Speaker Academy

Horn Speakers

Horn speakers use an acoustic horn to improve the coupling between a loudspeaker driver and the surrounding air. A properly designed horn can significantly increase acoustic efficiency and provide controlled sound dispersion. Horn loading is widely used in professional PA systems, compression-driver assemblies, cinema speakers and high-output loudspeakers.

What Is a Horn Speaker?

A horn speaker consists of a driver coupled to an expanding acoustic passage called a horn.

       Driver
         │
         ▼
      ┌─────┐
      │     │
      └──┬──┘
         │
         │ Narrow throat
         ▼
        / \
       /   \
      /     \
     /       \
    /         \
   /           \
  └─────────────┘
       Horn mouth

The narrow end of the horn is called the throat, while the large opening is called the mouth.

The driver produces the acoustic energy and the horn controls how that energy is transferred into the surrounding air.

Why Use a Horn?

A loudspeaker driver has to transfer mechanical energy into the air. The acoustic impedance of the driver and the surrounding air are very different.

A horn provides an acoustic transition between the driver and the environment.

This can improve acoustic coupling and increase efficiency over the frequency range for which the horn is designed.

Horn Loading

The horn changes the acoustic impedance presented to the driver.

The driver therefore does not operate into the same acoustic load that it would experience in free air.

The result can be substantially higher acoustic output for a given electrical input.

Horn Efficiency

One of the major advantages of horn loading is efficiency.

A horn system can produce high acoustic output while requiring less electrical power than many direct-radiating systems producing the same SPL over the relevant operating range.

This is one reason horns are widely used in professional sound reinforcement.

Horn Speakers and PA Systems

Professional PA systems frequently use horns for midrange and high-frequency reproduction.

The combination of a compression driver and horn can provide:

High acoustic efficiency
High maximum SPL
Controlled directivity
Good projection
Compact high-frequency driver assemblies

Horn Speakers vs Direct Radiators

Characteristic	Direct Radiator	Horn Loaded
Acoustic loading	Directly coupled to air	Horn provides acoustic loading
Efficiency	Generally lower	Can be substantially higher
Directivity	Often less controlled	Can be deliberately controlled
High SPL capability	Depends strongly on driver	Excellent when properly designed
Design complexity	Lower	Higher

Horn Throat

The throat is the narrow section where the driver couples to the horn.

Its geometry is extremely important because it determines how the driver interacts with the acoustic load.

A poorly designed throat can introduce reflections, resonances and distortion.

Horn Mouth

The mouth is the large opening through which the acoustic energy leaves the horn.

The mouth dimensions strongly influence the horn's low-frequency loading and directivity.

A horn designed for lower frequencies generally requires a larger mouth than a horn designed only for high frequencies.

Horn Length

The distance between the throat and mouth is the horn length.

Horn length contributes to the acoustic loading and phase behaviour of the system.

The appropriate length depends on the horn profile, throat size, frequency range and intended application.

Horn Profile

The horn profile describes how its cross-sectional area changes from the throat to the mouth.

Common horn profiles include:

Conical
Exponential
Tractrix
Hyperbolic
Constant-directivity

Different profiles provide different acoustic characteristics.

Conical Horn

A conical horn expands approximately linearly in cross-sectional dimensions.

Throat
  │
  ▼
  /\
 /  \
/    \
\     \
 \     \
  \_____\
   Mouth

Conical horns are relatively straightforward to construct and analyze.

Exponential Horn

An exponential horn increases its cross-sectional area exponentially along its length.

Exponential expansion can provide useful acoustic loading over a defined frequency range.

The profile is described mathematically rather than simply using straight walls.

Tractrix Horn

A tractrix horn uses a specific mathematical profile designed around the geometry of the wavefront leaving the horn.

Tractrix profiles are commonly encountered in high-fidelity horn loudspeakers.

They can provide smooth acoustic expansion when correctly designed.

Constant Directivity Horn

A constant-directivity horn is designed to maintain relatively consistent horizontal and vertical dispersion over a specified frequency range.

These horns are particularly useful in professional sound reinforcement where predictable coverage is important.

Why Directivity Matters

A loudspeaker does not radiate sound equally in every direction at all frequencies.

Horn geometry can be designed to control this behaviour.

Controlled directivity can improve:

Audience coverage
System efficiency
Feedback control
Room interaction
Clarity

Horizontal and Vertical Dispersion

A horn can have different horizontal and vertical coverage angles.

For example, a PA horn might be designed with a relatively wide horizontal angle and a narrower vertical angle.

This allows the loudspeaker to cover the audience while reducing unnecessary acoustic energy directed toward ceilings and floors.

Horn Coverage Angle

The coverage angle describes approximately how widely the horn distributes sound.

Common professional horn specifications include values such as:

40°
60°
80°
90°
100°
120°

The actual response is frequency dependent, so the stated angle should be understood as a design specification rather than an absolute constant at every frequency.

Compression Drivers

Many high-frequency horns use compression drivers.

A compression driver has a relatively small diaphragm coupled to a small throat.

The horn then expands this acoustic output into the surrounding air.

Compression drivers are capable of very high acoustic output.

Compression Driver Structure

       Diaphragm
          ↓
      ┌────────┐
      │        │
      └───┬────┘
          │
       Phase plug
          │
          ▼
       Throat
          │
          ▼
       Horn
          │
          ▼
        Mouth

The diaphragm, phase plug and throat geometry work together to create the acoustic output entering the horn.

Phase Plug

The phase plug is a component used in many compression drivers to couple the diaphragm to the small driver exit.

It helps control the path lengths between different parts of the diaphragm and the throat.

This is important for high-frequency operation.

Compression Driver Diaphragms

Compression-driver diaphragms can be made from various materials, including:

Polymer materials
Phenolic materials
Aluminium
Titanium
Other specialized materials

The diaphragm material affects mass, stiffness, damping and high- frequency performance.

Horn Cutoff Frequency

A horn cannot provide ideal acoustic loading down to arbitrarily low frequencies.

Its dimensions determine a lower frequency region below which horn loading becomes less effective.

This is commonly described using a horn cutoff frequency.

The exact relationship depends on the horn profile and acoustic geometry.

Horn Size and Frequency

Lower-frequency horns require larger physical dimensions.

This is a fundamental reason why very low-frequency horn systems can become extremely large.

High-frequency horns can be much smaller because the wavelengths are shorter.

Horn Mouth Size

The mouth must be sufficiently large for the horn to provide the desired acoustic loading at the lower end of its operating range.

If the mouth is too small, the horn may lose effective loading at lower frequencies and exhibit undesirable response changes.

Horn Loading and Low Frequencies

A horn intended to operate at low frequencies requires a large acoustic structure because low-frequency wavelengths are long.

This creates a practical compromise between:

Low-frequency extension
Efficiency
Cabinet size
Weight
Construction complexity

Front-Loaded Horn

A front-loaded horn places the driver at the beginning of the horn and uses the horn to load the front radiation.

The horn may form part of the front of the cabinet or be integrated into the enclosure.

Back-Loaded Horn

A back-loaded horn uses the rear radiation of the driver to excite a horn structure.

The front of the driver can radiate directly into the room while the rear radiation is routed through the horn.

This approach has been used in various full-range and high-efficiency loudspeaker designs.

Folded Horn

A folded horn uses bends and internal passages to obtain a long horn path inside a practical cabinet.

Driver
  │
  ▼
┌──────────────────────┐
│───────────────────┐  │
│                   │  │
│ ┌─────────────────┘  │
│ │                    │
│ └────────────────────│
│                      │
└──────────────────────┘
              │
              ▼
             Mouth

Folded horns are useful when a straight horn would be too large to fit into the available space.

Horn and Driver Matching

The driver and horn must be acoustically compatible.

Important factors include:

Throat diameter
Driver exit geometry
Frequency range
Driver diaphragm size
Driver resonance
Horn cutoff
Desired coverage

A horn should not simply be attached to any driver without considering these parameters.

Throat Diameter

The throat diameter must match the driver's exit or use an appropriate adapter.

A mismatch can introduce acoustic discontinuities and unwanted reflections.

Common compression-driver throat sizes include:

1 inch
1.4 inch
2 inch
3 inch

The appropriate size depends on the driver and application.

Driver Diaphragm Size

Compression drivers can have different diaphragm diameters.

A larger diaphragm can provide different low-frequency and power- handling characteristics, while smaller diaphragms may be more appropriate for higher-frequency operation.

The complete driver specification should be considered.

Horn Distortion

Poorly designed horns can introduce distortion caused by:

Reflections
Resonances
Nonlinear airflow
Throat discontinuities
Driver limitations
Insufficient mouth size

Good horn design attempts to control these effects.

Horn Resonances

The horn is an acoustic resonator and can support unwanted resonances.

These resonances can produce peaks and dips in the frequency response.

The horn profile, throat, mouth, length and damping all influence these resonances.

Horn Damping

Some horn structures use damping material to reduce unwanted reflections and resonances.

However, damping must be applied carefully because excessive absorption can reduce the desired acoustic output.

Horn Materials

Horn assemblies can be manufactured from many materials.

Common choices include:

ABS plastic
Polypropylene
Fibreglass
Wood
MDF
Plywood
Aluminium
Composite materials

The material must provide sufficient rigidity and dimensional stability for the intended application.

Plastic Horns

Plastic is widely used for commercial PA horns.

Injection-moulded or compression-moulded horns can provide accurate profiles and repeatable production.

ABS and similar engineering plastics can also be practical for DIY projects when suitable manufacturing methods are available.

Fibreglass Horns

Fibreglass-reinforced construction is useful for custom horns because it can produce complex curved shapes.

It is particularly useful when a horn profile would be difficult to construct from flat panels.

Adequate reinforcement is important to prevent the horn walls from vibrating.

Wooden Horns

Wood and plywood can be used to construct large horn systems.

Wooden horns can be built using segmented panels, curved sections or layered construction.

The internal surface should be reasonably smooth and accurately shaped.

3D Printed Horns

Smaller horns can also be produced using 3D printing.

3D printing allows complex profiles to be produced without traditional moulds.

For high-output applications, however, the printed structure must be sufficiently rigid and mechanically secure.

DIY Horn Construction

A practical DIY horn can be constructed using:

Wood
MDF
Plywood
Fibreglass
ABS sheet
3D-printed sections
Epoxy composite construction

The best method depends on the required horn shape, size and quantity.

Making a Curved Horn

Curved horn surfaces can be difficult to produce from flat sheet materials.

Possible DIY methods include:

Layered MDF construction
Wood laminations
Thermoformed plastic
Fibreglass moulding
Epoxy composite construction
3D printing

The finished horn should maintain the intended profile accurately.

Horn Mouth Shape

The mouth can be rectangular, circular, elliptical or another suitable shape.

The shape affects the horizontal and vertical acoustic dimensions and therefore the directivity.

A rectangular mouth is common in professional PA horns because it can provide separate control of horizontal and vertical coverage.

Horizontal vs Vertical Horn Expansion

A horn can expand differently in the horizontal and vertical directions.

This allows designers to create different coverage angles in each plane.

For example, a horn might provide wide horizontal coverage but narrow vertical coverage.

Constant Directivity Horn Geometry

Constant-directivity horns are designed so that the coverage remains relatively controlled over a wide frequency range.

The geometry is often more complex than a simple conical horn.

Such horns are particularly useful for professional sound systems.

Horn Flare Rate

The flare rate describes how rapidly the horn expands.

A slower flare produces a different acoustic loading characteristic from a rapidly expanding horn.

The flare must be chosen according to the desired frequency range and horn profile.

Horn Cutoff and Flare Constant

For some horn profiles, the flare can be described mathematically using a flare constant.

The exact relationship between flare rate and cutoff frequency depends on the mathematical horn profile.

This is why horn design software is useful when designing a precise horn rather than relying only on approximate dimensions.

Horn Length and Phase

The acoustic path through the horn introduces phase delay.

This becomes important when a horn is combined with another driver, such as a woofer and tweeter.

The physical position of the acoustic sources may therefore need to be considered when designing the crossover.

Horn and Crossover Design

A horn-loaded driver often has substantially higher sensitivity than a woofer or midrange driver.

The crossover may therefore require attenuation to match the acoustic level of the other drivers.

The horn's actual frequency response should be considered when designing the crossover.

Horn Driver Sensitivity

Compression-driver/horn combinations can have very high sensitivity.

For example, a horn system may produce substantially more SPL from one watt of electrical input than a typical direct-radiating driver.

This efficiency advantage is one of the main reasons horns are popular in PA systems.

Horn Speaker Power Handling

High sensitivity does not mean that the driver can tolerate unlimited power.

Power handling is determined by both thermal and mechanical limits.

A compression driver can still be damaged by excessive power, especially when operated below its recommended frequency range.

Minimum Recommended Crossover Frequency

Compression drivers normally have a recommended minimum crossover frequency.

Operating below this frequency can produce excessive diaphragm excursion and distortion.

The horn itself also has a lower operating limit.

The crossover should therefore protect the driver from frequencies it cannot safely reproduce.

Horn Driver Protection

A high-pass filter is normally used to prevent damaging low-frequency energy from reaching a high-frequency compression driver.

The filter order and crossover frequency should be selected according to the driver manufacturer's specifications and the desired acoustic response.

Horn Speaker Directivity

Horn directivity generally becomes narrower as frequency increases, although the exact behaviour depends on the horn geometry.

At sufficiently low frequencies, the wavelength becomes large relative to the horn mouth and the horn may lose its intended directional control.

Directivity and Horn Mouth Size

A larger mouth can maintain directional control to lower frequencies than a smaller mouth.

This is another reason why low-frequency horns become physically large.

Horn Speaker Applications

Horn systems are commonly used in:

Professional PA systems
Concert sound
Cinema sound
Auditorium systems
Stage monitors
High-efficiency hi-fi systems
Megaphones
Public-address systems

PA Horns

PA horns are designed primarily for high output and controlled coverage.

They are commonly paired with compression drivers and mounted above woofers in two-way or three-way loudspeaker systems.

Cinema Horns

Cinema systems have historically used horn-loaded drivers because of their high efficiency and ability to produce high SPL in large spaces.

Horn systems can also provide controlled coverage suitable for auditoriums and theatres.

Hi-Fi Horn Speakers

Horn-loaded hi-fi systems emphasize efficiency and dynamic capability.

Large horn systems can provide very high sensitivity, allowing substantial acoustic output with relatively modest amplifier power.

The quality of the final system still depends strongly on driver, horn, crossover and cabinet design.

Megaphone Horns

A megaphone is a simple acoustic horn.

The human voice or another sound source enters the narrow end and the horn directs the sound toward the large opening.

Although simple compared with a professional loudspeaker horn, the same general acoustic principle of impedance transformation is involved.

Horn and Woofer Integration

In a two-way speaker, the horn-loaded high-frequency driver and woofer must integrate smoothly around the crossover frequency.

Important factors include:

Frequency response
Sensitivity
Directivity
Acoustic phase
Driver spacing
Crossover slope

Horn and Woofer Directivity Matching

For a well-integrated loudspeaker, the horn's directivity should transition appropriately to the woofer's directivity near the crossover region.

If the directivity changes abruptly, the speaker may produce uneven off-axis response.

This is an important consideration in professional loudspeaker design.

Horn Speaker Construction

A horn cabinet should be mechanically rigid.

Large horn walls can vibrate if they are too thin or poorly supported.

Internal braces and reinforced structures may therefore be necessary.

Horn Surface Smoothness

The internal horn surface should be reasonably smooth and continuous.

Large steps, gaps or abrupt changes in the horn profile can cause reflections and unwanted response irregularities.

The throat region deserves particular attention because it carries high acoustic energy.

Horn Throat Quality

The throat should transition smoothly from the driver exit into the horn profile.

A poorly shaped throat can create strong reflections and resonances.

Commercial compression-driver horns are therefore normally manufactured with accurately controlled throat geometry.

Horn Mouth Edge

The mouth edge can influence diffraction.

The transition from the horn to the surrounding space should be considered when designing the mouth.

Large abrupt edges can affect the frequency response and directivity.

Measuring a Horn Speaker

Measurement is extremely useful when developing a horn speaker.

Useful measurements include:

On-axis frequency response
Off-axis frequency response
Impedance
Distortion
Polar response
Maximum SPL

Polar Measurements

Polar measurements show how the horn distributes sound at different angles.

They are particularly useful for evaluating professional PA horns.

Measurements can reveal whether the horn maintains its intended coverage angle across the operating range.

Horn Speaker Distortion Testing

High-frequency horn systems should be tested for distortion at different output levels.

Distortion can increase when:

The driver is operated too low in frequency
Power handling limits are exceeded
The horn has strong resonances
The throat geometry is unsuitable
The driver diaphragm reaches excessive excursion

Common Horn Speaker Problems

Problem	Possible Cause
Harsh sound	Horn resonances, driver distortion or poor crossover
Weak low frequencies	Horn too small for the intended low-frequency range
Narrow coverage	Horn geometry or mouth dimensions
Uneven response	Throat reflections, resonances or poor profile
High distortion	Driver overloaded or operated below recommended range
Uneven off-axis response	Poor directivity matching or horn geometry

Common Horn Design Mistakes

Using a horn with an incompatible driver throat.
Making the horn mouth too small for the intended frequency range.
Ignoring the horn's cutoff frequency.
Operating a compression driver below its recommended frequency.
Ignoring driver sensitivity when designing the crossover.
Using an inaccurate horn profile.
Creating abrupt transitions in the throat.
Ignoring higher-order horn resonances.
Failing to control horn directivity.
Using insufficiently rigid horn walls.
Ignoring acoustic phase when integrating the horn with a woofer.
Designing only for on-axis response and ignoring off-axis performance.

DIY Horn Design Workflow

Select the compression driver or other suitable driver.
Obtain the manufacturer's acoustic specifications.
Determine the required frequency range.
Select the desired horn coverage.
Choose a suitable horn profile.
Determine throat dimensions.
Determine the target mouth dimensions.
Determine the horn length.
Model the horn geometry.
Select the construction material.
Build the horn accurately.
Mount the driver securely.
Design the crossover.
Measure on-axis response.
Measure off-axis response.
Test distortion and power handling.
Adjust the design if necessary.

Horn Speaker Design Checklist

Driver selected
Throat diameter confirmed
Driver frequency range checked
Minimum crossover frequency checked
Target coverage angle selected
Horn profile selected
Horn length determined
Mouth dimensions determined
Cutoff frequency considered
Throat transition checked
Horn walls made sufficiently rigid
Internal surface finished smoothly
Driver mounted securely
Crossover designed
Driver protection included
On-axis response measured
Off-axis response measured
Distortion tested
Maximum output tested

Key Takeaways

A horn provides acoustic loading between a driver and the surrounding air.
Horn loading can greatly increase acoustic efficiency.
Compression drivers are commonly used with high-frequency horns.
The throat is the narrow end of the horn.
The mouth is the large opening.
Horn length and mouth dimensions influence low-frequency loading.
Large horns are generally required for low-frequency operation.
Conical, exponential, tractrix and constant-directivity horns are examples of different horn profiles.
Horn geometry can be used to control horizontal and vertical directivity.
Constant-directivity horns are particularly useful in professional sound reinforcement.
The driver and horn must have compatible throat and frequency characteristics.
Compression drivers require appropriate high-pass filtering.
High sensitivity does not mean unlimited power handling.
Horn resonances and reflections can affect frequency response.
Accurate throat geometry is particularly important.
Horn construction requires sufficient mechanical rigidity.
Plastic, wood, plywood, fibreglass, composite and other materials can be used for horn construction.
DIY curved horns can be produced using moulding, laminated construction, thermoforming, composites or 3D printing.
On-axis measurements alone are not sufficient for evaluating a professional horn.
Off-axis and polar measurements are important when controlled directivity is required.