Speech intelligibility performance while wearing three different hearing protective devices

Abstract

Purpose: This study was designed primarily to investigate the differences in speech-in-noise comprehension in normal hearing listeners while wearing passive low-pass foam earplugs (3M E-A-R), passive flat-attenuating earplugs (Etymotic Research ER-20), and active flat-attenuating adaptive earplugs (MusicPro MP9-15). All three earplugs have a similar attenuation of 13-15 dB. Furthermore, the study compared speech-in-noise comprehension with and without the use of earplugs. Lastly, the study assessed the subjective sound quality and comfort associated with each of the above-mentioned earplugs. Methods: The study employed a single group, non-randomized quasi-experimental design involving 33 participants with normal hearing. Each participant underwent a detailed audiometric evaluation to confirm normal auditory function. The evaluation included tympanometry, otoacoustic emissions, pure-tone testing, speech recognition, word recognition, and assessment of uncomfortable listening levels. Following the audiometric assessment, participants engaged in four rounds of speech-in-noise testing under sound field conditions. The tests administered were the QuickSIN and Words-in-Noise (WIN) tests. In one round, participants performed the tests without hearing protection at 80 dB HL. The other three rounds were conducted at 95 dB HL, with participants wearing each of the three different earplugs. To ensure consistency and reduce bias, all earplugs were fitted by a trained investigator, the order of the four rounds of testing was randomized, and all participants were blinded to the specific earplugs being used. Upon completion of each speech test battery, and while still blinded to the earplug type, participants rated both the sound quality and comfort of each earplug using a Likert scale ranging from 1 to 5. Results: The ER-20 and MP9-15 earplugs performed similarly to one another, with no statistically significant difference between them. However, both the ER-20 and MP9-15 earplugs statistically outperformed the 3M E-A-R earplugs. The MP9-15 earplugs yielded the highest mean percent correct scores on the WIN test (83.42%, 95% CI: 81.80-85.05), closely followed by the ER-20 earplugs (82.58%, 95% CI: 80.80-84.35). In contrast, the 3M E-A-R earplugs produced lowest mean percent correct scores (74.21%, 95% CI: 72.79-75.63). When comparing these results to the no hearing protection condition, which had a mean percent correct score of 83.09% (95% CI: 81.46-84.72), no significant differences were noted between the No HPD, ER-20, and MP9-15 conditions. However, all three of these conditions showed statistically significant improvements in speech-in-noise comprehension over the 3M E-A-R earplugs. A similar pattern of findings was observed in the QuickSIN segment of the test battery which can be viewed in detail in the study's results section. In terms of subjective ratings, both the ER-20 (mean score: 4.36; 95% CI: 4.12-4.61) and MP9-15 (mean score: 4.42; 95% CI: 4.19-4.66) earplugs received significantly higher evaluations for sound quality compared to the 3M E-A-R earplugs (mean score: 3.06; 95% CI: 2.70-3.43). Additionally, no statistically significant differences were observed among the three earplug types with respect to comfort ratings. Conclusions: The study found evidence that utilizing passive flat-attenuating ER-20 earplugs, and active flat-attenuating MP9-15 earplugs provide better speech understanding in noise for normal hearing listeners compared to wearing passive low-pass foam 3M E-A-R earplugs. The study also demonstrated that there was no observed difference in speech intelligibility between not wearing hearing protection and using ER-20 or MP9-15 earplugs. Furthermore, both the ER-20 and MP9-15 earplugs were regarded as providing higher sound quality than the traditional 3M E-A-R foam earplugs. Lastly, no significant differences in subjective comfort were identified among the various earplugs tested.