17-12-2012, 12:28 PM
A seminar report on Audio Spotlighting
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AUDIO SPOTLIGHTING
Audio spotlighting is a very recent technology that creates focussed beams of sound similar to light beams coming out of a flashlight. By “shining” sound to one location, specific listeners can be targeted with sound without others nearby hearing it. It uses a combination of non linear acoustics and some fancy mathematics. But it is real and is fine to knock the socks of any conventional loud speaker. This acoustic device comprises of a speaker that fires inaudible ultrasound pulses with very small wavelength which act in a manner very similar to that of a narrow column. The ultra sound beam acts as an air borne speaker and as the beam moves through the air gradual distortion takes place in a predictable way due to the property of non linearity of air. This gives rise to audible components that can be accurately predicted and precisely controlled. Joseph Pompei’s Holosonic Research Labs invented the Audio Spotlight that is made of a sound processor, an amplifier and the transducer. Audio spotlight can be either directed at a particular listener or to a point where it is reflected.
Introduction: What is audio spotlighting ?
The Audio Spotlighting Technique uses ultra sonic energy to create extremely narrow beams of sound that behave like beams of light . It exploits the property of non linearity of air. When inaudible ultrasound pulses are fired into the air, it spontaneously converts the inaudible ultrasound into audible sound tones, hence proved that as with water, sound propagation in air is just as non linear, and can be calculated mathematically. A device known as parametric array employs the non linearity of air to create audible by-products from inaudible ultrasound, resulting in an extremely directive, beamlike wide-band acoustical source. This source can be projected about an area much like a spotlight, and creates and actual specialised sound distant from the transducer. The ultrasound column acts as an air borne speaker, and as the beam moves through the air, gradual distortion takes place in a predictable way. This gives rise to audible components that can be accurately predicted and precisely controlled.
Non linearity of air
It exploits the property of non linearity of air. However, the problem with firing off ultrasound pulses, and having them interfere to produce audible tones is that the audible components created are nowhere similar to the complex signals in speech and music. Human speech, as well as music, contains multiple varying frequency signals, which interfere to produce sound and distortion. To generate such sound out of pure ultrasound tones is not easy. This is when teams of researchers from Ricoh and other Japanese companies got together to come up with the idea of using pure ultrasound signals as a carrier wave and superimposing audible speech and music signals on it to create a hybrid wave. If the range of human hearing is expressed as a percentage of shifts from the lowest audible frequency to the highest, it spans a range of 100000%. No single loudspeaker element can operate efficiently or uniformly over this range of frequencies. In order to deal with this speaker manufacturers carve the audio spectrum into smaller sections. This requires multiple transducers and crossovers to create a ‘higher fidelity’ system with current technology.
Using a technique of multiplying audible frequencies upwards and superimposing them on a ‘carrier’ of say, 200,000 cycles the required frequency shift for a transducer would be only 10%. Building a transducer that only needs to produce waves uniformly over only a 10% frequency range. For example, if a loudspeaker only needed to operate from 1000 to 1100 Hz (10%), an almost perfect transducer could be designed.
NEED OF AUDIO SPOTLIGHT
What ordinary audible sound & conventional sound systems lack ? What we need ? About half a dozen commonly used speaker types are in general use today. They range from piezoelectric tweeters that recreate the high end of the audio spectrum, to various kinds of mid-ranges speakers and woofers that produce the lower frequencies. Even the most sophisticated hi-fi speakers have difficult time in reproducing clean bass, and generally rely on a large woofer/enclosure combination to assist in the task. Whether they be dynamic, electrostatic, or some other transducer-based design, all loudspeakers today have one thing in common : they are direct radiating, i.e., they are fundamentally a piston-like device designed to directly pump air molecules into motion to create the audible sound we hear. The audible portions of sound tend to spread out in all directions from the point of origin. They do not travel as narrow beams-that is why you don’t need to be right in front of a radio to hear music. In fact, the beam angle of audible sound is very wide, just about 360 degrees. This effectively means the sound that you hear will be propagated through air equally in all directions.
Technology overview
The Audio Spotlight & Hyper Sonic Sound Technology, uses ultrasonic energy to create extremely narrow beams of sound that behave like beams of light. Ultrasonic sound is that sound that has very small wavelength-in the millimeter range and you can’t ultrasound since it lies beyond the threshold of human hearing.
Components and specifications
Audio Spotlight consists of three major components: a thin, circular transducer array, a signal processor and an amplifier. The lightweight, nonmagnetic transducer is about .5 inches(1.27 centimetres) thick and it typically has an active area 1 foot(30.48 cm) in diameter. It can project a three-degree wide beam of sound that is audible even at distances over 100 meters9328 feet). The signal processor and amplifier are integrated into system about the size of a traditional audio amplifier, and they use about the same amount of power.
TYPES OF AUDIO SPOTLIGHT
There are two ways to use Audio spotlight. First, it can direct sound at specific target, creating a contained area of listening space which is called Direct Audio. Second, it can bounce off a second object, creating an audio image. The audio image gives the illusion of a loudspeaker, which the listener perceives as the source of sound, which is called Projected Audio. This is similar to the way light bounces off of objects. In either case, the sound source is not the physical device you see, but the invisible ultrasound beam that generates it.