Sound transducer calibration of ambulatory audiometric system utilizing delta learning rule

An efficient calibration algorithm for an ambulatory audiometric test system is proposed. This system utilizes a personal digital assistant (PDA) device to generate the correct sound pressure level (SPL) from an audiometric transducer such as an earphone. The calibrated sound intensities for an audio-logical examination can be obtained in terms of the sound pressure levels of pure-tonal sinusoidal signals in eight-banded frequency ranges (250, 500, 1 000, 2 000, 3 000, 4 000, 6 000 and 8 000 Hz), and with mapping of the input sound pressure levels by the weight coefficients that are tuned by the delta learning rule. With this scheme, the sound intensities, which evoke eight-banded sound pressure levels by 5 dB steps from a minimum of 25 dB to a maximum of 80 dB, can be generated without volume displacement. Consequently, these sound intensities can be utilized to accurately determine the hearing threshold of a subject in the ambulatory audiometric testing environment.

输气管道泄漏声源特性及其变化规律

泄漏声源基本特征及变化规律是声波传播研究的基础,对泄漏信号预处理、特征准确提取及泄漏识别算法改进具有重要意义。为此,以输气管道泄漏喷注产生的声源为研究对象,基于气动声学理论推导泄漏喷注流场中的声源项构成,建立了泄漏声源区域三维仿真模型,基于M？hring声类比提取高马赫数和高雷诺数流场中的等效声源,采用气动噪声混合数值模型进行仿真。分析过程中提取了不同条件下（压力及泄漏孔径）泄漏声源的质点最大速率和平均速率、声压级及声功率级等基本特征参数,并利用管道泄漏模拟测试平台进行验证,明确了泄漏声源基本特征及其变化规律。研究结果表明：（1）泄漏喷注噪声主要是由气体高速喷射湍流和气固耦合引起的,声源以四极子和偶极子为主;（2）针对管道运行压力和泄漏孔径,得出了泄漏声源基本特征参数的变化规律;（3）泄漏产生的能量集中于低频部分,各频段（小于等于200 Hz）能量分布分析结果表明0-20 Hz能量比大于等于0.81,无泄漏及正常输送条件下能量分布趋于平均,可作为泄漏识别的特征指标。