Search

This paper describes a new method for measuring the insertion loss of panels or partitions based on time delay spectrometry (TDS). Using a TEF 12 analyzer the insertion loss of single leaf steel panels were measured. The results are shown to be in reasonable agreement with existing measurements giving confidence to the use of the method for design purposes. Based on several measurements, the performance and the limitations of the method proposed are analyzed and discussed.

Software for estimation and processing simulation of microphone line arrays was developed, based on the fundamentals of sensor array theory and the basic concepts governing the array beamforming. Periodical, nonperiodical, and logarithmic microphone line arrays can be designed in a convenient way. Spatial structures, directivity patterns, and other properties of the microphone arrays are shown and examined diagrammatically. Optimization of the microphone array directivity index through the entire audio spectrum, using the logarithmic design and the apropriate filters, is shown as well. All properties can be easily examined and dynamically changed via a useful user interface. The designed microphone arrays can also be simulated using sound recordings of a single microphone or WAV files in PCM format. The program’s output is an audio processing simulation of the acoustic field which can be accessed through WAV file registering. This stand‐alone, fully adjustable simulation software can be a user‐friendly tool in understanding the basic concepts of the microphone array design theory.

Musical rhythm patterns are mainly characterized by durational relationships between their different time levels. As written rhythmic values imply, these relationships are graphically represented by simple integer ratios and that fact reflects a basic criterion for their perceptual encoding into discrete perceptual categories. Temporal analysis of any musical performance reveals that deviations from accurate metronomic timing is a very common practice among musicians and these deviations are perceived either as musical expressivity, or just as inaccurate performance of rhythm. The degree of deviation also affects the categorization of a certain rhythmic pattern. In the present study, a mapping of the perceptual space between adjacent rhythm categories was attempted, through a systematic timing variation of simple rhythm patterns, as well as the investigation of the perceptual magnet effect [P. Iverson and P. Kuhl, J. Acoust. Soc. Am. 97, 553–562 (1995)] at various musical tempi. Sixteen musicians participated in identification, goodness rating, and discrimination tasks. The relative strength of the prototype within each category was determined, as well as the change in the position of category boundaries in different tempi. Discrimination graphs were finally plotted and comparisons were performed between the positions of discriminability peaks and the related category boundaries.

This paper presents a study for the optimum design and construction of an omnidirectional point source. The point source model of theoretical acoustics is used as an elementary unit for electroacoustic measurements in the area of room and free‐field acoustics. The spherical radiation requirement for the entire acoustic spectrum and the finite dimensions of the point source model contradict the construction in practice. This is because of high‐frequency beaming and the existing dimensions of radiators. A new design approach of using horn loaded cone loudspeakers and properly placed high‐frequency diffusers was used to minimize these problems. Twelve radiators loaded on pentagon‐shaped horns were placed in a dodecahedron topology to build a practical point source with a useful frequency response of 80–16 000 Hz and an omnidirectional radiation pattern up to 12 000 Hz. The results display improvement in the radiation pattern compared to those of the already existing point sources, due to the use of horns and diffusers. Increase in the sound pressure level is also displayed because of the obvious increase of the directivity index of each individual radiating element.

This paper presents the design of noninvasive systems for the investigation of the small bowel motility patterns. The basic idea was to implement dedicated devices for the recording and analysis of human bowel sounds. Properly modified transducers were used for the caption of gastrointestinal sound signals. A data acquisition ambulatory system, consisting of a preamplifier and a recording unit, was initially designed capable for maximum continuous recording of 6 h. After the first experimental results with this system, the necessity for longer recording duration was obvious. For this reason the installation of a computer‐based stationary system in a special reformed examination room was the next development step. Triggering of the input data and rejection of the regions with absence of gastrointestinal activity allowed much more recording duration. A computerized signal processing system, which involves equalizing procedures, noise cancellation techniques, and neural network algorithms, was used for the off‐line analysis of the recorded data. Novel measures and 2‐D and 3‐D representation techniques were employed for the exposition of results. The new approach gave flexibility to the system because longer recording times offer more information to the doctor so that the statistical analysis is much more effective and reliable.

Aspects of esophageal speech are investigated in this paper. Esophageal speech is produced by laryngectomized people who utter by expelling air constricted under the entrance of the esophagus, forcing the cricopharyngeal muscle to oscillate equivalently to vocal cords in normal speakers. Nine male esophageal speakers were used for the analysis. Spoken material consisted of Greek vowels and syllables (CV, CCV, VC), each repeated three times continuously by each speaker. F0 values and plots were obtained for all speakers using central clipping autocorrelation, cepstrum analysis, and a modified Hilbert transform envelope method that seemed to give more consistent results among others. Most frequently observed F0 values varied from speaker to speaker with an average of 73 Hz. F1 vs F2 plots for Greek phonemes α, e, ι, o, oυ, were obtained by LPC. Deviations from normal speakers were very small. Significant similarity to English equivalent phonemes was also observed. Speech power versus time slope for vowel‐ty...

The flogera is a simple structured bamboo woodwind and the most typical musical instrument played by the Greek shepherds. It consists of a cylindrical bore, with uniform internal diameter, open at both ends and a system of seven finger holes. The higher open end acts as the sound production mechanism, by blowing a narrow air stream against its sharp edge. The equivalence between musical tones, emitted by a medium sized flogera, and various ‘‘effective lengths’’ of its bore were investigated on the basis of A. H. Benade’s ‘‘Mathematical theory of woodwind finger holes’’ [J. Acoust. Soc. Am. 32, 1591–1608 (1960)]. Laboratory spectral analyses have been done for sound samples produced by some basic fingerings of the instrument. Embouchure’s ‘‘effective length corrections’’ have been calculated throughout the hole range of the instrument, concerning the fundamental and the first three overtones of each musical tone. On the basis of the above results, tables and histograms have been constructed, concerning var...