Ryota Shimokura

Effects of sound source location and direction on acoustic parameters in Japanese churches

In 1965, the Catholic Church liturgy changed to allow priests to face the congregation. Whereas Church tradition, teaching, and participation have been much discussed with respect to priest orientation at Mass, the acoustical changes in this regard have not yet been examined scientifically. To discuss acoustic desired within churches, it is necessary to know the acoustical characteristics appropriate for each phase of the liturgy. In this study, acoustic measurements were taken at various source locations and directions using both old and new liturgies performed in Japanese churches. A directional loudspeaker was used as the source to provide vocal and organ acoustic fields, and impulse responses were measured. Various acoustical parameters such as reverberation time and early decay time were analyzed. The speech transmission index was higher for the new Catholic liturgy, suggesting that the change in liturgy has improved speech intelligibility. Moreover, the interaural cross-correlation coefficient and early lateral energy fraction were higher and lower, respectively, suggesting that the change in liturgy has made the apparent source width smaller.

Benefit of a new hearing device utilizing cartilage conduction

OBJECTIVE Our previous study demonstrated that sound was effectively transmitted by attaching a transducer to the aural cartilage even without fixation pressure. This new method for sound transmission was found by Hosoi in 2004, and was termed cartilage conduction (CC). CC can be utilized even in hearing-impaired patients who cannot use air-conduction hearing aids owing to continuous otorrhea or aural atresia. A prototype hearing aid employing CC was investigated in this study. METHODS Four patients with conditions such as continuous otorrhea and acquired aural atresia after surgery participated in this study. The CC hearing aid was fitted, and its benefits were assessed by audiometric tests and interview. RESULTS Thresholds and speech recognition scores improved in all subjects. However, in subjects with continuous otorrhea, it was difficult to obtain the gains according to the target gains owing to their severe hearing loss and the limitation of the output level. On the other hand, unexpectedly large gains were obtained below 2kHz in the patient with acquired aural atresia. These large gains were probably caused by soft tissue filling the postoperative space. No subjects complained of pain associated with the attachment of the transducer, although such problems are usually observed for a bone-conduction (BC) hearing aid. This feature is considered one of the advantages of the CC hearing aid. CONCLUSION The results of the audiometric tests and interview suggest that the CC hearing aid has potential as a useful amplification device for hearing disability. Unfortunately, if the soft tissue pathway is not involved, the current device is insufficient for the patients with severe hearing loss. The improvement of the output level will lead to develop a reliable CC hearing aid as an alternative to BC hearing aids or bone anchored hearing aids.

Sound transmission by cartilage conduction in ear with fibrotic aural atresia.

A hearing aid using cartilage conduction (CC) has been proposed as an alternative to bone conduction (BC) hearing aids. The transducer developed for this application is lightweight, requires a much smaller fixation force than a BC hearing aid, and is more convenient to use. CC can be of great benefit to patients with fibrotic aural atresia. Fibrotic tissue connected to the ossicles provides an additional pathway (termed fibrotic tissue pathway) for sound to reach the cochlea by means of CC. To address the function of fibrotic tissue pathway, BC and CC thresholds were measured in six ears with fibrotic aural atresia. The relationship between the CC thresholds and the results of computed tomography was investigated. In the ears with the presence of a fibrotic tissue pathway, the CC thresholds were lower than the BC thresholds at 0.5 and 1.0 kHz. At 2.0 kHz, no significant difference was observed between the BC and CC thresholds. The current findings suggest that sound in the low to middle frequency range is transmitted more efficiently by CC via a fibrotic tissue pathway than BC. The development of hearing devices using CC can contribute to rehabilitation, particularly in patients with fibrotic aural atresia.

The impact of external environments on noise inside a train car

Trains travel through various environments typically on tracks above ground or in tunnels. There are three main types of tunnels, which have different cross-sections according to their excavation methods. When trains pass through different environments, the perceived noise inside a train car can change. To consider appropriate acoustic treatment, the effects of the environment on noise inside train cars were investigated in this study. The noise inside a train car traveling through tunnels had a salient sound energy around 250 Hz, and came from the doors and windows of the train car. This suggests the effectiveness of acoustic treatment in the side walls of the car for the low frequency band. More reflections enter the train cars from tunnels with a circular cross-section in tunnels constructed by a boring machine, which drills tunnels before the insertion of lining segments. Acoustic treatment is likely to be needed in tunnels constructed using this method

Cartilage Conduction Is Characterized by Vibrations of the Cartilaginous Portion of the Ear Canal

Cartilage conduction (CC) is a new form of sound transmission which is induced by a transducer being placed on the aural cartilage. Although the conventional forms of sound transmission to the cochlea are classified into air or bone conduction (AC or BC), previous study demonstrates that CC is not classified into AC or BC (Laryngoscope 124: 1214–1219). Next interesting issue is whether CC is a hybrid of AC and BC. Seven volunteers with normal hearing participated in this experiment. The threshold-shifts by water injection in the ear canal were measured. AC, BC, and CC thresholds at 0.5–4 kHz were measured in the 0%-, 40%-, and 80%-water injection conditions. In addition, CC thresholds were also measured for the 20%-, 60%-, 100%-, and overflowing-water injection conditions. The contributions of the vibrations of the cartilaginous portion were evaluated by the threshold-shifts. For AC and BC, the threshold-shifts by the water injection were 22.6–53.3 dB and within 14.9 dB at the frequency of 0.5–4 kHz, respectively. For CC, when the water was filled within the bony portion, the thresholds were elevated to the same degree as AC. When the water was additionally injected to reach the cartilaginous portion, the thresholds at 0.5 and 1 kHz dramatically decreased by 27.4 and 27.5 dB, respectively. In addition, despite blocking AC by the injected water, the CC thresholds in force level were remarkably lower than those for BC. The vibration of the cartilaginous portion contributes to the sound transmission, particularly in the low frequency range. Although the airborne sound is radiated into the ear canal in both BC and CC, the mechanism underlying its generation is different between them. CC generates airborne sound in the canal more efficiently than BC. The current findings suggest that CC is not a hybrid of AC and BC.

Is cartilage conduction classified into air or bone conduction

The aim of this study was to establish the sound transmission characteristics of cartilage conduction proposed by Hosoi (2004), which is available by a vibration signal delivered to the aural cartilage from a transducer.

Interior Noise Characteristics in Japanese, Korean and Chinese Subways

The aim of this study was to clarify the characteristics of interior noise in Japanese, Korean, and Chinese subways. The octave-band noise levels, A-weighted equivalent continuous sound pressure level (LAeq) and parameters extracted from interaural cross-correlation/autocorrelation functions (ACF/IACFs) were analyzed to evaluate the noise inside running train cars quantitatively and qualitatively. The average LAeq was 72-83 dBA. The IACF/ACF parameters of the noise showed variations in their values, suggesting they are affected by the characteristics of the trains running, wheel-rail interaction, and cross-section of the tunnels.

Cartilage conduction efficiently generates airborne sound in the ear canal

OBJECTIVE By attaching a transducer to the aural cartilage, a relatively loud sound is audible even with a negligibly small fixation force. Previous study has identified several pathways for sound transmission by means of cartilage conduction. This investigation focused on the relative contribution of direct vibration of the aural cartilage to sound transmission in an open and in an occluded ear. METHODS Thresholds with and without an earplug were compared for three experimental conditions: the transducer being placed on the tragus, pretragus, and mastoid. Eight volunteers with normal hearing participated. RESULTS The thresholds increased with distance of the transducer from the ear canal (tragus, pretragus, mastoid, in that order). The differences were statistically significant for all conditions except for the occluded ear at 4 kHz. With the earplug inserted, the thresholds for the tragus condition were most sensitive below 2 kHz, indicating a significant contribution of direct vibration of the aural cartilage. CONCLUSION Direct vibration of the aural cartilage can enhance sound transmission. At low frequencies, cartilage conduction can deliver sound efficiently across a blockage in the ear canal. Stray airborne sound radiating from the transducer dominates cartilage conduction in the open ear at high frequencies.

Advantages of cartilage sound conduction in hearing aids

A cartilage conduction hearing aid has been developed for patients who cannot use conventional hearing aids owing to particular diseases of the external or middle ear. A user of such a hearing aid places the ring-shaped transducer gently at the entrance of the external auditory canal, so that it does not cause any feeling of discomfort. The cartilage conduction transducer vibrates the aural cartilage of the user, and the transmitted vibration generates sound in the external auditory canal, particularly in the low and middle-frequency ranges. In this regard, the cartilage conduction hearing aid has a different principle of sound transmission from conventional hearing aids. In this study, the performance and possible advantages of cartilage sound conduction in hearing aids were examined. This was achieved through two experiments focusing on important indicators: (i) the susceptibility toward acoustic feedback compared with air sound conduction and (ii) the ability of the user to realize sound directivity during binaural use of the cartilage conduction hearing aid. It was found that cartilage conduction was less susceptible to acoustic feedback than air conduction through an open-fitting earplug, even though both the cartilage conduction transducer and the open-fitting earplug keep the external auditory canal open. With respect to the second experiment, the binaural use of cartilage conduction transducers was found to facilitate subjective lateralization for users when examined using the interaural intensity difference (IID) cue. These results show that the cartilage conduction hearing aid has distinct advantages over the conventional air conduction hearing aid in terms of the robustness against the acoustic feedback and effective binaural use. Although the cartilage conduction hearing aid was once considered merely an expedient alternative for patients suffering from particular diseases, the advantages highlighted in the present study may attract patients with mild and moderate hearing loss, who are currently using air conduction hearing aids.

Listening level of music through headphones in train car noise environments

Although portable music devices are useful for passing time on trains, exposure to music using headphones for long periods carries the risk of damaging hearing acuity. The aim of this study is to examine the listening level of music through headphones in the noisy environment of a train car. Eight subjects adjusted the volume to an optimum level (L(music)) in a simulated noisy train car environment. In Experiment I, the effects of noise level (L(train)) and type of train noise (rolling, squealing, impact, and resonance) were examined. Spectral and temporal characteristics were found to be different according to the train noise type. In Experiment II, the effects of L(train) and type of music (five vocal and five instrumental music) were examined. Each music type had a different pitch strength and spectral centroid, and each was evaluated by φ(1) and W(φ(0)), respectively. These were classified as factors of the autocorrelation function (ACF) of the music. Results showed that L(music) increased as L(train) increased in both experiments, while the type of music greatly influenced L(music). The type of train noise, however, only slightly influenced L(music). L(music) can be estimated using L(train) and the ACF factors φ(1) and W(φ(0)).