Why Horns?

August 29, 2023 hanson@gotlink.cn

Horns are not new to us. You have done this at some point: gather your palms close on your mouth, and your speech spreads further. This is an example of horn’s principle. In fact, our months and ears are also of horn-shapes, although the ear is reversed. A horn is basically a sound concentrating amplifier which gathers dispersed sound energy and raise the sound level. Horn speakers appeared very early, including the very first phonograph. Then what are horn speakers’ advantages?

First of all is high sensitivity. Because of the pressure increasing structure of horns, the diaphragm positioned near the throat has to overcome great mechanical resistance, causing its excursion to be minimal. This saves a lot of power overcoming air resistance and increases the electro-acoustic energy transform efficiency. What’s more, the sound waves have higher directivity with the horn gathering them, and most of them are able to reach the listener without getting damped by room reflection.

Second is good transient response. Also because of the pressure increasing structure of horns, a diaphragm in a horn only travels 1/10 of the distance a same one in a box would do. Thus we can realize quick start and quick stop. This is unrivaled by other normal speakers.

Third is high fidelity. Based upon the high directivity of horn speakers, the sound waves go straight to the listeners. Therefore, they don’t get coloration during room reflection and remain consistent, hence less loss in details. This is why horn speakers usually sound loud but also relaxing.

Fourth is a wide listening range. Interestingly, despite its high directivity, a horn is good for listening within all its coverage because the sound is not reflected. Applying normal speakers requires thorough consideration of the whole room environment. Only with a lot of adjustment is someone able to guarantee that sound waves reflected from various directions are in good stance reaching the “sweet spot”. Therefore, changing the seat will lead to rapid drop of balance. Based on the same reasons above, horn systems are more adaptive to different circumstances.

Why All-horn Systems?

As mentioned above, horns have high sensitivity, good transient response, high fidelity and wide listening range. Horn’s quality is widely applauded by the audiophiles, and people have come up with all-horn systems early on. However, in spite of all the advantages, one thing is what horn cannot get around: volume. According to acoustic principles, a horn’s mouth dimension depends on its cut-off frequency. Meanwhile, lower frequencies have longer wavelengths. When reaching 20 Hz, the sound has a wavelength of 17 meters, corresponding a round horn of 5.4 meters in diameter, or 1.35 meters if it’s a quarter horn.

 

Before ESD Acoustic does, there also have been people trying all-horn systems. However, these pioneers use folded horns or spiral horns for the low frequencies. The founding father of our horn technology, Dr. Bruce Edgar has used folded horn as well. The system is Edgarhorn Titan system and was a milestone of all-horn system (fig.1). The principle behind folded horns is simple – applying specially designed boards in a box to extend sound waves while turning the direction (fig.2). Spiral horns shape like nautilus, extending while spinning (fig.3). Both designs solved the volume problem of bass horn and unify the efficiency of the whole system, but like a fly in the ointment, the twisted sound path causes time delay problem and loss of phase and details.

ESD Acoustic strives to create the most uncompromised all-horn system. By applying carbon fiber material, Ten inches titanium diaphragm and a six inches throat (introduced elsewhere), we greatly reduced the weight of the horns, shortened their lengths, hence came up with a new all-horn system (fig.4). Although this system’s volume is still quite big, but it satisfies standard room dimensions and does not take much ground. As for the sound quality, the problems of bass horn mentioned above are greatly improved.

Why Carbon Fiber?

What material is best for making a horn? First, we need to know that in order to guide and concentrate the sound wave, the inner surface of the horn should be as insulative as possible, especially preventing low frequencies’ penetration. Second, the material should be of low coloration, not adding too much “flavor” to the sound; Finally, the material should be good at damping out resonance.

 

In order to make nice sounding horns, folks have tried different materials including metal, plastic and wood. Among them, wooden horns have been widely praised by audiophiles with their low coloration, nice insulation and resonance sluggishness, wooden horns. The success of wood should attribute to its fiber structure. Like light, sound gets reflected and refracted while entering a different medium. In the horn’s situation, the reflected part goes back to the horn, while the refracted part keeps on penetrating it. When the horn uses fiber material, since it is not uniform, the sound waves are actually entering into new medium all the time, and the refraction waves damped out very quickly before it penetrates the horn, while those that return remain gathered in the horn. What’s more, uniform objects tend to have the same resonant frequency, thus they are easy to resonate, but wood as a fiber material is not so – this is also why heavier horns are usually considered better, because heavier things are harder to resonate. As for the coloration, first wood’s natural sound is comfortable to human ears, second the coloration is small since the resonance level is low.

 

Thanks to the quick development of new materials, glass fiber and carbon fiber has entered our eyesight. Based on the same fiber structure, these two materials share the same acoustic traits that wood has. The first to be applied was glass fiber. A single wood fiber is thick enough to be seen, but glass fiber is as thin as 1/5-20/1 of a hair. Thinner fiber means that glass fiber has more layers of fiber, thus it should be better than wood. Carbon fiber is even better than glass fiber, as its fiber is as thin as only 1/50 of a hair. What’s more, different from the chaotic formation of wooden and glass fiber, carbon fiber has a very orderly stratified structure, with its layers connected by Van der Waals’ force. This makes the number of layers of carbon fiber much greater than that of wooden or glass fiber of same thickness. Aside from nice acoustic characters, carbon fiber has some other outstanding physical characters. Its density is only 1.78g/cm^3, which is less than 1/4 of steel, but it’s around 10 times as strong, which makes the design in fig.5 possible, reducing its floor space enormously. Furthermore, carbon fiber’s thermal expansivity is only 0.7*10^-6 /K, while glass fiber’s is about 4.8*10^-6 /K and wood’s is around 8.0*10^-6 /K (determined by specific material’s category). This means that when temperature changes, the change of shape in a carbon fiber horn is the least of three, hence keeping its inner curve stable.

Although this article has illustrated the theoretical superiority of carbon fiber as a horn material, its manufacturing difficulty cannot be ignored. Without anyone setting foot on this field, ESD Acoustic has self-developed the entire process of making carbon fiber horns by long time research and practice. Now we  offer you the world’s first carbon fiber all-horn system.

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