ANSI S12 Research Articles

Design of digital filters for frequency weightings (A and C) required for risk assessments of workers exposed to noise.

Many workers are exposed to noise in their industrial environment. Excessive noise exposure can cause health problems and therefore it is important that the worker’s noise exposure is assessed. This may require measurement by an equipment manufacturer or the employer. Human exposure to noise may be measured using microphones; however, weighting filters are required to correlate the physical noise sound pressure level measurements to the human’s response to an auditory stimulus. IEC 61672-1 and ANSI S1.43 describe suitable weighting filters, but do not explain how to implement them for digitally recorded sound pressure level data. By using the bilinear transform, it is possible to transform the analogue equations given in the standards into digital filters. This paper describes the implementation of the weighting filters as digital IIR (Infinite Impulse Response) filters and provides all the necessary formulae to directly calculate the filter coefficients for any sampling frequency. Thus, the filters in the standards can be implemented in any numerical processing software (such as a spreadsheet or programming language running on a PC, mobile device or embedded system).

An approach for estimating noise induced hearing loss because of indoor and outdoor environment noise factors in healthcare facilities

This paper investigates a number of healthcare centers from University Medical Schools and State Hospitals, Baskent University Medical School and Private Research Hospitals, and the State Hospital. The sound levels present in these centers were compared with number international as well as Turkish standards. Research was carried out in the following way: First, physicians and nurses were surveyed by means of a questionnaire. Then, the hospital buildings were examined in terms of their architectural design features. Lastly, sound levels were measured in the consequent spaces where questionnaires were also conducted. In addition, noise in hospitals can be detrimental as it helps to present their environment as quiet and peaceful. WHO provides guidelines for hospitals in this respect in its Guidelines for Community Noise published in 1995 (4). ANSI S12.2, recommends a maximum Room Criterions Curves (NCC) value ranging on the room type, and a maximum Noise Criteria Balanced (NCB) value ranging. A document issued by the Environmental Protection Agency (EPA) summarizing significant community noise studies provides recommendations in terms of the Ld&n (day-night sound pressure level). The Institute of Turkish Standards (TSE) is also working on this subject and the first national standard about ambient at Table 11.

Top opportunities and challenges in meeting acoustics criteria in green buildings—Specific case studies

Acoustics criteria found in for example LEED, DODEA, and ANSI S12.60 (classroom acoustics in schools) often must be met either in addition to or as part of the sustainable design project requirements. The challenge is that building designs are changing to meet the goals of sustainable design, often with unanticipated effects on building acoustics. The criteria themselves are evolving as experience is gained. Acoustics materials are also adapting to meet sustainable design goals. We will discuss the top opportunities and challenges we are finding in meeting acoustics criteria in green buildings.

Meeting the classroom acoustics standard on a historical room

The Department of Speech-Language-Hearing Sciences at University of Minnesota occupies Shevlin Hall built in 1906. We were called in 2013 to help with the acoustic and sound system redesign of room 110 to be used as a classroom, as the room had very poor speech intelligibility due to the very high ceiling and hard walls, resulting in a very reverberant environment. Our goal was to meet the current classroom acoustics standard ANSI S12.60. Reverberation time and noise measurements were performed, and the room was modeled using EASE for the prediction of results. The model was compared with measurements, and several alternatives were explored. After the changes were implemented, measurements confirmed the improvement to the room's intelligibility was acquired and the historic character of the room was preserved.

Neuromorphic Pitch Based Noise Reduction for Monosyllable Hearing Aid System Application

This paper presents a low computational complexity hardware-oriented neuromorphic pitch based noise reduction (NR) algorithm and hardware implementation for monosyllable hearing aid system applications. The proposed NR design consists of a pitch-based voice activity detector (pitch-based VAD) for speech detection and a neuromorphic noise attenuator for speech enhancement. The pitch-based VAD is developed on ANSI S1.11 based filter bank architecture and employs the characteristics of monosyllable and nonlinear energy operator (NEO) to improve the accuracy of VAD. The neuromorphic noise attenuator reduces the background noise by using the characteristics of human hearing system and the clues of speech. Simulation results show that the proposed algorithm has better SNR and PESQ performance than other non-pitch based NR algorithms in non-stationary background noise environments. Compared with multiband (mband) spectral subtraction and minimum mean square error (mmse) algorithms, the computational complexity of the proposed algorithm can save 90% computational complexity. The hardware implementation consumes 47.74 μW at 0.5 V operation with 65 nm HVT standard cell library.

Exchange Rates for Intermittent and Fluctuating Occupational Noise

The aim of this study was to review the literature regarding human noise-induced permanent threshold shift and to determine whether the observed data agreed with the predictions of two different exchange rates (ERs). An initial list of possibly relevant studies included those cited by authors who endorsed the 3 dB ER, as well as studies in personal files, studies retrieved by a MEDLINE search, and the reference lists of all of these. Criteria for relevance were designed to ensure that exposures were sufficiently intermittent or fluctuating that effective exposure levels based on the 3 dB (LAeq8h) and 5 dB (time-weighted average [TWA]) ERs would differ by at least 1 dB, that at least one of these metrics could be estimated, and that audiometric data were available for groups of defined age, sex, and exposure. Relevant studies were reviewed in detail, and their audiometric data were compared with the predictions of the ISO-1999/ANSI S3.44 model. Nine relevant studies were identified. For six articles, the reported hearing levels were substantially less than would have been predicted from LAeq8h. In each of these cases, TWA would have predicted lower hearing levels than LAeq8h and would have better fit the observed data. In three cases it was not possible to say which ER would have better fit the observed data. The 3 dB ER systematically overestimates the risk of noise-induced hearing loss for intermittent or fluctuating noise. The 5 dB ER appears to be more accurate, but also overestimates risk, particularly for exposures above 100 dBA.

10-ms 18-Band Quasi-ANSI S1.11 1/3-Octave Filter Bank for Digital Hearing Aids

The ANSI S1.11 1/3-octave filter bank is suitable for digital hearing aids, but its large group delay and high computational complexity complicate matters considerably. This study presents a 10-ms 18-band quasi-ANSI S1.11 1/3-octave filter bank for processing 24 kHz audio signals. We first discuss a filter order optimization algorithm to define the quasi-ANSI filters. The group delay constraint of filters is limited to 10 ms. The proposed design adopts an efficient prescription-fitting algorithm to reduce inter-band interference, enabling the proposed quasi-ANSI filter bank to compensate any type of hearing loss (HL) using the NAL-NL1 or HSE prescription formulas. Simulation results reveal that the maximum matching error in the prescriptions of the mild HL, moderate HL, and severe-to-profound HL is less than 1.5 dB. This study also investigates the complexity-effective multirate IFIR quasi-ANSI filter bank. For an 18-band digital hearing aid with a 24 kHz sampling rate, the proposed architecture eliminates approximately 93% of the multiplications and up to 74% of the storage elements, compared with a parallel FIR filters architecture. The proposed analysis filter bank (AFB) was designed in UMC 90 nm CMOS high-VT technology, and on the basis of post-layout simulations, it consumes 73 μW (@VDD=1 V). By voltage scaling (to 0.6 V), the simulation results show that the power consumption decreases to 27 μW, which is approximately 30% of that consumed by the most energy-efficient AFB available in the literature for use in hearing aids.

Noise pollution analysis in Tehran cement plant

Background : Cement industry has many process units. Basically all of these units can be considered as a source of noise. Since noise pollution is defined based on its offensive hearing effects, the importance of the noise sources depends directly on the number of workers in the unit. Materials and Methods : An experimental study has been done at Tehran cement factory to recognize and analyze the major noise pollution source machineries. In this survey, first, the mean A-weighted sound pressure level and the number of workers in each unit have been measured and the obtained data has been analyzed in Microsoft Excel. Afterwards, based on the mentioned ISO, some experiments have been done to calculate the A-weighted acoustic power level of the crusher which emits the highest level of noise. Results: The noisiest units have been recognized and some applicable suggestions have been offered to reduce the sound exposure level. Also by calculating the sound power levels and considering the design parameters which affect the sound power generated by the crusher, an empirical equation has been presented to calculate the acoustic power level as a function of horsepower, number of hammers and the weight of each hammer. Conclusion: The acoustic measurement results show that the crusher, cement mill and row mill units are the three major noise emission sources. In another experiment, based on ANSI S1.36 and ISO 3746 guidelines, the sound power level of the crusher unit has been measured indirectly. Afterwards, by using a multiple regression algorithm and minimizing the mean square error, an empirical equation has been proposed to correlate the acoustic power level as a function of the horsepower and the mass of all hammers of the crusher.

Point source equalised by inverse filtering for measuring ground impedance

A point source for measuring ground impedance which complies with the omnidirectionality requirements of the ANSI S1.18 standard is presented. The source consists of a small aperture connected to a conventional loudspeaker through a cone. Whilst this source radiates with deviations lesser than ±1dB within ±45°, its frequency response exhibits strong peaks arising from resonances of air inside the cone. To equalise these resonances, inverse filtering is applied. Inverse filters pre-emphasise the electrical signal driving the sound source so that zero-phase (or minimum-phase) cosine-magnitude signals are radiated. Equalisation by inverse filtering has two main advantages in the ground impedance measurement. On the one hand, flattening the frequency response avoids large fluctuations of the excess attenuation curve, which can make difficult its inversion to ground impedance data. On the other hand, inverse filtering shorten the time response of the sound source, this in turn making easier the positioning of a time window to separate ground reflection from reflections/diffractions coming from nearby objects usually present in the acoustic scenario.

Underwater measurement of narrowband sound power and directivity using Supersonic Intensity in Reverberant Environments

A laboratory underwater acoustic measurement technique, Supersonic Intensity in Reverberant Environments (SIRE), is developed analytically and validated experimentally and numerically. Unlike standard free or diffuse field techniques, SIRE enables the measurement of narrowband sound power and directivity in an environment with inexact field conditions. The technique takes advantage of underwater vector sensors, measuring only acoustic pressure and the normal component of particle velocity/acceleration, and supersonic wavenumber filtering in the near field of a source. The result is outward-propagating acoustic waves separated from interfering incoming and/or evanescent waves. The SIRE technique was experimentally applied to monopole and dipole sources and the results are compared with theory and standard methods. SIRE is shown to accurately measure radiated sound power to within the limits of ANSI S12.51 and to accurately measure the directivity indices of simple sources to within ±3dB. A coupled finite element/boundary element model of a point-driven, thin-walled cylinder is also developed to establish the limitations of the SIRE technique. The model results show that the measurement standoff distance should be less than the reciprocal of the largest wavenumber in the frequency band of interest. Furthermore, the maximum measurement grid spacing must be less than twice the standoff distance.

Hearing Threshold Levels at Age 70 Years (65–74 Years) in the Unscreened Older Adult Population of the United States, 1959–1962 and 1999–2006

To provide hearing threshold percentiles from unscreened older adults for creating new Annex B reference standards. Percentiles are calculated, and 95% confidence intervals for medians from two U.S. surveys are compared graphically. Median thresholds are lower (better) in the 1999-2006 National Health and Nutrition Examination Survey for men across all frequencies except 1 kHz. Results for women are similar; however, there is more overlap in confidence intervals across frequencies. The prevalence of hearing impairment in older adults, age 70 years (65-74 years), is lower in 1999-2006 compared with 1959-1962, consistent with our earlier findings for younger adults.

Measurement of impulse peak insertion loss for four hearing protection devices in field conditions

Objective: In 2009, the U.S. Environmental Protection Agency (EPA) proposed an impulse noise reduction rating (NRR) for hearing protection devices based upon the impulse peak insertion loss (IPIL) methods in the ANSI S12.42-2010 standard. This study tests the ANSI S12.42 methods with a range of hearing protection devices measured in field conditions. Design: The method utilizes an acoustic test fixture and three ranges for impulse levels: 130–134, 148–152, and 166–170 dB peak SPL. For this study, four different models of hearing protectors were tested: Bilsom 707 Impact II electronic earmuff, E·A·R Pod Express, E·A·R Combat Arms version 4, and the Etymotic Research, Inc. Electronic BlastPLG™ EB1. Study sample: Five samples of each protector were fitted on the fixture or inserted in the fixture's ear canal five times for each impulse level. Impulses were generated by a 0.223 caliber rifle. Results: The average IPILs increased with peak pressure and ranged between 20 and 38 dB. For some protectors, significant differences were observed across protector examples of the same model, and across insertions. Conclusions: The EPA's proposed methods provide consistent and reproducible results. The proposed impulse NRR rating should utilize the minimum and maximum protection percentiles as determined by the ANSI S12.42-2010 methods.

1.Comparison of the HPDLab and REATMaster software/hardware systems for ANSI S12.6 testing

The American National Standard Methods for Measuring the Real-Ear Attenuation of Hearing Protectors (ANSI S12.6-2008) requires a Békésy procedure for testing occluded and unoccluded thresholds. Since 2002, the National Institute for Occupational Safety and Health (NIOSH) has used the custom-designed HPDLab software operating Tucker-Davis Technologies System 3 hardware. ViAcoustics, Nelson Acoustics, NASA, and NIOSH researchers recently developed REATMaster which runs on National Instruments hardware in the LabVIEW environment. Ten subjects were trained by the experimenter on how to fit a passive earmuff and were qualified according to the requirements of ANSI S12.6-2008. The laboratory was configured such that diffuse sound field thresholds were tested with either the HPDLab or REATmaster hardware by flipping a toggle switch. The earmuff was not touched or re-positioned between test trials with the two different hardware/software systems. The test sequence for the order of open and occluded measurements was counterbalanced across occluded conditions and hardware system. Results from this testing were used to validate the REATMaster system for its ability to produce accurate threshold data. Preliminary results indicate no significant differences between the two systems.

A multicenter study on the audiometric findings of styrene-exposed workers

Objective: The objective of this study was to evaluate hearing loss among workers exposed to styrene, alone or with noise. Design: This cross-sectional study was conducted as part of NoiseChem, a European Commission 5th Framework Programme research project, by occupational health institutes in Finland, Sweden, and Poland. Study sample: Participants’ ages ranged from 18–72 years (n = 1620 workers). Participants exposed to styrene, alone or with noise, were from reinforced fiberglass products manufacturing plants (n = 862). Comparison groups were comprised of workers noise-exposed (n = 400) or controls (n = 358). Current styrene exposures ranged from 0 to 309 mg/m3, while mean current noise levels ranged from 70–84 dB(A). Hearing thresholds of styrene-exposed participants were compared with Annexes A and B from . Results: The audiometric thresholds of styrene exposed workers were significantly poorer than those in published standards. Age, gender, and styrene exposure met the significance level criterion in the multiple logistic regression for the binary outcome ‘hearing loss’ (P = 0.0000). Exposure to noise (<85 dBA p = 0.0001; ≥85 dB(A) p = 0.0192) interacted significantly with styrene exposure. Conclusions: Occupational exposure to styrene is a risk factor for hearing loss, and styrene-exposed workers should be included in hearing loss prevention programs.SumarioObjetivo: El objetivo de este estudio fue evaluar la pérdida auditiva en trabajadores expuestos a estireno, aisladamente o con ruido. Diseño: Se realizó este estudio transversal como parte del NoiseChem, Comisión Europea del 5°. Proyecto Marco de investigación, en institutos de salud ocupacional de Finlandia, Suecia y Polonia. Muestra de estudio: La edad de los participantes fue de 18–72 a os (N = 1,620 trabajadores). Los trabajadores (n = 862) estuvieron expuestos a estireno, solo o con ruido, en plantas de fabricación de productos de fibra de vidrio reforzada. Los grupos de comparación fueron trabajadores expuestos a ruido (n = 400) y los de un grupo control (n = 358). Las exposiciones reales a estireno variaron de 0 a 309 mg/m3, mientras que los niveles reales de ruido, variaron de 80–84 dB(A). Se compararon los niveles de audición de los participantes expuestos a estireno con los de los anexos A y B de . Resultados: Los umbrales audiométricos de los trabajadores expuestos a estireno, fueron significativamente más pobres que los que se han publicado como estándar. La edad, el género y la exposición a estireno, cubrieron los criterios de niveles de significatividad de la regresíón logística múltiple para los resultados binarios de la “perdida auditiva” (P = 0.0000). La exposición a ruido (<85 dB(A) p = 0.0001; ≥85 dB(A) p = 0.0192) interactu significativamente con la exposición a estireno. Conclusiones: La exposición ocupacional a estireno es un factor de riesgo de pérdida auditiva por lo que los trabajadores expuestos a estireno deben ser incluidos en programas de prevención de pérdidas auditivas.

Ultrasonic anechoic chamber qualification: Accounting for atmospheric absorption and transducer directivity

Qualifying an anechoic chamber for frequencies that extend into the ultrasonic range is necessary for research work involving airborne ultrasonic sound. The ANSI S12.55/ISO 3745 standard which covers anechoic chamber qualification does not extend into the ultrasonic frequency range, nor have issues pertinent to this frequency range been fully discussed in the literature. An increasing number of technologies employ ultrasound; hence the need for an ultrasonic anechoic chamber. This paper will specifically discuss the need to account for atmospheric absorption and issues pertaining to source transducer directivity by presenting some results for qualification of a chamber at Brigham Young University.

Measurement of impulse peak insertion loss for five hearing protectors.

In 2009, the US Environmental Protection Agency proposed an impulse noise reduction rating (NRR) for hearing protection devices. The impulse NRR is based the American National Standard, ANSI S12.42-2010, and requires measurements with an acoustic test fixture for three ranges of impulse noises: 130–134, 148–152, and 166–170 dB peak SPL. Five protectors of each of five models (The Combat Arms Linear, Combat Arms Nonlinear, EAR Pod Express, Etymotic EB1, and Bilsom 707 Impact II, all in passive mode) were evaluated per the levels specified in the ANSI standard. Impulses were generated by an acoustic shock tube in the laboratory and by a 0.223 caliber rifle in the field. At each peak impulse level, protector samples were fitted on the test fixture five times and for each insertion, at least three impulses were measured. The impulse NRR increased with peak pressure and ranged between 20 and 38 dB. For some protectors, significant differences were observed across protector examples of the same model and across insertions. Relationships between the continuous noise NRR, the impulse NRR, and the increase in allowable impulse exposures due to the protector will also be presented.

Ecma International Acoustic Standard Activities: An enabler for controlling information technology noise emissions.

Ecma International is an organization that facilitates the timely creation of a wide range of standards for Information Technology (IT) products, including acoustics standards. Ecma standards have a history of short development time and revision. Each Ecma acoustics standard will be discussed demonstrating how it promotes the analysis and control of IT product noise. ECMA-74 is the test code for sound emissions from IT equipment. Annex C includes uniform operation and installation conditions for most types of IT equipment and is now referenced by the latest versions of ISO 7779:2010 and ANSI S12.10. This reference by other standards ensures that there is a world-wide consistency on mounting and operating conditions and that these procedures are up to date. The latest edition of ECMA-109 on noise declarations for customers presents revised guidelines to manufacturers on making declarations when testing a small sample size. ECMA-108 presents methods for determining high frequency sound power and has been submitted to ISO for revision to ISO 9295. ECMA TR/275 on measuring fan structure-borne noise was the basis of ANSI S12.11/Part2 (ISO 10302/Part 2). ECMA TR/99 covers constant sound power fan curves to assist product developers to select low-noise operation of fans at realistic operating points.

Atmospheric effects on voice command intelligibility from acoustic hail and warning devices

Voice command sound pressure levels (SPLs) were recorded at distances up to 1500 m. Received SPLs were related to the meteorological condition during sound propagation and compared with the outdoor sound propagation standard ISO 9613-2. Intelligibility of received signals was calculated using ANSI S3.5. Intelligibility results for the present voice command indicate that meteorological condition imposes little to no effect on intelligibility when the signal-to-noise ratio (SNR) is low (<-9 dB) or high (>0 dB). In these two cases the signal is firmly unintelligible or intelligible, respectively. However, at moderate SNRs, variations in received SPL can cause a fully intelligible voice command to become unintelligible, depending on the meteorological condition along the sound propagation path. These changes in voice command intelligibility often occur on time scales as short as minutes during upward refracting conditions, typically found above ground during the day or upwind of a sound source. Reliably predicting the intelligibility of a voice command in a moderate SNR environment can be challenging due to the inherent variability imposed by sound propagation through the atmosphere.

Americans Hear as Well or Better Today Compared With 40 Years Ago: Hearing Threshold Levels in the Unscreened Adult Population of the United States, 1959–1962 and 1999–2004

(1) To present hearing threshold data from a recent nationally representative survey in the United States (National Health and Nutrition Examination Survey, 1999-2004) in a distributional format that might be appropriate to replace Annex B in international (ISO-1999) and national (ANSI S3.44) standards and (2) to compare these recent data with older survey data (National Health Examination Survey I, 1959-1962) on which the current Annex B is based. Better-ear threshold distributions (selected percentiles and their confidence intervals) were estimated using linear interpolation. The 95% confidence intervals for the medians for the two surveys were compared graphically for each of the four age groups and for both men and women. In addition, we calculated odds ratios comparing the prevalences of better-ear hearing impairment (thresholds > 25 dB HL) between the two surveys, for 500, 1000, 2000, and 4000 Hz, and for their four-frequency average. Across age and sex groups, median thresholds were lower (better) in the 1999-2004 survey at 500, 3000, 4000, and 6000 Hz (8000 Hz was not tested in the 1959-1962 survey). For both men and women, the prevalence of hearing impairment was significantly lower in 1999-2004 at 500, 2000, and 4000 Hz, but not at 1000 Hz. For men and women of a specific age, high-frequency hearing thresholds were lower (better) in 1999-2004 than in 1959-1962. The prevalences of hearing impairment were also lower in the recent survey. Differences seen at 500 Hz may be attributable at least in part to changes in standards for ambient noise in audiometry. The National Health and Nutrition Examination Survey 1999-2004 distributions are offered as a possible replacement for Annex B in ISO-1999 and ANSI S3.44.

Design and Implementation of Low-Power ANSI S1.11 Filter Bank for Digital Hearing Aids

Due to well matching the frequency characteristics of human ears, ANSI S1.11 1/3-octave filter bank is popular in acoustic applications, such as acoustic analyzers and equalizers. It is also desirable in hearing aids because the famous hearing aid prescription formula, NAL-NL1, prescribes its gains at ANSI 1/3-octave frequencies. However, the high computation complexity limits its usage, in which the power consumption is a critical concern. To address this issue, a low-power design and implementation of ANSI S1.11 filter bank for digital hearing aids is present. We first develop the complexity-effective multirate FIR filter bank algorithm. And, a systematic coefficient design flow is elaborated for the proposed filter bank to minimize the order of the FIR filter thereof. In an 18-band digital hearing aid with 24-kHz sampling rate, the proposed algorithm saves about 96% of multiplications and additions, comparing that with a straightforward FIR filter bank. Moreover, various low-power VLSI design techniques are investigated in detail and applied on our design. The proposed complexity-effective ANSI S1.11 FIR filter bank has been implemented in the TSMC 0.13-μ m CMOS technology with an area-efficient architecture. The test chip consumes only 87 μW, which is 30%-79% of that of the others available in the literature. The proposed low-power ANSI 1/3-octave bank makes itself being able to precisely apply the prescribed gains obtained by NAL-NL1 prescription formula for hearing-impaired people.