What are horn speakers?

The Horn Basics

Everyone probably remembers an interesting experiment from school where a thick paper was rolled into a cone with a wider base and a narrower top. When you speak into the smaller end of this paper cone, a fascinating phenomenon occurs: the sound becomes louder and clearer at the direct line facing the cone. This effect is often taken for granted as common knowledge and has practical applications in daily life. For instance, when calling someone from a distance, we naturally cup our hands around our mouth to form a makeshift horn, amplifying and clarifying our voice. This simple physical principle not only allows sound to travel further but also focuses the direction of the sound, making it louder. This is the basic advantage of a horn.

In fact, this principle was understood and utilized in the very first of audio inventions. Thomas Edison, the famous inventor, used this concept in his phonographs. Sound was initially picked up by a bamboo needle from the grooves of a wax cylinder, and transmitted to a small diaphragm. Without a horn, one had to listen closely to the diaphragm to hear the faint sound. However, attaching a horn to the diaphragm greatly amplified the sound, increasing its volume and expanding its bandwidth, filling the room with music. Hence, those large horns seen on old phonographs are essentially examples of this principle in action. This shows the most significant advantage of horn loudspeakers - their efficiency. Early amplifiers, developed during the late 19th and early 20th centuries, had limited power output. Horns were able to significantly increase the acoustic output of these low-powered amplifiers, making them ideal for projecting sound in large spaces.

Therefore, we now know a horn loudspeaker is a type of speaker that employs an acoustic horn to enhance the efficiency of its driving elements. Horn speakers are notably 3 times more efficient compared to ordinary cone speakers. An authentic horn design includes a compression driver that generates sound waves through a small metal diaphragm vibrated by an electromagnet. This diaphragm is connected to an expanding duct or horn, that channels the sound waves into the open air. 

Nostalgic Horn Usages in Daily Life 

Historically, horn speakers were not designed for the intricacies of high-fidelity audio but for their prowess in projecting loud sounds. This fundamental quality made horn speakers omnipresent in various sectors of society, especially in the early 20th century, like:

• Military Communications: In military settings, especially during the World Wars, horn loudspeakers were crucial. They were used for broadcasting orders and alerts across vast fields and barracks. Their ability to cut through ambient noise made them indispensable for coordinating troop movements and conveying critical information.

• Maritime Announcements: On ships, especially during the era of large ocean liners and naval vessels, horn loudspeakers were used to communicate across the decks and to other ships. The horn's capacity to send clear messages across the noisy backdrop of the sea was vital for navigation and safety announcements.

• Railway Stations: Railway stations, bustling with travelers and trains, relied on horn loudspeakers for announcements regarding arrivals, departures, and platform changes. Their effectiveness in a noisy, open-air environment ensured smooth transit and communication for passengers and staff alike.

• Early Automotive Heralds: In the early days of automobiles, horns were not just signaling devices but also a form of announcing the vehicle's presence in a predominantly pedestrian and horse-drawn carriage environment. These horns, loud and distinctive, played a key role in the safety and navigation of early automobiles.

• Classroom Order: In schools, particularly in outdoor settings or large classrooms, horn loudspeakers facilitated the management of students. They were used for signaling the change of classes, making general announcements, and even for outdoor teaching sessions, ensuring that the teacher's voice was heard by all students.

• Emergency Broadcasts: In times of emergency, such as natural disasters or public crises, horn loudspeakers were vital for disseminating urgent information and instructions to the public. Their ability to deliver messages clearly over large areas made them indispensable tools for civil defense and emergency response teams.

• Factory Announcements: In the bustling environment of factories and industrial settings, horn loudspeakers were used to convey important announcements. They helped in coordinating shifts, announcing breaks, or relaying safety warnings, ensuring that messages were heard over the noise of machinery.

• Sports Events: At outdoor sports events, especially in stadiums without modern PA systems, horn loudspeakers were used to announce players, relay scores, and provide commentary. Their use was crucial in keeping the audience engaged and informed throughout the event.

• Movie Theaters: In the early days of cinema, particularly during the silent film era, horn loudspeakers were sometimes used to project music or live commentary alongside the film. They helped create a more immersive experience for the audience in a time when synchronized sound was not yet a feature of films.

In these applications, horn speakers are valued for their simplicity and ability to produce loud sounds efficiently to broadcast sound over large areas or through noisy environments at low cost. The volume of speech or signals is prioritized. Basic horns for these functional uses often compromise on aspects like frequency range and distortion. Thus, it is quite common to hear low-fidelity, distorted sound in old videos that feature audio from broadcasting horn speakers. 

High Fidelity: Advanced Horn Speakers Nowadays

On the other end of the spectrum, horn speakers can be engineered for sophisticated, high-end audio reproduction in audiophile-grade sound systems. 

This requires a more precise design approach, involving complex engineering, advanced materials, and an in-depth understanding of acoustic principles. In HiFi applications, horns are valued for their efficiency, directivity, and dynamic range. 

In modern days, computer-aided design (CAD) and computational acoustic modeling have revolutionized horn speaker design. Early horn designs were often based on trial and error, with limited understanding of the complex interactions between sound waves and horn geometry. Today, designers can use sophisticated software to model and simulate horn behavior, allowing for precise control over factors like dispersion patterns, frequency response, and distortion. This has led to more refined and accurate horn designs.

Characteristics of Modern Horn Speakers:

• Efficiency: Horns can increase the acoustic output of a speaker driver for a given power input. This is because the horn structure directs more of the driver's energy into the listening space as opposed to being absorbed as heat within the driver or dissipated in other directions.

• Directivity: Horns provide more control over the directivity of the sound, which means they can be designed to focus sound in a particular direction. This is useful in situations like public address systems or concert halls, where sound needs to be directed over long distances or controlled to avoid reflections and echoes.

• Bandwidth: Horn speakers are often used for their ability to reproduce a wide range of frequencies, but their size can limit the reproduction of low frequencies. Very large horns are needed to effectively reproduce bass frequencies, which is why horn-loaded subwoofers are large and not commonly used in home audio.

• Distortion: When designed and implemented correctly, horn speakers can reduce certain types of distortion because the driver itself does not have to move as much air directly; the horn does a lot of the work.

• Applications: Due to their high efficiency and directivity control, horn speakers are commonly used in professional audio systems for concerts, cinemas, and public address systems. They are also favored in some high-fidelity audio systems and in certain styles of loudspeakers for home use.

• Types of Horns: There are various types of horn designs such as exponential horns, which expand at an exponential rate, and constant directivity horns, which maintain the same directivity at all frequencies.

• Design Complexity: Designing a horn speaker is more complex than designing a traditional cone speaker. Horn shape and length must be carefully calculated to ensure that the expansion of the horn correctly matches the acoustic impedance of the air to the driver over the desired frequency range.

The Drawback: Space Requirement of Horn Speakers

Although horn speakers were the first practical loudspeakers around the 20th century, their popularity has waned in recent decades due to the development of cone loudspeakers, the availability of inexpensive amplifier power, and the need for very large structures to adequately handle bass frequencies. In the following paragraph, we dive deeper into the relationship between horn size and frequency reproduction.

Horn speakers, known for their distinctive design, occupy more space than conventional cone speakers due to their operational principles. High Frequencies (Treble): Horns can be smaller when dealing with higher frequencies like treble. This is because high frequencies have shorter wavelengths. For instance, a 20 kHz frequency has a wavelength of about 1.7 cm (0.67 inches). Therefore, horns designed for tweeters or compression drivers, which handle these high frequencies, can be compact while still being efficient in directing and amplifying sound.

Low Frequencies (Bass): The challenge is more pronounced with low-frequency sounds, ranging from 20 Hz to 200 Hz. These frequencies have much longer wavelengths, from about 17 meters (56 feet) at 20 Hz to 1.7 meters (5.6 feet) at 200 Hz. To effectively direct and amplify such long wavelengths, the horn must be similarly large, leading to the construction of significantly larger structures for adequate bass response.

To effectively reproduce bass frequencies, the horn would be quite large and bulky. As a result, in contemporary horn speaker designs, horns are typically used for mid and high frequencies. For bass frequencies, they often incorporate standard cone drivers where their size can be more manageable.

Conclusion

Horn speakers, with their rich historical roots and fundamental acoustic efficiency, have played a pivotal role in the development and evolution of audio technology. From their early use in Edison's phonographs to diverse applications across various sectors, horn speakers have demonstrated remarkable versatility. Modern advancements in design and computational modeling have further refined horn speakers, making them a valuable component in high-fidelity audio systems. However, the physical size requirements for effective low-frequency reproduction remain a challenge, often leading to a combined use with cone speakers in contemporary designs to fit in smaller modern living spaces.