what is Summary of line array speakers knowledge points?

1. The production of line array speaker system

In the 1960s and 1970s, rock music represented by the Beatles emerged in Europe and the United States. Hundreds of thousands of people went to the square to watch rock concerts, so sound amplification was a big problem.

For example, a rock concert held in New Jersey, England, on September 3, 1977 was attended by 600,000 people. The sound reinforcement system uses a "sound tower" composed of multiple speakers stacked together, which is very troublesome to install and debug.

After careful design and debugging, a lot of effort has been spent, but the sound amplification effect is always unsatisfactory. This phenomenon provides market information that large-scale touring performances require sound reinforcement systems with high power and easy installation and debugging.

Some large companies have spotted market demand and are committed to developing high-power, long-throw sound reinforcement systems. From an acoustic point of view, there are two ways to achieve high-power, long-range projection effects.

01One is the horn

The sound energy is concentrated and radiated in one direction through the horn, controlling the directivity, improving the radiation efficiency, and achieving the effect of long-range projection. For example, in the 1950s, our broadcasting systems in Kinmen and Matsu used large horns. Each horn was more than ten meters long and the propagation distance was several kilometers. The research on horns has successfully developed constant directivity horn loudspeakers, multi-drive unit horn loudspeakers, etc.

02The other is the speaker array

The loudspeaker array proposed in the 1930s uses the interference principle to control directivity. In fact, a type of column speaker - sound column - was already popular at that time. The sound column has a relatively narrow vertical directivity, but the power is not high enough, the projection is not far, and there are still some problems that need to be overcome in terms of sound dynamics and bandwidth. Some large companies have their own priorities based on their own circumstances.

The French brand company first launched the V system in 1993. It is an array composed of a row of unit speakers, and its working principle is similar to a sound column. Its vertical directivity is controllable, determined by the number of unit boxes, and its horizontal radiation angle is 120°.

The frequency response of each unit box is 50Hz~18kHz±3dB, the power is 1500W, and the sensitivity is 134dB. The high-frequency unit radiates outward through the waveguide. This was the earliest line array product launched and attracted people's attention from the beginning.

Market demand, the development and application of high-tech, make line array speaker systems become iconic products for companies to show off their strengths. Now the line array is a combination of horn technology and array technology, making the radiation performance more perfect.

2、Features of two-line array speaker system

01Unit box regular arrangement

The line array speaker system is composed of a row of unit boxes. These unit boxes are arranged according to certain rules and can be arranged in straight lines or "J" shapes according to the needs of the sound field. The number of unit boxes is determined by the needs of the sound reinforcement field, but must meet the basic requirements for forming a line array;

That is, the length of the line array should be at least greater than half the wavelength of the radiated sound wave. The radiation characteristics of each unit box have strict requirements. For example, radiated sound power, frequency characteristics, horizontal directivity, distortion and linear phase must meet the requirements of the line array.

02High power and long projection distance

For example, the low-frequency unit in the EAW KF761 unit box withstands a power of 1200W and has a sensitivity of 96dB; the mid-frequency unit has a power of 500W and a sensitivity of 107dB; and the high-frequency unit has a power of 150W and a sensitivity of 112dB.

After the unit boxes are formed into an array, due to the interaction between the unit boxes, the radiation impedance of the speaker is improved and the radiation efficiency is improved. Therefore, it is easy to use a line array speaker system as a sound source to obtain a sound pressure level of more than 100dB at a distance of 100m.

03 The sound field covered is relatively uniform, the interference area is small, and the playback resolution is high

The vertical directivity of the line array is very sharp, generally around 10°, and the narrowest can reach 3°. The radiated sound beam is narrow, the direct sound reaching the corresponding audience area is relatively strong, and the radiation distance is relatively long;

The change in sound pressure level over a large area is relatively small. Due to the side lobe control of the line array, the overlapping area of the radiation sound field is relatively small and the interference surface is small. Direct sound dominates the area, with good listening experience, clear sound and high resolution.

3. How do line array speakers work?

How line arrays work can be a fairly in-depth discussion. Here, we will not explain the details of the entire theory in too much detail. The following will use simple language and mathematical calculations to let you first understand how the sound emitted by a typical speaker disperses as the distance increases.

01Inverse Square Law

The content of the inverse square law in acoustics is that the intensity of sound is inversely proportional to the square of the distance between the listening position and the sound source. The result is that every time the distance between the listener and the point sound source doubles, the sound pressure decreases by 6dB. This is the performance of the speakers we usually use, although there are many subtle differences between practice and theory.

02 point sound source

The inverse square law assumes that the loudspeaker radiates omnidirectionally. For physical speakers, this situation is rare, unless the speaker emits very low frequencies (this is why we always emphasize that bass or subwoofer has no directivity).

However, as sound propagation distance increases, even a typical directional loudspeaker (such as a horn loudspeaker with a 90° horizontal coverage angle and a 90° vertical coverage angle) will obey the inverse square law and behave like a theoretical point source. Diffusion of sound (i.e. omnidirectional radiation）

03 line sound source

The sound pressure coverage of line array speakers is close to the so-called line sound source theory. Whenever the listening distance doubles, the level will not drop by 6dB. In theory, it only drops 3dB, but in practice, the results are not so ideal.

This article will not discuss in detail why there are these differences. But even so, compared to point source speakers, line array speakers have unique advantages in vertical coverage angle.

Speakers with linear sound source radiation characteristics can achieve the following effect: you can feel a relatively large sound pressure level in the rear area of a hall or outdoor space, and to do this, you do not need to operate ordinary point source speakers like Similarly, the power is deliberately increased so that people in front of the PA system who are closer to the PA system hear the sound that is too loud. Its advantage lies in the complex and changeable controllability of the vertical sound diffusion angle.

So how to achieve linear sound source radiation? The answer is phase cancellation.

Phase cancellation is often one of the things engineers try to avoid in sound systems, but it plays a central role in the narrow vertical coverage angles that line array speakers are able to provide when working together.

Even with high-level speaker cabinet designs that shape vertical coverage, there is still a lot of actual overlap between the speakers in a line array. In other words, the vertical coverage angle of the line array speaker is not formed by a single speaker, but is the result of effective interference of multiple speakers at the exit.

However, in reality, each line array loudspeaker will be at a slightly different distance from the audience, causing a small degree of phase cancellation. Of course, you can also manually intervene and make fine adjustments to the vertical coverage angle of the line array speakers by introducing electronic delay (EAW Anya and Anna systems apply this technology).

04 Precautions when using line array systems

Although applying phase cancellation can have the effect of narrowing the vertical coverage angle of speakers in a line array, their horizontal coverage angle is not affected. Therefore, a single loudspeaker in a real line array can have a 90° horizontal coverage angle and only a 20° or smaller vertical coverage angle.

In addition, even though phase cancellation can achieve line source distribution and significantly improve long-distance coverage, as the distance increases, the line array will begin to exhibit point source characteristics and succumb to the inverse square law of attenuation of 6dB for every doubling of distance. .

Line arrays have the ability to approximate line source functions, but they also have some limitations and caveats. First, the overall top-to-bottom length of the array determines the lowest frequency with line source coverage characteristics.

This is because as the wavelength becomes longer, the gap between the corresponding times of sound arriving at the listener's position from different speaker units at the listening position must be larger to achieve the effect of a linear sound source.

This requires a larger array length. At the other end of the spectrum, the wavelengths become so short that the drivers are too large to be placed close enough together, so the relative phase difference becomes too great to function as a line source.

In these cases, major manufacturers will use waveguide structures to convert point sound sources to line sound source functions. Although all waveguide structures are designed to achieve the same purpose, almost every manufacturer uses a different structure and has its own patents to protect its intellectual property. This is also the most difficult link for a manufacturer in the process of developing linear array speakers.

Line arrays are useful in acoustically challenging spaces because you can control their vertical dispersion and reduce sound reflections.

Finding ways to get the sound's coverage area away from the ceiling and floor is a good start, then choosing speakers with a specific horizontal coverage angle will help you keep unwanted sound away from the side walls, resulting in better room sound reinforcement clarity.