Transmission loss of sound into incubators: implications for voice perception by infants

To assess the transmission of sound into incubators as a function of talker position (i.e., standing or sitting), incubator port position (i.e., opened or closed), and center frequency (i.e., 125 to 10,000 Hz in one-third octave steps). The second objective was to estimate the audibility of the human voice inside the incubator.

L(eq) measures of signal transmission loss and motor noise were obtained from two incubators.

In general, signal transmission loss was greater for the standing-talker position, with front portholes closed, and for high-frequency spectra. Motor noise was greater with both front portholes closed and for lower-frequency spectra. The greatest signal delivery to an infant would be obtained when the speaker is sitting using a raised vocal effort while the incubator ports are opened.

Measured signal transmission loss and motor noise characteristics of two incubators suggest that only mid-frequency speech spectra would be audible to infants and only at a speech-to-noise ratio of approximately 5 to 10 dB with a raised vocal effort.