Performance of noise indices in air-conditioned landscaped office buildings

Determination of preference-equivalent levels for fan noise and their prediction by indices based on specific loudness patterns

In a previous study by the authors, two indices were identified as appropriate descriptors for perceptual dimensions of fan noise. The index N_low describes the amount of low-frequency loudness relative to the overall loudness. The index N_ratio represents the ratio between the amount of loudness resulting from mid-frequency content and that from high frequencies. The aim of this study is to quantify how variations in these two indices affect subjects' preferences and loudness judgments. In listening experiments, fan noise signals were adjusted separately to equal loudness and equal preference compared to a common reference sound by varying their level in an adaptive procedure. The fan noises used in the listening tests consisted of 11 typical signals from three major groups of fan sounds from the earlier study and 18 signals that were parametrically varied in terms of the two indices. Reductions in A-weighted sound pressure level of up to 15 dB were necessary to make unpleasant fan sounds equally preferred as the fixed reference sound. A regression model based on the index N_ratio explains 81% of the variation in the evaluation data with a root-mean-squared error of 2.53 dB.

Impact of noise on self-rated job satisfaction and health in open-plan offices: a structural equation modelling approach

This study uses a structural equation model to examine the effects of noise on self-rated job satisfaction and health in open-plan offices. A total of 334 employees from six open-plan offices in China and Korea completed a questionnaire survey. The questionnaire included questions assessing noise disturbances and speech privacy, as well as job satisfaction and health. The results indicated that noise disturbance affected self-rated health. Contrary to popular expectation, the relationship between noise disturbance and job satisfaction was not significant. Rather, job satisfaction and satisfaction with the environment were negatively correlated with lack of speech privacy. Speech privacy was found to be affected by noise sensitivity, and longer noise exposure led to decreased job satisfaction. There was also evidence that speech privacy was a stronger predictor of satisfaction with environment and job satisfaction for participants with high noise sensitivity. In addition, fit models for employees from China and Korea showed slight differences.

PRACTITIONER SUMMARY

This study is motivated by strong evidence that noise is the key source of complaints in open-plan offices. Survey results indicate that self-rated job satisfaction of workers in open-plan offices was negatively affected by lack of speech privacy and duration of disturbing noise.

Relating traffic, construction, and ventilation noise to cognitive performances and subjective perceptions

The present study investigates the cognitive performance and subjective perceptions in the context of road traffic noise alone and multiple noises, including construction and ventilation noises. A total of 20 university students were exposed to seven noise conditions. Laboratory experiments employed semantic and episodic memory tasks. Self-reports of perception were collected from the participants. It was found that multiple noise sources impaired the free recall of words, and free recall scores were affected by noise type. Significant differences in free recall scores were found when the noise level difference between the individual noise and multiple noise sources was more than 5 dB. In contrast, word comprehension did not mediate the effects of noise on semantic memory. Annoyance caused by multiple noise sources correlated highly with the results of the free recall and word comprehension tasks. Moreover, loudness and roughness were found to account for the annoyance ratings of combinations of road traffic noise with construction or ventilation noises.

Interaural correlation and the binaural summation of loudness

The effect of interaural correlation (rho) on the loudness for noisebands was measured using a loudness-matching task in naive listeners. The task involved a sequence of loudness comparisons for which the intensity of one stimulus in a given comparison was varied using a one-up-one-down adaptive rule. The task provided an estimate of the level difference (in decibels) for which two stimulus conditions have equal loudness, giving measures of loudness difference in equivalent decibel units (dB(equiv)). Concurrent adaptive tracks measured loudness differences between rho=1, 0, and -1 and between these binaural stimuli and the monaural case for various noisebands. For all noisebands, monaural stimuli required approximately 6 dB higher levels than rho=1 for equal loudness. For most noisebands, rho=1 and rho=-1 were almost equal in loudness, with rho=-1 being slightly louder in the majority of measurements, while rho=0 was about 2 dB(equiv) louder than rho=1 or rho=-1. However, noisebands with significant high-frequency energy showed smaller differences: for 3745-4245 Hz, rho=0 was only about 0.85 dB(equiv) louder than rho=+/-1, and for 100-5000 Hz it was non-significantly louder (perhaps 0.7 dB(equiv)).

Implications of human performance and perception under tonal noise conditions on indoor noise criteria

This research investigated differences in task performance and perception under six non-time-varying ventilation-type background noise spectra with differing tonality. The results were related to five indoor noise criteria systems: noise criteria, balanced noise criteria, room criteria, room criteria mark II, and the A-weighted equivalent sound pressure level (L(Aeq)). These criteria systems are commonly used in the U.S. building industry, but concerns exist over whether they are appropriate for all noise situations. Thirty test subjects completed three types of performance tasks (typing, reasoning, and math) and answered questions about their perception of the indoor environment under each noise condition. Results showed that performance scores did not change significantly across the six noise conditions, but there were differences in subjective perception. For example, perception trends for tonality, annoyance, and distraction changed based on the frequency and prominence of discrete tones in noise. However, these perceptual changes were not fully reflected in the criteria level or spectral quality ratings. Additionally, task performance was related to subjective perception but not to criteria level predictions. As a result, the authors suggest that the current criteria should be modified to account for the frequency and prominence of tones in background noise.

No consistent risk factor pattern for symptoms related to the sick building syndrome: a prospective population based study

OBJECTIVES

To examine associations between perceived indoor environment at work and the non-specific symptoms that are often referred to as the sick building syndrome (SBS), using cross-sectional and prospective analyses for a large cohort from the general population.

METHODS

The sample comprised 2,164 adults in employment, who completed a postal questionnaire in April 2001. Of these 1,402, who were still working and living in the same place, completed a second questionnaire a year later. The outcome measures were the prevalence of mucous membrane symptoms and general symptoms at baseline and the incidence and persistence of these symptoms at follow-up. Self-reports of the indoor environment from the baseline questionnaire were used as predictors in the analyses.

RESULTS

Inconsistent results were found between the cross-sectional and the longitudinal analyses for the associations between perceived indoor environment factors at work and symptoms. Whereas mucous membrane symptoms in the cross-sectional analysis were significantly associated with self-reported high temperature and dry air, the prospective analyses showed that onset of mucous membrane symptoms was associated with the sensation of draught, dry air, and noise. Persistent mucous membrane symptoms were associated only with stuffy air. General symptoms were associated with self-reported stuffy air and dry air in the cross-sectional analysis, while draught was the only predictor of onset of general symptoms. We found no predictors in the indoor environment for the persistence of general symptoms.

CONCLUSIONS

The symptoms that are often connected with SBS are very common symptoms in the general population among manual workers as well as non-manual workers. Our study gives only limited support to the hypothesis of causal relationships between the indoor environment and these symptoms. We found no evidence of persistent mucous membrane symptoms and general symptoms related to specific factors in the indoor environment.