What Horn & Directivity should I use? When distance mater

Introduction

This diagram helps to understand what is the most adapted and interesting choice depending on the critical distance:

Here we will see how to choose a type of horn and an opening coverage according to our listening distance.

In a room, about half of the sound energy comes from reflections on the walls so if the balance between direct sound from the speaker and reflected sound isn’t close to 50/50 or 60/40, the result won’t be optimal. This balance depends on maintaining a proper coverage angle and directivity control adapted to the listening distance, as explained in our articles on critical distance and constant directivity.

Several ADAPT horns are available, and the choice depends on the listening distance and intended use.

In short: the closer you are, the wider the coverage angle should be; the farther you are, the narrower it needs to become. Naturally, we always maintain Constant Directivity to preserve the balance between direct and reverberant sound over the widest possible bandwidth.

These values serve as guidelines: if your room has close side walls, aim for coverage towards the lower end of the indicated range to reduce reflections.

On the other hand, if your side walls are farther apart and your listening area is wider, coverage should be towards the upper end of the indicated range.

Close distance

At close distance, below 2m (6.5 ft), we have several solutions. A waveguide on tweeter is a good option as it fits a wide range of situations at a very accessible price.

At close distance, the vertical center-to-center spacing between the tweeter section and the mid-woofer becomes an important factor. It still has to be considered relative to the crossover wavelength, but the closer we are, the more sensitive the system is to that spacing.

So crossing low and placing elements closer together is a good solution. Rectangular or elliptical mouth horns have a big advantage here compared to round horns.

Medium distance

At medium distances—between 2m and 5 to 6m (6.5 to 17/20 ft)—we typically use compression horns with a 90° coverage.

X-Shape

The X-Shape is relatively accessible. It can be completely 3D printed or partially integrated into the front baffle. We can use 1", 1.4", or 1.5" compression drivers from BMS or 18Sound.

Bi-radial with fins

The bi-radial horn with fins is another good solution. Its vertical coverage is narrower compared to the X-Shape horns.

We use 1.4 or 1.5 compression drivers such as 18Sound ND3N, FaitalPRO HF1440/1460, TAD TD4003, TAD TD4002, or JBL 2450SL.

2-way systems with a 15" or 14" woofer plus a subwoofer are a good solution.

Long range distance

From 6m (20 ft) and beyond, it becomes necessary to restrict radiation, typically using a 70° or 80° horn.

We have developed an MX-Shape line-up of 70° or 80° horns.

Ideally with 1.4" or 1.5" compression drivers, it can also be used as a pure mid horn with 6.5", 8", or 10" horn midrange drivers. This kind of big throat with cone drivers without phase plug must be crossed low—around 700 Hz for an 8" horn, and around 600 Hz for a 10". Above these frequencies, a phase plug is needed.

These big 3-way systems will be used at further listening distances—after 9 or 10m (30 ft).
2-way systems with subwoofers work perfectly for around 6m (20 ft).

Stadium usage, Music Festival, The line Array

For these applications, line arrays are the preferred solution.
Line arrays operate as near-field plane wave sources where, within this range, sound pressure decreases by about -3 dB per doubling of distance.

Since crossovers with subwoofers are typically set around 70–80 Hz, the line array must be long enough (generally around 4 to 5 meters minimum) to maintain plane wave behavior down to the crossover frequency.
If the array is too short — shorter than the wavelength of the lowest frequency it reproduces — it won’t behave as a plane wave source at those frequencies.
For frequencies with wavelengths longer than the array length, the sound pressure will decrease faster than -3 dB per doubling of distance, typically around -6 dB, which creates a mismatch in sound propagation behavior.

In summary: the taller the line array, the better its low-frequency performance and its ability to integrate smoothly with subwoofers.

The line array must be positioned away from nearby surfaces or obstacles to avoid disrupting the wavefront, which would compromise its planar propagation. This requirement, combined with the minimum length discussed above, makes line arrays poorly suited for regular room or home-cinema environments.

The vertical directivity of the line array is also very narrow, as it behaves as a cylindrical wavefront.

Line array indoor ?

All the characteristics discussed above are beneficial for outdoor use, but for indoor environments, line arrays are generally not well suited.

First, when the array is too short relative to the wavelengths it reproduces, its behavior changes with frequency. At higher frequencies, where the wavelength is shorter than the array height, the system can approximate a cylindrical wavefront with a decay close to −3 dB per doubling of distance. At lower frequencies, where the wavelength exceeds the array length, this behavior progressively transitions toward spherical radiation, with a decay closer to −6 dB.

This transition is gradual, not abrupt, but it leads to a distance-dependent spectral imbalance: as listening distance increases, low frequencies decay faster than mid and high frequencies, which alters the tonal balance.

Indoor environments introduce additional limitations.

Nearby surfaces and obstacles (walls, ceiling, furniture) interfere with the formation of the wavefront. A line array does not produce a perfect theoretical cylindrical wave: it is the result of multiple discrete sources combined through geometry (if not arc delayed) and shading. This combined wavefront requires distance to fully develop and stabilize.

Outdoors, this condition is typically met. Indoors, listening distances are much shorter, so the array is often heard in a region where the wavefront is not fully formed, reducing effective coherence.

Vertical directivity is another key limitation.

A line array produces a very narrow vertical directivity, which is advantageous for long-throw outdoor coverage. However, in small rooms, this becomes a drawback: the perceived vertical envelopment is very reduced, creating either an “empty” vertical impression or/and a very narrow vertical sweet spot, due to the lack of energy interacting with the room in the vertical dimension. In contrast, a controlled-directivity system such as a horn with adapted vertical coverage (e.g. 60°) provides a more uniform and natural listening experience in indoor environments, preserving a better vertical soundstage.

For more details, see Wavefront Propagation.