Transmission Loss of Automotive Textile Recycling

Automotive textile waste is a potential secondary raw material for acoustic insulation; however, the sound transmission loss (TL) of loose textile recyclate under controlled compaction remains insufficiently described. This study evaluates TL in loose, compacted, and compact forms. Loose fractions were tested without compaction and after compaction at 250, 500, and 750 kPa, while compact textile specimens served as references. Specimens 20, 45, and 70 mm thick were measured in a four-microphone impedance tube over 100–2500 Hz. Transmission coefficients, a relative transmission ratio, regression models, and dominance analysis were used to compare configurations and quantify the effects of frequency, thickness, and compaction pressure. The uncompacted fraction showed the lowest TL, increasing only from 4.20 to 6.27 dB as thickness increased from 20 to 70 mm. At 750 kPa, average TL increased from 14.98 dB at 20 mm to 36.34 dB at 70 mm. For loose fractions, the pressure–thickness interaction dominated TL (Std. beta = 0.764; R2 = 0.933), whereas compact specimens were governed mainly by the frequency–thickness interaction (Std. beta = 0.806; R2 = 0.976). Within the tested configurations, increasing compaction resulted in a pronounced reduction in the transmission of acoustic energy through the loose textile fraction, and at the highest compaction levels the TL values were comparable to or higher than those measured for the reference CT configurations.