1、2010 ASHRAE 541This paper is based on findings resulting from ASHRAE Research Project RP-1322.ABSTRACT This study investigated the effects of noise from building mechanical systems with tonal components on human task performance and perception. Six different noise conditions based on in-situ measure
2、ments were reproduced in an office-like setting; all were set to approximately the same sound level (47 dBA) but could have one particular tonal frequency (120 Hz, 235 Hz, or 595 Hz) at one of two tonal prominence ratios (5 or 9). Thirty participants were asked to complete typing, grammatical reason
3、ing, and math tasks plus subjective ques-tionnaires, while being exposed for approximately 1 hour to each noise condition. Results show that the noise conditions that had tonal prominence ratios of 9 were generally perceived to be more annoying than those of 5, although statistically significant dif
4、ferences in task performance were not found. Other findings are (1) that higher annoyance/distraction responses were significantly correlated with reduced typing task performance; (2) that the noise characteristics most closely correlated to higher annoyance/distraction responses in this study were
5、higher ratings of loudness followed by roar, rumble, and tones; and (3) that perception of more low frequency rumble in particular was significantly linked to reduced performance on both the routine and cognitively demanding tasks.INTRODUCTIONModern mechanical systems in buildings for heating, venti
6、lation and air-conditioning can produce noise with perceptible tonal components, often due to rotating parts, such as fans, motors, impellers, etc. The tonal aspects of the back-ground noise may then result in increased occupant discomfort and reduced worker performance, but these effects have not b
7、een systematically investigated across a range of controlled conditions that represents what can be found in existing spaces. Additionally, methods of rating the acceptability of indoor noise characteristics, such as Noise Criteria (NC), Room Criteria (RC), and others listed in the ASHRAE Appli-cati
8、ons Handbook (2007) do not clearly account for tonal noise components or necessarily reflect their effects on human performance and perception. The goal of this research study has been to determine how a variety of building mechanical system noise conditions with varying degrees of tonal compo-nents
9、 affect human performance and perception in a typical office setting. The performance and perception results have been subsequently correlated with a number of indoor noise criteria ratings to evaluate the limitations of current criteria methods and suggest improvements, if applicable.Many researche
10、rs have investigated effects of noise on human perception and performance; a number of early studies focused on the consequences of very high noise levels (e.g. greater than 70 dBA) (Kryter 1985, Jones and Broadbent 1998). Begin-ning in the 1950s, much work focused on defining acceptable noise condi
11、tions found more commonly in office buildings (Beranek 1956, Keighley 1966, 1970, Hay and Kemp 1972, Blazier 1981, Beranek 1989, Blazier 1997). This resulted in the development of a number of indoor noise criteria, including Noise Criteria (NC), Balanced Noise Criteria (NCB), Room Criteria (RC), Roo
12、m Criteria Mark II (RC-Mark II), which are described in Ch. 47 of the ASHRAE Applications Handbook (2007). More recently, Tang and colleagues have surveyed occupants in built offices (Tang et al. 1996, Tang 1997, Tang and Wong 1998) and in The Effects of Noise from Building Mechanical Systems with T
13、onal Components on Human Performance and Perception Erica E. Ryherd, PhD Lily M. Wang, PhD, PEMember ASHRAE Member ASHRAEErice E. Ryherd is an assistant professor in the Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA. Lily M. Wang is an associate professor in
14、 the Durham School of Architectural Engineering and Construction, University of NebraskaLincoln, Lincoln, NE.AB-10-018 (RP-1322)2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For perso
15、nal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.542 ASHRAE Transactionsresidential apartments (Tang and Wong 2004), and statistically correlated participant responses to the measured noise
16、conditions as quantified by a variety of noise criteria and indices. Ayr and colleagues have also conducted such occupant surveys in offices (Ayr et al. 2001, Ayr et al. 2003). Both of these groups have concluded that among the indices tested, the A-weighted equiva-lent sound pressure level (LAeq) c
17、onsistently correlates most strongly with subjective responses of loudness, annoyance and dissatisfaction. In addition to sound level, though, spectral qualities of the noise are considered important. As found by Persson and colleagues in lab studies (1985, 1988), noise conditions with more low freq
18、uency content resulted in greater annoyance than those with higher frequency content with the same LAeq. Results from a subsequent investigation in the field also suggested that the dominance of low-frequency content in residential noise conditions was better related to long-term annoyance perceptio
19、n than LAeq(Persson Waye and Rylander 2001). The loudness level of the signal is an important link to annoyance, but when comparing signals of equal loudness or perhaps over long-term exposures, spectral qualities such as rumble become more significant. Some of the indoor noise criteria listed above
20、, including NCB, RC, and RC Mark II, include such spectral quality descriptors (e.g. “R” for rumble or excessive low frequency content, and “H” for hiss or exces-sive high frequency content). A number of investigations have specifically focused on the effects of noise with excessive low frequency co
21、ntent on task performance, as reviewed by Leventhall et al. (2003). Some of these have utilized ventilation-type spectra while testing differ-ent tasks, such as vision tasks (Kyriakides and Leventhall 1977), figure identification tasks (Landstrm et al. 1991), proofreading tasks (Holmberg et al. 1993
22、), and other cognitively demanding tasks like grammatical proofreading and verbal reasoning (Pers-son Waye et al. 1997, 2001). There is evidence that background noise with rumble can affect task performance negatively in certain cases, but these previous studies often compared only two or three nois
23、e conditions at a time, making it difficult to make broader quantitative recommendations.The topic of noise with tones, particularly in terms of how the addition of tones impacts perception of loudness or annoy-ance, has also generated much interest over the years, as aircraft, industrial machinery,
24、 and other office equipment can generate such spectra (Kryter and Pearsons 1965, Hellman 1982, 1984). A number of methods for quantifying the prominence of the tone in the noise or its tonalness have been developed, includ-ing Tone-to-Noise Ratio (ANSI S1.13-2005), Prominence Ratio (ANSI S1.13-2005)
25、, and Aures Tonalness metric (1985). In Annex C of ISO Standard 1996-2 (2007), Tone-to-Noise Ratios are further linked to decibel adjustments that can be applied to measured A-weighted equivalent sound pressure levels for use in environmental noise assessment. Of particular note is a round robin tes
26、t conducted to compare the two metrics discussed in ANSI S1.13, Tone-to-Noise Ratio and Prominence Ratio (Balant et al. 1999, Hellweg et al. 2002). They found that for broadband noise with a single prominent tone, the two metrics correlate well with each other and also with the degree of tonalness p
27、erception, but further issues need to be clarified regarding more complex tones (e.g. multiple tones in the same critical band, harmonic series of tones, or time-varying tones). Some work has been directed towards dealing with these more complex cases (Hellman 1985; Hastings et al. 2003, Lee et al.
28、2004, 2005). Ventilation-like noise spectra that specifically include tones have been utilized in a few investigations involving perception or performance. Landstrm et al. used two noise signals with tones at 100 Hz, one of which was additionally masked by other low frequency pink noise; they found
29、that performance on figure identification tasks was significantly lower when participants were exposed to the unmasked tone as compared to the masked tone (1991). One of Holmberg et al.s five noise signals had a superimposed tone at 43 Hz, but in this study no statistically significant differences w
30、ere found in the proofreading task performance across the signals (1993). To study acceptable levels of tones while performing tasks, Land-strm et al. asked test subjects to adjust the levels of a 100 Hz tone, a 1000 Hz tone, or broadband noise centered around one of these two frequencies to accepta
31、ble levels while working on various tasks, and found that much lower levels of the high frequency tone were tolerable (1993). In a subsequent inves-tigation, Landstrm et al. asked subjects to adjust the frequency of a tone in ventilation noise between 35 Hz to 500 Hz until it was considered to be th
32、e least or most annoying. Results showed that participants found 58 Hz to be least annoying and 380 Hz to be most annoying (1994). What differentiates the work reported herein from previ-ous research is that a wider range of realistic tonal spectra from building mechanical systems are tested systema
33、tically, includ-ing three different tonal frequencies and two different tonal prominence ratios. Specifically, the effects of that tonal noise on human task performance using three types of tasks (typing, grammatical reasoning and math tests) and perception in a typical office setting are quantified
34、. These results may then be related to commonly used indoor noise criteria, suggested within the ASHRAE Applications Handbook, in an effort to improve those methods. METHODOLOGYThe protocol described in this section for this phase of research is similar to one used for a subsequent phase of test-ing
35、, presented in an accompanying paper (Wang and Novak 2010). As the authors believe that readers may not necessarily access both papers, some of the same methodology is discussed in both manuscripts.Thirty test subjects (15 males and 15 females) from the University of Nebraska community were recruite
36、d to partici-pate in this study, ranging in age from 19 to 44 with a mean of 25 years. All participants first underwent a series of pre-test screens to gauge the subjects vision, hearing, and typing skills. The minimum requirements to participate in the study 2010, American Society of Heating, Refri
37、gerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions (2010, Vol. 116, Part 2). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.2010 ASHR
38、AE 543were as follows: normal vision as verified by a Keystone Opthalmic Telebinocular, hearing thresholds below 25 dB hearing level in octave bands from 125 Hz to 8 kHz, and a minimum typing speed of 20 wpm.Testing was conducted in a 906 ft (25.7 m) indoor envi-ronmental test chamber at the Univers
39、ity of Nebraska, outfit-ted as a typical office with two desks, carpet, gypsum board walls, and acoustical ceiling tile. The test chambers envelope has a high sound transmission class of STC 47, and its interior acoustic condition demonstrates low background noise level of RC 26(H) (or an equivalent
40、 A-weighted sound level of 35 dBA) and a low reverberation time of 0.25 sec at 500 Hz. During all tests, the test chamber was thermally controlled to maintain a temperature of 68F (20C). Overhead fluorescent lighting provided an constant average illuminance of 71 foot-candles (764 lux) at the work p
41、lane. The sound in the test chamber was the only environmental characteristic that changed between test sessions, with the signals being presented in an inconspicuous manner over two loudspeakers: (i) an Armstrong i-ceiling loudspeaker which has the same appearance as the other ceiling tiles in the
42、room, and (ii) a JBL Northridge E250P subwoofer, disguised to resemble an endta-ble in the corner of the room. The test administrator and vari-ous equipment (e.g. the hard drive to the test computers and other audio gear) were located in a control room, adjacent to the chamber. Each subject was expo
43、sed to the same six noise condi-tions, each for a period of 55 minutes at a time. This length of exposure time was selected due to the results from a previous phase of the ASHRAE 1322-RP project (Ryherd and Wang 2007). Participants were asked to come for their six listening sessions at approximately
44、 the same timeslot on different days. For each session, the test subjects spent the first 25 minutes adapting to the noise condition and completing a test on paper, developed from material taken from the verbal portion of the Graduate Record Examination (GRE). Unbeknownst to the subject, this materi
45、al was not to be marked but was simply to keep the subject mentally alert during the adaptation period. The next 15 minutes consisted first of three skill tests, administered on a computer using SkillCheck software: typing, grammatical reasoning, and math. The typing test was allotted five minutes,
46、and involved typing a passage from a piece of paper with the mouse disabled. The reasoning task was allotted two minutes, and included 20 questions in which subjects indicated whether a statement regarding a presented sequence of letters was true or false. The math test was allotted seven minutes, a
47、nd included 11 problems involving the four basic functions with integers, fractions, and decimals, presented either mathematically or as a word problem. Partic-ipants were provided with pencil and paper but no calculator. Results for the typing test were output as an adjusted typing speed, accountin
48、g not only for the subjects typing speed but also the number of errors made. Results for the reasoning and math tasks were output as a percent correct, with questions that were not answered within the time limit considered incorrect. Further details on the development of the test material may be fou
49、nd in Ryherd and Wang (2007). The skill tests were followed by a subjective question-naire that asked the participant to rate his/her perception on discrete seven-point scales of various indoor environmental qualities of the space, where 1 generally represented a low rating and 7 represented a high rating. Eight questions focused on perceptions related to the acoustic condition: loudness, rumble, roar, hiss, tones, changes over time, annoyance, and distraction. The remaining five focused on other conditions of the working environment, including lighting, thermal comfort a
