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Design and Implementation of "Spatial Equalizer"
Three dimensional sound field (3D sound field) is what human being has dreamed to have. It is interesting; however, 3D sound is not scientifically well defined. Therefore, there is no absolute measure that can determine the quality of 3D sound. People may want to define his/her own 3D sound! There have been many attempts that claim some success or practical achievements of implementing 3D sound field by using multiple speakers or speaker array. Wave field synthesis, Ambisonics, and what are based on HRTF(Head Related Transfer Function) are some of them. The methods have tried to regenerate the sound field in time and space as they wish. In other words, they wish to make sound field exactly same as what they designed. These approaches, however, ignores what we or whom want to have ‘3D sound field’ at their home or the space they want to have: ignoring their acoustic sensation. It is noticeable that very primitive stereo system came with a knob that is simply designed to control the volume of two loudspeakers. The knob, which is generally called as ‘balance knob’, is essentially provides the means that control the sound from two loudspeakers so that it meet what we want to hear. It is therefore our ultimate goal to have a similar human-sound interface for 3D sound realization. As for the case of a conventional stereo system, how well the interface achieves will be evaluated by who really controls the interface. We developed ‘the knobs’ that can really implement the desired 3D sound in space and time. This objective can be achieved simply by introducing a means that can make sound field that sounds like what user or operator wants. This can be done by attempting to make a point focusing or several focused points in the space of interest. Very simple case can be done by making two focused sound sources in front of us, and one focused sound source along line passing our head in perpendicular to our ear to ear line. Using these three points, we are ready to hear the sound field that can be made. This arrangement allows us to have ‘spatial equalizer’, analogous to a frequency equalizer or simply equalizer that has been used for the most of radio or audio system. We select the magnitude of each frequency band and listen until we satisfy. Very similar thing can be done by using the three point focused sound.
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