Speech Interference Levels Research Articles

Orthopedic Surgical Helmet Systems Significantly Impair Speech Intelligibility.

Surgical suits provide protection to orthopedic surgeons, but the suits and fan noise may interfere with communication between operative team members. The goal of this study was to quantify the fan sound and effect of the suit, fan, and N95 mask. Sound levels were measured using a specialized manikin and evaluated using preferred speech interference levels (PSILs), noise criterion (NC) ratings, and comparison with speech sound levels from the literature. Additionally, sound blocking due to the surgical suit was measured and combined effects of the fan and suit were described using a signal to noise ratio (SNR). The noise with the fan at medium and high speed was louder than average speech and the PSILs at these speeds were significantly higher than with the fan off. The fan NC rating of 50 to 60 exceeded the recommended range of 25 to 30 for operating rooms. The N95 mask, space suit, and distance between speaker and receiver all reduced the sound signal at the receiver's ear, with the worst case being full personal protective equipment on both and speaker distanced from receiver. The estimated SNR for the suit and fan system was negative for many frequency bands used in speech, indicating more noise than signal. Multiple measures indicated that the fan noises were at levels associated with speech interference. This noise combined with sound blocking provided by the suit produced SNRs commonly associated with noisy to very noisy environments. This study suggests the combined effects of the suit, fan, and distance may negatively impact operating room communication. [Orthopedics. 2021;44(4):208-214.].

Acoustic quality on board ships

Approaches to determine acoustic quality on board ships are usually based on a three- or five-stage classification system using critical A-weighted sound pressure levels. At times other criteria such as the sound insulation between cabins, impact noise from upper decks, speech interference levels or general noise-rating curves are also taken into account. With regard to increasing requirements of passenger comfort and crew accommodation, a more detailed evaluation of auditory perception on board would be worthwhile. Furthermore, other industrial sectors have stated that psychoacoustic or room acoustic models are useful tools to analyze and guarantee product-sound quality. In order to find better indicators for the quantification of acoustic performance of (luxury) vessels, audio material was acquired at a sea trial and evaluated with the help of a paired-comparison listening test in the laboratory by 30 test-persons. Also, the possibility to comment the judgments was given to the subjects. The results were then analyzed by using the statistic model of the “Law of Comparative Judgment” and compared by correlation analysis with physical, psychoacoustic, and room acoustic parameters. Highly correlating parameters could be identified.

Noisiness in Operating Theatres: Nurses’ Perceptions and Potential Difficulty Communicating

Elevated operating theatre noise can be hazardous to patient safety and may cause occupational stress. In a nine-hospital study, background noise and average noise were measured, during operations in different subspecialties, and found to be higher than noise levels recommended by the World Health Organization (WHO) for hospital areas in which patient care takes place. In operations in which nurses had also answered a question about hearing 'quiet', 'normal', and 'loud' talking, speech interference levels were estimated and indicated that nurses and other personnel had to substantially raise their voices to be well understood.

Noise levels, spectra, and operational function of an occupied newborn intensive care unit built to meet recommended permissible noise criteria

A group of clinical experts developed recommended permissible noise criteria for newly constructed or renovated hospital nurseries [Philbin et al., J. Perinatol. 19, 559–563 (2000); R. White, ibid. 23, S1–22 (2003)]. These criteria are based principally on research regarding wake-up thresholds for term newborns and speech interference levels for adults. These criteria are: The overall continuous A-weighted, slow response, sound level at any bed or patient care area shall not exceed: (1) an hourly Leq of 50 dB, (2) an hourly L10 of 55 dB, and (3) a 1-s Lmax of 70 dB. A new hospital building was designed to meet these criteria by using specific acoustical criteria for the structure and space arrangement [J. B. Evans and M. K. Philbin, J. Perinatol. 20, S105–S112 (2000)]. Acoustical criteria for sound isolation, background NC, structural vibration, and reverberation will be presented along with space arrangements that ensure staff efficiency, clinical safety, and family privacy. Post-occupancy measurements of sound levels and spectra along with photographs of a nursery in operation will be presented to illustrate how an ICU can have a quiet, highly functioning intensive care environment while meeting the operational goals and acoustical criteria.

Noise Reduction Retrofit on Historic Structures

Cost-effective noise reduction techniques for historic buildings can be accomplished affordably and without altering the structure's historic status. Techniques include adding sashes to existing historic windows, replacing windows with visually compatible acoustic units, and using jamb extensions to accommodate manufacturers' standard window units. Wood-truss roofs can be insulated from noise on the interior through the addition of a light-gauge metal framing support with alternating layers of gypsum board, plywood, and batt insulation. Ventilation solutions include a unique over-the-sill air intake system that functions as an acoustic baffle and visually spares a historic facade from random louver punch-throughs. Acoustically rated doors and vestibule construction address noise reduction at entry ways. At an example installation, sound levels were reduced by 12 dB, and speech interference levels were reduced by 18-23 dB. Continuous use is the best method for preservation of historic buildings. Noise redu...

Noise Reduction Retrofit on Historic Structures

Cost-effective noise reduction techniques for historic buildings can be accomplished affordably and without altering the structure's historic status. Techniques include adding sashes to existing historic windows, replacing windows with visually compatible acoustic units, and using jamb extensions to accommodate manufacturers' standard window units. Wood-truss roofs can be insulated from noise on the interior through the addition of a light-gauge metal framing support with alternating layers of gypsum board, plywood, and batt insulation. Ventilation solutions include a unique over-the-sill air intake system that functions as an acoustic baffle and visually spares a historic facade from random louver punch-throughs. Acoustically rated doors and vestibule construction address noise reduction at entry ways. At an example installation, sound levels were reduced by 12 dB, and speech interference levels were reduced by 18–23 dB. Continuous use is the best method for preservation of historic buildings. Noise reduction, sensibly applied, gives a historic structure occupational viability in the modern world.

Noise problem in a polyester fiber plant in Pakistan.

Noise study has been undertaken in the three units of a polyester fiber plant. The level and frequency characteristics of the prevailing noise have been studied and speech interference levels evaluated. The results are discussed with reference to the maximum permissible occupational noise exposure limits as allowed by the ISO and other national standards. Some recommendations have also been made to provide safety measures to the workers against high level noise in these units.

Audio‐visual equipment noise in the meeting room—An uninvited participant

Even meeting spaces that have been designed to have excellent acoustics and low background noise can exhibit noise problems when audio‐visual equipment is introduced into the room. Several common A‐V equipment types were evaluated with the goal of assessing sound power, tonal content, and directivity. Results of the measurements, and predicted NC and speech interference levels are presented. Concepts for design of quiet equipment are discussed.

New systems for intercommunications—Synergy of acoustics and telecommunications

Proper room acoustics for audio teleconferencing and video teleconferencing facilities has been, at best, a matter of guesswork. In this paper, room acoustic treatments are varied in material and location within a typical conference room and the results studied using binaural analysis techniques. The relationship between room acoustics, speech intelligibility, speech interference, and mechanical noise levels in regard to teleconferencing systems will be explored in a quantitative manner, including the effects of ‘‘echo cancelling’’ technology.

Noise Pollution in the Operating Theatre

Sound levels during a typical major operation were measured to identify the main sources of noise in the operating theatre. Although overall sound levels were within the recommended levels for a satisfactory working environment, loud intermittent noises of up to 108 dB were emitted from sources such as suckers, intercoms, and alarms on anaesthetic monitoring devices. The noisiest time was usually during the preparation period of the operation; during surgery, noise levels were much higher than levels of normal speech between staff. Preferred speech interference levels were often exceeded which made communication difficult and sometimes impossible. Communication and concentration were also disrupted by unnecessary background conversation.

Noise pollution in the operating theatre

Sound levels during a typical major operation were measured to identify the main sources of noise in the operating theatre. Although overall sound levels were within the recommended levels for a satisfactory working environment, loud intermittent noises of up to 108 dB were emitted from sources such as suckers, "intercoms", and alarms on anaesthetic monitoring devices. The noisiest time was usually during the preparation period of the operation; during surgery, noise levels were much higher than levels of normal speech between staff. Preferred speech interference levels were often exceeded which made communication difficult and sometimes impossible. Communication and concentration were also disrupted by unnecessary background conversation.

Speech interference level as a predictor of face-to-face communication in noise

An experiment was performed to check the validity of the distance versus speech interference level (SIL) curves for face-to-face communication in noise [Beranek, Proc. IRE 35, 880–890 (1947); Webster, Proc. Natl. Conf. Noise as a Public Health Hazard (1969)]. Monosyllabic word intelligibility was measured both with and without visual cues at talker-to-listener distances of 2, 4, and 8 ft, and at speech interference levels of 65, 75, and 85 dB. The distance-versus-SIL curves were found to be reasonably consistent with the intelligibility data when no visual cues were available, but substantially underestimated tolerable speech interference levels for barely reliable communication with visual cues. Another major source of error was the difference between the observed rate of attenuation with distance of the speech signal and the idealized, free-field rate of attenuation assumed for the distance-versus-SIL curves. Errors resulting from this assumption were found to be consequential only at the larger talker-to-listener distances. Other important factors which affected the accuracy of the curves were the total speech power of the talker, the shape of the speech power spectrum, and the rate at which the talker raises his/her voice in noise.

Speech Intelligibility in and Speech Interference Levels of Traffic Noise in Hearing-Impaired and Normal Listeners

Speech intelligibility (phonetically balanced monosyllables = PB words) in traffic-like noise (random noise) as well as the speech interference levels (75% intelligibility) of this noise were investigated in three common listening situations, two indoors and one outdoors. A total of 279 persons were examined; 56 had normal hearing, 90 a presbycusic-type hearing loss, 95 noise-induced hearing loss, and 38 conductive hearing loss. In the indoor situation the hearing-impaired groups mainly retained their intelligibility in 40 dBA. Lowering of the noise level to less than 40 dBA resulted in only a minor, mostly insignificant improvement in speech intelligibility. Normal-hearing listeners maintained good speech intelligibility in the outdoor listening situation with noise levels up to 60 dBA, without lip-reading. For hearing-impaired groups, representing more than 1/2 million (8% of the population) people in Sweden, with hearing loss due to age and/or noise, the noise level outdoors must be lowered to 45 dBA in order to achieve good speech intelligibility at 1 m, without lip-reading.

The advantages of using four octaves versus three octaves for calculating speech interference levels (SIL)

Three sets of preferred frequency octaves have been proposed to replace the old 600–4800-Hz SIL calculation; 500, 1000, 2000 (3L); 500, 1000, 2000, 4000 (4); and 1000, 2000, 4000 (3H). Similarly, sets of frequency weighting contours have been proposed as substitute weighting networks (for A-level) for sound level meters. One hundred twelve environmental noises were adjusted in level to get equal articulation indices (AIs) of 0.1, 0.2, … 0.9. For each of six C − A groupings of noises 3L, 4, 3H SIL, and SI-50, 60, 70, 80, A and D weighting measures were calculated at each AI level. Standard deviations of calculated levels show that except for C − A ⩾ 15 dB (1) the 4-band SIL is the best estimate of AIs between 0.3 and 0.6; (2) the 3H SIL is generally best for higher AIs and the 3L for lower ones (and when C − A ⩾ 15 dB). When averaged over all AIs and over all C − A levels the 4-band SIL gives the best estimate of AI (av SD = 1.2 dB) followed by 3H (1.5 dB), SI-60 (1.9), 3L (2.1), and A (2.2). No speech intelligibility tests were run to verify the validity of these findings.

Airplane cockpit noise levels and pilot hearing sensitivity.

Audiometric testing of 89 commercial airline pilots indicated hearing losses which increased with age and logged flight time and were greater than one would expect in the normal population. Cockpit noise level determinations were made in 18 different types of airplanes at various power settings. Hearing protective devices, for the cockpit crews, are indicated for seven types of airplanes. Fifteen types of airplanes exhibited cockpit speech interference levels of 76 db or greater during takeoff, climb, or cruise power settings.

Loudness and Impulsive Noise

A commonly accepted criterion for noise control is a family of curves known as the NC or N curves. This criterion was based upon a study by Beranek relating speech interference levels and loudness levels to subjective limits of acceptibility within various environments. Impulsive noise is sufficiently different from ordinary background noise so that these relationships no longer apply. The difficulty of using present-day limits for other than typical background noise is that, if the spectral shape of the noise does not follow the NC contour, there is no way of relating measurable parameters to subjective annoyance factors. Previous studies have shown that loudness limits based upon the relative loudness of impulsive noise as subjectively compared to random noise leave something to be desired. The purpose of this paper is to present certain assumptions and related subjective data showing the correlation between measured noise levels and subjectively evaluated “noisiness” for both continuous and some types of impulsive noises. Various noise-measuring techniques were evaluated in an effort to find out which method would provide consistent results regardless of the type of noise applied. The results presented in this paper can be used as a basis for future work on establishing noise limits for office, data processing, and even factory-type impulsive noise environments. Characteristic responses of present acoustical instrumentation are discussed and compared to the subjective noise evaluations.

Predicting Speech Interference and Annoyance from A-Weighted Sound Levels

A sample of 741 noises measured in factories and in construction equipment was used to relate speech interference levels to A-weighted sound levels. A mathematical formula was developed which predicts the speech interference level from the A-weighted sound level with little error. A graph was drawn for use in predicting speech interference effects directly from A-weighted sound levels. Another sample of 235 noises measured along industrial plant boundaries was used to relate A-weighted sound levels to the level rank used for rating annoyance. A method was developed for predicting the level rank from the A-weighted sound level with satisfactory accuracy. A graph was drawn for predicting the degree of annoyance directly from the A-weighted sound level. The methods developed for predicting speech interference and annoyance effects directly from A-weighted sound levels are believed to be as accurate as the methods utilizing octave-band sound-pressure levels on which they are based.

Physical Measurements of Equally Speech-Interfering Navy Noises

The sound level of each of 16 diverse noises was adjusted so that loudspeaker-reproduced rhyme words at a level of 78 dB (C) at one meter were reduced to 50% word intelligibility. Spectrum analyses (octave band and 20-cps band), physical measurements (C, B, A, DIN 3 sound-level meter weightings), calculations [Speech Interference Levels (SIL)], and peak fittings [to noise criteria (NC)-type curves] were made to find which method came closest to agreeing that the noises were equally speech-interfering. SIL calculations that included the octave 300–600 cps predicted the speech-interference aspects of the 16 noises best. The A and DIN 3 weighting networks, the conventional (600–4800 cps) SIL, and use of a restricted region (350–2800 cps) of NC-type curves gave the next best prediction. The poorest predictors were the B or C frequency-weighting networks and use of the NCA, NC, or ISO contours over their total frequency range.

Physical and Psychophysical Descriptions of Sixteen Equally Speech-Interfering Noises

Physical and psychophysical measurements and/or calculations were made on 16 equally speech-interfering noises. Speech-interference levels (SIL) based on octaves with center frequencies of 500, 1000, and 2000 cps or at 425, 850, and 1700 cps predicted very well that the noises were equally speech-interfering. These SIL's predicted better than the more conventional SIL based on octaves between 600 and 4800 cps. Articulation-index (AI) scores based on 5 or 6 weighted octaves were equivalent to the 20-band AI methods and were not necessarily better than SIL methods. Fitting the peaks of plotted spectra to noise-criteria (NC or NCA) curves was not adequate, although averaging that part of the spectra centered on octaves from 500 through 2000 cps through NC or NCA curves gave good prediction. Equally speech-interfering noises were not equal in loudness as calculated by Stevens' method, or in PNdB. There was evidence to show that the frequency that divided noise-masked speech into two equally intelligible frequency regions was 850 or 1000 cps, and was not 1700 and 1900 cps, which is the dividing frequency when the speech in quiet is progressively restricted in bandwidth by high- or low-passed filtering.

Speech Interference Levels as Criteria for Rating Background Noise in Offices

On the basis of a number of surveys in commercial offices, criteria for tolerable office background noise levels are proposed. Questions were asked of people working in these offices regarding their ability to telephone, to confer and to perform their work under the existing noise conditions. The speech interference levels of the background noises were determined in each case. The results are presented in a chart, which rates the noise conditions as a function of speech interference levels in each of three general types of offices, (a) executive offices, (b) general clerical offices, and (c) business machines offices.