Development and application of line array speaker system

Linear array speaker systems have been widely used in large sound reinforcement venues due to their unique advantages. The line array speaker system is produced in response to market demand and is also a high-tech product, so it attracts attention.

Production of line array system speakers

In the 1960s and 1970s, rock music represented by "The Beetle" emerged in Europe and the United States. There are thousands of spectators going to the square to see rock concerts, and amplification is a big problem. For example, 60,1977 people attended a rock concert in New Jersey on September 9, 3. The sound reinforcement system uses "towers" stacked on top of multiple speakers, which is cumbersome during installation and commissioning. After careful design and debugging, a lot of effort was spent, and the amplification effect was always unsatisfactory. This phenomenon provides market information. Large tours require sound reinforcement systems with high power and easy installation and commissioning.

Some large companies are looking at market demand and are working on developing high-power, long-range projection sound reinforcement systems. From an acoustic point of view, there are two ways to achieve high power and far projection effects.

• One is the horn, which makes the sound energy radiate out in one direction through the horn to control directionality, improve radiation efficiency, and achieve the effect of long-distance projection. For example, in the 1950s, we used large horns in the Golden Gate and Matsu broadcasting systems. The length of the horn is more than ten meters, and the transmission distance is several kilometers.

• The other is a speaker array proposed in the 1930s, which uses the principle of interference to control directionality. In fact, there is already a popular columnar speaker sound column. The vertical directivity of the sound column is relatively narrow, but the power is not large enough, the projection distance is not far, and some problems still need to be overcome, such as the dynamism and bandwidth of the sound. Some large companies have their own priorities depending on their situation.

Horn research has successfully developed constant directional speakers, horn speakers with multiple driver units, etc. The French company L-Acoustics first introduced the V-DOSC system in 1993. It is an array of one-line unit speakers. It works similarly to a sound column. Its vertical directivity is controllable, depending on the number of unit boxes, the horizontal radiation angle is 120 °. The frequency response of each cell box is 50Hz to 18kHz±3dB, the power is 1500W, and the sensitivity is 134dB. The high-frequency unit directs external radiation through the wave. This was the first line array product to be launched and attracted attention from the very beginning.

Market demand, high-tech development and application, make line array speaker system become a landmark product for companies to show their strength. Now, line arrays are a combination of horn technology and array technology to perfect radiation performance.

Features of the concert line array speaker system

1. Arrange the unit box regularly

The line array speaker system consists of a row of unit boxes, which are arranged according to certain rules and can be arranged in straight lines and "J" shapes according to the needs of the sound field. The number of cell boxes is determined by the requirements of the sound field, but the basic requirements for forming a line array must be met, i.e. the length of the line array should be at least half of the wavelength of the radiated sound wave. Ocean wave. Each unit box has strict requirements for its radiation characteristics. For example, radiated sound power, frequency characteristics, horizontal directivity, distortion, and linear phase must meet the requirements of the line array.

2. High power, long projection distance

For example, the low-frequency unit Vera36 outdoor line array speaker in the Sanway unit box has a power of 1000W and a sensitivity of 98dB; The power of the IF unit is 800W and the sensitivity is 110dB. The power of the high-frequency unit is 150W and the sensitivity is 112dB. After the unit box forms an array, the radiation impedance of the speaker is increased and the radiation efficiency is improved due to the interaction between the unit boxes. Therefore, it is easy to use a line array speaker system as a sound source to obtain sound pressure levels of 100dB or higher over 100m.

3. The coverage sound field is relatively uniform, the interference area is small, and the playback resolution is high

The vertical directionality of the line array is very sharp, usually around 10°, and the narrowest can reach 3°. The radiation beam is narrow, the direct sound reaching the corresponding audience area is relatively strong, the radiation distance is far, and the change in sound pressure level over a large area is small. Due to the sidelobe control of the line array, the overlapping area of the radiated sound field is relatively small and the interference surface is small. Areas dominated by direct sound have good hearing, clear sound and high resolution.

How do PA line array speakers work?

How power cord arrays work can be discussed in considerable depth. Here, we will not go into too much detail about the details of the entire theory. Simple linguistic and mathematical calculations will be used below to give everyone a first idea of how the sound of a typical speaker propagates with increasing distance.

1. The law of inverse square proportionality

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

2. Point sources

The premise of the inverse square law is that the speaker can radiate Omni directionally. For physical speakers, this is rare unless the speaker emits a very low frequency (which is why we emphasize bass all the time, or why subwoofer has no directionality). However, as the distance of sound propagation increases, even a typical directional loudspeaker (such as a horn speaker with a horizontal coverage angle of 90° and a vertical coverage angle of 90°) will follow the inverse square law, just like a theoretical point sound source. , omnidirectional radiation).

3. Line sound source

The sound pressure range of passive line array loudspeakers is close to the so-called linear source theory. As long as the listening distance is doubled, this level will not be reduced by 6dB. Theoretically, it would only drop by 3dB, but in practice, the results are not so ideal. As to why these differences exist, this article will not repeat them. But even so, line array loudspeakers offer unique advantages over point source loudspeakers in terms of vertical coverage.

Speakers with linear source radiation characteristics can achieve the following effect: in the rear area of the hall or outdoor space, you can feel a relatively large sound pressure level, and for this you do not need to operate an ordinary point sound source. Lecturer. Again, the power is intentionally increased so that people closer to the PA system in front can hear too loudly. The advantage lies in the complex and variable controllability of the vertical sound diffusion angle.

So how do you achieve linear source radiation? The answer is phase cancellation.

Phase cancellation is usually one of the things engineers avoid in audio systems, but when line array speakers work together, it plays a central role in providing narrow vertical coverage angles. Even with an advanced speaker cabinet design to determine vertical coverage, there is still a lot of practical overlap between speakers in the line array. In other words, the vertical coverage angle of a line array loudspeaker cannot be formed by a single speaker, which is the result of effective interference from multiple speakers at the exit. However, in reality, the distance between each line array speaker and the listener will be slightly different, which will result in a smaller degree of phase cancellation. Of course, you can also manually intervene and fine-tune the vertical coverage angle of the line array speakers by introducing electronic retarders (a technique used by EAW Anya and Anna systems).

Considerations for using a line array system

Although the application of phase cancellation can have the effect of narrowing the vertical coverage angle of the speakers in the line array, their horizontal coverage angle is not affected. Thus, a single speaker in a solid array can have a horizontal coverage angle of 90° and only a vertical angle of 20° or less. In addition, even though phase cancellation can achieve line-source distribution and significantly improve long-range coverage, as distance increases, the line array will begin to exhibit point-source characteristics and succumb to the inverse square law, which attenuates by 6dB for every doubling. Distance..

Line arrays have the ability to approximate line source functionality, but there are some limitations and caveats. First, the total length of the array from top to bottom determines the lowest frequency with line source coverage characteristics. This is because as the wavelength becomes longer, the difference between the corresponding time between the corresponding time when the sound arrives at the listener's position from the different speaker units must be greater in the listening position to achieve the effect of a linear sound source. This requires a larger array length. At the other end of the spectrum, the wavelength becomes so short that the driver is too large to be placed close enough, so the relative phase difference becomes too large to implement the line-source function. In this case, major manufacturers will use waveguide structures to enable the conversion from point to linear sources. Although all waveguide structures serve the same purpose, almost every manufacturer uses a different structure and has its own patents to protect their intellectual property. This is also the most difficult part of the manufacturer's process of developing line array loudspeakers.

Line arrays are useful in spaces that are challenging for sound because you can control its vertical diffusion and reduce sound reflections. Finding a way to keep the sound coverage area away from the ceiling and floor is a good place to start, and then choose speakers with specific horizontal coverage angles, which will help you move excess sound away from the sidewalls and thus get better sound reinforcement in the room.

Line array form

Since the vertical radiation of each speaker is very narrow, it is possible to effectively divide the listening space into multiple parts from front to back. The front only covers a small number of speakers, and more speakers can cover the rear. Based on this idea, a very popular J-shaped line array was formed, which is often found in concert halls and outdoor venues.

The exact installation shape of the line array will vary depending on the layout and size of the area to be covered. Typically, only a few forward coverage is required to meet sound pressure requirements due to close line spacing, but mounting angles between line arrays also need to be designed for greater due to uniform coverage. However, due to the relatively long distance between the middle and back, it is necessary to install a large number of speakers at a concentrated angle, so that the effect of long-distance coverage can be achieved. The approach just outlined helps improve consistency in overall coverage. In recent years, a method has also been developed for users to fine-tune the energy distribution by adjusting the power delivered to each speaker box, a technique commonly referred to as power grading.

Challenges and limitations of line arrays

Although line arrays can help solve some spatial problems, they have complex limitations. In addition to the challenge of requiring sufficient length to control the coverage angle of lower frequencies, line arrays sometimes suffer from strange anomalies, such as the fact that certain frequencies may form lobes in the area directly above and below the array. If this happens to happen in a bad sound space, it can have serious consequences. For example, if your vocal microphone is placed under an online array, you may experience feedback issues.

Line array settings

In order for a line array to function better, it needs to undergo a rigorous mechanical mounting design and establish the correct electronic crossover and calibration procedures. All of this is important due to the complex interactions involved. The exact mounting angle, exact suspension point and height of each cabinet, as well as the individual drives and delays, phases, gains, and high- and low-pass filter settings for each cabinet must be precise for optimal performance. Luckily, most existing big brand manufacturers have sound overlay simulation software based on their product's virtual space.

quality

Even in the best of circumstances, line arrays cannot match the sound purity produced by high-quality single-driver loudspeakers or single-way two- or three-way driven loudspeakers. This is one of the reasons why they are unlikely to appear in tight spaces. For smaller occasions, it will be more suitable if there are fewer speakers that can produce sound. Of course, cost and space are also considerations.

Microwire array

Although line array technology is most commonly used in specialized large-scale indoor and outdoor sound reinforcement applications, there are many companies such as Bose, Turbosound, etc. that offer small personal sound reinforcement systems that use small speaker arrays (usually 2 inches). -4" size) to produce the same line source overlay effect. Proper use of these systems allows them to provide good coverage in small venues.