Room Noise Criteria Research Articles

The future of ANSI/ASA S12.2 and room noise criteria

A working group is evaluating the American National Standard, "Criteria for Evaluating Room Noise" (ANSI/ASA S12.2-2019). This presentation will give an overview of our progress and areas of significant proposed change. The goal is to simplify the standard body so that the criteria reflect industry practice. Historical references and less common criteria will be relegated to annexes. Since the beginning of this standard, there has been interest in determining spectral imbalance, temporal variation, and the presence of tones. This talk will briefly mention proposals to quantify these aspects. Feedback from the industry is welcome to minimize the challenges associated with implementing this standard.

Acoustical design of heathcare facilities for leadership in energy and environmental design green building certification: Odd harmonic filter for mechanical system noise control.

To achieve the leadership in energy and environmental design (LEED) indoor environmental quality credit 2: acoustic environment, healthcare facilities must meet stringent sound and vibration criteria. Mechanical system noise presents one of the largest obstacles to meeting the room noise design requirements. Code requirements intended to promote indoor air quality, and infection control limits the use of typical absorptive materials such as fiberglass duct liner, packed duct silencers, and other porous absorbers. Energy code requirements force mechanical system designers to locate large noise sources such as air handlers, fan‐powered terminal air boxes, and exhaust fans close to the spaces they serve, adding to background noise levels. One innovative, practical solution to tonal mechanical system noise is an odd harmonic filter. Acoustical performance of odd harmonic filters and strategies to achieve the room noise criteria for the LEED acoustic environment credit will be discussed.

The room noise criteria (RNC) metric.

The recent ANSI S12.2:2008 room noise criteria contains both a survey and an engineering method to specify room noise criteria. The methods use A‐weighting and extended NC, respectively. A new metric, titled like the standard, room noise criteria (RNC) is included as a diagnostic tool. It is based on human hearing and more correctly assesses low‐frequency sound. In particular, it is sensitive to the standard deviation to random noise and/or low‐frequency surging in the 16–125 Hz octave bands such as the sound that can be produced by HVAC systems or other devices. It provides a bridge between the NC and RC criteria by correctly predicting the need for the less stringent (at low frequencies) NC criteria when the HVAC system is well designed (no surging, moderate standard deviation) and also correctly predicting the more stringent (at low frequencies) RC criteria when the HVAC system noise has a large standard deviation and/or surging.

Relationship between noise criteria and room criteria ratings

The September 2000 issue of Noise/News International featured a paper entitled ‘‘Room Noise Criteria—The State of the Art in the Year 2000’’ by Gregory C. Tocci. The paper in part investigated the relationship between NC (tangency), NCB, and RC ratings for a series of 268 spectra measured in building spaces during the course of Cavanaugh Tocci Associates, Inc. consulting work. These spectra ranged from uniform to widely varying in shape. This presentation extends this work to document the relationship between RC and NC tangency ratings for these 268 spectra, which was not included in the original 2000 NNI paper.

Comments on draft ANSI S12.2, American National standard on criteria for evaluating room noise

In 1995, American National Standard S12.2‐1995 on room noise criteria was issued. Two methods for specifying and evaluating room noise were presented, the NCB noise‐criterion curves [J. Acoust. Soc. Am. 86, 650–664 (1989)] and the RC curves [Noise Control Eng. J. 45, 243–250 (1997)]. The NCB curves were derived from the characteristics of hearing with emphasis on speech interference level and loudness level, while the RC curves were derived from experimental studies in offices where the HVAC noise was low enough that there were no complaints from room occupants. The NCB curves were applicable to rooms ranging from concert halls to factory spaces, while the RC curves were largely restricted to office, hospital, and residential spaces. The two sets were incompatible at low frequencies and low sound levels. The NCB curves assumed that the HVAC noise was free of surging and strong turbulence. The RC curves demanded lower levels at low frequencies, thus permitting some degree of surging and turbulence. The new draft standard specifies two methods for evaluating room noise, the NC [Noise Control 3, 19–27 (1957)] and the RNC methods [Noise Control Eng. J. 48, 85–96 (2000)]. The former (NC) have found widespread use and the latter (RNC) bridges the differences between the NC (and NCB) and the RC criteria curves. This paper comments on the promise of the new RNC method and compares measured data were available.

For purposes of environmental noise assessment, A-weighting needs to be retired

Currently, most countries use some form of A-weighted equivalent level (ALEQ) to assess the annoyance of most noises. But A-weighting fail to properly assess multiple noise sources such as planes, trains, and automobiles relative to one another, and it fails to properly assess sound with strong low-frequency content. It performs better outdoors than indoors even though the receivers are indoors. It certainly cannot be used for room noise criteria. A-weighted LEQ cannot assess the audibility of sound, and, in fact, LEQ in fractional octave bands cannot be used to assess the audibility of sounds at low frequencies. A-weighting needs to be retired. There are better measures for all of these functions such as loudness-level weighting using ISO 226. At low frequencies, data show some people (about one-third) are ‘‘C-weighted’’ listeners. For all noise, it may be that one model just does not fit all. Experiments show that a majority of listeners make categorical judgments and merely count events based on level with the minority of subjects fitting three other models. There are many ways to clearly move forward but we must give up our A-weighting, it has now reached old age.

The importance of loudness functions in assessing noise annoyance

Outdoors, Schomer et al. have shown that loudness weighting according to ISO 226 can be used to great advantage as a direct substitute for A-weighting. That is, loudness-weighted sound exposure level (LLSEL) can be used as a direct substitute for A-weighted sound exposure level (ASEL). LLSEL, computed with a time constant commensurate with the time constant of the human hearing process, provides significantly better correlation with community response across different noise sources than does ASEL. Indoors, room noise criteria (RNC) curves have been developed using these same human hearing function considerations. The RNC curves and associated computational procedure successfully bridge the gap between the PNC curves of Beranek and the RC curves of Blazier. Taken together, this body of outdoor and indoor research results shows the great importance of the human hearing function in assessing noise annoyance.

Room noise criteria - THe state of the art in the year 2000

Room noise criteria - THe state of the art in the year 2000

A test of proposed revisions to room noise criteria curves

A test of proposed revisions to room noise criteria curves

Proposed revisions to room noise criteria

Proposed revisions to room noise criteria

Hot new topics in ASA/ANSI standardization

The ASA Committee on Standards has many new work efforts underway. As chairman of the ANSI S12 committee (noise), this author is primarily versed in the hot new noise standards being developed. Hence, this paper will concentrate on noise standards. (The S12 committee can be considered the counterpart to ISO TC 43/SC 1 and concentrates on noise.) Several new efforts are underway in S-12, including (1) classroom acoustics, (2) room noise criteria, (3) model community noise ordinances, (4) community noise assessment, (5) consumer product noise labeling, and (6) in situ hearing protector measurements. In addition, there is a new effort in the S-3 committee (bioacoustics) dealing with warning signal definitions. Clearly, these new topics depart from many of the traditional standards topics such as measurement of workplace machinery noise or office and business equipment noise. Rather, these new work efforts concentrate on criteria development, measures to assess response to noise in various settings, or various human interactions with sound, etc. Several of these topics, such as community noise assessment, noise labeling, or hearing protector measurement, relate to ongoing international efforts. This paper will briefly describe the goals, progress, key contacts, and schedules for these work efforts.

A new approach to low-frequency room noise criteria

There are three different and conflicting room criteria methods that are widely used by consultants today: room criterion (RC), balanced noise criterion (NCB), and noise criteria (NC). The RC procedure is documented in ANSI S12.2-1995 ‘‘Criteria for evaluating room noise’’ and the ‘‘1995 ASHRAE Applications Handbook;’’ the NCB procedure in ANSI S12.2; and the NC ‘‘tangency’’ method in the ‘‘1991 ASHRAE Applications Handbook.’’ There are significant differences in the three criteria, especially for low frequencies, which can impact the costs both of new designs and of remedial actions to existing facilities. In order to promote a resolution to these differences, NOISE-CON96 and NOISE-CON97 held special technical sessions on room noise criteria. Based on our analysis of published research and on experiences dealing with other noise sources, the authors suggest an approach to resolve the low-frequency differences: (1) establish basic room criterion curves for noises without abnormal temporal or spectral characteristics, and (2) apply correction factors to the measured data to account for abnormal features before comparison to the basic criterion. This paper presents details of the suggested approach, the status of revisions to ANSI S12.2 and to the ASHRAE handbook, and other ongoing research.

Room noise criteria standards: What features are important?

At the joint meeting of ASA and NOISE-CON 97 in June 1997, the authors organized a special session on room noise criteria, in which a ‘‘questionnaire’’ on the features of several existing noise criteria methods was answered by panel experts and distributed to the noise control community for their inputs. The four methods were: the A-weighted sound-pressure level; the noise criteria (NC) tangency method contained in older versions of the ASHRAE handbook; the balanced noise criterion method (NCB) contained in ANSI S12.2; and the room criteria method (RC) contained in ANSI S12.2 and the current ASHRAE handbook. The features considered were: speech interference, high-frequency annoyance, mid/low frequency annoyance, very low-frequency annoyance, pure tones, temporal fluctuations, user friendliness, wider frequency range, speech privacy, costs, and ability to handle noises with abnormal characteristics and complexity. The questionnaire rating was twofold: (1) how well does each method adequately account for each of the ‘‘features’’ (or characteristics) relative to the other methods, and (2) what is the relative importance of each of the ‘‘features’’ in a noise criteria method. This paper presents the results of the questionnaires and reports progress since the joint meeting in ANSI S12 WG18 and ASHRAE TC2.6.

Room noise criteria—A status report

After more than 20 years of effort, American National Standard ‘‘Criteria for Evaluating Room Noise’’ ANSI S12.2-1995 was released. ANSI S12.2 is not a good standard because it offers two different possibilities to evaluate the acceptability of the sound in an occupied space with the potential for large differences in the cost of conformance and insufficient guidance to a user on how to choose between them. As members of both the ASHRAE TC2.6 and ASA S12/WG18 committees responsible for the preparation of the ANSI S12.2 standard the authors see the need for inter-society partnership to resolve the conflict. Two panel discussion sessions (ASA Boston Chapter meeting on 21 November 1995; and NOISE-CON96 Conference on 30 September 1996); one technical session (NOISE-CON96 ‘‘Room Noise Criteria—The Next 25 Years’’) and the response from the acoustical and engineering community have served to show that there are enough data to develop a road map for consensus. After the NOISE-CON96 sessions, many attendants have asked for a report. A report entitled ‘‘Room Noise Criteria—The Next 25 Years’’ was generated, which documents the findings of these sessions. This paper is a brief summary of the said report. [See NOISE-CON Proceedings for full paper.]

Room noise criteria—A consultant’s experience

There has been much controversy in recent years regarding the various room noise criteria that have been proposed and are in use today. Included in these criteria are the NC curves, the PNC curves, the RC curves, and most recently, the NCB curves. The NR curves, which are commonly used in Europe, must also be mentioned. The recent adoption of ANSI S12.2 has not resolved the controversy—in fact, it has actually heightened the debate because it acknowledges two room noise criteria (RC and NCB) that are clearly at odds with each other in the low-frequency region. This paper examines the limitations of each method (RC and NCB) and provides possible suggestions for modifications that might create a path for eventual resolution of this controversy. This paper also emphasizes the important characteristics of any room criteria method: it must be as simple as possible without sacrificing effectiveness, relatively easy to measure, and credible from the standpoint of human perception. In any event, it is the opinion of the author that any resolution will have to await the completion of the ASHRAE research project which is currently in progress in Australia. [See NOISE-CON Proceedings for full paper.]

Room noise criteria—A new approach at low frequencies

ANSI S12.2-1995, ‘‘Criteria for Evaluating Room Noise,’’ permits two different sets of criterion curves for evaluating room noise—room criterion (RC) and balanced noise criterion (NCB)—with little guidance as to the selection. These different procedures can have significant impacts on the cost of designs, especially in the low-frequency regions, since the difference in the criteria is more than 10 dB in the 16- and 31-Hz octave bands at lower levels. The authors suggest there are sufficient data to support a modification to ANSI S12.2, resulting in a single evaluation procedure based on the strengths of each of the two existing procedures. The authors suggest establishing room criterion curves for steady noise without abnormal temporal or spectral characteristics, with correction factors for noises with abnormal features. The suggested criteria for steady noise are the NCB curves based on time-average octave band sound pressure levels, and as a starting point, the correction factors for low-frequency tones and fluctuation differences between the NCB and RC curves. Analyses of currently funded research and re-examination of existing cases can determine the exact correction factors and measurement techniques to quantify these abnormal characteristics. A revised ANSI S12.2 could have basic criterion curves for steady, continuous, and broadband room noises, which could be used for design with correction factors to these basic criterion curves for sounds with abnormal characteristics. [See NOISE-CON Proceedings for full paper.]

Room noise criteria--the S12.2-1995 standard raises serious technical and economic considerations.

The key issue with the S12.2-1995 standard is not the differences in the assessment of sound quality, particularly at the low frequencies, but rather the use of octave-band data to describe low-frequency equipment misbehavior. Unfortunately, the "NCB vs RC" controversy leads research efforts and technical discussions in the wrong directions, disregarding serious economic and technical considerations. This conflict can be resolved by: (1) avoiding the use of octave-band data to rate noise with abnormal (spectral and/or temporal) characteristics, (2) addressing the widespread need for the room noise criteria as a practical design tool for general use in architectural spaces, and (3) developing adequate descriptor/procedures to qualify, quantify, and determine the impact of "rumble" on human response. A further goal should be to develop integrated criteria that would apply to both HVAC and computer noise sources.

Room noise criteria—Time for common sense

The acoustical environments of the many types of rooms designed for occupancy are supposed to be established in the design phase of a new project or during a project retro-fit so that the intended use of a room is not compromised by intrusive noise sources. A major tool in accomplishing the desired environment is the application of room noise criteria. However, given the many types of noise sources with a wide range in sound quality, frequency content, and temporal features, it seems impossible to achieve a desired, yet cost effective, acoustical room environment by using venerable noise criteria (NC) curves alone. ANSI S12.2-1995 is an attempt to include the means to account for different characteristics in noise sources by introducing the balanced noise criteria (NCB) and room criteria (RC) methods for evaluating noise. As a result of the introduction of ANSI S12.2-1995, a controversy has arisen over the practicality and even the viability of the new standard(s). The people who must live or work in the designed space will ultimately determine whether an adequate acoustical room environment has been achieved. The economics of the acoustical design often dictates whether a working solution is ever implemented at all. A practical basic criteria with just a handful of adjustment factors and guidelines to account for quality, frequency, and temporal anomalies, would be better suited to standardizing the design methodology in room acoustics. This paper provides examples of applications of standards in the everyday world of environmental acoustics. [See NOISE-CON Proceedings for full paper.]

Review and revision of room noise criteria

Review and revision of room noise criteria

Increasing the Acoustical Society’s role in noise control and noise effects

At the meeting of the Technical Committee on Noise at the fall 1991 meeting of ASA in Houston, a discussion was held on how, or if, the Acoustical Society should develop more concrete policies or action concerning noise control and noise effects. As a result of that discussion, a Noise Task Group was formed by the authors at the direction of the Chair of the Technical Committee to explore the issues involved. Since that time, several special sessions have been held to help establish a direction for this activity. This talk will briefly review some of the more important elements of that activity which, properly, are beginning to involve members of other technical committees within the Society in such areas as hearing screening tests at ASA meetings, development of lecture materials for use in presenting talks to youth on acoustics and noise, and potential development of room noise criteria and/or rating schemes for meeting spaces. Other such action areas that have evolved from these special sessions will be mentioned. These offer other opportunities for ASA members to help achieve a goal worthy of the Society—to preserve quiet and tranquility in concert with advances in technology and population growth.