Audiometry Study Notes

B/7 Audiometry, determine the Audiatory threshold curve and of the Audigram. Sound intensity -> amount of energy delivered by the sound wave to 1 m² area in 1s time. it is the average power of the sound (P) incident perpendicularly to a surface divided by the surface area -> J = P/A (W/m²) it can also be expressed by square of effective power divided by the acoustic impedance. J = P²_rms / Z Sound with higher intensity will appear louder. intensity -> is an objective, physical quantity characterizing the stimulis arriving at the ear. loudness -> is a subjective, psychophysical quantity that corresponds to our psychological sensation. sensation of loudness depends on 1- frequency (pitch) 2- intensity pitch -> physilogical sensation of the height of the sound note, which is the logarithmic function of frequency -> valid up to 1 kHz there is an enormous range of sound intensity that human ear is sensetive to -> 13 orders of magnitude. The value of loudness does not vary directly with intensity. So a logarithmic scale is used to describe the response of the ear to stimuli of different intensity -> Weber-Fechner's law for more accurate measurment the intensity dependence of loudness is a power law -> steven's law (sone scale) strong dependence of hearing to frequency is because of the resonance process of outer and ... ear. Equal - loudness curves. is a plot of intensity level VS frequency for sounds of equal loudness. -> Fletcher and manson performed the first measurment of equal loudness contours. -> in a silent room (anechoic chamber) -> 2 sound generators used. -> with the first, a sound of given intensity level at 1000 Hz frequency was generated. -> The examined person was instructed to compare the loudness of this reference sound with the loudness of a different frequency emitted by the second generator. -> The intensity of the second sound could be adjusted until the sensation of its loudness became identical to the reference sound. it is observed that if the second sound had a frequency lower than reference, then a higher intensity than the reference had to be chosen in order to match the loudness. -> at the end points corresponding to equivalent loudness sensation were connected to obtain the equal loudness curve. reference intensity -> sound intensity that can be just heard at the reference frequency (1000 Hz). J₀ = 10⁻¹² W/m² intensity level of a sound (J_dB) J_(dB) = 10 log (J / J₀) (dB) threshold of hearing (hearing-threshold) contour is defined as the 0 phon loudness level. lower contour in equal-loudness contour plot. By raising the intensity level of the reference frequency to 10, 20, 30... (dB) -> the respective equal loudness contours of 10, 20, 30, ... (phon) were determined. The loudness level (L_phon) corresponds to the intensity level of the reference sound. L_phon = 10 log (J / J₀) at 1000 Hz -> [Boxed equation: L_phon = J_dB at 1000 Hz] it was found that increasing the loudness level by 10 phons corresponds to doubling the sound sensation. loudness level (L_phon) + 10 (phon) = 2. louder sensation values of the weber-fechner's type phon-scale donot reflect the linear change in our hearing sensation. Fletcher and Munson -> introduced Sone values. corresponds to the unchanged equal loudness curves. reflecting the linear psychophysical sensation.