Comparison of three calibration procedures for free-field reference speech audiometry

Area of Science:

• Audiology
• Acoustics
• Speech Science

Background:

• IEC 60645-1 and ANSI S3.6 standards reference the free-field equivalent earphone output level for speech audiometry.
• Accurate calibration is crucial for reliable speech recognition threshold (SRT) measurements.

Purpose of the Study:

• To compare three distinct calibration procedures for the free-field equivalent earphone output method.
• To evaluate the effectiveness of these methods for TDH39 earphones in speech audiometry.

Main Methods:

• Speech audiometry was performed using Dutch consonant-vowel-consonant words under three conditions: TDH39 earphones, loudspeaker, and simulated free-field with TDH39 earphones.
• Three calibration procedures were assessed: empirical SRT difference, theoretical free-field correction, and simulated free-field results.
• Twenty normal-hearing subjects participated in the study.

Main Results:

• The observed difference between free-field and earphone SRT was 7.1 dB.
• The difference between free-field and simulated free-field conditions was 0.6 dB.
• All three calibration procedures produced comparable outcomes.

Conclusions:

• The three calibration procedures for the free-field equivalent output method are effective and interchangeable for TDH39 earphones.
• These findings support the use of these methods for accurate speech audiometry calibration.