what makes a sound source directional?

The inherent directivity (narrowness) of all wave producing sources depends on little more than the size of the source, compared to the wavelengths it generates. Audible sound has wavelengths ranging from a few inches to several feet, and because these wavelengths are comparable to the size of most loudspeakers, sound generally propagates omnidirectionally. Only by creating a sound source much larger than the wavelengths it produces can a narrow beam be created. In the past, loudspeaker manufacturers have created large speaker panels or used reflective domes to provide some directivity but, due to the sound's large wavelengths, the directivity of these devices is still extremely weak.

No loudspeaker can ever approach the directivity of Audio Spotlight technology.

ultrasound as a sound source!

Since the goal is a small loudspeaker but strong directivity, the only possible solution is to generate very small wavelengths - such as those of high-frequency ultrasound. The ultrasound used in Holosonic technology has wavelengths only a few millimeters long, which are much smaller than the source, and therefore naturally travel in an extremely narrow beam.

Of course, the ultrasound, which contains frequencies far outside our range of hearing, is completely inaudible. But as the ultrasonic beam travels through the air, the inherent properties of the air cause the ultrasound to change shape in a predictable way. This gives rise to frequency components in the audible band, which can be accurately predicted, and therefore precisely controlled. By generating the correct ultrasonic signal, we can create, within the air itself, any sound desired.

SOUND IS LITERALLY MADE FROM THIN AIR.

Note that the source of sound is not the physical device you see, but the invisible beam of ultrasound, which can be many meters long. This new sound source, while invisible, is very large compared to the audio wavelengths it's generating. So, the resulting audio is now extremely directional, just like a beam of light.

Often incorrectly attributed to so-called "Tartini tones", the technique of using high-frequency waves to generate low-frequency signals was pioneered over forty years ago. Over the past several decades, many others have attempted – and failed – to use this technique to make a practical audio source.

Through a combination of careful mathematical analysis and engineering insight based on pioneering work at MIT in the early 2000's, the patented Audio Spotlight sound system has become the very first, and still the only, truly directional audio system which generates high quality sound in a reliable, professional package.