Noisy journeys: An investigation of the sound environment in an incubator during ambulance transports

Each year, between 300 and 350 transports are carried out by the Neonatal Transport Team Göteborg in Västra Götaland Region (VGR). The majority of these transports (approximately 80 %) are conducted using road ambulances, and most patients are premature infants born before 37 weeks of gestation. The central nervous system of premature infants is not sufficiently developed, resulting in a reduced ability to self-regulate and selectively limit or inhibit incoming stimuli, thereby increasing their vulnerability to stress and its negative physiological effects. Noise is one of the main stress-inducing stimuli that premature infants are exposed to in the extrauterine environment. Unlike the acoustic environment of the womb, which is characterized by low-frequency background noise where the mother’s voice stands out distinctly, the extrauterine environment in neonatal intensive care units (NICU) or during transport is dominated by unpredictable and highly variable sounds with a broad frequency spectrum. Research has shown that high noise levels can cause serious health effects in premature infants and negatively impact their growth and healing processes. Results from noise measurements conducted during neonatal transports with VGR’s incubator transport ambulance indicate that the transported infants are frequently exposed to noise levels exceeding 70 dB(A), with peak levels surpassing 110 dB(C), which are far above the guidelines for perinatal care established by the American Academy of Pediatrics. This study examines the noise levels in VGR’s incubator transport ambulance as well as the infants’ heart rates during transport. The report also outlines the various guidelines and requirements for noise in environments where neonatal infants receive care and highlights the discrepancies between these standards. The aim of this study is to provide an overview and analysis of the auditory environment to which premature and sick neonatal infants are exposed during ambulance transports in incubator and to serve as a basis for future measures to protect infants from harmful noise during transport.

I försöket användes basilikaplantor som odlades med eller utan kammarmusik från Malmö symfoniorkester under tre veckor i ett kommersiellt växthus. Syftet var att se om just den här musiken påverkade basilika i dess tillväxt. De tillväxtparametrarna som mättes vid försökets början var planthöjd och plantvikt inklusive kruka med jord. Vid försökets avslut mättes plantvikt med kruka och jord, antal bladpar, förgreningar, höjd och vikt efter klippning vid jordytan. Störningar i försöksmiljön tros ha påverkat plantorna som odlades med musik eftersom krukorna vägde mindre efter tre veckor än vid start. Det påverkade även de andra uppmätta parametrarna. Resultatet var att plantorna som odlats utan musiken växte lika bra eller bättre än de plantor som växte till musik. Resultatet pekar på vikten av en kontrollerad miljö för att kunna dra slutsatser av försök.

In the experiment, basil plants were grown with or without chamber music from the Malmö Symphony Orchestra for three weeks in a commercial greenhouse. The purpose was to see if this specific music affected the basil’s growth. The growth parameters measured at the beginning of the experiment were plant height and plant weight, including the pot with soil. At the end of the experiment, the plant weight with pot and soil, number of leaf pairs, branches, height, and weight after cutting at the soil surface were measured. Disturbances in the experimental environment are believed to have affected the plants grown with music, as the pots weighed less after three weeks than at the start. This also affected the other measured parameters. The result was that the plants grown without this music grew as well or better than the plants grown with music. The result highlights the importance of a controlled environment to draw conclusions from experiments.

Low-frequency impact sound caused by upstairs neighbors walking on the floor is a key acoustic challenge regarding lightweight floors and a major source of disturbance particularly in wooden buildings. To investigate the effect of floor design on the perceived walking sound, a virtual design tool has been developed, which allows for auralising the impact sounds containing low frequencies down to 20 Hz. Using this tool, footstep sounds on 10 different lightweight floors were auralised by a loudspeaker grid mounted in the ceiling of an acoustically controlled lab, which is furnished as a common living room. The walking sounds were subjectively evaluated through listening tests while the subjects were sitting freely on a sofa without needing to use any extra listening equipment. The listening test results suggest that loudness, thumpiness and reverberation are correlated with the perceived annoyance. The results also indicate a correlation between annoyance and age as well as the individual experience of earlier exposure to noise. © 2023 First author et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 3.0 Unported License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Experience with wooden multi-storey houses have shown that impact sound insulation is one of most critical issues to ensure a good indoor environment. Even in cases where the impact sound insulation is fulfilled, people perceive the sound from e.g. walking neighbours as very disturbing. To investigate the subjective perception, a test facility is needed which allows for a coherent evaluation of different floor designs by listening test. The facility should ensure, that when comparing different floors, the same excitation by a walker and the same receiving room are involved. Only the floor design should be changed. As a consequence the spread in the data will only be due to the spread in the perception by subjects. In this paper a virtual design tool for low frequency impact sound insulation is presented, which consists of four parts; measured walking forces, floor models, an auralisation system which consists of a grid of loudspeakers simulating the vibration of the floor and a receiving room furnished as a common living room. In a pilot study a listening test is carried out for 13 different floors with different impact sound spectra at frequencies below 100 Hz. The results indicate that the judged annoyance strongly correlates with the judged loudness. However, there is a substantial spread observed in between the subjects participating in the listening tests. To understand this spread, a more extended study is needed with more participants and a classification of the subjects with respect to criteria such as noise sensitivity or age.

In recent years there has been a growing interest for building lightweight multistorey woodenresidential buildings in countries like Sweden with large and renewable forests. While positive aspectsof these buildings, such as sustainability, ease of construction and lightness, motivate building more inwood, poor acoustic performance is a risk which concerns the wooden-building industry.Low-frequency impact sound from walking of the neighbors upstairs is the main source of complaintsabout the acoustic performance of these buildings. The disturbance caused by walking sounds,transmitted through lightweight wooden floors, results in acoustic discomfort and impairs theperceived quality of the building; sometimes even when the building has fulfilled an acoustic classhigher than minimum requirement, according to the national standard on sound classification and itssingle number ratings. The standard methods for objective evaluation of impact sound insulation offloors cannot predict, at a satisfactory level, the walking sound annoyance that the inhabitants ofwooden buildings experience. This causes an uncertainty about the resulting perceived quality of thesebuildings, which greatly concerns the building manufacturers and demotivates them from choosinglightweight wooden elements over heavyweight building materials such as concrete. This uncertaintycan be overcome by evaluating the perceived acoustic quality of the building prior to its construction.

One solution is to build test houses where the subjective acoustic performance of floor samples can beevaluated in advance to the building construction. However, building a test house is expensive;besides, for evaluating the effect of every design modification on the experienced acoustic comfort ofthe building, a real floor sample has to be built and installed in the house, which would be timeconsumingand costly. An alternative solution is to use virtual acoustic test facilities.In this thesis a virtual design studio for impact sound is developed. It is a tool that facilitates creatingand listening to the acoustic field generated by impact forces such as footsteps on lightweight floors. Italso provides the possibility to evaluate the acoustic performance of floor elements in an early designphase, and to investigate the correlation between design parameters and the perceived impact soundinsulation of the floor. The tool is demonstrated and a very first listening test shows that one can obtainresults which are in good agreement with the results in literature. Loudness, reverberation andthumping are shown to influence the annoyance. It is also shown that there is a difference in judgementof walking sounds by persons who have experience with lightweight floors at home and by those whodo not have that experience.

Measurement and modeling of low frequency ground reaction forces (GRFs) from human walking have been the subjects of research in different fields from biomechanics to civil engineering and structural dynamics. Many of the existing models are developed based on experiments which alter natural walking by for example presence of force transducers, limitations in the speed and path of walking and replacing the real floor with a transducerfacilitated measurement rig. These alterations result in contact forces which do not represent real GRFs. In this study, a time-domain inverse measurement method based on LMS algorithm is used to measure low-frequency (<100 Hz) forces induced by human footsteps. The LMS-based force identification method is first validated for low-frequency excitations with less complexity in number of excitation positions and frequency content compared with the footsteps. The method is then applied to measure ground reaction forces created by human walking.

Despite many advantages of wooden buildings, low-frequency noise disturbance, mainly from human footsteps on timber floors, is a major hindrance for widespread application of wood in multi-storey buildings. In many cases the impact noise evaluations of the wooden floors according to ISO 140-7 and ISO 717-2 standards do not correspond to subjective experiences. This study aims to investigate the characteristics of footstep forces to support further studies related to discrepancies between standard evaluations and low-frequency noise disturbances in lightweight buildings. Transient footstep forces in vertical direction made by different walkers and different footwear on two floor structures were measured and compared. The vertical footstep forces were then compared with the impact forces made by a standard tapping machine. Analysis revealed that footstep forces contain large amplitudes at low frequencies (20 < f < 50) which are not included in the standard evaluation procedure. Therefore, by extending the frequency range of the standard measurements down to 20 Hz and designing an accurate adaptation term for evaluations, a better correlation between standard impact noise evaluations and acoustic performance of the lightweight buildings might be achieved.

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ISO plans to replace the current ISO 140-7 standard for the measurement of impact sound pressure level by a new standard, ISO 16283-2. Within the standardization work, we have examined the influence of the position of the tapping machine (TM) on top of a timber joist floor (built as the reference light weight floor 2 in ISO 10140 and the previous ISO 140-11). The question is whether it is sufficient to prescribe that the TM positions shall be randomly distributed over the floor area (as in ISO 140-7) or if they should be specified to hit the joists with one hammer (as in ISO 10140) or even hit the joists with all hammers. The room average sound pressure level was measured with 63 evenly distributed TM positions on the floor, either on top of a joist or on the web. The influence of the TM position relative the joists is rather stable at low frequencies (25-160 Hz). Having the TM at right angles to the joists and one hammer striking a joist, the average difference is 3 dB to when no joist is being hit. Comparing positions where all hammers hit the joists with positions in between the joists, the difference is typically 4-7 dB in the frequency range 25-160 Hz. The results indicate that the ISO 16283-2 could prescribe more precisely where the TM shall be positioned in order to reduce the random variations. One choice is then to follow ISO 10140-1, where the TM is placed at 45 degrees centered on the joists, such that one hammer strikes a joist.