An active free-field equalizer for headphones used in functional magnetic resonance imaging

Abstract

The free-field response of NordicNeuroLab AudioSystem electrostatic headphones for use in functional magnetic resonance imaging (fMRI) is determined by loudness comparisons with freefield equalized Beyerdynamic DT 48 headphones. Based on these measurements, an active equalizer with resonances at 0.55, 1.5, and 6.9 kHz is developed, realized, and tested. A free-field equivalent level independent of frequency within AE3 dB between 63 Hz and 10 kHz is obtained when using the AudioSystem headphones with the described free-field equalizer.