How does point source radiate?

Point source is a set designed to behave as much as possible like a single source with a specific directional characteristic. In practice, its task is to cover a specific sector of the audience both horizontally and vertically.

If the set has the correct dispersion and is located in the right place, its application is very simple: one system covers the designated area without the need to build a long array of many modules.

Point source can have:

• a wide pattern for short and wide rooms,
• a narrower pattern for greater distances,
• a rotating or variable directional setup,
• high efficiency sufficient for concert applications.

Therefore, one should not equate point source with a small set on a stand. There are very efficient designs intended for concerts, halls, and large distributed systems.

Their limitation is primarily that the characteristics of a single set are largely determined by design. If the audience has a very large depth, it is harder for one source to deliver a similar level to the first and last rows. 

How does a properly constructed line of sources behave?

Line array uses multiple modules that are meant to work together as one larger source. The key word is indeed "work together" — simply hanging several identical enclosures one under the other does not guarantee the correct behavior of the line system.

The operation of the array is influenced by:

• the length of the array,
• the number of modules,
• the distances between sources,
• the angles between elements,
• the geometry of the waveguides,
• the frequency,
• the distance of the listener.

In a properly designed array, vertical coverage can be shaped. The upper part of the array can provide energy to the farther sectors, the middle to the middle part of the audience, and the lower to the closer listeners.

This gives the designer significantly greater control over the level distribution at great depth.

At the same time, the line array does not behave identically across the entire frequency range. The lower the frequency, the greater the physical length of the source must be to maintain effective directional control. 

Vertical and horizontal directivity

The biggest design difference between point source and line array concerns the way vertical dispersion is controlled.

In a point source, the vertical characteristic mainly results from the design of the system. Its mounting angle can be changed, but the shape of the beam remains fundamentally defined by the design.

In a line array, vertical coverage is created by the entire array. By changing:

• the length of the array,
• the angles between the modules,
• the height of the suspension,
• the tilt of the entire structure,

energy can be distributed differently among the individual sectors.

Horizontal directivity is also of great importance. If the system has too wide a characteristic relative to the audience, energy may hit the walls or go beyond the audience area. If it is too narrow, outfills or additional PA sectors will be needed.

Therefore a line array or classic PA systems should be evaluated not based on the type of construction alone, but on how specific models cover specific spaces.

Near field, far field, and actual range

The concepts of near field and far field describe different areas of source behavior with respect to distance and frequency. In the case of line array, they are particularly important because a finite array does not behave like an ideal linear source at infinite distance.

A popular simplification states that a point source loses about 6 dB for every doubling of distance, while a line source loses about 3 dB. This is a useful theoretical model, but it does not mean that every true line array always loses only 3 dB..

A real array:

• has a finite length,
• behaves differently at different frequencies,
• transitions between different propagation areas,
• depends on the geometry of the array.

As distance increases and frequency changes, the system's behavior increasingly deviates from the ideal model of an infinite linear source.

Therefore, "range" should not be defined by a single phrase like "line array plays at 100 meters." A prediction is needed for a specific configuration.

Short and wide audience – advantage of point source

A point source often has an advantage in short and wide spaces where wide horizontal coverage is needed, but there is not a huge difference in distance between the first and last listener.

An example could be:

• a club,
• a wide event hall,
• a small concert hall,
• a stage with the audience close by.

In such a venue, one well-chosen set on each side of the stage can cover most of the audience.

A line array may not provide a real advantage, especially if:

• there is no space for the appropriate length of the array,
• the ceiling is low,
• the system must hang very close to the audience,
• a wide beam is needed.

In such conditions, a high-quality point source may be simpler, lighter, and more predictable.

That’s why the sound system for a concert in a club or concert hall should not be automatically designed as a small line array.

Long audience – when does a line array start to have an advantage?

A line array starts to provide a real advantage when the depth of the audience increases and the distance difference between the closest and farthest listeners grows.

If the first sector is a few meters from the stage, and the last is several dozen meters further, a single source must cope with a very large distance difference.

In a line array, energy can be distributed differently:

• further sectors can be served by modules with smaller angles,
• closer sectors can be covered by a more diverging part of the array,
• and excessive energy sent outside the audience can be limited.

This way, the SPL difference between the front and back can be more easily controlled.

This is particularly important when sound system for a large space and equalizing sound coverage, where simply increasing the level of the main PA does not solve the problem.

However, a line array does not eliminate the need for a delay line. With a very deep audience, even a large main system may require additional sources placed further away.

How does the number of modules affect the behavior of the array?

The number of modules affects not only the maximum SPL, but primarily the length of the source and its directivity.

A greater length of the array can improve control in the lower frequency range. A short array maintains effective vertical control mainly in the higher range, while the lower band can radiate significantly wider.

Therefore, a very short system made up of several small modules can formally be a line array, but may not provide the advantage that the user expects from a large concert array.

The number of elements results, among other things, from:

• the required length of the source,
• the depth of the audience,
• the height of suspension,
• the needed SPL,
• the capabilities of the specific model.

There is no universal threshold like "from six modules the line array starts to work."

For one system, a certain number may be sufficient, for another it may not be. The answer should come from the manufacturer's model and predictions.

What happens at low frequencies?

The directivity control of the line array deteriorates with the decrease in frequency if the length of the array becomes small in relation to the wavelength.

This is one of the most important things that can easily be overlooked when only looking at the appearance of the system.

A large array can maintain useful control in the lower band than a short array. A short line, on the other hand, can operate very directionally in the mid and high frequencies, but behave significantly wider at the bottom of the band.

Therefore, the physical length of the system matters.

One should not confuse the low-frequency control of the main system with the directionality of the subwoofer section. Subwoofers are a separate element of the design and often use their own spatial arrangements, e.g. cardioid or end-fire.

This also shows why a small array is not automatically a "miniature" of a large system that behaves identically across the band.

Hanging vs ground stack

A line array does not always have to hang. It can also operate as a ground stack, which is a group set on the ground, platform, or on subwoofers, if the manufacturer allows for such a configuration.

Hanging does provide a significant geometric advantage, because the system can be placed high above the audience.

This allows for:

• improving the acoustic visibility of further sectors,
• reducing the distance difference between the front and back,
• more precisely controlling the vertical coverage.

A ground stack works well when:

• there is no possibility of hanging,
• the space is relatively small,
• the height of the structure is limited,
• the system needs to serve a shorter audience.

It also has limitations. The first people may be very close to the lower modules, and further sectors may be blocked by the audience.

A point source can also be hung or placed on the ground. The type of system and the method of installation are therefore two separate design decisions.

Why is the predictive program part of the line array design?

The predictive program allows checking the behavior of a specific group even before it is physically built.

The model defines:

• the audience,
• the position of the system,
• the height of the suspension,
• the number of modules,
• the angles between them,
• the tilt of the array.

The software shows the predicted SPL distribution and coverage in different areas and frequency ranges.

This is particularly important with line arrays, as small changes in geometry can affect the energy distribution between closer and further sectors.

Prediction also allows checking whether a longer array actually provides an improvement, or if the problem is better solved by:

• a different height,
• changing the angle,
• adding outfill,
• using a delay line,
• choosing a different system.

Therefore, a professional line array should not be configured using the method of "hang as many modules as we have".

Prediction is part of system design, not a supplement done only for the largest concerts.

Examples of choices for clubs, halls, arenas, and outdoor venues

The best choice is well illustrated by four typical scenarios.

In a small club the priority may be wide, short coverage and limiting energy hitting the walls. Point source often fulfills this task without the need to build an array.

In a medium concert hall the choice mainly depends on depth and height. Point source can be completely sufficient, but for a long audience, a short or medium line array may provide better control.

In a hall a major problem becomes reverberation and height of the object. A long array can limit the energy directed to the ceiling and better serve further sectors. However, an appropriately designed distributed system based on point source may be an alternative.

At a large outdoor event a line array often provides the greatest flexibility for a long audience. In a wide but shallow area, efficient point sources or a hybrid system can still be very effective.

Therefore the sound system design and system prediction should precede the choice of technology. It is the geometry that shows whether a real advantage is provided by a line array, point source, or a combination of several types of sources.

Summary

Point source and line array are tools designed for different tasks. Point source is often optimal in small and medium spaces, especially when the audience is relatively short and wide. Line array offers greater possibilities for controlling vertical dispersion and SPL distribution with a large distance difference between the first and last listener.

However, the length and geometry of the array are key. A few modules do not yet guarantee the behavior characteristic of a large linear source, especially at lower frequencies.

Therefore, the choice should be based on the geometry of the audience, the required directivity, mounting height, needed SPL, and predictions of the specific system. A line array makes sense when its properties solve a real design problem, not just because it looks like a more advanced system.

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