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Building services equipment often produce noise with prominent tones that can lead to complaints from occupants in the built environment. Previous studies have investigated human perception to tones in noise but it is still unclear at what threshold of prominence these tones lead to human annoyance. The goal of this research is to apply two different methods towards defining thresholds of annoyance to two tonal frequencies: 125 Hz and 500 Hz. In Method I – Direct Assessment with Task, subjects are exposed to 10 minutes of broadband noise with a tonal frequency set at a certain level of prominence while completing a task. They are subsequently asked to fill out a subjective questionnaire after exposure to each noise condition. Five prominence levels of each of the two tonal frequencies are tested above two different background noise levels (40 dBA and 55 dBA) for a total of 20 test trials. In Method II – Magnitude Adjustment, subjects are exposed to each of the two tonal frequencies set at a certain level above each of the two background noise levels and are then asked to adjust the level of the tone, up or down, until it becomes just annoying. The same two tonal frequencies (125 Hz and 500 Hz) and two background noise levels (40 dBA and 55 dBA) that were used in Method I are also used in Method II with one repetition for a total of eight trials.
The potential thresholds of annoyance that were found for both methods were right around thresholds of prominence (as defined by Prominence Ratio in ANSI S1.13-2005). Subjects rated annoyance higher for the louder background noise condition at same prominence levels for both of the tonal frequencies. Results as well as strength and weaknesses of both methods are compared.
Advisor: Lily M. Wang