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adjustments to their methodologies may improve the results. For example, part of the reason for the RC Mark II results may be due to the fact that this criterion currently only allows for a rumble, roar, or hiss characterization of any one noise condition, and not for a combination. That is, you may obtain an RC Mark II “40-Roaring” rating, or an RC Mark II “40- Rumbly” rating, but not an RC Mark II “40-Roaring-and- Rumbly” one. We are currently working with a subcommittee of ASHRAE’s Technical Committee 2.6 on Sound and Vibration regarding possible adjustments to the RC Mark II method.
Now we will turn our attention to the connections between criteria and the performance test results. So far, we have found no significant relationships between the indoor noise criteria predictions of level and task perform- ance results. What exactly does this tell us? It might indi- cate that these five criteria simply do not relate to task per- formance. This may not be entirely surprising, as the crite- ria were developed based on perception surveys, not on productivity.
We have also investigated how performance changes when participants perceive the noise to be different, regardless of what the criteria indicate. To examine this, we have compared performance test results to perception questionnaire results. We consistently find that perform- ance significantly decreases as participants perceive the noise to be louder or more spectrally imbalanced (p<0.01); this is demonstrated in Fig. 4 which shows subjective rat- ing of hiss versus typing speed. Our on-going work involves running more subjective tests and analyzing the growing data bank to determine how specific relationships depend on the characteristics of the noise conditions. We already see that negative perception of background noise can significantly decrease productivity, but it would be interesting to know which perceived traits (rumbly? roar- ing? hissy? tonal? time-fluctuating?) may impact perform- ance more than others.
Summary
Our overall goal is to determine how closely widely-used indoor criteria systems relate to task performance and psy- choacoustic perception of HVAC sound. We are finding that perception of background noise can significantly impact pro- ductivity, but that these performance effects are not fully rep- resented by NC, NCB, RC, RC Mark II, or LAeq. Additionally, our results show that indoor noise criteria predictions of spectral imbalance, such as excessive rumble, roar, or hiss, may not always agree with subjective perception. We contin- ue to investigate how these criteria and our own testing methodology may be altered to produce clearer results, and we hope to expand our analyses to include a number of more recently proposed indoor noise criteria measures in the near future.AT
Acknowledgments
This work has been supported by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (ASHRAE), the Institute of Noise Control Engineering (INCE), and the University of Nebraska–Lincoln Center for Building Integration. Many thanks to Marc Choiniere and Jessica Errett for their assistance in administering the subjective tests, and to Warren Blazier, Norman Broner, Mark Fly, Jerry Lilly, and Mark Schaffer for their recording contributions.
References and Further Reading
1. L. Beranek, “Revised criteria for noise in buildings,” Noise Control 3, 19-27 (1957).
2. L.Beranek,“BalancedNoise-Criterion(NCB)curves,”J.Acoust. Soc. Am. 86(2), 650-664 (1989).
3. W.Blazier,“Revisednoisecriteriaforapplicationintheacousti- cal design and rating of HVAC Systems,” Noise Control Eng. J. 16(2), 64-73 (1981).
4. W.Blazier,“RCMarkII:Arefinedprocedureforratingthenoise of heating, ventilating, and air-conditioning (HVAC) systems in buildings,” Noise Control Eng. J. 45(6), 243-250 (1997).
5. International Organization for Standardization, ISO Standard 226:1987(E): Acoustics – Normal Equal-Loudness Level Contours (ISO, Switzerland, 1987).
6. L.Goodfriend,ASHRAERP-126FinalReport:AStudytoUpdate Indoor Sound Criteria for Air Conditioning Systems (American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA, 1975).
7. G.Tocci,“Roomnoisecriteria–Stateoftheartintheyear2000,” Noise/News Int. 8(3), 106-119 (2000).
8. L.M. Wang and E.E. Bowden, “Performance review of indoor noise criteria,” Proceedings of Building Integration Solutions - AEI Conference, Austin, TX (Architectural Engineering Institute, Reston, VA, 2003).
9. American National Standards Institute, ANSI Standard 12.2- 1995: Criteria for Evaluating Room Noise (Acoustical Society of America, Melville, New York, 1995).
Fig. 4. Typing performance decreases as the subjects perceive there to be more hiss in the noise condition. The typing speeds in characters per second are averaged data compiled from 30 test subjects and displayed with standard error bars. Similar relationships with performance were found when subjects had negative perceptions of the noise in terms of loudness, annoyance and the other spectral qualities.
36 Acoustics Today, January 2006