Accelerometer based measurement for the mapping of neck surface vibrations during vocalized speech

This paper presents a detailed study of the vibrations on the surface of the neck during a vocalization of predefined fundamental frequency and intensity. This study was carried out as part of a wider investigation into the use of laryngeal vibrations as a channel of communication. Another potential application of this study is in identifying a suitable location for a hands-free electro-larynx for laryngectomees. An analog accelerometer, with dimensions 5times5times1.6 mm and of mass 80 mg, was used to perform the measurements. It was connected to a 12-bit analog to digital converter via single strands of insulated wire with a diameter of 100 mum. The resulting low inertia of the measuring device minimised the effect of the measuring device on the phenomenon under investigation. The analog to digital converter simultaneously sampled the accelerometer output and a pre-amplified audio signal from a microphone. This preliminary study was carried out on two able-bodied male subjects. Measurements were taken from forty-five preselected locations on the neck. Each subject made the vowel sound /i/ (long `e') at three different fundamental frequencies, 150 Hz, 200 Hz and 250 Hz. Once the vocal pitch and intensity matched pre-defined target values, a 200 ms recording was captured by a virtual instrument designed in LabVIEW. A detailed map of skin surface vibration amplitude during vocalization is presented and suitable locations for laryngeal vibration measurement are identified. Further more, detailed analysis of the time varying acceleration function at various measurement positions reveals a rich and complex source of information. Novel visualizations of these signals are presented.