Experimental Study On The Bone Conduction Transfer Function Of The Ears

In recent years,with the development of technology,bone conduction hearing devices have been gradually applied in consumer market,medical hearing aids and military equipment.However,compared with air conduction,the study of bone conduction is still in the development stage,and there is little research on the measurement of bone conduction.Previous studies have shown that the transmission characteristics of bone conduction hearing cannot be attributed to a single factor,and the external auditory canal radiation sound is considered to be an important part of it.The measurement of the transfer function of the radiated sound from the external auditory canal of the binaural bone conduction has become the basis of many subsequent studies.Therefore,this paper proposes a method to measure the radiated sound transfer function of the external auditory canal,and studies and analyzes the measurement steps,experimental parameter settings,experimental precautions and experimental results.This paper first summarizes the experimental methods and results of bone conduction auditory transmission characteristics measurement,and finds the following main problems: the non living experiments can not fully represent the real bone conduction in vivo;the experimental procedures for measuring cochlear response to bone conduction sound are complex,and the experimental time is long,and some experiments may be affected by the subjects,resulting in deviation;the measurement of bone conduction ear canal sound pressure simply lists some experimental results,without in-depth analysis.In order to solve the above problems,this paper first designs the method of radiated sound measurement of external auditory canal of binaural bone conduction,which is divided into ipsilateral ear and contralateral ear.It mainly includes selection and analysis of experimental equipment,design of excitation signal,calculation method of transfer function based on experimental data,etc.In this paper,the advantages and disadvantages of different excitation signals are compared,the swept sine signal is selected as the excitation signal of this experiment,and the design method and parameter selection of swept sine signal are analyzed.It is concluded that the sweep signal with 32 kHz sampling rate,200-8k Hz sweep range,5s sweep time and 0dBFS(corresponding to the actual 2Vp-p output)is more suitable for excitation.Through theoretical analysis of different transfer function calculation methods and experimental comparison of the influence of different transfer function calculation methods on the results,it is finally concluded that the transfer function calculation using cross-correlation function method can effectively avoid the influence of measurement noise and harmonic distortion by adding window truncation to the calculated impulse response in the pre-processing.The external auditory canal radiated sound produced by bone conduction has good linear phase characteristics.In addition,the effects of different device gain settings,different excitation signal intensities,different excitation times and heartbeat on the measurement results are analyzed.Secondly,the radiated sound transfer function of the external auditory canal of binaural bone conduction wre measured and analyzed in 5 subjects and compared with the results of other researchers.This paper gets the following features: due to the incomplete symmetry of the human physiological structure,the radiation sound transfer function between the left and right ears is not symmetrical;the radiation conduction function of the ipsilateral ear is generally stronger than that of the contralateral ear,but this relationship may be reversed in individual frequency bands;whether it is the ipsilateral or contralateral ear,bone conduction external auditory canal radiation sound transfer function has a relatively strong amplitude performance in the frequency band around 1kHz;a trough can be clearly identified in the frequency range of 200-400 Hz for the transfer function of the ipsilateral ear;a trough can be clearly identified in the frequency range of 400-800 Hz for the transfer function of the contralateral ear;the transfer function of each subject shows certain comb effect.Lastly,this paper analyzes the transfer function differences between different bone conduction transducer wearing positions through experiments,as well as the isolation between the playback of bone conduction external auditory canal radiation sound and the playback of loudspeakers and headphones through experiments.It is concluded that the isolation of the playback of bone conduction external auditory canal radiation sound is between speaker playback and headphone playback.In this paper,the measurement method of the radiated sound transfer function of the external auditory canal of binaural bone conduction can be used to measure the transfer function quickly.Subsequently,a database of the radiated sound transfer function of the external auditory canal of binaural bone conduction with high accuracy and multiple samples can be established according to the method in this paper.At the same time,this paper provides basic support for the research of equalizer,Crosstalk cancellation and spatial hearing of binaural bone conduction.