Browsing by Subject "Acoustic noise"

Now showing 1 - 12 of 12

Open Access
A comparison study on sound defects of Bilkent Amphitheatre in terms of intelligibility of the speech
(2007) Yilmazer, S.
The 4000 seated multi-purpose hall Bilkent Amphitheater is a semi-closed amphitheater with a large volume of 90,000 m3.At the beginning, the amphitheater was designed only for open-air performances. Afterwards it was decided to be roofed with a tensile membrane in order to protect the spectators against atmospheric effects. However, the covered amphitheater was turned into a very resounding and a problematic place with a reverberation time even more than 6 s. when the hall is unoccupied. After that time, some acoustical interventions were implemented, but these have not been sufficient in decreasing the number of problematic areas of echoes and dead spots. In 2000, Akukon Oy Consulting Engineers, Finland, carried out the real-size measurements when the hall was unoccupied, in order to find out the values of different acoustical parameters. In 2004, the computer simulation of the hall for the unoccupied condition was made [2]. In order to test speech intelligibility in the hall, besides the computer simulation and real size measurements, in 2006, articulation testing (AI) was made by using normal hearing listeners in the hall. In this paper, comparison between the measurements and the experimental studies are presented. Results confirm that excessive values of reverberation time cause too much reverberant and liveliness throughout the hall, besides the lack of warmth subjectively. Clarity is undermined by excessive reverberate and the sound becomes blurred. Sound energy are not satisfactory in reflecting the sound sufficiently through the hall and the direct sound becomes insufficient at some locations as back and mid sides.
Open Access
The effect of soundscape on the students' perception in the high school environment
(Institute of Noise Control Engineering, 2016) Çankaya, Sıla; Yılmazer, Semiha
In 2014, ISO 12913-1 standard was established for the conceptual soundscape framework to assess soundscape studies. According to this framework, soundscape process includes the examination of acoustic environment and its sound sources, and their influences on the humans' auditory sensation, as to react that, humans' interpretation of auditory sensation, responses and outcomes. Aim of the study is to create this conceptual soundscape framework in high-school environment and to examine the effect of soundscape on the students' perception. The study was conducted in two spaces as classroom and computer laboratory with 30 students in Bilkent High School; Ankara. To understand acoustic environment, in-situ measurements were conducted. Moreover, semi-structure interview results were evaluated to understand the students' perception of soundscape. Generated conceptual framework revealed different relations between students' perception and sound preferences. Students mostly expect to hear speech in classroom whilst computer fan sound in computer laboratory. Moreover, the most positive sound sources are birds singing in classroom whilst laughter in computer laboratory. Speech is found as most negative sound source in both spaces. Students responded these sound sources with positive approaches such as promoting the relaxation, interaction and with negative approaches such as distraction and annoyance. © 2016, German Acoustical Society (DEGA). All rights reserved.
Open Access
Effect of speech intelligibility on visual short-term memory performance
(2007) Kitapci, K.; Yılmazer, Semiha; Erkip F.
The aim of this study is to find out effects of speech intelligibility on visual short-term memory performance by testing 34 interior architecture students in three different sound environments. Those sound environments were composed of real office sounds and a speech sample that are mixed to achieve varying STI levels of 'continuous noise', 'masked speech' and 'speech' sound environments [2]. Test procedure had three steps: first questionnaire, computer based short-term memory test and second questionnaire. Results show that there is no significant difference of visual short-term memory performance between varying sound environments, however subjective results derived from questionnaires show that students were distracted most by 'speech' sound environment.
Open Access
Experimental study of linear closed-loop control of subsonic cavity flow
(2006) Yan P.; Debiasi, M.; Yuan X.; Little J.; Özbay, Hitay; Samimy, M.
A study is presented of the modeling and implementation of different concepts for linear feedback control of a single-mode resonance shallow cavity flow. When a physics-based linear model is used for cavity pressure oscillations-, an H∞ controller was designed and tested experimentally. It significantly reduced the main Rossiter mode for which it was designed, while leading to strong oscillations at other Rossiter modes. Other linear control methods such as Smith predictor controller and proportional integral derivative (PID) controller exhibited similar results. The ineffectiveness of using fixed linear models in the design of controllers for the cavity flows is discussed. A modification of the PID design produced a parallel-proportional with time-delay controller that remedied this problem by placing zeros at the frequencies corresponding to other resonance states. Interestingly, it was observed that introducing the same zero to the H∞ controller can also successfully avoid the strong oscillations at other Rossiter modes otherwise observed in the single-mode-based design. The parallel-proportional with time-delay controller was compared to a very effective open-loop method for reducing cavity resonance and exhibited superior robustness with respect to departure of the Mach number from the design conditions. An interpretation is presented for the physical mechanisms by which the open-loop forcing and the parallel-proportional with time-delay controllers reduce the cavity flow noise. The results support the idea that both controls induce in the system a rapid switching between modes competing for the available energy that can be extracted from the mean flow.
Open Access
An experimental study on speech interference in public leisure spaces
(Institute of Noise Control Engineering, 2010) Yilmazer, Semiha; Gezginer, Pelin Meriç
Physical comfort requirements of users in the non-acoustical spaces, leisure space, and usability of the space in long-term period should be taken into consideration in terms of sustainability of the space. The aim of this study is to investigate the speech interference of users' in an openplaned public leisure space. Bilkent Rollhouse was chosen as a leisure space because of its variance of activities in an open-plan like bowling, dart, billiards, play station and dining area. In this respect, a questionnaire was prepared to check the perception of sound of different user types in the area. The questionnaires were applied at the most crowded day of the week that is Friday and in between 18:00 to 21:00. The results of the survey were evaluated statistically. In addition to this, the equivalent continuous noise level, Leq, of the leisure space were taken in parallel to the questionnaire application to the users. Measuring of speech intelligibility via articulation index (AI) subjectively was the second phase of this study. Via application of the word list to the normal hearing users, the AI contours were prepared. Finally, objective and subjective measurements were analyzed in terms of speech interference during leisure activity in the space. As a leisure space, the relation between noise annoyance ratings and Leq did not show any significant difference in dart, billiards and play stations activities. However, in bowling activity and dining area, it was found that there is a significant relation between noise annoyance and Leq. This study reveals that users submit ambient noise of the space during leisure activity, they get in a common behaviour psychologically, they adjust their vocal noise that they create and finally these issues lead controlling of ambient noise by them. It means that users give up loudly speaking, they accept repeating or silence, focus on meal and they do not like getting in uncomfortable situation since their main activity is dining. For further study, the number of the samples in not only different leisure spaces, but also measurement points and sampling times should be increased to make clear hypothesis given above, since the study reveals completely different behaviour that is introduced in literature like cocktail party effect phenomenon.
Open Access
Identification of individuals' emotional response to the indoor soundscape in public study areas via semantic differentiation
(Institute of Noise Control Engineering, 2017) Acun, Volkan; Yilmazer, Semiha
Aims of this research is to identify individuals' emotional response to the sound environment of public study areas. The research has taken place in the public study areas of Bilkent University Campus. These study areas are located at the Dormitories, the Fine Arts Buildings, the library, and the Faculty of Science. In order to explore individuals' response to the auditory environment, a questionnaire survey and in-situ measurement of sound levels (LAeq) have been conducted. Questionnaire survey consisted of two main parts. In first part students have identified the sound source, how often they hear each one, and their satisfaction with the sound environment. Second part consisted of twelve seven point semantic differential scales (SD). Semantic scales were chosen in order to identify individuals' emotional response to the soundscape. Questionnaire survey are held with 30 student from each public study area, 120 students in total. The data gathered from the questionnaire survey are analysed using IBM SPSS 21 Statistics Software. Factor analysis was used to identify the perceptual dimensions of soundscape. Three factors were identify as a result of the analysis, which are, well-being, activity/communication and functionality. Even though the ANOVA F-Test found no statistically significant difference between the study areas in terms of satisfaction with the soundscapes, each areas has sound environment characteristics.
Open Access
Non-Markovian decoherence: A critique of the two-level approximation
(Elsevier B.V., 2006) Hakioǧlu T.; Savran, K.; Sevinçli, H.; Meşe, E.
The environmental decoherence in multilevelled systems in the context of two-level approximation is examined. It is found that the environmental temperature plays a minor role in the magnitudes of the decoherence rates whereas, the system-environment coupling and the environmental energy spectrum are dominant. Particularly, the latter is important in zero temperature quantum fluctuations and/or the nonequilibrium noise sources due to the large range of energies present in the environmental modes. Decoherence is found to be dominated by the short time nonresonant processes and this observation severely questions the use of the two-levelled models on decoherence.
Open Access
Recognition of vessel acoustic signatures using non-linear teager energy based features
(IEEE, 2016-10) Can, Gökmen; Akbaş, Cem Emre; Çetin, A. Enis
This paper proposes a vessel recognition and classification system based on vessel acoustic signatures. Teager Energy Operator (TEO) based Mel Frequency Cepstral Coefficients (MFCC) are used for the first time in Underwater Acoustic Signal Recognition (UASR) to identify platforms the acoustic noise they generate. TEO based MFCC (TEO-MFCC), being more robust in noisy conditions than conventional MFCC, provides a better estimation platform energy. Conventionally, acoustic noise is recognized by sonar oper-ators who listen to audio signals received by ship sonars. The aim of this work is to replace this conventional human-based recognition system with a TEO-MFCC features-based classification system. TEO is applied to short-time Fourier transform (STFT) of acoustic signal frames and Mel-scale filter bank is used to obtain Mel Teager-energy spectrum. The feature vector is constructed by discrete cosine transform (DCT) of logarithmic Mel Teager-energy spectrum. Obtained spectrum is transformed into cepstral coefficients that are labeled as TEO-MFCC. This analysis and implementation are carried out with datasets of 24 different noise recordings that belong to 10 separate classes of vessels. These datasets are partially provided by National Park Service (NPS). Artificial Neural Networks (ANN) are used as a classification method. Experimental results demonstrate that TEO-MFCC achieves 99.5% accuracy in classification of vessel noises. © 2016 IEEE.
Open Access
Relationships between measured levels and subjective ratings: A case study of the food-court area in CEPA shopping center, Ankara
(SAGE, 2012-03-01) Dökmeci, P. N.; Yilmazer, S.
Physical comfort requirements of users; such as, thermal, visual, and acoustic comfort, should be considered and studied in detail when planning and designing public spaces. However, there is not enough research on the relations between the acoustical parameters, and the acoustic comfort level of users in enclosed non-acoustic public spaces, which are directly connected with a central atrium. In such spaces, evaluation on auditory perception and noise annoyance should be performed in parallel with objective parametric measurements. The food-court area of CEPA Shopping Center, with a central atrium and a glass ceiling structure, in the capital city of Turkey, Ankara is chosen for the case. The aim of this study is to investigate the relationships between the users' subjective ratings of noise levels and the measured equivalent continuous sound pressure levels (Leq). In addition, the demographical differences and user profile variances, as well as the auditory perception classifications are investigated in this case space. The present acoustical indices are measured and then discussed by pointing out the architectural features of the case space, which are the central atrium, glass ceiling structure and the sound reflective material applications. The research methods include, noise measurements to obtain Leq and questionnaires to assess the subjective ratings and auditory perception of the users. This study mainly concentrates on the food-court space, which is within CEPA Shopping Center and displays the significant results regarding this space. These results show that Leq values vary by different day types (weekdays and weekends) and time of day, and the subjective ratings correlate well with these Leq variances. The most dominant sound perceived by the users was found to be the hum of voices. One other significant result implies that, subjective ratings of noise level becomes significant above 67 dBA and shows a sudden increase in the ratings. Furthermore, the time spent in the food-court area correlated significantly with noise annoyance ratings.
Open Access
Subband analysis for robust speech recognition in the presence of car noise
(IEEE, 1995-05) Çetin, A. Enis; Yardımcı, Y.; Erzin, Engin
In this paper, a new set of speech feature representations for robust speech recognition in the presence of car noise are proposed. These parameters are based on subband analysis of the speech signal. Line Spectral Frequency (LSF) representation of the Linear Prediction (LP) analysis in subbands and cepstral coefficients derived from subband analysis (SUBCEP) are introduced, and the performances of the new feature representations are compared to mel scale cepstral coefficients (MELCEP) in the presence of car noise. Subband analysis based parameters are observed to be more robust than the commonly employed MELCEP representations.
Open Access
Teager energy based feature parameters for robust speech recognition in car noise
(IEEE, Piscataway, NJ, United States, 1999) Jabloun, F.; Çetin, A. Enis
In this paper, a new set of speech feature parameters based on multirate signal processing and the Teager Energy Operator is developed. The speech signal is first divided into nonuniform subbands in mel-scale using a multirate filter-bank, then the Teager energies of the subsignals are estimated. Finally, the feature vector is constructed by log-compression and inverse DCT computation. The new feature parameters have a robust speech recognition performance in car engine noise which is low pass in nature.
Open Access
Teager energy based feature parameters for speech recognition in car noise
(Institute of Electrical and Electronics Engineers, 1999-10) Jabloun, F.; Çetin, A. Enis; Erzin, E.
In this letter, a new set of speech feature parameters based on multirate signal processing and the Teager energy operator is introduced. The speech signal is first divided into nonuniform subbands in mel-scale using a multirate filterbank, then the Teager energies of the subsignals are estimated. Finally, the feature vector is constructed by log-compression and inverse discrete cosine transform (DCT) computation. The new feature parameters have robust speech recognition performance in the presence of car engine noise.