Virtual acoustics

Kahana, Y., P.A. Nelson, and M. Petyt. 1998. Boundary element simulation of HRTFs and sound fields produced by virtual acoustic imaging. Proceedings of the Audio Engineering Society s 105th Convention. Preprint 4817, unpaginated. 

There are different possibilities to address the above set of equations which can be solved provided 2in > 3i, and provided the measured ToF information varies between measurement points. For the purpose of the present work we have taken two simplifying assumptions (a) one virtual source predominates at each measurement point, m and (b) each virtual source predominates at more than one measurement point. Note that assumption (b) ensures the condition 2m > 3i that is necessary to obtain solutions for Equations (2) and (3). These assumptions are justified by considering the defect surface as an acoustic secondary field source. At each measurement point the transducer predominantly receives signals from an... 

A simple geometrical analysis of this can be given in terms of third-order aberration theory for a single surface (Jenkins and White 1976 Hecht 2002). The situation is illustrated in Fig. 4.1. Rays propagating towards a virtual focus at a distance s below the surface of a solid are refracted so that a ray that passes through the surface at a distance h from the axis crosses the axis at a depth sa, with the paraxial focus at Sb- The refractive index n is the ratio of the velocity in the liquid to the velocity in the solid in acoustics this usually has a value... 

This paper has discussed algorithms for rendering reverberation in real-time. A straightforward method for simulating room acoustics is to sample a room impulse response and render the reverberation using convolution. Synthetic impulse responses can be created using auralization techniques. The availability of efficient, zero delay convolution algorithms make this a viable method for real-time room simulation. The drawback of this method is the lack of parameterized control over perceptually salient characteristics of the reverberation. This can be a problem when we attempt to use these systems in interactive virtual environments. 

Meddis and Hewitt, 1991] Meddis, R. and Hewitt, M. J. (1991). Virtual pitch and phase sensitivity of a computer model of the auditory periphery. I Pitch identification. J. Acoust. Soc. Am., 89 2866-2882. 

Two basic types of flame atomising systems have been used for atomic absorption. Firstly, the total consumption or turbulent burner system in which the total sample aerosol in the oxidant stream and the fuel gas are fed separately through concentric tubes to the burner jet, where the flame is burned. Considerable turbulence, both optical and acoustic, takes place. On the positive side these burner systems are very simple in construction and thus were cheap to manufacture, did not flash-back and could handle virtually any mixture of gases. However, this system is now obsolete. 

The wave resistance drops by 7 times with cavitation development, being virtually unchanged with further increasing amplitude of radiator oscillations, although additional acoustic power is transferred into the melt. 

In most materials, however, the modification of the forces at the surface is such that the surface localized modes have frequencies which lie below the frequencies of an associated bulk band with the same symmetry they have the appearance of having been peeled down from this bulk band [24]. In the usual case, the lowest energy of all these peeled -down modes derives from the bulk transverse acoustic band and is normally sagittally polarized. This dispersion branch is called the Rayleigh wave (RW) because it was predicted by Lord Rayleigh from continuum wave theory over a century ago [38]. Helium atom scattering experiments on virtually every material so far investigated have detected the RW on clean crystalline surfaces. 

Acoustic displays can be used to provide feedback concerning the virtual environment. Sound plays an important role in localization and interaction. Due to the application of simple audio in many other areas outside of VE, it is known as a mature technology. Synthesizers creating, mixing, and reproducing sounds and systems for speech in- and output have been made available. 

With a fully immersive VE, the user wears a head-mounted display (HMD) equipped with headphones and a visual stereo display directly in front of the eyes. The user is visually and acoustically sealed off from the physical environment and primarily perceives impressions the virtual environment. 

In other cases, the eyes can be fooled into perceiving colors not reaUy there, and stereo sound can be formed from a virtual sonic environment coming from speakers with different acoustic delays. 

Castle Acoustics has developed a 170 mm bass/midrange, which uses a cone fabricated from woven carbon fiber reinforced resin to produce a diaphragm, which is light and stiff, with negligible energy storage potential, resulting in rapid sound transmission and dynamic sound quality, with virtually no coloration. 

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