Changing the directivity of the sound system to meet the requirements of sound reinforcement coverage

Not all decoration is completed according to the initial design requirements. In the later work, the decoration has changed, such as the height and the range of sound reinforcement coverage. Then how should we adjust the installation angle of the linear array sound system to meet the existing sound reinforcement range? After a sound system is installed, if there is no need to change the installation method of the linear array sound system, we should change the directivity of the sound system to meet the requirements of the sound reinforcement coverage range.

The formation and requirements of directionality

Any sound source has a certain directivity within a certain frequency range. Similarly, any speaker system also has directivity. Directivity is caused by the mutual interference of sound waves. Directivity has both advantages and disadvantages for the speaker system. The main reason why we use linear array sound systems for sound reinforcement is to make full use of the directivity of linear array sound systems that can produce lower frequencies. The principle, structural shape, and transmission characteristics of the speaker system itself determine the size of the directivity. Since the principle and sound wave characteristics cannot be changed, people now achieve changes in directivity by changing the shape and structure!

Why does the linear array sound system have a high sound pressure level and a long transmission distance? The main reason is that the linear array sound system has some control over the directivity of the high, medium and low frequency bands (how to control directivity is the key to the linear array sound system). Controlling directivity means controlling the sound pressure level, and controlling the sound pressure level means controlling the attenuation characteristics and transmission distance. The relationship between the directivity characteristics of the sound source and the sound pressure level is shown in Figure 1. From the figure, we can see that when the directivity changes from 360 degrees to 45 degrees, the sound pressure level increases by 6dB, and for the sound reinforcement distance, the distance increases by 1 times. This is why it is necessary to control directivity.

Figure 1 Relationship between directivity and sound pressure level

For ordinary speaker systems, the axis of its directivity is shown in Figure 2. Its characteristic is that the directivity axis is perpendicular to the speaker. The directivity that is larger than the structural size of the speaker system is a 360-degree circle (lower frequency). If you want to adjust the directivity angle of the speaker system, you have to adjust the axis direction of the speaker, so it is more complicated. It is even more complicated for linear array sound systems. Therefore, many different installation forms such as arc arrays and J-shaped arrays appear in the current linear array sound systems, all of which are to meet the directivity requirements. See Figure 3 for several installation methods of linear array sound systems.

Figure 2 Directivity diagram of the speaker

It can be seen from Figure 3 that in order to change the directivity of the linear array sound system, the structural form of the speaker must be changed. For coverage areas with different numbers of people, the structural form must be adjusted frequently to meet the requirements of different coverage areas. Therefore, the application and adjustment are very complicated. This is also the reason why the application range of the linear array sound system is limited. In order to solve this problem, we have developed a linear array sound system with adjustable directivity angle.

Figure 3 Several installation methods of linear array speaker systems

How to change the directionality

Directivity is formed by the interference of sound waves. If we can control the interference of sound waves, can't we control directivity? From the formation of directivity of the linear array sound system in Figure 3, we can see that when the linear array sound system is in a vertical state, the axis of directivity is perpendicular to the array. When the linear array sound system is in other states, the axis of directivity deviates from the horizontal state, and directivity appears at a certain angle to the ground.

Figure 4 Relationship between the directivity angle of the linear array speaker system and the system axis angle

Therefore, to change the directivity angle of the speaker system, we need to change the axis offset angle of the speaker system, as shown in Figure 4. From the offset angle, we can see that there is a position offset after the accumulation of the speaker systems from the top to the bottom of the linear array speaker system. This position offset is the position movement of a sound image (delay distance). Based on this phenomenon, we can not change the axis offset of the linear array speaker system, but only gradually delay the sound of a single speaker system to generate a virtual axis, so as to achieve the change of the directivity angle of the linear array speaker system.