| Popis: |
The ratio of the minimum perceptible increment in sound intensity to the total intensity, $\frac{\ensuremath{\Delta}E}{E}$, which is called the differential sensitivity of the ear, was measured as a function of frequency and intensity. Measurements were made over practically the entire range of frequencies and intensities for which the ear is capable of sensation. The method used was that of beating tones, this method giving the simplest transition from one intensity to another. The source of sound was a special moving coil telephone receiver having very little distortion, actuated by alternating currents from vacuum tube oscillators. Observations were made on twelve male observers. Average curves show that at any frequency, $\frac{\ensuremath{\Delta}E}{E}$ is practically constant for intensitites greater than ${10}^{6}$ times the threshold intensity; near the auditory threshold $\frac{\ensuremath{\Delta}E}{E}$ increases. Weber's law holds above this intensity, the value of $\frac{\ensuremath{\Delta}E}{E}=\mathrm{constant}$ lying between 0.05 and 0.15 depending on the frequency. As a function of frequency $\frac{\ensuremath{\Delta}E}{E}$ is a minimum at about 2500 c.p.s., the minimum being more sharply defined at low sound intensities than it is at high. This frequency corresponds to the region of greatest absolute sensitivity of the ear. Analytical expressions are given [Eqs. (2), (3), (4) and (5)] which represent $\frac{\ensuremath{\Delta}E}{E}$, within the error of observation, as a function of frequency and intensity. Using these equations it is calculated that at about 1300 c.p.s. the ear can distinguish 370 separate tones between the threshold of audition and the threshold of feeling. |
