Browsing by Author "Robinson, Gary S."
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- The Detection of Warning Signals While Wearing Active Noise Reduction and Passive Hearing Protection DevicesChristian, Erika (Virginia Tech, 1999-07-15)The research described herein was undertaken to determine how masked thresholds changed when individuals wore an active noise reduction (ANR) hearing protection device (HPD), a passive HPD, or no HPD. An ANR earmuff, a passive earmuff, and a user-molded foam earplug were tested in two types of noises (pink and red) at two different noise levels (85 dBA and 100 dBA). The signal used was an industry-standard backup alarm. The experimental design was completely within-subjects. An ascending method of limits was used to obtain 15-20 correct positive responses, which were then averaged to obtain the masked thresholds for each treatment condition. A visual probability monitoring task was incorporated in the experimental design to provide a loading task for the participants. In addition to masked thresholds, comfort and mental workload were assessed. Finally, participants were asked to rank each of the three HPDs with respect to their perceived ability to facilitate hearing the signal in noise. Results indicated that in 85 dBA noise, masked thresholds were lower when hearing protection devices were worn, compared to the unoccluded condition. Additionally, the results indicated that the ANR device provided a significant advantage (lower masked thresholds) over the passive earmuff in the low-frequency biased red noise (across both noise levels) and the 100 dBA noise level (across both noise spectra). However, the ANR earmuff exhibited no significant advantage over the user-molded foam earplug in any of the conditions. Rather, the user-molded foam earplug produced significantly lower masked thresholds at 100 dBA. The results also indicated that there was no difference between the three devices in their perceived ability to facilitate detection of the signal. There was also not a significant difference in comfort ratings between the three HPDs, although there were several complaints about the comfort of the ANR earmuff during the experiment.
- The Effect of Directional Auditory Cues on Driver Performance in a Simulated Truck Cab EnvironmentPowell, Jared Alan (Virginia Tech, 1999-12-10)A human factors experiment was conducted to investigate the potential benefits of using directional auditory cues in intelligent transportation system technologies in commercial vehicles. Twelve licensed commercial vehicle operators drove a commercial truck-driving simulator and were prompted to select highway numbers on a side-task display. Prompts were presented visually or aurally. Auditory prompts were presented either diotically (both ears simultaneously) or directionally (to either the left or right ear). The search task varied in map density and timing of the prompts in relation to speed limit changes. All experimental conditions were compared to a control condition containing no secondary task. Both driving performance (lane deviation, steering wheel angle, road heading angle error, accidents, and adherence to the speed limit) and secondary task performance (accuracy and response time) measures were collected. Results showed that drivers were able to respond more quickly and accurately to the search task when directional auditory cues were used. Results also showed that driving performance degrades when display density increases and that the use of directional auditory prompts lessens this deterioration of performance for high-density conditions.
- Effects of anechoic vs. reverberant sound-field, subject gender, and outlier dismissal on the real-ear attenuation of hearing protection devicesRobinson, Gary S. (Virginia Tech, 1991)An experiment was conducted to determine the effects of different acoustic characteristics of the testing environment on the measured attenuation of hearing protection devices (HPDs) when using a standard real-ear attenuation at threshold (REAT) protocol. In the experiment, three earmuffs and three earplugs were tested in two diffuse sound fields implemented in two different sound environments with different loudspeaker configurations. In the first case, the testing environment was reverberant, with frequency-specific reverberation time characteristics as specified in ANSI $3.19- 1974, "Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs" and with three loudspeakers, one in each principal plane of the room. In the other case, a diffuse sound field was established within an anechoic chamber (free-field), as permitted by ANSI S12.6-1984 "Method for the Measurement of the Real-Ear Attenuation of Hearing Protectors" using four loudspeakers, one at each vertex of a tetrahedron with the subject's head center position at the centroid. Each of the environments met the requirements of the applicable ANSI standard as well as the requirements of standards adopted by several foreign countries. The experimental design allowed a direct comparison of the testing environments (reverberant vs. free-field) permitted by the two aforementioned ANSI standards. Results indicate that for both earmuffs and earplugs, the environment in which a REAT evaluation is performed has a statistically significant impact on the results of the evaluation. These results have implications for ongoing standards development efforts not only in the United States but also abroad since the testing environments investigated in this research are either required or allowed by several international standards. These international standards include: International Standard ISO 4869-1981, Canadian Standard CSA Z94.2-M1984, British Standard BSI 5108:1983, and Swedish Standard SS 882151 (1981). The impact of outlier dismissal on the results of REAT tests of HPDs was also investigated and found to have minimal impact on the results obtained in this experiment. However, this result is most likely case-specific and it is doubted that any generalizations can be made concerning outlier tests and their impact on HPD evaluations. As a side issue, it was also determined that ear canal size is highly correlated with attenuation achieved using premolded earplugs with attenuation decreasing with increasing ear canal size. No consistent gender effects were found in the analysis, indicating that gender alone may not be an important factor in determining how much attenuation can be obtained with a given HPD. Finally, the lack of a significant trial effect points to the absence of a strong practice effect over the three trials of a REAT evaluation, at least for subjects who are highly practiced in the REAT procedures.
- Effects of display type and steering force feedback on performance in a medium-fidelity driving simulatorPerala, Chuck H. (Virginia Tech, 2003-04-22)Research has shown that head-mounted displays can produce greater presence in a virtual environment than direct-view displays. It has also been shown that after vision, haptic response is one of the most important inputs for humans in a simulated environment. This research was designed primarily to determine the performance differences associated with different display types, levels of steering force feedback, and the interaction between these two factors in a low-to-medium fidelity, PC-based driving simulator. Participants drove on a simulated driving course during which both objective driving performance data were collected (lane deviation, speed control, steering wheel angle variance, and time to the complete course) as well as subjective self-report measures including questionnaires designed to tap immersive tendencies and perceived levels of presence. Results of the research show that the use of a head-mounted display can significantly impact driving performance in terms of speed control and lane deviation. Speed control was significantly improved (increased) and lane deviation was significantly improved (decreased) in three of the four roadway segments with the use of an HMD. Results for active steering force feedback, however, showed a significantly negative effect on driving performance with an increase in average lane deviation. Descriptive statistics showed that participants preferred the HMD and D-V equally and all but one participant preferred active steering force feedback.
- Effects of display type, age, and gender on driving performance and simulator-induced sickness in a medium-fidelity driving simulatorPenhallegon, William James (Virginia Tech, 2003-06-30)This study investigated the link between age and gender susceptibility to simulator-induced sickness in conjunction with display type. Simulator-induced sickness and ataxia were measured before and after exposure to a medium-fidelity driving simulator. Participants in four age and gender categories (older and younger males and females) operated the simulator with a consumer-grade head-mounted display (HMD), and then with a large screen, direct-view plasma display. This study set out to recommend a particular display type that would be appropriate for use with particular age/gender groups in a general-purpose driving simulator. Unfortunately, practice effects affected the simulator-induced sickness and driving performance results for display type, which precludes making recommendations regarding the appropriate use of each display. Despite this, several important discoveries were made, including: 1) older participants did experience significantly increased simulator-induced sickness discomfort than the younger participants - regardless of display type; and 2) there was no significant difference found between genders in either simulator-induced sickness or driving performance; although females generally expressed a subjective preference for the direct-view display. Display type was not found to affect the degree of ataxia experienced by participants; however, this study did find that although older participants exhibited significantly higher rates of simulator-induced sickness discomfort than the younger participants, they recovered their postural equilibrium significantly faster. This indicates that the older participants had greater difficulty adapting to the simulation environment than younger persons. It also suggests that younger persons are at greater risk during immediate post-simulation activities such as driving. Although it is likely that this effect would disappear over time, it has implications for agencies such as the Department of Motor Vehicles or drivers education schools that are considering the use of a driving simulator device before an on-road skills test.
- The Effects of Noise on Speech Intelligibility and Complex Cognitive PerformanceUrquhart, Ryan L. (Virginia Tech, 2002-04-24)A human factors experiment was conducted to assess whether a reduction in noise at the ear would cause an improvement in speech intelligibility, an improvement in cognitive performance, and/or a reduction in subjective mental workload. Modified Rhyme Test (MRT) stimuli were used to determine intelligibility and specific tests within the Complex Cognitive Assessment Battery (CCAB) were used to assess cognitive performance. The tests chosen from the CCAB were: Tower Puzzle, Logical Relations, and Numbers and Words. These tests were chosen because of the specific set of cognitive functions that they measure which corresponded to command and control tasks. Participants performed the MRT and CCAB tests simultaneously in a 114 dBA noise environment at two speech levels, 83 dB (linear) and 96 dB (linear), using two communication microphones, Gentex Model 1453 and a prototype communication microphone developed by Adaptive Technologies Inc. (ATI). The noise used in the experiment was from a recording made inside a US Army Bradley Fighting Vehicle. Subjective mental workload was assessed using the NASA-TLX and Modified Cooper-Harper (MCH) immediately after the experiment. Results indicated that the communication microphone developed by ATI reduced the noise level at the ear better than the current Gentex microphone. However, the Gentex microphone produced significantly higher speech intelligibility scores at the 96 dB speech level. Cognitive performance scores significantly improved with increasing speech level for both communication microphones, with the ATI microphone having the advantage at 83 dB and the Gentex at 96 dB. The results also indicated that the main effects of speech level and communication microphone did not have an effect on subjective mental workload. A correlation analysis revealed that there was a positive relationship between the two workload measurement tools, indicating that either scale may be used to assess mental workload. Therefore, it was concluded that the MCH could have been used instead of the NASA-TLX, since the overall workload score was of interest.
- Empirical Studies Concerning Aural Alerts for Cockpit Use Leading to an Aural Alerting Signal Categorization SchemeBurt, Jennifer L. (Virginia Tech, 1999-11-11)The only way to simplify and promote the effective use of an alerting system that must be comprehensive in its coverage of hazardous or non-normal conditions is to convey top level information that provides an indication of criticality and identity. In an attempt to reduce the number of aural alerting signals presented in aircraft flight decks, this investigation pursued advances toward the development of a simple aural alert categorization scheme that provides flight deck function and urgency level information. In Experiment 1, 20 subjects having "normal" hearing threshold levels provided magnitude estimation urgency ratings for a series of aural alerts. These ratings revealed that subjects perceived low, moderate, and high urgency levels within each of four equally urgent aural alerting sets. In Experiment 2, 12 subjects having "normal" hearing threshold levels participated in a brief training session and then performed a sound identification task in conjunction with an automated and manual tracking task. Sound identification data revealed that subjects correctly identified the alerting set (i.e., major flight deck function) and urgency level associated with each of 12 aural alerts in 96.53% of the trials occurring during automated tracking and in 95.83% of the trials occurring during manual tracking; furthermore, subjects correctly identified each alerting set, urgency level, and aural alert equally often during each tracking task condition. Electroencephalogram (EEG) data recorded throughout the performance of each tracking task condition revealed that manual tracking required a significantly higher level of attentional engagement than automated tracking. Subjective assessments of workload collected after the performance of each tracking task condition revealed that a significantly higher level of workload was experienced during the manual condition of the tracking task than during the automated condition of the tracking task. Collectively, this investigation's results indicated that acoustic parameter manipulations can be used to create four distinctive alerting sets that each convey three levels of urgency and that these alerting sets and urgency levels can be accurately identified when two levels of workload and attentional engagement are experienced.
- Evaluation of MIRE Testing Methods for Rating of an Open-Back Active Noise Reduction HeadsetCro, Matthew B. (Virginia Tech, 1997-04-16)Active noise reduction was first proposed as a solution for environmental noise over fifty years ago. The use of active noise reduction (ANR) systems, however, was not demonstrated until much later. Recent advances in technology have made the use of active noise reduction systems in personal hearing protection devices (HPDs) practical. Through the use of advanced electronics technology, ANR equipped devices offer the potential to provide increased low frequency attenuation for hearing conservation applications. In order to use ANR equipped devices in an Occupational Safety and Health Administration (OSHA) sanctioned hearing conservation program, a testing standard for ANR equipped HPDs needs to be developed. Existing HPD testing standards offer the most promise for developing an acceptable standard for testing ANR-equipped HPDs. The microphone in real ear (MIRE) testing method is one method that offers a practical method for determining the performance of ANR devices for use in hearing conservation programs. A modified version of this method was successfully used in this study to determine the performance profile of an open-back ANR equipped headset. The results of this and other studies that have used a modified MIRE testing method can be used to support the acceptance of this method as the basis of an approved standard for testing ANR-equipped hearing protection devices.
- Impact of Sleeper Berth Usage on Driver Fatigue, Final Project ReportDingus, Thomas A.; Neale, Vicki L.; Garness, Sheila A.; Hanowski, Richard J.; Keisler, Aysha S.; Lee, Suzanne E.; Perez, Miguel A.; Robinson, Gary S.; Belz, Steven M.; Casali, John G.; Pace-Schott, E. F.; Stickgold, Robert A.; Hobson, J. A. (United States. Federal Motor Carrier Safety Administration, 2002)The goal of this project was to assess the impact that sleeper berth usage has on operator alertness. Forty-seven males and nine females participated in this study, constituting 13 teams and 30 single drivers. All drivers who participated in this study were recruited from one of four for-hire commercial trucking companies. Two tractors, a 1997 Volvo L4 VN-series tractor and a 1995 Peterbilt 379, with functionally identical instrumentation packages and data collection systems, were used for the study. The data acquisition system functioned to record four camera views, including the drivers face; driving performance information, including steering, lane departure, and braking; sleeper berth environmental data, including noise, vibration, and temperature; subjective alertness ratings; and data from the Nightcap sleep-monitoring system. The following results were obtained: (1) Sleeping in either a stationary or moving sleeper berth was shown to adversely affect sleep quality and quantity when compared to the home sleep data. This was particularly true for team drivers in moving trucks. (2) Team drivers generally acquired more sleep (greater than one hour per day on average) than did single drivers, with single drivers reporting six hours of sleep per 24-hour period and team drivers reporting just over seven hours per 24-hour period. (3) Team drivers had significantly more sleep disturbances than did single drivers. A primary cause of these disturbances appeared to be noise and vibration present in the sleeper berth of a moving truck. (4) In general, single drivers were rated as not drowsy more often and team drivers, who were rated as somewhat drowsy or moderately drowsy more often. However, of the 20 very/extremely drowsy episodes captured by Observer Ratings of Drowsiness, 16 were from single drivers. (5) Single drivers had many more critical incidents at all levels of severity relative to team drivers. (6) The frequency of critical incidents and driver errors varied significantly by the Hour of Day. However, many more incidents occurred during the afternoon and early evening as opposed to late at night. (7) Single drivers were more alert in the morning and gradually become fatigued during the day, whereas team drivers maintained a relatively constant level of alertness throughout the 24-hour clock.
- Investigating Pilot Performance Using Mixed-Modality Simulated Data LinkLancaster, Jeff A. (Virginia Tech, 2004-04-09)Empirical studies of general aviation (GA) pilot performance are lacking, especially with respect to envisioned future requirements. Two research studies were conducted to evaluate human performance using new technologies. In the first study, ten participants completed the Modified Rhyme Test (MRT) in an effort to compare the intelligibility of two text-to-speech (TTS) engines (DECtalk and AT&T's Natural Voices) as presented in 85 dB(A) aircraft cockpit engine noise. Results indicated significant differences in intelligibility (p £ 0.05) between the two speech synthesizers across the tested speech-to-noise ratios (S/N) (i.e., −5 dB, -8 dB, and −11 dB S/N) with the AT&T engine resulting in superior intelligibility in all of the S/N. The AT&T product was therefore selected as the TTS engine for the second study. In the second study, 16 visual flight rules (VFR) rated pilots were evaluated for their data link performance using a flight simulator (ELITE i-GATE) equipped with a mixed-modality simulated data link within one of two flight conditions. Data link modalities included textual, synthesized speech, digitized speech, and synthesized speech/textual combination. Flight conditions included VFR (unlimited ceiling, visibility) or marginal VFR (MVFR) flight conditions (clouds 2800 feet above ground level [AGL], three miles visibility). Evaluation focused on the time required accessing, understanding, and executing data link commands. Additional data were gathered to evaluate workload, situation awareness, and subjective preference. Results indicated significant differences in pilot performance, mental workload, and situation awareness across the data link modalities and between flight conditions. Textual data link resulted in decreased performance while the other three data link conditions did not differ in performance. Workload evaluation indicated increased workload in the textual data link condition. Situation awareness (SA) measures indicated differences in perceived SA between flight conditions while objective SA measures differed across data link conditions. Actual or potential applications of this research include guidance in the development of flight performance objectives for future GA systems. Other applications include guidance in the integration of automated voice technologies in the cockpit and/or in similar systems that present elevated levels of background noise during normal communications and auditory display operations.
- An Investigation of Auditory Icons and Brake Response Times in a Commercial Truck-Cab EnvironmentWinters, John (Virginia Tech, 1998-02-16)In the driving task, vision, hearing, and the haptic senses are all used by the driver to gather required information. Future Intelligent Transportation Systems components are likely to further increase the volume of information available to or required by the driver, particularly in the case of commercial vehicle operators. The use of alternate modalities to present in-vehicle information is a possible solution to the potential overload of the visual channel. Auditory icons have been shown to improve operator performance and decrease learning and response times, not only in industrial applications, but also as emergency braking warnings. The use of auditory icons in commercial truck cabs has the potential to increase the number of auditory displays that can be distinguished and understood by commercial vehicle operators, and this experiment sought to determine the utility of auditory icons in that situation. Nine auditory icons were evaluated by commercial vehicle operators as they drove an experimental vehicle over public roads. A comparison of the data collected in the truck-cab environment to data collected in a laboratory study on the same auditory icons revealed some differences in the perceived meaning, perceived urgency, and association with the auditory icons' intended meanings between the two conditions. The presence of these differences indicates that driver evaluations of auditory icons can be affected by the environment, and testing should therefore be conducted in a situation that approximates the end-user environment as closely as possible. A comparison of the drivers' brake response times across the three warning conditions (no warning, auditory icon, and soft braking) was also conducted on a closed, secure handling course. Dependent measures included overall brake reaction time and its components, steering response time, time to initial driver action, and categorical measures of driver responses (steering, swerving, braking, and stopping). The results indicated numerically shorter mean response times (on the order of 0.5 seconds for Total Brake Response Time) for the two conditions with warnings, but the differences were not statistically significant. The most likely reason for this lack of significance is the extreme between-subject variability in response times in the no warning condition. An analysis of the response time variance across the three conditions did indicate significantly less variability in operator responses in the two warning conditions. Two of the five dependent measures (Brake Pedal Contact Time and Total Brake Response Time) exhibited significantly reduced variance in the auditory icon warning condition compared to the no warning condition. The soft braking warning condition exhibited significantly reduced variance for four of the dependent measures (Accelerator Reaction Time, Brake Pedal Contact Time, Total Brake Response Time, and First Reaction Time). These results indicate that a soft braking stimulus like that used in this study could potentially prove to be a more effective emergency braking warning than simple auditory warnings alone.
- An On-Road Investigation of Commercial Motor Vehicle Operators and Self-Rating of Alertness and Temporal Separation as Indicators of Driver FatigueBelz, Steven M. (Virginia Tech, 2000-09-06)This on-road field investigation employed, for the first time, a completely automated, trigger-based data collection system capable of evaluating driver performance in an extended duration real-world commercial motor vehicle environment. The complexities associated with the development of the system, both technological and logistical and the necessary modifications to the plan of research are presented herein This study, performed in conjunction with an on-going three year contract with the Federal Highway Administration, examined the use of self-rating of alertness and temporal separation (minimum time-to-collision, minimum headway, and mean headway) as indicators of driver fatigue. Without exception, the regression analyses for both the self-rating of alertness and temporal separation yielded models low in predictive ability; neither metric was found to be a valid indicator of driver fatigue. Various reasons for the failure of self-rating of fatigue as a valid measure are discussed. Dispersion in the data, likely due to extraneous (non-fatigue related) factors (e.g., other drivers) are credited with reducing the sensitivity of the temporal separation indicators. Overall fatigue levels for all temporal separation incidents (those with a time-to-collision equal to or less than four seconds) were found to be significantly higher than for those randomly triggered incidents. On this basis, it is surmised that temporal separation may be a sensitive indicator for time-to-collision values greater than the 4-second criterion employed in this study. Two unexpected relationships in the data are also discussed. A "wall" effect was found to exist for minimum time-to-collision values at 1.9 seconds. That is, none of the participants who participated in this research effort exhibited following behaviors with less than a 1.9-second time-to-collision criterion. In addition, based upon the data collected for this research, anecdotal evidence suggests that commercial motor vehicle operators do not appear to follow the standard progression of events associated with the onset of fatigue.
- Role of Driver Hearing in Commercial Motor Vehicle Operation: An Evaluation of the FHWA Hearing RequirementLee, Suzanne E. (Virginia Tech, 1998-08-20)The Federal Highway Administration (FHWA) currently requires that all persons seeking a commercial driver's license for interstate commerce possess a certain minimal level of hearing. After an extensive literature review on topics related to hearing and driving, a human factors engineering approach was used to evaluate the appropriateness of this hearing requirement, the methods currently specified to test drivers' hearing, and the appropriate hearing levels required. Task analysis, audiometry, dosimetry, in-cab noise measurements, and analytical prediction of both speech intelligibility and masked thresholds were all used in performing the evaluation. One of the methods currently used to test truck driver hearing, the forced-whisper test, was also evaluated in a laboratory experiment in order to compare its effectiveness to that of standard pure-tone audiometry. Results indicated that there are truck driving tasks which require the use of hearing, that truck drivers may be suffering permanent hearing loss as a result of driving, that team drivers may be approaching a 100% OSHA noise dose over 24 hours, and that truck-cab noise severely compromises the intelligibility of live and CB speech, as well as the audibility of most internal and external warning signals. The forced whisper experiment demonstrated that there is significant variability in the sound pressure level of whispers produced using this technique (in the words, word types, and trials main effects). The test was found to be repeatable for a group of listeners with good hearing, but was found to have only a weak relationship to the results of pure-tone audiometry for a group of 21 subjects with hearing levels ranging from good to very poor. Several truck cab and warning signal design changes, as well as regulatory changes, were recommended based on the overall results of this evaluation.
- A Simulator-Based Investigation of Visual, Auditory, and Mixed-Modality Display of Vehicle Dynamic State Information to Commercial Motor Vehicle OperatorsBelz, Steven M. (Virginia Tech, 1997-11-11)This simulator-based study examined the use of conventional auditory warnings (tonal, non-verbal sounds) and auditory icons> (representational non-verbal sounds), alone and in combination with a dash-mounted visual display, to present information about impending collision situations to commercial motor vehicle operators. Brake response times were measured for impending front-to-rear collision scenarios under six display configurations, two vehicle speeds, and two levels of headway. Accident occurrence was measured for impending side collision scenarios under two vehicle speeds, two levels of visual workload, two auditory displays, absence/presence of mirrors, and absence/presence of dash-mounted iconic display. Subjective preference data was also obtained from participants. For both front-to-rear and side collision scenarios, auditory icons elicited significantly improved driver performance over conventional auditory warnings. Driver performance improved when collision warning information was presented through multiple modalities. Brake response times were significantly faster for impending front-to-rear collision scenarios using the longer headway criterion. The presence of mirrors significantly reduced the number of accidents for impending side collision scenarios. Subjective preference data indicated that participants preferred multi-modal displays over single-modality displays. A technique for systematically identifying, selecting, and evaluating candidate auditory icons was also developed. The potential exists to expand upon these developments, toward the goals of identifying appropriate auditory icons, improving operator performance, and developing information display techniques to effectively managing workload across multiple modalities.
- A Study of Smart Foam for Noise Control ApplicationsGentry-Grace, Cassandra Ann (Virginia Tech, 1998-10-28)Smart foam is a composite noise control treatment that consists of a distributed piezoelectric actuator, known as polyvinylidene fluoride (PVDF), embedded within a layer of partially-reticulated polyurethane foam. The principal function of smart foam is to yield broadband sound attenuation. Passive acoustic foams are a very reliable high-frequency sound reduction method. With regard to smart foam, the embedded piezoelectric actuator is introduced to overcome the limitations of the passive foam in the low-frequency region. The piezoelectric actuator excites the structural and acoustic phases of the foam when driven by an externally supplied control voltage. This generates a secondary acoustic field which destructively interacts with the acoustic field created by a primary noise source. Initial experiments employ the composite "active/passive" treatment to yield attenuation of piston sound radiation. For this simple source, the global farfield pressure is minimized according to the feedforward, Filtered-x LMS control algorithm using one error sensor. Significant broadband sound attenuation is obtained. A more advanced noise control problem is investigated which minimizes plate radiation. The vibrating plate has a distributed modal response requiring a collective array of independently-phased smart foam actuators to yield reduction of the radiated sound power. This is accomplished by minimizing the sound pressure at an array of nearfield microphones. Good broadband sound power reduction is obtained using a MIMO (multiple-input/multiple-output) Filtered-x LMS control scheme. Various techniques for improving smart foam's acoustic control authority are identified during manufacturing and finite element modeling. of the actuator. These improved smart foam actuators are employed as an active/passive liner to suppress the transverse propagating acoustic modes within an anechoically-terminated rectangular duct. A section of a duct wall is lined with an array of smart foam and the sound downstream of the control actuators is minimized at several error microphones. Successful harmonic and broadband noise control is achieved. A full-scale numerical model of the duct acoustic control application is presented based on the finite element method. The purpose of the model is to study the sensitivity of this active/passive control approach relative to the spatial distribution of control channels and error sensors. A comparison of the numerical and experimental results yields similar trends.
- Using signal detection theory to model the detection of warning signals in normal and hearing-impaired listeners while wearing hearing protectionRobinson, Gary S. (Virginia Tech, 1993)The question of whether or not an individual suffering from a hearing loss is capable of hearing an auditory alarm or warning is an extremely important industrial safety issue. International standard ISO 773 1—1986(E), Danger Signals for Work Places — Auditory Danger Signals, requires that any auditory alarm or warning be audible to all individuals in the workplace, including those suffering from a hearing loss and/or wearing hearing protection devices (HPDs). Very little research has been conducted to determine how an individual's hearing level affects his/her ability to detect an auditory alarm or warning in a high-noise environment while wearing an HPD. The research effort described herein was undertaken to determine how the ability to detect an alarm or warning signal changed for individuals with normal hearing and two levels of hearing loss as the levels of masking noise and alarm were manipulated. Pink noise was used as the masker since it is a generally-accepted, generic substitute for industrial noise. A heavy-equipment reverse alarm was used as the signal since it is a common alarm in industrial facilities and construction sites. The rating method paradigm of signal detection theory was used as the experimental procedure in order to separate the subjects’ absolute sensitivities to the alarm from their individual criteria for deciding to respond in an affirmative manner. Results indicated that even at a fairly low signal-to-noise ratio (0 dB), individuals with a substantial hearing loss [a pure-tone average (PTA) hearing level on the order of 45-50 dBHL in both ears] are capable of hearing the alarm while wearing a high-attenuation earmuff. Predictive models were developed using nonlinear regression techniques. These models may be used to predict whether or not individuals with known hearing levels will be capable of hearing the alarm under known conditions or to determine the level of alarm presentation in order to be heard reliably by individuals with a specified range of hearing for given noise levels