Investigations of indoor noise criteria systems based on human perception and task performance

Several noise criteria methods commonly used in architectural acoustics have been quantitatively related to human noise perception and task performance under a variety of heating, ventilating, and air-conditioning (HVAC) systems-induced background noise conditions. The five criteria examined were: Noise Criteria (NC), Balanced Noise Criteria (NCB), Room Criteria (RC), Room Criteria Mark II (RC Mark II), and A-weighted Equivalent Sound Pressure Level (LAeq ). The project was completed over three phases. Phase I included twelve background noise conditions controlled to be non-varying over time and non-tonal, while exhibiting neutral, rumbly, roaring, or hissy characteristics. Phase II was conducted as an intermediate study to examine specifically the effects of exposure time length and types of performance tasks used. Phase III investigated the effects of background noise exposures containing various levels of discrete tones across a frequency range from 120 to 595 Hz. Under each noise condition, subjects completed performance tasks and answered questions about their perception of the acoustic environment. Results show that task performance is significantly affected by occupant perception of noise, but this relationship is not fully demonstrated by the criteria systems analyzed. It was also found that the five criteria analyzed are generally well suited in describing subjective loudness perception, but that some discrepancies in criteria ratings of spectral quality and subjective perception exist. Finally, perception of annoyance and tonality changed based on the frequency and prominence of discrete tones in noise, but these changes were not reflected in the criteria level or spectral quality ratings. Based on the findings of this work, modifications to the existing criteria are recommended