At which frequencies must the average be measured for a standard threshold shift (STS)?

The criteria for measuring a standard threshold shift (STS) are specifically focused on frequencies that are critical for assessing hearing impairment typically associated with occupational noise exposure. For a reliable measurement of STS, the average is specifically taken at 2000 Hz, 3000 Hz, and 4000 Hz.

These frequencies are crucial because they are within the range where many speech sounds are found and are particularly sensitive to high-frequency hearing loss due to noise exposure. Occupational safety guidelines often emphasize these frequencies, as they can provide early indications of hearing deterioration caused by prolonged exposure to loud environments.

In contrast, the other frequency sets mentioned do not align with the established standards for assessing a standard threshold shift in hearing. The inclusion of frequencies like 500 Hz or 1000 Hz, while important in other contexts, does not meet the specific criteria defined for STS measurement. Thus, option C reflects the correct standard practices for evaluating potential hearing damage in audiology.