Three Dimensional Immersive Sound System (3D-X)
United States Patent Number US 8,442,244 B1
The reproduction of recorded sound has progressed from a single loudspeaker to the universal acceptance of stereo in professional and entertainment audio. In most stereo listening experiences there is little or no perception of the acoustic environment. However in better recordings there can be a limited sense of a sound stage in front of the listener, where a sensation of depth can be achieved.
In surround sound, additional loudspeakers are added around the listener to fill in the sounds coming from the side. These can improve the sense of space, but no source can be localized closer to the listener than the loudspeakers and angular accuracy is limited. These all-loudspeaker systems expand the angle of the sound stage from about 30 degrees on either side of the head in stereo to a sense of being surrounded, and thus deliver a more realistic perception of the environment. They are most effective in a theater where the requirements for intimacy and source direction accuracy are limited.
Further improvement in spatial realism can be achieved by using binaural recordings. Here microphones are located at the ear positions of a real or artificial head, and played back using headphones or earbuds. The primary difficulty encountered with this technique is that sounds, which originate in front of the listener, are perceived as coming from inside the listener’s head. Thus frontal sounds are poorly localized.
The two reproduction techniques, loudspeakers and earphones, have areas where each is preferred: loudspeakers for front sounds and earphones for side and rear sounds. 3D-X combines the best of both technologies producing an environment that is seamless in both direction and distance perception.