The current version ACCV4 of our acceleration sensor device is presented and used to study the influence of vowel duration to the estimates of resonances of the subglottal system of 7 female and 9 male speakers. The sensor records movements in all three spatial directions below 5 kHz. It is gently pressed to the neck of the speaker in front of the cricothyroid ligament, a soft tissue in the lower part of the larynx. Linear prediction is used the estimate three resonances between 500 Hz and 2 kHz. Statistically significant differences in the estimates taken for the first two subglottal formants are found.