Loudspeaker directivity is the extent to which loudspeakers focus the sound in a particular direction (typically towards the listener) instead of broadcasting it in all directions around the room. Loudspeaker Directivity: An Ongoing Experimental Survey, 3D3A Lab, Princeton University
In other words, the stronger the sound straight in front of the loudspeaker compared to that in all the other directions, the more directional the loudspeaker is (which is the same as saying that the loudspeaker has high directivity).
Advantages of directional loudspeakers
Directional loudspeakers are very effective at aiming sound where it is supposed to go and keeping it away from areas where it is unwanted. This makes them less sensitive to the acoustical properties of its environment. There are many advantages to this:
- Reduced noise pollution, both within a venue and in neighbouring areas
- High sound quality, even in environments where acoustical treatment is impossible or undesirable
- Good intelligibility of speech due to reduced reverberation
- Low acoustic feedback
Constant Directivity means that the directivity of a loudspeaker does not vary with frequency.
A directivity sonogram is a two-dimensional representation of a loudspeaker's radiation pattern. The horizontal axis shows the frequency, the vertical axis shows the angle relative to the reference axis. The colour represents the strength of the sound. For example, in the plot below, it can be seen that output at 2 kHz and an angle of 40 degrees is about 5 dB down from the on axis output.