Precision Sound Level Meter Research Articles

Research on U.S. military base aircraft noise aircraft and aircraft flight routes in Okinawa Prefecture

Currently, about 70% of the area of US military bases nationwide is concentrated in Okinawa Prefecture, occupying an area of about 186.09 km2, which is about 10.4% of the prefectural land area of Okinawa Prefecture. Many of the US military bases are located in or near the center of urban areas and have a great influence on urban planning. Among them, the aircraft noise problem is serious, and it has a great influence on the living environment of the surrounding residents, such as the sound of takeoff and landing and the sound of engine adjustment. In response to this, the government is taking measures such as soundproofing work, but the current situation is that it has not been resolved. The purpose of this study is to (1) grasp and consider the actual situation of noise problems related to US military training through visual surveys, (2) derive the trajectory of US military aircraft from the measurement results of precision sound level meters and visual surveys, and use the results to determine whether the measurement environment is appropriate. (3) Based on the obtained noise data and track charts, consider the noise damage situation at each point.

On the test method for short-term level fluctuation of sound calibrators

Most noise bylaws state that a precision sound level meter which meets the International Electrotechnical Commission Publication 651 or the American National Standards Institute S1.4-1983 needs to be used for noise measurements. To ensure measurement accuracy, sound calibrators are used to check the sound level meter accuracy before and after any such measurements, as required by most noise regulations. The sound calibrator itself needs to be calibrated routinely and traceable to national standards. The International Standard IEC 60942, Electroacoustics - Sound calibrators, specifies performance requirements for the sound pressure level, short-term level fluctuation, frequency, and distortion and associated test methods. However, the test method for short-term level fluctuation specified in IEC 60942 is problematic. The short-term level fluctuation cannot be measured in some cases using the method specified in IEC 60942. In this paper, a detailed theoretical analysis is presented addressing this particular issue. Closed-form solutions are obtained for typical sinusoidal sound signals. Two experimental setups and measurement results for the validation of the theoretical analysis are also presented. One uses a commercial sound level meter and the other uses a precision sound pressure measurement system developed recently at the National Research Council Canada.

Smartphone Recordings are Comparable to “Gold Standard” Recordings for Acoustic Measurements of Voice

PurposeThe purpose of this study was to assess the relationship and comparability of cepstral and spectral measures of voice obtained from a high-cost “flat” microphone and precision sound level meter (SLM) vs. high-end and entry level models of commonly and currently used smartphones (iPhone i12 and iSE; Samsung s21 and s9 smartphones). Device comparisons were also conducted in different settings (sound-treated booth vs. typical “quiet” office room) and at different mouth-to-microphone distances (15 and 30 cm). MethodsThe SLM and smartphone devices were used to record a series of speech and vowel samples from a prerecorded diverse set of 24 speakers representing a wide range of sex, age, fundamental frequency (F0), and voice quality types. Recordings were analyzed for the following measures: smoothed cepstral peak prominence (CPP in dB); the low vs high spectral ratio (L/H Ratio in dB); and the Cepstral Spectral Index of Dysphonia (CSID). ResultsA strong device effect was observed for L/H Ratio (dB) in both vowel and sentence contexts and for CSID in the sentence context. In contrast, device had a weak effect on CPP (dB), regardless of context. Recording distance was observed to have a small-to-moderate effect on measures of CPP and CSID but had a negligible effect on L/H Ratio. With the exception of L/H Ratio in the vowel context, setting was observed to have a strong effect on all three measures. While these aforementioned effects resulted in significant differences between measures obtained with SLM vs. smartphone devices, the intercorrelations of the measurements were extremely strong (r's > 0.90), indicating that all devices were able to capture the range of voice characteristics represented in the voice sample corpus. Regression modeling showed that acoustic measurements obtained from smartphone recordings could be successfully converted to comparable measurements obtained by a "gold standard" (precision SLM recordings conducted in a sound-treated booth at 15 cm) with small degrees of error. ConclusionsThese findings indicate that a variety of commonly available modern smartphones can be used to collect high quality voice recordings usable for informative acoustic analysis. While device, setting, and distance can have significant effects on acoustic measurements, these effects are predictable and can be accounted for using regression modeling.

Occupational noise emitted by digital printing machines

The aim of this study was to determine noise level of different digital printing machines in Egyptian printing companies, More extensive studies are needed to determine the exact impact of noise on the workers. Technical and organizational measures in order to control noise and prevent noise exposure, and general hearing conservation program to protect workers, should be introduced in digital printing industry. The paper research followed the Experimental analytical methodology. The extent of noise in one of the Egyptian digital printing companies determined using Integrated precision Sound Level Meter (Class 1) QUEST type Sound Level Calibrator (Class 1) and sound software toolkit to calculate the collected data of sound pressure levels on equivalent A-level (dBA), the collected data performed inside two rooms in digital printing company, and measure token on two types of digital printing machines and other printing equipment. The A-weighted noise levels inside room1 were on Leq, Leq 8hr (80.4dB), whereas inside room2 (72.9dB), the paper suggested different recommendations and procedures for noise reduction, absorption and future procurement.

Comprehensive study of the response of inexpensive low energy wireless sensors for traffic noise monitoring

Precision noise monitoring can prove to be prohibitively expensive and labour intensive. Low cost, wireless, environmental sensor systems, referred to as motes, are being developed as alternatives. Whilst considered of lower accuracy than precision sound level meters, they can be deployed for much longer periods and monitor continuously at one minute resolution. This paper reports the performance of two commercially available motes, the eMote developed to monitor traffic and the nMote to monitor airport noise, in both controlled laboratory conditions, and deployment in the field. Under controlled conditions the performance was assessed by co-location with precision sound level meters (Brüel and Kjær Type, 2260) and exposed to coloured (‘white’ and ‘pink’) noise at different levels. Both units exhibited strong linear relationships (R2 > 0.98) for LAeq when compared to the precision instruments. The performance of three individual eMotes, in terms of similarity and variability, were broadly consistent across the tested units, though levels were systematically overestimated by approximately ±3 dBA when uncorrected. The eMote units were found to exhibit a lower detection limit of ~55 dBA, potentially limiting their application to (a) urban daytime conditions when levels generally exceed that threshold and (b) at other times and locations as screening tools for excessive noise levels, to justify more expensive precision monitoring confirming findings of Marouf et al. (2018). Further research here demonstrates that the systematic error could be corrected by an algorithm resulting in a random error of better than ±1.5dBA. Both nMote units exhibited a lower detection limit (~40dBA). One nMote was electronically calibrated at the manufacturing stage and found to slightly underestimate at lower and overestimate at higher levels. Some improvement was made by developing an algorithm giving overall measurement accuracy better than ±2dBA. The other nMote not calibrated at the manufacturing stage underestimated values at low levels. This could be corrected resulting in a random error of better than ±2.5dBA. Similar results for both Mote types were observed in the field but with more variability due to the data synchronisation, local reflection and refraction etc. and the continually varying noise characteristics of traffic. Whilst the nMote was designed for airport noise, it is considered along with the eMote suitable for monitoring traffic noise in urban areas, and demonstrates much potential to be incorporated into existing Intelligent Transport System technologies to measure, manage and control population exposure to traffic noise (e.g. as a ‘noise camera’ analogous to the existing speed camera). Given that deriving correction algorithms for motes in controlled test environments is impractical, the knowledge gained from these studies has led to modifications to the design and with electronic calibration as part of the manufacturing process measurement errors of better than ±2dBA across the range of sensitivity can be achieved. With advancements in technologies and if power consumption was not an issue, then nowadays a device could quite easily be designed with a dynamic range and linearity quite close to the precision instruments for little extra cost.

Comparison of crown fit and operator preferences between tooth preparation with electric and air-turbine handpieces

Statement of problemTooth preparations for ceramic crowns require precision and accuracy, which may be influenced by the choice of dental handpiece. However, comparisons of the accuracy of tooth preparations made with traditional air-turbine handpieces and electric handpieces are lacking. PurposeThe purpose of this in vitro study was to evaluate operator preferences and tooth preparation performance by using electric and air-turbine handpieces with self-reported preferences, sound levels, surface roughness, and the fit of the crown produced. Material and methodsTwenty dentists were asked to use the air-turbine or the electric handpiece. Feedback on the noise, weight, feel of grip, flexibility, and tooth preparation in general was scored according to a visual analog scale (VAS). Additionally, the dentists were asked to complete a questionnaire on their handpiece preference. The noise of the 2 handpieces was measured by using a precision sound level meter. The surface roughness of 10 teeth was measured by using a profilometer. The other 18 teeth were prepared to measure the marginal and internal fit of ceramic crowns by the replica technique. The VAS scores of operator preferences were analyzed with the Wilcoxon signed ranks test. Decibel levels were analyzed with the Mann-Whitney U test. The McNemar test was used to compare the ratio of preferred handpiece. The surface roughness and marginal and internal fit were analyzed with the independent t test to determine significant differences (all α=.05). ResultsThe electric handpiece was heavier, had a poorer grip feel, was less flexible (P<.001), produced lower noise and better feeling of the tooth preparation in general (P<.001), and was preferred in the finishing stage for its greater smoothness (P<.05). The noise produced by the electric handpiece was lower during both idling and tooth preparation at 15-cm, 30-cm, and 45-cm distances (P<.01). The electric handpiece produced surface roughness values (Sa) similar to those of the air-turbine handpiece (P>.05). No significant differences were noted for the marginal and internal crown fit between the air-turbine handpiece and electric handpiece groups (P>.05). ConclusionsDespite its heavier weight, poorer grip feel, and less flexibility, the electric handpiece emitted lower noise, produced better feeling of the tooth preparation in general, and was preferred in the finishing step of tooth preparation for its greater smoothness than the air-turbine handpiece. The surface roughness of the prepared teeth and the crown fit between the tooth and ceramic crown were not affected by the air-turbine or electric handpiece.

Pervasive wireless sensors: A new monitoring tool for road traffic noise evaluation

Noise pollution is estimated to affect 170 million citizens in Europe, causing serious public health problems [1]. The World Health Organisation claims that at least one million healthy life years are lost per year in Europe due to road traffic noise [2]. Effective management of noise requires an understanding of its causes. This understanding is limited by traditional monitoring methods, which employ expensive equipment and are labour intensive. This paper presents the results of a comprehensive programme of correction and validation of a low-cost device referred to as an eMote for pervasive monitoring and is the first to quantify the accuracy of inexpensive noise systems that use microphones typically costing about one Euro.Pervasive wireless noise sensors (eMotes) were validated by co-location with precision sound level meters in controlled indoor, and at roadside outdoor environments. Strong linear relationships between the eMotes and the precision systems, across a noise range between 55 dBA and 94 dBA were observed and exhibited consistent bias compared to the precision measurement. Therefore, a generic, corrective relationship was derived and validated in three contrasting outdoor traffic noise environments, employing both short-term attended, and long-term unattended measurements, which were carried out during day and/or evening and/or night periods.The eMotes were shown to respond consistently to white and pink generated noise during the evaluation of the accuracy process, and the generic correction algorithm for white noise delivered better than 3 dBA accuracy in comparison to precision data at a one-minute averaging resolution. The correction algorithm improved the concordance correlation coefficient (ccc) and coefficient of determination (R2) of the eMote measurements against those of the precision instrument. Removal of short-duration, excessively loud events (e.g. sirens), which represented 2% of the total data, improved the ccc and R2 values further typically to 0.74 and 0.60 respectively, which is considered good, given the limitations of the experimental procedure. The research provides scientific evidence that whilst not acceptable for compliance monitoring to standards for noise exposure, the eMote is a valuable system to screen for excessive exposure; to understand the causes of traffic related noise in urban areas; to provide an indication of the spatial and temporal variation in noise levels and the knowledge to design appropriate solutions, in turn this will lead to more effective abatement. The continued monitoring allows the impact to be quantified giving confidence that intervention measures are worthwhile, delivering added value compared to current measurement methods.

Changes in work accuracy in a noisy environment : A case of work accuracy in the marine engine room environment

It is a requirement that the noise level in the engine rooms of modern ships meet the International Maritime Organization (IMO) noise level code criteria. This standard comes as it had been revealed that, in noisy environments, ship engineers are uncomfortable and lack concentration, and as a result might experience a reduction in work accuracy. In a noisy environment, it has been found that engineers not only feel fatigued but also work with less precision. These facts have been empirically demonstrated. In the laboratory, a noisy environment was reconstructed by playing the machine operating sound, recorded in a ship engine room, and laying down metal floor plates similar to those found in a ship engine room. Speakers were installed under the metal floor plates, and the recorded machine operating sounds were played back from the speakers during the experiments. In the experiments, the participants were asked to perform work tasks in the noisy environment. The participants’ biological responses were measured during the experiment. The output from speakers during the experiment was measured by a precision sound level meter at a height corresponding to the ear level of the participant. In this study, we measured biological responses, such as heartbeat and brain waves (alpha band wave, beta band wave, etc.), as an evaluation index. From the biological responses, we estimated the participants’ mental workload in the noisy environment.

Experimental Investigation on Functional Parameters of the Engines Exhaust Mufflers

The paper presents the results obtained by investigating some functional parameters as the noise level, the pressure – drop and the temperatures of three different manufacturing solutions for mufflers. The results emphasize the corroboration between these parameters and contribute to the improvement of the muffler fabrication and design since it is a complex function that affects noise characteristics, emission and fuel efficiency of engine. It was designed a measurement chain for the noise level evaluation of the mufflers including a microphone Bruel&amp;Kjaer type 4133, a Impulse Precision Sound Level Meter Bruel&amp;Kjaer, type 2209, with standard filters and a multifunctional external data acquisition board type-NI DAQPad-6015 . We assessed the noise level, using two based LabVIEW virtual instruments, measuring total band power and the equivalent continuous sound pressure level. It was also created a measurement chain for the pressure – drop evaluation and temperature distribution on the external surface of the mufflers.

건설장비에 의한 터널작업의 소음환경 실태

Workers engaged in construction works have been exposed to high levels of noise during their work in tunnels. Noise is one of the major health hazards for employees working in construction sites. The aim of this study is to evaluate the noise levels generating from tunneling equipments such as jumbo drills, backhoes, payloaders, shotcrete machines and service cars. Explosion and turbo fan noises were also monitored. A high precision sound level meter was introduced for measuring LAeq, LAFmax, LAFmin and LCpeak noises in 5 tunneling work sites that were located in Seoul, Kyunggi-do and Kangwon-do areas with NATM and shield methods. The highest noise was recorded by explosion(151.9 dB LCpeak) followed by jumbo drills of higher than 110 dB(A) LAeq. Backhoe normally generated 90~110 dB(A) LAeq while breaking work of rock showed additional around 5~15 dB(A). Noise exposure levels for payloader and shotcrete machine scored more than 90 dB(A) which might be a source of noise-induced hearing loss. Additional research in revealing noise levels from construction equipments operating in tunneling works may enhance the protection of workers who exposed to noise primarily at the sites.

아이폰 4 및 아이폰 3Gs의 소음측정 애플리케이션에 대한 정확도 평가

This article evaluates the accuracy of noise measurements for 37 noise measurement applications for iPhone 4 and iPhone 3Gs. Noise levels were measured using simultaneously a precision sound level meter and iPhones installed noise measurement applications at the levels of 70 dB, 80 dB and 90 dB at 1,000 Hz. Measurement errors were estimated by subtracting two measurements between iPhone and sound level meter. It was found that measurement errors of 34 applications(89.2%) were greater than <TEX>${\pm}2$</TEX> dB which is the maximum allowable error range for the Type II sound level meter. It was only 4 applications that measurement errors lie within <TEX>${\pm}2$</TEX> dB error range. There was no significant differences among measurements with four iPhone 4s. However, there were significant differences between the measurements with iPhone 4 and iPhone 3Gs using the same application. It was due to the different hardware specifications such as microphone. Therefore, noise measurement applications, for example, which has to utilize hardware of the smartphone, should be programmed to identify hardware specifications and to adopt appropriate correction factors upon hardware specifications. In conclusion, it is necessary to check accuracy and validity before using the noise measurement applications for iPhones. Also, it was suggested that it should develop an evaluation guideline or protocol on accuracy testing for the measurement applications using a smartphone.

Cross-Language Identification of Long-Term Average Speech Spectra in Korean and English

To identify the quantitative differences between Korean and English in long-term average speech spectra (LTASS). Twenty Korean speakers, who lived in the capital of Korea and spoke standard Korean as their first language, were compared with 20 native English speakers. For the Korean speakers, a passage from a novel and a passage from a leading newspaper article were chosen. For the English speakers, the Rainbow Passage was used. The speech was digitally recorded using GenRad 1982 Precision Sound Level Meter and GoldWave® software and analyzed using MATLAB program. There was no significant difference in the LTASS between the Korean subjects reading a news article or a novel. For male subjects, the LTASS of Korean speakers was significantly lower than that of English speakers above 1.6 kHz except at 4 kHz and its difference was more than 5 dB, especially at higher frequencies. For women, the LTASS of Korean speakers showed significantly lower levels at 0.2, 0.5, 1, 1.25, 2, 2.5, 6.3, 8, and 10 kHz, but the differences were less than 5 dB. Compared with English speakers, the LTASS of Korean speakers showed significantly lower levels in frequencies above 2 kHz except at 4 kHz. The difference was less than 5 dB between 2 and 5 kHz but more than 5 dB above 6 kHz. To adjust the formula for fitting hearing aids for Koreans, our results based on the LTASS analysis suggest that one needs to raise the gain in high-frequency regions.

Spatial Mapping of Traffic Noise Levels in Urban Areas

This paper combines field data with an analytical approach to spatially map noise levels due to traffic movements at relatively high traffic volume signalized intersections utilizing the potential of Geographic Information Systems (GIS). Noise data were collected using a discrete mapping technique at 29 signalized intersections, as well as between intersections, and at their respective neighborhood areas in Amman, capital of Jordan. Data were collected in three different highly congested traffic peak periods: 7:30 a.m.-9:00 a.m., 1:30 p.m.-3:00 p.m., and 9:00 p.m.-11:00 p.m. A portable precision sound level meter capable of measuring noise levels from 34 to 134 decibels (dB) was used during the data collection process. The highest recorded noise level at some signals was 80 dB, while the lowest was 34 dB. In fact, some signalized intersections showed higher noise levels than the acceptable or the standard ones, i.e., 65 dB for daytime and 55 dB for nighttime in residential areas at city center. Two-dimensional (2D) vector and raster maps of noise levels, at different time periods for signals' areas and neighborhoods, were spatially displayed. Results showed that the developed GIS maps could be useful for city planning and other environmental management applications for the purpose of: 1) temporal monitoring and queries of noise level changes as a function of time, 2) spatial queries to find the highest noise disturbance location and its time of the day, 3) development of an online noise information system, 4) using noise level based spatial maps as indicators of variation in land prices, and 5) forecasting and current assessment of the acoustic climate of urban areas.

Vocalization source levels of adult male northern elephant seals (Mirounga angustirostris).

Aerial vocalization source levels were obtained for adult male northern elephant seals from 1999–2010. Vocalizations from known individuals (marked within years) were selected from three breeding seasons (1999–2000, 2004–2005, and 2009–2010) evenly spaced during this interval so that it is unlikely animals were resampled across seasons. Sound pressure levels of calls were measured on‐axis (0‐deg orientation) at 1‐m range using Brel and KJær 2203 and 2250 precision sound level meters. Calls almost always occurred in series, as previously described; the maximum received level for any pulse in each series is used as the source level. Source levels are reported for individuals with at least four complete bouts. All sex/age classes were measured; the adult male data will be discussed and compared with other mammals in terms of rms levels (two temporal weighting functions) and peak sound pressure levels. Results indicate that calls almost always exceed 100 dB rms (re: 20 μPa) with peak levels regularly exceeding 120 dB. These loud sounds might suggest long‐range communication, but considering hearing data Ron Schusterman and Dave Kastak first collected on this species and environmental noise levels in their rookeries, intense signals are likely required even for the small ranges over which they apparently function. [Funding provided by ONR.]

Noise Trauma Induced by a Mousetrap—Sound Pressure Level Measurement of Vole Captive Bolt Devices

While ballistic parameters of vole captive bolt devices have been reported, there is no investigation on their hazardous potential to cause noise trauma. The aim of this experimental study was to measure the sound pressure levels of vole captive bolt devices. Two different shooting devices were examined with a modular precision sound level meter on an outdoor firing range. Measurements were taken in a semi-circular configuration with measuring points 0 degrees in front of the muzzle, 90 degrees at right angle of the muzzle, and 180 degrees behind the shooting device. Distances between muzzle and microphone were 0.5, 1, 2, 10, and 20 m. Sound pressure levels exceeded 130 dB(C) at any measuring point within the 20-m area. Highest measurements (more than 172 dB[C]) were taken in the 0 degrees direction at the 0.5-m distance for both shooting devices proving the hazardous potential of these gadgets to cause noise trauma.

Assessment and ANN Modeling of Noise Levels at Major Road Intersections in an Indian Intermediate City

The noise generated from vehicular traffic is a major source of environmental pollution. This paper discusses a comprehensive study on the assessment and ANN modeling of noise levels due to vehicular traffic flow at interrupted traffic flow condition, i.e., at SBI (State Bank Intersection) and BSI (Bus Stand Intersection) in Yavatmal city, district place of Vidarbha Region in Maharashtra State (India). Traffic volume data and noise level data were collected simultaneously at ten selected locations. The noise level data were recorded with precision sound level meter (TES-1352 A data logger SLM, IEC651 Type2, ANSI S 1.4 peak hours (morning and evening). Instantaneous noise levels in dBA were recorded (one count per two seconds or at a rate of 30 counts per minute) and processed through Excel by grouped into 15 minutes data to evaluate noise descriptors in the form of Lmax, Lmin, L 10 , L 50 , L 90 , L eq , LNP, TNI ( Traffic Noise Index) & NC (Noise climate). Artificial Neural Network software (Elite ANN) was utilized to perform modeling. Total traffic, traffic composition (Bus/Truck), LCV (Light Commercial Vehicle), TW (Two Wheelers), bicycle and others in % and carriageway width, distance of sound level meter from pavement edge were considered as input data. The observed input and output data were processed using ANN at interrupted traffic flow conditions. The output was estimated as L 10 , L eq , LNP, TNI and NC. The performance of the model was tested by root mean square error (RMSE), the mean absolute error (MAE) and correlation coefficient. The model was validated using linear regression analysis where it was observed that there is no significant difference between the observed and predicted output parameters.

Phonometrical precision measurements during a high end classical music live recording and four standardized recording systems’ signal comparison

Discographical sound recording process is very seldom accompanied by real sound pressure, intensity and level measurements. Usually available data are often referred to mathematical extrapolations calculated on sound recording audio signals. This article investigates the situation defined as ‘‘real’’ from a scientifical point of view, having as a referring base a Swedish precision sound level meter fresh from calibration, during the stereophonic multichannel live recording session of the Philharmonische Camerata Berlin. Comparison among reference signal and eight high quality microphone capsules signals coming from four different stereophonic standardized microphone systems devoted to discographical purpose recording (XY, ORTF, Binaurale and AB) shows big differences among the respective signals and the same recording spot measurement system position. It is noticeable how differences even higher than 6 dB can make microphone positioning particularly critical. A standardizing method is proposed.

Noise levels in dental schools

To measure and analyse noise levels in the learning-teaching activities at the Dental School of the University of Porto (Portugal). Sound levels were measured in five different practice areas and laboratories, selected as representative of a variety of learning-teaching activities. The noise levels were determined using a precision sound level meter that was positioned at ear level and at 1 m distance from the operator. The noise levels registered vary between 60 and 99 dB(A) and are similar to the data of other international studies. The results recorded differences in sound levels when the equipment was merely turned on and during cutting operations. Differences between brand new and used equipment were also noted. It appears that hearing damage risk may be lesser amongst dentists who use brand new equipment. The noise levels detected in this study are considered to be close to the limit of risk of hearing loss.

Audio spectrum and sound pressure levels vary between pulse oximeters

The variable-pitch pulse oximeter is an important intraoperative patient monitor. Our ability to hear its auditory signal depends on its acoustical properties and our hearing. This study quantitatively describes the audio spectrum and sound pressure levels of the monitoring tones produced by five variable-pitch pulse oximeters. We compared the Datex-Ohmeda Capnomac Ultima, Hewlett-Packard M1166A, Datex-Engstrom AS/3, Ohmeda Biox 3700, and Datex-Ohmeda 3800 oximeters. Three machines of each of the five models were assessed for sound pressure levels (using a precision sound level meter) and audio spectrum (using a hanning windowed fast Fourier trans-form of three beats at saturations of 99%, 90%, and 85%). The widest range of sound pressure levels was produced by the Hewlett-Packard M1166A (46.5 +/- 1.74 dB to 76.9 +/- 2.77 dB). The loudest model was the Datex-Engstrom AS/3 (89.2 +/- 5.36 dB). Three oximeters, when set to the lower ranges of their volume settings, were indistinguishable from background operating room noise. Each model produced sounds with different audio spectra. Although each model produced a fundamental tone with multiple harmonic overtones, the number of harmonics varied with each model; from three harmonic tones on the Hewlett-Packard M1166A, to 12 on the Ohmeda Biox 3700. There were variations between models, and individual machines of the same model with respect to the fundamental tone associated with a given saturation. There is considerable variance in the sound pressure and audio spectrum of commercially-available pulse oximeters. Further studies are warranted in order to establish standards.

Live recordings of sound levels during the use of powered instruments in ENT surgery.

Otolaryngology is one of the surgical specialities employing high-powered instruments and this study was designed in order to establish whether sound levels at work conform to HSE guidelines. No study to date has measured intra-operative noise levels in ENT operation theatres. A prospective observational study was therefore performed. Sound levels were measured during the use of bone drills for mastoid surgery and microdebriders for endoscopic sinus surgery. A SLM/IS Acos Class I sound level meter calibrated to BS 1259 was employed. A spectrum analysis of drill-generated noise was measured using a calibrated B and K precision sound level meter. Sound levels emitted varied as follows: Large burrs- 72.4 dB (A), medium size; 71.2 dB (A), small sized burrs- 68.8 dB (A) (all values for cutting burrs) and 60.8 dB (A) for diamond burs. With microdebriders, the average sound level was 60.1 dBA. Spectrum analysis revealed that the maximum intensity was at 3.15 kHz, followed by 4 kHz, while the least sound was produced at 40 kHz and 31.5 kHz. Essentially sound produced by drills was between 1.6 kHz and 6.3 kHz. Powered instruments used in ENT surgery are safe and pose no occupational hazard.