We demonstrate that a suspended metal wire array can be used to produce high-pressure sound waves over a wide spectrum using the thermoacoustic effect. We fabricated air-bridge arrays containing up to 2 ϫ 10 5 wires covering an area of a few square centimeters. The supporting silicon wafer was isotropically plasma etched to release the wires thereby avoiding heat contact with the substrate. Sound pressure levels reaching 110 dB at a distance of 8 cm were demonstrated near 40 kHz in free field. The devices are also able to reproduce music and speech. They have potential for applications especially in the ultrasound range.

An adaptive perceptual equalizer for headphones is introduced. It estimates the effect of auditory masking while considering the char acteristics of the headphones, ambient noise, and music. The sys tem utilizes a psychoacoustic masking model to estimate the level to which the music should be raised to have the same perceived tonal balance in noise as it has in a quiet environment. Prototype testing showed that the most important task is to make the music audible in each Bark band. The compensation of the partial masking further improves the perceived sound quality. The system uses a micro phone of a headset to capture the ambient noise. The equalization is implemented using a high-order graphical equalizer that does not require subband decomposition of the music signal. The proposed equalizer also retains reasonable SPL levels: in an example case, the maximum gain in one Bark band was 11 dB while the overall SPL increase was only 2.5 dB.

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An audio transformer is used in a guitar amplifier to match the impedances of the power amplifier and a loudspeaker. It is important to understand the influence of the audio transformer on the overall sound quality for realistic tube amplifier emulation. This paper proposes to simulate the audio transformer using a wave digital filter model, which is based on the gyrator-capacitor analogy. The proposed model is two-directional in the sense that it outputs the loudspeaker current, but it also connects backward to the power amplifier thus affecting its behavior in a nonlinear manner. A practical parameter estimation procedure is introduced, which requires only the measurement of basic electrical quantities but no knowledge of material properties. Measurements of a Fender NSC041318 and a Hammond T1750V transformer are presented as case studies, as well as parameter fitting and simulation for the Fender transformer. The results show that these practical transformer designs introduce distortion at low frequencies only, below about 100 Hz for the Fender and 30 Hz for the Hammond transformer, and that the proposed model faithfully reproduces this effect. The proposed audio transformer model is implemented in real time using the BlockCompiler software. Parametric control allows varying and also exaggerating the model nonlinearities.

A prerequisite in many systems for virtual and augmented reality audio is the tracking of a subject's head position and direction. When the subject is wearing binaural headset microphones, the signals from them can be cross-correlated with known sound sources, called here anchor sources, to obtain an accurate estimate of the subject's position and orientation. In this paper we propose a method where the anchor sources radiate in separate frequency bands but with common modulation signal. After demodulation, distance estimates between anchor sources and binaural microphones are obtained from positions of cross-correlation maxima, which further yield the desired head coordinates. A particularly attractive case is to use high carrier frequencies where disturbing environment noise is lower and sensitivity of hearing to detect annoying anchor sources is also lower.