Study On The Acoustic Attenuation Characteristics And Speech Recognition Ability Of Different Types Of Face Masks

Objective: To measure the attenuation effects of face masks(N95 masks,surgical masks,cotton masks,transparent masks and face shields,et al.)on the sound intensity by overall and individual speech frequencies.To quantitatively investigate the effect of three different types of face masks(surgical mask,N95 mask with face shield,and transparent mask)on speech recognition of medical staff or patients with mild to moderate hearing loss,,and the related influencing factors.The accuracy and convenience of mobile smartphone-based selfservice audiometric applications(APPs)in a normally hearing population was evaluated.Methods: The KEMAR head and torso simulator was used to emit white noise and speech sound while wearing different kinds of face masks.A microphone was used to record the mask’s attenuated sound.Amplitude and spectral analysis were then performed.To test the effect of three different types of face masks on speech recognition,the test conditions were divided into four groups:(1)no mask group(unattenuated speech sounds and visual cues with lip reading);(2)surgical mask group(surgical mask attenuated speech sounds and visual cues with lip reading);(3)N95 mask with face shield group(N95 mask with face shield attenuated speech sounds and visual cues with lip reading);(4)transparent mask group(transparent mask attenuated speech sounds and visual cues with lip reading).Then the subjects’ speech recognition thresholds or speech recognition scores were measured.And subjects were instructed to apply three audiometric APPs to complete the binaural air conduction thresholds test and to use a stopwatch to record the time required to complete each APP.Differences in hearing thresholds and time consumption measured by audiometric APPs and clinical audiometers were compared.Results: The magnitude of the attenuation effect of different types of masks on acoustic signals varied.There was less attenuation in the low-frequency region below 2000 Hz and more attenuation in the high-frequency region above 3000 Hz.The 24 medical staff’s speech recognition thresholds in the four test conditions were-10.5 ± 1.1 dB for the no mask group,-10.4 ± 2.7 for the transparent mask group;-3.5 ± 0.9 dB for the surgical mask group;and-1.9 ± 1.0 dB for the N95 mask with face shield group.Multiple comparisons showed no significant difference between no mask group and transparent mask group(P = 1.000),no significant difference between surgical mask group and N95 mask with face shield group(P= 0.152),and a significant difference between the remaining groups in both direct(all P less than 0.000).The speech recognition scores of the 40 subjects with hearing loss in the four test conditions were 85.1 ± 7.5 % for the no mask group,85.1 ± 7.6 % for the transparent mask group,71.2 ± 10.8 % for the surgical mask group,and 53.9 % ± 9.4 % in the N95 mask with face shield group.There was no significant difference between the no mask group and the transparent mask group,and all remaining pairwise comparisons were significant.The air conduction thresholds measured by *Assistant and Mimi were in good agreement with clinical pure tone audiometry;but those measured by the *Tone had significant deviations in the low frequencies.*Tone had the shortest duration and the highest level of satisfactionConclusion: The magnitude of the attenuation effect of different face masks varied.The magnitude of attenuation effect is related to the material of the mask,thickness and other factors.The attenuation effect of the mask on speech sound was similar to a low-pass filter.The effect of different types of face masks on speech recognition performance varied.Two masks that blocked lip reading(surgical mask,N95 mask with face shield)significantly reduced subjects’ speech recognition performance compared to the remaining two condition,while the transparent mask significantly improved speech recognition performance to the level of no mask.Mask type,degree of hearing loss,duration of hearing loss,and age had significant effects on subjects’ speech recognition score.The air conduction thresholds measured by *Assistant and Mimi were in good agreement with clinical pure tone audiometry;but those measured by the *Tone had significant deviations in the low frequencies.