There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Introduction to the Finite Element Method

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Regularization Of Inverse Problems

http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

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Data Analysis A Bayesian Tutorial

Talkers adjust their vocal effort to communicate at different distances, aiming to compensate for the sound propagation losses. The present paper studies the influence of four acoustically different rooms on the speech produced by 13 male talkers addressing a listener at four distances. Talkers raised their vocal intensity by between 1.3 and 2.2 dB per double distance to the listener and lowered it as a linear function of the quantity “room gain” at a rate of −3.6 dB/dB. There were also significant variations in the mean fundamental frequency, both across distance (3.8 Hz per double distance) and among environments (4.3 Hz), and in the long-term standard deviation of the fundamental frequency among rooms (4 Hz). In the most uncomfortable rooms to speak in, talkers prolonged the voiced segments of the speech they produced, either as a side-effect of increased vocal intensity or in order to compensate for a decrease in speech intelligibility.

/pdf/vocal-effort-with-changing-talker-to-listener-distance-in-1num9ur0bp.pdf

Vocal effort with changing talker-to-listener distance in different acoustic environments

Teachers often suffer from health problems related to their voice. These problems are related to their working environment, including the acoustics of the lecture rooms. However, there is a lack of studies linking the room acoustic parameters to the voice produced by the speaker. In this pilot study, the main goals are to investigate whether objectively measurable parameters of the rooms can be related to an increase in the voice sound power produced by speakers and to the speakers' subjective judgments about the rooms. In six different rooms with different sizes, reverberation times, and other physical attributes, the sound power level produced by six speakers was measured. Objective room acoustic parameters were measured in the same rooms, including reverberation time and room gain, and questionnaires were handed out to people who had experience talking in the rooms. It is found that in different rooms significant changes in the sound power produced by the speaker can be found. It is also found that these changes mainly have to do with the size of the room and to the gain produced by the room. To describe this quality, a new room acoustic quantity called “room gain” is proposed.

/pdf/increase-in-voice-level-and-speaker-comfort-in-lecture-rooms-1e4vuz3hdd.pdf

Increase in voice level and speaker comfort in lecture rooms.

Teachers adjust their voice levels under different classroom acoustics conditions, even in the absence of background noise. Laboratory experiments have been conducted in order to understand further this relationship and to determine optimum room acoustic conditions for speaking. Under simulated acoustic environments, talkers do modify their voice levels linearly with the measure voice support, and the slope of this relationship is referred to as room effect. The magnitude of the room effect depends highly on the instruction used and on the individuals. Group-wise, the average room effect ranges from −0.93 dB/dB, with free speech, to −0.1 dB/dB with other less demanding communication tasks as reading and talking at short distances. The room effect for some individuals can be as strong as −1.7 dB/dB. A questionnaire investigation showed that the acoustic comfort for talking in classrooms, in the absence of background noise, is correlated to the decay times derived from an impulse response measured from the ...

Speakers’ comfort and voice level variation in classrooms: Laboratory research

Lightweight walls are often designed as frameworks of studs with plates on each side—a double-plate structure. The studs constitute boundaries for the cavities, thereby both affecting the sound transmission directly by short-circuiting the plates, and indirectly by disturbing the sound field between the plates. The paper presents a deterministic prediction model for airborne sound insulation including both effects of the studs. A spatial transform technique is used, taking advantage of the periodicity. The acoustic field inside the cavities is expanded by means of cosine-series. The transmission coefficient (angle-dependent and diffuse) and transmission loss are studied. Numerical examples are presented and comparisons with measurement are performed. The result indicates that a reasonably good agreement between theory and measurement can be achieved.

The influence of finite cavities on the sound insulation of double-plate structures.

Objective acoustic parameters have been measured in 30 school classrooms. These parameters include usual descriptors of the acoustic quality from the listeners’ standpoint, such as reverberation time, speech transmission index, and background noise level, and two descriptors of the acoustic properties for a speaker: Voice support and room gain. This paper describes the measurement method for these two parameters and presents a prediction model for voice support and room gain derived from the diffuse field theory. The voice support for medium-sized classrooms with volumes between 100 and 250 m3 and good acoustical quality lies in the range between −14 and −9 dB, whereas the room gain is in the range between 0.2 and 0.5 dB. The prediction model for voice support describes the measurements in the classrooms with a coefficient of determination of 0.84 and a standard deviation of 1.2 dB.

Jonas Brunskog

Papers

Vocal effort with changing talker-to-listener distance in different acoustic environments

Increase in voice level and speaker comfort in lecture rooms.

Speakers’ comfort and voice level variation in classrooms: Laboratory research

The influence of finite cavities on the sound insulation of double-plate structures.

Measurement and prediction of voice support and room gain in school classrooms