A free-field equalizer for TDH 39 earphones

Area of Science:

• Acoustics
• Audio Engineering
• Psychoacoustics

Background:

• Accurate sound reproduction is crucial for audiology and hearing research.
• Standard audiometric earphones like the TDH 39 may exhibit frequency-dependent responses.
• Free-field equalization aims to compensate for earphone-specific acoustic characteristics.

Purpose of the Study:

• To determine the free-field response of TDH 39 earphones.
• To develop and implement a passive equalizing network for TDH 39 earphones.
• To achieve a frequency-independent free-field equivalent sound level for the TDH 39 earphone.

Main Methods:

• Loudness comparison measurements were conducted in an anechoic chamber.
• A passive equalizing network was designed based on the measured free-field response.
• The equalizer featured two resonant frequencies at 720 Hz and 6000 Hz.

Main Results:

• The TDH 39 earphone, when used with the developed equalizer, demonstrated a free-field equivalent level independent of frequency.
• This independence was achieved within a tolerance of +/- 2.5 dB across the 100 Hz to 10 kHz frequency range.
• The passive equalizing network was successfully realized.

Conclusions:

• A passive equalizer effectively corrects the free-field response of TDH 39 earphones.
• The equalizer enables accurate, frequency-independent sound level delivery for audiometric testing.
• The developed equalizer is potentially applicable to TDH 49 earphones due to their similarity to TDH 39.