Just like how a spot light cancels out light pollution by providing illuminance to only the area that needs to be lit, parametric speaker adds sound only to the area required and preserves the quiet.
Instead of producing sound waves with a single electromagnetic coil and cone, parametric speakers generate ultrasonic waves using piezoelectric transducers. The high-frequency waves are produced as they have a shorter wavelength and does not diffract as the conventional speaker, thus travelling like a flashlight beam. When the ultrasound hits an object, it is converted to normal sound waves that we hear.
These one-directional speakers have various uses. By using these, we shall avoid unwanted noise pollution by transmitting sound to only the certain group of audience. This is also a boon for museums and exhibitions, where different information are to be shared with different groups.