Incubator-based active noise control device: comparison to ear covers and noise reduction zone quantification

Abstract

Background: Noise exposure in the neonatal intensive care unit (NICU) is consistently higher than current recommendations. This may adversely affect neonatal sleep, weight gain, and overall health. We sought to evaluate the effect of a novel active noise control (ANC) system.

Methods: An ANC device's noise reduction performance was compared to that of adhesively affixed foam ear covers in response to alarm and voice sounds in a simulated NICU environment. The zone of noise reduction of the ANC device was quantified with the same set of alarm and voice sounds.

Results: The ANC device provided greater noise reduction than the ear covers in seven of the eight sound sequences tested in which a noise reduction greater than the just noticeable difference was achieved. For noise in the 500 Hz octave band, the ANC device exhibited consistent noise reduction throughout expected patient positions. It provided better performance for noise below 1000 Hz than above 1000 Hz.

Conclusions: The ANC device provided generally superior noise reduction to the ear covers and provided a zone of noise reduction throughout the range where an infant would be placed within an incubator. Implications for patient sleep and weight gain are discussed.

Impact: Active noise control device can effectively reduce noise inside an infant incubator due to bedside device alarms. This is the first analysis of an incubator-based active noise control device and comparison to adhesively affixed silicone ear covers. A non-contact noise reduction device may be an appropriate means of reducing noise exposure of the hospitalized preterm infant.

Fig. 1. Elements of the ANC device placed inside the incubator.

The ANC device includes two speakers and a residual noise sensor placed within the incubator.

Fig. 2. Ear covers adhered to manikin with hair extensions.

Test conditions included ear covers adhered to the manikin over the auricles and adhered to the manikin over hair extensions that simulate the hair present in many infants.

Fig. 3. Position of the manikin in the incubator.

An outline of the manikin is shown for positions 1 through 6 with a faint image of the manikin shown at positions 1 and 6. Right and left ear positions are indicated by triangles as indicated. The position of the incubator’s imaging sensor tray under the mattress frame is indicated by the light blue rectangle. All dimensions are in cm.

Fig. 4. Effects of the three noise reduction methods on the octave band power spectrum for a high-priority patient monitor alarm.

The octave bands for all octave bands from 125 to 8000 Hz are shown for the control condition (no noise reduction device) and each of the three noise reduction methods: ANC device, ear cover with no hair, and ear cover over hair.

Fig. 5. ANC device noise reduction at each location for each octave.

The average noise reduction for the primary tonal signals of all sound sequences is shown for locations 1–6. For display in this figure, the tonal signals were grouped in octave band (500, 1000 or 2000 Hz) that includes the frequency of each tone. The order of locations 1–6 is arranged from closest to furthest from the residual noise sensor of the ANC device.

Fig. 6. ANC device noise reduction at each location for 1000 Hz octave band.

The bar graph shows the average noise reduction for all primary tonal frequencies falling within the 1000 Hz octave band, separating frequencies above and below 1000 Hz. The order of locations 1–6 is arranged from closest to furthest from the residual noise sensor of the ANC device. The combined responses in the entire 1000 Hz band are shown in the middle, the responses to the tonal signals below 1000 Hz are shown on the left, and the responses to the tonal signals above 1000 Hz are shown on the right.