Optimized sound diffusers based on sonic crystals using a multiobjective evolutionary algorithm.

Sonic crystals have been demonstrated to be good candidates to substitute for conventional diffusers in order to overcome the need for extremely thick structures when low frequencies have to be scattered, however, their performance is limited to a narrow band. In this work, multiobjective evolutionary algorithms are used to extend the bandwidth to the whole low frequency range. The results show that diffusion can be significantly increased. Several cost functions are considered in the paper, on the one hand to illustrate the flexibility of the optimization and on the other hand to demonstrate the problems associated with the use of certain cost functions. A study of the robustness of the optimized diffusers is also presented, introducing a parameter that can help to choose among the best candidates. Finally, the advantages of the use of multiobjective optimization in comparison with conventional optimizations are discussed.

[Acute psychotic productivity in cerebral imaging]. / Akute psychotische Produktivität in der zerebralen Bildgebung1.

Regional cerebral blood flow (rCBF) was analysed in 24 neuroleptically never treated schizophrenics by 99m-Tc-HMPAO-SPECT. Psychopathological symptoms (PANSS) were correlated with rCBF-measures using multidimensional scaling (MDS). Highest degrees of correlation were found for ideas of grandiosity and formal thought disorders compared to different regions of interest (ROIs). An adynamic cluster was defined by basic symptoms which showed signs of deficiency. This cluster was by the highest degree correlated with a cluster defined by rCBF compared to four different clusters of basic symptoms. A fMRI-study was performed in schizophrenic patients with auditive hallucinations in comparison to healthy controls. We offered simple acoustic stimuli perceived as coming from the outside versus inside. For the outside condition, controls activated the medial temporal gyrus on the left side and the rightsided precuneus and postcentral gyrus which represent the auditive source locating and the stimulus processing systems, for inside, they activated the left insula. Hallucinating schizophrenic neither activated the one nor the other system. We discussed the findings as a possible explanation of the schizophrenics' tendency to misinterpret hallucinations as real perceptions.

The impact of background speech varying in intelligibility: effects on cognitive performance and perceived disturbance.

Noise abatement in office environments often focuses on the reduction of background speech intelligibility and noise level, as attainable with frequency-specific insulation. However, only limited empirical evidence exists regarding the effects of reducing speech intelligibility on cognitive performance and subjectively perceived disturbance. Three experiments tested the impact of low background speech (35 dB(A)) of both good and poor intelligibility, in comparison to silence and highly intelligible speech not lowered in level (55 dB(A)). The disturbance impact of the latter speech condition on verbal short-term memory (n=20) and mental arithmetic (n=24) was significantly reduced during soft and poorly intelligible speech, but not during soft and highly intelligible speech. No effect of background speech on verbal-logical reasoning performance (n=28) was found. Subjective disturbance ratings, however, were consistent over all three experiments with, for example, soft and poorly intelligible speech rated as the least disturbing speech condition but still disturbing in comparison to silence. It is concluded, therefore, that a combination of objective performance tests and subjective ratings is desirable for the comprehensive evaluation of acoustic office environments and their alterations.

Acoustic load on the ear caused by headphones.

The standardized method for measurement of complex impedances according to ISO 10534 Part 2 is applied to the acoustic impedance of the ear with an "open-pinna" condition and with different types of headphones. The method is based on measurement of the transfer function of two microphone locations in an impedance tube and subsequent signal processing of the complex signal spectra. The termination of the tube is interpreted as ear canal entrance, while the measurement direction is, apparently, from "inside" the head towards outside. A tube which was specifically designed for this purpose works well, even though extremely small impedances must be measured. The impedances of the free pinna are similar to the "soft" end condition in the open tube, approximately following the radiation impedance of a piston into free space. The headphone impedances can be separated according to the type of headphone. In addition, the absolute impedances as the differences to the open ear compared with a number of headphones are interesting and may be starting point for further investigations. One possibility is, of course, quality control of headphones. The results are also expected to be useful for psychoacoustic research, for better understanding of sound perception, and for use in development of audio equipment.