13-10-2010, 12:02 PM
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audio spotlighting full report
An Alternative Approach
P. Hong, IMTC, Georgia Institute of Technology
Abstract
The purpose of this project was to design a system that would actively direct audio in desired directions and locations. Although there already exist proven methods of achieving this goal, including ultrasound modulation in [8] and sound direction by parabolic dishes, a digital signal processing (DSP) and antenna theory approach was developed for this system.
Introduction
The applications for a directive sound system range greatly from public address systems to personal notification systems in a room. Because of the many potential applications, system development becomes a higher priority than before. Here, the system to be developed consists of a computer equipped with an 8 audio output soundcard and the amplifiers and loudspeakers associated with each audio channel. The computer uses a multi-track audio program to playback individual sound files on each channel. These sound files were generated by MATLAB with delays and gains dependent on the loudspeaker positions as well as the desired optimal observation point coordinates within a specified room which can also correspond to a direction depending on the equations used in MATLAB and whether a near-array or far-array approach is desired. This system differs greatly from the aforementioned systems for directing sound. To briefly explain: • The ultrasound modulation system simply does that, it modulates a carrier wave that operates in the ultrasound frequency range with the desired audio signal. By doing this, the system takes advantage of the non-linearities of air at those frequencies thereby causing demodulation of the desired signal for hearing. This scheme provides very high directivity as noted in [8]. The primary disadvantage is the damage it causes to the human auditory system although this is currently being studied and will hopefully be circumvented in the future. • The parabolic dish approach essentially is an antenna approach. Just as in antenna applications, a relatively omni-directional loudspeaker is placed at the focal point of a parabolic dish, pointing towards it. Consequently, when a desired sound is sent to the loudspeaker, it acts like a point source letting out a spherical wave to reflect off of the dish creating a directive beam of sound. This system has already been implemented by several companies. Its primary disadvantage is its bulk; the parabolic dish has to be relatively large in order to accommodate the longer wavelengths of lower frequencies and to provide a suitably sized listening area. Both systems also require mechanical means to change the location they are “illuminating” with sound. The system we wish to develop will not require mechanical means for steering and will not be particularly bulky either. Steering is controlled by the delays of the signal to each loudspeaker, i.e. the steering is electrically controlled. A diagram of the set up can be seen in Figure 1: Diagram of System Set Up.
audio spotlighting full report
An Alternative Approach
P. Hong, IMTC, Georgia Institute of Technology
Abstract
The purpose of this project was to design a system that would actively direct audio in desired directions and locations. Although there already exist proven methods of achieving this goal, including ultrasound modulation in [8] and sound direction by parabolic dishes, a digital signal processing (DSP) and antenna theory approach was developed for this system.
Introduction
The applications for a directive sound system range greatly from public address systems to personal notification systems in a room. Because of the many potential applications, system development becomes a higher priority than before. Here, the system to be developed consists of a computer equipped with an 8 audio output soundcard and the amplifiers and loudspeakers associated with each audio channel. The computer uses a multi-track audio program to playback individual sound files on each channel. These sound files were generated by MATLAB with delays and gains dependent on the loudspeaker positions as well as the desired optimal observation point coordinates within a specified room which can also correspond to a direction depending on the equations used in MATLAB and whether a near-array or far-array approach is desired. This system differs greatly from the aforementioned systems for directing sound. To briefly explain: • The ultrasound modulation system simply does that, it modulates a carrier wave that operates in the ultrasound frequency range with the desired audio signal. By doing this, the system takes advantage of the non-linearities of air at those frequencies thereby causing demodulation of the desired signal for hearing. This scheme provides very high directivity as noted in [8]. The primary disadvantage is the damage it causes to the human auditory system although this is currently being studied and will hopefully be circumvented in the future. • The parabolic dish approach essentially is an antenna approach. Just as in antenna applications, a relatively omni-directional loudspeaker is placed at the focal point of a parabolic dish, pointing towards it. Consequently, when a desired sound is sent to the loudspeaker, it acts like a point source letting out a spherical wave to reflect off of the dish creating a directive beam of sound. This system has already been implemented by several companies. Its primary disadvantage is its bulk; the parabolic dish has to be relatively large in order to accommodate the longer wavelengths of lower frequencies and to provide a suitably sized listening area. Both systems also require mechanical means to change the location they are “illuminating” with sound. The system we wish to develop will not require mechanical means for steering and will not be particularly bulky either. Steering is controlled by the delays of the signal to each loudspeaker, i.e. the steering is electrically controlled. A diagram of the set up can be seen in Figure 1: Diagram of System Set Up.
