The Importance of Reverberation for the Design of Neonatal Incubators

Abstract

Low frequency noises are predominant in neonatal intensive care units (NICUs). Some studies affirm that neonates can perceive noises from 113 Hz, and can therefore be affected by sound sources with high spectral content at low frequencies (e.g., incubator engine, air fan). Other studies suggest that reverberation amplifies noise within incubators. In this paper, the reverberation time (T, T30) within an incubator with standard dimensions was measured in one-third octave bands. To get reliable results, the T was measured in 15 positions at the neonate's ear height, in a room with low T values (to reduce the influence of the room in the results), using an impulsive sound method. Results show a heterogeneous T distribution at the neonate's ear height, with maximum average T differences between positions of 1.07 s. The highest average T of all microphone positions is 2.27 s at 125 Hz, an extremely high mean value for such a small space. As the frequency of electrical devices in America is 60 Hz, some harmonics lay within the one-third octave band of 125 Hz, and therefore may create a very reverberant and inappropriate acoustic environment within the audible spectrum of neonates. As the acoustic environment of the incubator and the room are coupled, it is expected that the results are higher in the NICUs than in the room where the measurements were conducted, as NICUs are more reverberant. Therefore, it is recommended that the T will be limited in the international standards, and that incubator designers take it into account.

The noise: a silent threat to the recovery of patients in Neonatal Intensive Care Units

“…Due to the sensitivity of these types of rooms, reverberation time (RT) has not been measured in any of the NICUs under study [49][50][51]. RT is a crucial parameter in assessing noise levels within any environment, significantly influenced by the volume of the space, as well as other factors such as geometry and construction materials [48].…”

“…The reverberation time (TR) in the room where the incubator is located can have a considerable impact, especially due to the limited acoustic isolation of the incubator dome [49][50][51]. This emphasizes the need to implement effective acoustic conditioning measures to minimize any adverse effects on neonates.…”

The Importance of Noise Attenuation Levels in Neonatal Incubators

“…The first one is that the power supply may emit noise when connected to the mains even when the incubator is turned off. It is also possible that the reverberation times are important at low frequencies [51,52], so it would be necessary to carry out another study that is far from the scope of the objectives of this one. In any case, these values are very low and can also be influenced by the minimum SPL that can be measured by the equipment; for values below 24 dB, the results are not reliable due to the electrical noise of the measurement equipment itself.…”

Pilot Clinical Trial on Supportive Rehabilitation Care in Neonatal Intensive Unit. Influence of Ambient Noise on Premature Infants

“…The NICU is often characterized by loud, unpredictable noise originating from alarms, respiratory therapy equipment, air conditioning, door closings, portable x-ray exams, staff conversation and infant fussiness, to which preterm infants are highly susceptible [2,3,4]. Furthermore, the interiors of incubators are quite reverberant spaces [5]. Ambient noise levels in the NICU, especially in areas of concentration of staff activity, can reach 59 dB(A), with peak noise levels exceeding 120 dB(A) [6].…”