What is Directional sound?

After reading a lot about directional sound, I think I have come up with the define definition of directional sound.

DEFINATION
Directional sound is a technology that concentrates acoustic energy into a narrow beam so that it can be projected to a discrete area, much as a spotlight focuses light. Focused in this manner, sound waves behave in a manner somewhat resembling the coherence of light waves in a laser. When a sound beam is aimed at a listener, that person senses the sound as if it is coming from a headset or from "inside the head." When the listener steps out of the beam, or when the beam is aimed in a different direction, the sound disappears completely.

There are many possible applications of directional sound, for example:

• People driving in a car could listen to different music without using headphones.
  
• One person could watch a loud television program while someone sitting next to them listened to classical music or enjoyed peace and quiet.
  
• A high-power sound beam could be directed at an assailant or fleeing criminal suspect, subduing that person while minimizing the effects on other people in the area.

Why directional sound
In most buildings, exit routes are identified by visual means using exit signage. However, signage can be easily obscured by even low levels of smoke. Exits can also be difficult to find in visually cluttered areas, such as an airport or shopping mall. In the event of a fire, people often evacuate a building by the route through which they entered. This is rarely the quickest or most appropriate way out. Many people fail to spot nearby exits and can easily walk straight past them without realizing it. ExitPoint directional sounders fitted in addition to normal building evacuation sounders, draw people to evacuation routes in both good and poor visibility. The directional sounder can be used in a wide range of building applications.

Guidance Sound Patterns
The ONYX ExitPoint directional sounder incorporates four different field selectable sound pulse patterns. The four pulse patterns are used to create an sound pathway out of a building and mark perimeter exits. Additional tone pulses can be added to each of the four pulse patterns to alert occupants that they are approaching a stairway and need to proceed either up or down, providing a clear direction for building evacuation.

Range of onyx exit point sound
The decibel (dB) is commonly used in acoustics to quantify sound levels relative to some 0 dB reference. The sound output level is 75 dB, which will clearly be heard at close range of the speaker. The further the person is from the speaker the less the dB will be, but 75 dB, is ample amplitude to be heard in a class room, when the speaker is in the corridor.