Does this type of speaker sound familiar to you? Well, most audio engineers and audiophiles would definitely know about it. Consumers on the other hand, might not have a clue on how it looks like or what it does. Well, if you are in the mood to learn more about sound systems, then you just have to find out what is a Horn Speaker!
There are many speaker systems out there in the market, that uses this special type of speaker design. However, for today, we will focus on the basic principles behind the function of horn speakers, and not go into too much detail with regards to the other derivative designs. You will also find out about its applications in the audio world!
Horn Speaker – Just Looks Unique?
A loudspeaker that uses an acoustic horn in order to improve the performance of its driving element(s), is called a horn loudspeaker. A typical design (below) consists of a “compression driver” which uses a small metal diaphragm (vibrated by an electromagnet) to produce sound. It is attached to a “horn”, which is a flaring duct to conduct the sound waves to the air.
The narrow part right next to the driver is called the “throat” and the large part farthest away from the driver is called the “mouth”. The shape and flare of the “mouth” determines the horn’s radiation pattern. Horn speakers often have rectangular openings, with the width optimized for better horizontal coverage angle, and height optimized for better vertical coverage angle.
Horn loudspeakers are known to exhibit much better efficiency, and they can usually produce up to 10 times (10 dB) more sound power, as compared to a typical cone loudspeaker from a given amplifier output. Because of this, horns are widely used in public address systems, megaphones, and sound systems for large venues like theaters, auditoriums, and sports stadiums.
Here are the topics we’ll be looking at:
- Operating principle
- Common designs
Acoustic horns convert large pressure variations with a small displacement area into low pressure variations with a large displacement area and vice versa. This is done through the gradual, often exponential increase of the cross sectional area of the horn. Hence, based on this principle, the sound waves at the “throat” will be of high pressure and low displacement.
The horn’s tapered shape actually allows the sound waves to gradually decompress and increase in displacement until they reach the “mouth” where they will be of low pressure but large displacement. The typical modern, electrically driven horn speaker, works the same way, but the mechanically driven diaphragm is replaced with a dynamic or piezoelectric driver.
Modern horns are generally designed to have a conical, exponential taper. Basically, the slower the flare rate, the lower the frequencies the horn will reproduce for a given length of horn. For instance, a horn area growth rate of 30% per foot will produce frequencies down to about 30 Hz; 10 times area per foot is ideal for midrange; 100 times area per foot is used for high frequencies.
The throat part of modern horns are usually smaller than the diaphragm area. This is often called the “compression” ratio of the horn, which is the diaphragm area divided by the throat area. Horns with higher compression are better at properly coupling the diaphragm to the air at the horn’s mouth, thus increasing efficiency. Typical ratios include “1.5:1” (low) and “3.5:1” (high).
There are quite a few horn designs that have been produced throughout the years. Going through all of them would probably take a lifetime. So, for today, I’ll just go through some of the more common ones:
- Folded horn
- Multicell horn
- Radial horn
The driver is mounted in a loudspeaker enclosure, consisting of internal partitions that forms a zigzag flaring duct which functions as a horn. This design improves the coupling efficiency between the speaker driver and the air. The horn acts as an “acoustic transformer”, providing impedance matching between the relatively dense diaphragm material and the less-dense air. This produces greater acoustic output power from the driver.
This design consists of a number of symmetrical, narrow dispersion, usually exponential horns that are combined in an array driven by a single driver. Multicell horns are mainly used to address the problem of directivity at higher frequencies, other than providing excellent low frequency loading. Although expensive, these horns are still commonly used in public address applications as they sound relatively good.
These horns have two surfaces based on an exponential flare rate, and two straight walls that determine the output pattern. A variation of the radial design called the “diffraction” horn (by JBL), uses a very small vertical dimension at the mouth as a means of avoiding the mid-range horizontal beaming of radial horns that have a larger vertical dimension at the mouth. The diffraction horn is popular in monitor designs and for near-field public address applications, due to its wide horizontal dispersion pattern.
Live Concert and Public Address
Horn loudspeakers are capable of very high sound pressure levels that are needed for live performances and public address applications. However, in these high sound pressure applications, sound fidelity may sometimes be compromised for volume efficiency, and also for the controlled dispersion characteristics which are generally required in most large concert venues.
Large arrays of horn speakers are used for high-volume bass reproduction, which produces bass that audiences can not only hear but feel. An array of multiple horn speakers exhibits the same benefits as having a single horn with a greater mouth area: the low frequency cut-off extends lower as the horn mouth gets larger, and the array has the greater output power of multiple drivers.
Audiophiles and Consumers
Horn speakers are ideal for controlled directivity, which helps to limit sound reflections from room surfaces (such as walls, floor, and ceiling) and they also have better sensitivity. Since horn speakers are capable of very high efficiency, they are ideal for very low-powered amplifiers, such as single-ended triode amps or other tube amplifiers, that are often used at home.
Some audiophiles also use horn speakers, but there are others who dislike them for their harmonic resonances, which sounds like an unpleasant form of distortion. Since there are a variety of horn designs (of differing length, material, and taper, as well as different drivers), it is somewhat impossible to give such blanket characterizations to horn loudspeakers.
Furthermore, since movie soundtracks have a great dynamic range where peak levels are 20 dB higher than average, a horn speaker would be ideal, as its higher sensitivity allows for movie theatre sound levels at the listening position, with typical 100 watts-per-channel amplifiers used in home theatres.
That’s about all I have for you folks today. Do you use horn speakers at home? Or maybe you don’t think it would make a big difference?
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