Despite the physiological complexity involved in the perception of vibration (see section 2.2.1), psychophysical laboratory investigations have gone some way towards characterising this phenomenon. From the laboratory studies detailed in section 2.2, it is evident that the perception of whole body vibration is dependent on frequency, magnitude, and duration. The results of some of these laboratory studies have informed the development of single figure descriptors and frequency weightings for the assessment of vibration exposure with regards to human response some of which have been adopted by national and international standards. There is however a lack of laboratory investigations into the perception of vibration from “real world” sources.
A review of national and international standards reveals three basic groups of vibration exposure descriptors recommended to describe human response: root-mean-squared energy equivalent values, maximum running root-mean-squared values, and the fourth power Vibration Dose Value. The use of the Vibration Dose Value as a vibration exposure descriptor is a contentious issue due to the relative complexity of its calculation and non- intuitive units (m/s1.75). Although the use of the Vibration Dose Value is supported by
laboratory findings, there is no field evidence supporting its applicability. There is a general agreement between standards regarding the use of frequency weightings although some differ in the use of acceleration or velocity. However as the Wband Wkweightings, which are to be applied to acceleration signals, drop off at around 6 dB/octave above around 10 Hz, above this frequency these weightings approximate velocity. As with the single figure descriptors, the applicability of these frequency weightings under field conditions is unknown. Studies by Kaneko et al. (2005), Morioka and Griffin (2006b), Bellmann (2002),
frequency weightings recommended in current standards with increasing magnitude of vibration exposure. However, at the magnitudes of vibration expected in residential environments from environmental sources, laboratory evidence supports the use of the standard frequency weightings.
Recent studies into the community response to noise have advocated the use of an equivalent level noise exposure raised to the 0.3 power to approximate the psychophysical relation between the magnitude of sound pressure and subjective loudness (Fidell et al., 2011; Schomer et al., 2012). As discussed in section 2.2.2, laboratory studies have suggested that the growth constant for the subjective magnitude of vibration exposure fluctuates around unity. If this assumption were to be followed for modelling the community response to vibration, a growth function of unity suggests the use of a linear psychometric function.
In both socio-acoustic and socio-vibrational studies the relatively small amount of variance explained by the resulting exposure-response relationships has been acknowledged. It is often hypothesised that the predictive power of these exposure-response relationships can be improved through the investigation of non-acoustical factors (see, for example, Marquis-Favre and Premat, 2005; Marquis-Favre, 2005) and improvements in the metrics used to quantify exposure to the stimulus of interest (see, for example, Dittrich and Oberfeld, 2009; Kryter, 2007). In 1974, the Environmental Protection Agency (EPA) in the USA (Abatement and Control, 1974) proposed the use of a “normalised” noise exposure metric (termed Normalised DNL) which aimed to reduce the scatter in exposure-response relationships for noise annoyance. This normalised metric is calculated from a table of adjustment factors which impose penalties or bonuses expressed in decibels for non- acoustical factors and characteristics of the noise exposure. These factors include seasonal
corrections, corrections for previous noise exposure, and corrections for noise exposures with impulsive or tonal characteristics. The use of the normalised DNL resulted in a reduction in the scatter around the exposure-response relationship. Schomer (2002) proposed an update to the EPA’s adjustment factors which included not only non- acoustical factors but also additional factors relating to the quality of the noise such as rattle, tonal components, and different levels of impulsiveness. The improvement of the exposure-response relationship with the use of these adjustment factors raises the question of whether the variation in individual annoyance at the same noise exposure level is due to the inadequacy of a single figure energy equivalent noise metric to quantify objective features of noise exposure which are salient to human perception (i.e. temporal features, changes in frequency content).
Although laboratory studies have developed improved metrics for the prediction of annoyance due to environmental sources (see, for example, Alayrac et al., 2010; Fastl et al., 2003; Nilsson, 2007), they are difficult to validate and hence difficult to justify the use of. Data available from previous field studies into the community response to noise are generally only in terms a single figure descriptor of the noise exposure. As time history data is generally not retained in these studies it is impossible to validate new metrics.
Compared to the human response to environmental noise, there is a relative lack of field data relating to the human response to vibration in residential environments. The use of different vibration exposure descriptors in the field studies reported in the literature makes comparison of the results between these studies problematic. As the human response to vibration in residential environments emerges as a field of research, the shortcomings of research into the human response to noise in residential environments should be borne in
exposure in field studies into the community response to vibration means there is not enough variance in the data to investigate new descriptors. If the applicability of vibration exposure metrics are to be assessed via socio-vibrational surveys, it is vital that measurements of vibration exposure are conducted in as many properties as practicable and that time histories of these measurements are retained.