Indoor Noise Criteria Research Articles

Predicting tonal noise problems in HVAC systems

Current indoor noise criteria for occupied spaces in buildings can be found in Table 1 of the 2019 ASHRAE Applications Handbook. Table 1 of this handbook provides design guidelines for recommended NC, RC, dBA, and dBC ratings for a wide variety of interior spaces, but there is nothing in the table or the table notes that mentions the issue of audible tones in the background noise spectrum. There is a comment in the handbook text that essentially states that ideally, there should be no audible tones such as hum or whine. However, no guidance is provided as to how to predict or even measure (after the fact) if an audible tone is present. This presentation provides some guidance as to how a person might go about predicting the presence of an audible tone in the background noise of the HVAC system, including an example of a fully installed system.

Sound insulation design by using noise maps

The EU Directive 49 urges countries to prepare the strategic noise maps and the action plans for the agglomerations along major transportation routes and major industrial premises. Environmental engineers, town planners and architects are involved in preparation of action plans in which sound insulation of buildings are to be considered. This article describes a model to determine the required insulation performances for buildings’ external elements by using strategic noise maps. The model employs certain categorization for buildings in relation to indoor noise criteria and for insulation values to be assigned on building facades. A calculation procedure is integrated with the outputs of a noise mapping software to obtain the required noise reduction indexes in terms of both spectral values and the single-number ratings, i.e. “weighted- standardized level differences”. Calculated results are displayed graphically to be able to observe variation of insulation requirement throughout the surface exposed to noise source. Insulation map as a visual tool can facilitate building noise control and can be utilized in preparation of building specifications prior to construction phase and in developing the insulation codes by local administrations. Implementation of the model for two sample buildings located at different environments are explained in the article.

Proposed components of an “ideal” indoor noise criteria rating system.

A number of studies have been conducted at the University of Nebraska on correlating human performance and perception to indoor noise criteria systems. Task performance and subjective perception data were gathered from subjects exposed to background noise conditions commonly due to mechanical systems, including some with tonal components and some with time‐varying fluctuations. Results show that perceptions of annoyance and distraction are highly correlated to the character of the noise, but the current indoor noise criteria systems (such as noise criteria and room criteria) do not accurately reflect that relationship. This paper presents a proposal for what an indoor noise criteria rating system should ideally include, to quantify acceptable building mechanical system noise in commercial buildings. [Work supported by the American Society of Heating, Refrigeration and Air‐Conditioning Engineers.]

Using indoor room criteria when the “room” is outside.

Indoor noise criteria have applicability in the analysis of outdoor performance spaces. The presentation will provide an overview of the environmental noise issues at the Jay Pritzker Pavilion in Chicago, IL. The project design was largely influenced by noise concerns, in its physical form, audio design strategy, and building systems design. During the postconstruction tuning of the audio system a number of parameters were adjusted to contend with the unusually low signal‐to‐noise ratio, including the overall loudness of amplified music, audio signal compression, the content and level of the acoustic enhancement system, and the approach to the active in‐house mix of the audio system. An investigation was also undertaken to investigate the continuous and impulsive noise levels and frequency content at various times of day as compared with traditional environmental noise criteria and indoor room criteria. Subsequent studies regarding the impact of nearby construction noise on rehearsals and performances were influenced by the use of indoor noise criteria methods.

Correlation of subjective and objective measures of spectral quality.

Common indoor noise criteria with spectral quality indicators have been compared to task performance and subjective noise perception. The analysis seeks to identify a relationship between criteria spectral quality ratings and human perception of common heating, ventilating, and air conditioning background noises. The three criteria evaluated include Balanced Noise Criteria, Room Criteria, and Room Criteria Mark II, due to their inclusion of rumble, hiss, or roar classifications. Study participants worked on typing, math, and verbal tasks while being exposed to various background noise signals, and then completed a questionnaire to describe their perception of the room acoustics. During the data analysis, background noise signals with a non‐neutral spectral quality rating were weighted according to their respective spectral indicator, with greater weighting given to lower‐frequency signals. Results demonstrate relationships between spectral quality designation and subjective perception of noise fluctuation and tonality. However, a relationship was not found between spectral quality designation and subjective perception of the same parameters (rumble, hiss, or roar). These findings warrant further investigation of the correlation between common criteria ratings and subjective perception. [Work supported by the Univ. of Nebraska Undergraduate Creative Activities and Research Experience Grant.]

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.

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 noise perception and task performance under a variety of ventilation systems-induced background noise conditions. Noise criteria, balanced noise criteria, room criteria, room criteria mark II, and A-weighted equivalent sound pressure level were examined. The first phase of the project included noise conditions controlled to be non-time-varying and nontonal, with neutral, rumbly, roaring, or hissy characteristics. An intermediate study examined exposure time length and types of performance tasks used. The final phase included noise conditions containing various levels of discrete tones from 120 to 595 Hz. Under each noise, subjects completed performance tasks and perception questionnaires. Results indicate task performance was significantly affected by perception of noise, but this relationship was not fully demonstrated by the criteria systems analyzed. The five criteria were generally well suited in describing subjective loudness perception, but some discrepancies in criteria spectral quality ratings and subjective perception existed. Finally, perception of annoyance changed based on the frequency and prominence of tones in noise, but these changes were not reflected in the criteria level or spectral quality ratings. Modifications to the existing criteria are recommended.

Finding Connections Among Indoor Noise Criteria, Human Perception, and Worker Performance

Finding Connections Among Indoor Noise Criteria, Human Perception, and Worker Performance

When octave bands are not enough: Case histories of indoor room noise

All of the published indoor noise criteria evaluation methods are defined on the basis of either the octave band or the overall A‐ or C‐weighted sound pressure levels. While this may be sufficient for some acoustic environments, there are many situations where these sound level descriptors are totally inadequate. This paper uses case histories to show that 1/3‐octave and narrow‐band analysis is sometimes required to properly assess the acoustic environment. To take it one step further, a recommendation is made to avoid the use of octave bands altogether and to routinely use 1/3‐octave band analysis for acoustical measurements and analysis relating to indoor noise criteria.

Evaluations of indoor noise criteria systems based on human response

The goal of this research is to examine human response to background noise, and relate results to indoor noise criteria. In previous work by the authors, subjects completed perception surveys, typing tasks, and proofreading tasks under typical heating, ventilating, and air‐conditioning (HVAC) noise conditions. Results were correlated with commonly used indoor noise criteria systems including noise criteria (NC), room criteria (RC) and others. The findings suggested that the types of tasks used and the length of exposure can impact the results. To examine these two issues, the authors conducted a new study in which each test subject completed 38 total hours of testing over multiple days. Subjects were exposed to several background noise exposures over 20, 40, 80, and 240 minute trials. During the trials, subjects completed a variety of performance tasks and answered questions about their perception of the noise, the thermal environment, and various other factors. Findings from this study were used to determine optimum testing conditions for on‐going research examining the effects of tonal or fluctuating background noise on performance, annoyance, and spectral perception. Results are being used to evaluate the effectiveness of commonly used indoor noise criteria systems. [Work supported by INCE and ASHRAE.]

Relating human productivity and annoyance to indoor noise criteria systems

The goal of this research is to determine a noise criteria system which best relates the effects of background noise to human productivity and annoyance. A number of indoor noise criteria systems are currently used to rate the background noise in built environments, including noise criteria (NC), balanced noise criteria (NCB), room criteria (RC), room criteria Mark II (RC-Mark II), and others. Many questions still remain about the accuracy of these predictors in assessing human response to background noise under the variety of ambient noise situations encountered. To support the use of any individual criterion, subjective testing was performed under a range of background noise situations and statistically related to the various noise criteria predictors listed above. Subjects completed an annoyance survey and performed typing and proofreading tasks in an acoustically controlled environment under 12 simulated background noise settings. These settings varied across three sound levels and four spectral qualities. Subjective testing methodology and results are presented. [Work supported by INCE and ASHRAE.]

Rating criteria for facade insulation against transportation noise sources

Designers need sufficient knowledge about insulation characteristics for buildings to be constructed in areas subjected to transportation noises. Existing standards for facades do not seem to be satisfactory in taking into account the type of source, and, at present, there is no international standard for this purpose. In this paper, the effective factors in proposing insulation standard for facades are analysed and the previous literature regarding insulation studies and insulation criteria are briefly reviewed. A set of rating curves which can be implemented in various situations are introduced in order to determine the minimum required noise reduction for facades exposed to three types of transportation noises, such as road, railway and aircraft noises. The input data are simply the most available factors in design: (1) type of source, (2) noise level at the facade in L eq , dB(A), (3) function of rooms behind the facade. The charts have been prepared by using typical source spectra measured in the field and the indoor noise criteria proposed by Beranek (NCB), so as to give the required insulation values both in terms of frequency dependent transmission loss and the single number weighting ( R w ). An analytical expression is also given based on a regression analysis for the above parameters as independent factors. A comparison is made between the National Standard Curve recommended in Belgium Legislations and the proposed rating curves, yielding higher insulation values depending on the sound frequency and source type.

Indoor noise level limits for residential areas affected by transportation noise

Noise criteria for buildings are often set on the basis of expected annoyance levels, which in turn may be seen as a function of activity interference, particularly speech or sleep disturbance. The relationships between various physical measures of noise, reported activity interference, annoyance due directly to the activity interference, and overall annoyance are as yet not clear. This paper describes a probabilistic model linking these variables, and presents a preliminary test of the model using a small data set. Houses exposed to road traffic noise and aircraft noise were chosen. At each house, detailed noise measurements were taken simultaneously outside and inside the house, using two real time one‐third octave band analyzers. In addition, a member of the household was asked about activity interference around the house, and about overall annoyance. These data permit feasibility tests of the model, which will later be tested on a more extensive data set. If successful, the model will help to identify acoustical insulation requirements for different noise environments, as well as permitting identification of those aspects of outdoor noise which lead to indoor speech interference and annoyance. This in turn is essential information for setting indoor noise criteria.