TECHNOLOGY |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Avantgarde Hornspeakers -- Evolution or Revolution?
The theoretical advantages of horn loudspeakers are common knowledge to specialists in this field. Nevertheless, this construction principle is only rarely put into practice. One reason may be the considerable efforts and the ensuing costs. But the major obstacle is to put theory into operational practice. The horn loudspeaker emphasizes not only the positive aspects of musical enjoyment, but also impurities, which were not perceivable before. Simply imagine the horn loudspeaker to be a magnifying glass with which everything can be seen much more clearly, which means its beauty as well as its impurities. Thus, the most infinite errors occurring during developing of a loudspeaker will be indiscriminately brought to light. A very simple example may explain this fact: Consider a loudspeaker driver with a frequency range of ± 0.5 dB. A fabulous value! Now place a horn in front of the driver and you will obtain deviations of the frequency range of ± 5 dB. The very same driver once performing brilliantly and now with a horn -- performing badly. A horn loudspeaker is like a magnifying glass. It is extremely sensitive, blatantly showing every single mistake. Therefore, our horn loudspeakers are not just beautiful horns mounted to an attractive frame, but an expression of affectionate dedication to detail and meticulous and careful manufacturing. With our spherical horn system we prove the true potential of the horn technology. Therefore, we would like to acquaint you with the technical subtleties which distinguish our loudspeakers from ordinary horn concepts... The Proper Horn Function The shape of our horn curvature does not follow the whim of our designer, but is precisely calculated by means of complex mathematical procedures. This is aiming at a controlled increase of the soundwave front within defined limits from the beginning of the horn to the end. The slightest imprecision of the horn shape will be mirrored by the sound waves. These will take on a slightly "crooked" shape instead of their original form. Just imagine, for example, a trumpet. The design, which means the length and the curvature of the horn, a particular sound namely the typical sound of a trumpet, is intentionally achieved. Horn loudspeakers follow an entirely different aim since the sound must be reproduced unbiased and undistorted! Various Algorithms for Calculating the Horn Shape Exponential horns, which emerged in the 1920's, are based on the conception that an even sound wave is emitted at the beginning of the horn. As one part of the sound wave, namely that along the central horn axis, has to travel a shorter distance than those parts who follow the horn curvature, this theory turned out to be wrong. The wave front within an exponential horn is slightly bent and causes so-called colorations, which means changes of tonality during reproduction. A substantial improvement in sound can be achieved by using a spherical horn. Instead of the 90-degree horn opening of an exponential horn, the spherical horn allows an even transition due to its broad opening of 180 degrees. This algorithm is based on the fact that the wave surface at the horn throat is not a plane, but is dome shaped. (See Figure 1.) |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
Figure 1 -- Construction Design of Spherical and Exponential Horns. The comparative figure shows that the spherical horn has a larger opening (h1). It is, however, shorter (L1) than an exponential horn with the same frequency range. In an exponential horn, part of the sound waves located along the axis inevitably have to cover, indeed, a longer distance than those on the rim of the horn. If this influence is taken into account as well as the fact that the surface of the dome (not the even diameter) should rise according to the exponential principle, one obtains an altered shape of the spherical horn. Altogether, this results in a linear and constant sound wave emission along the entire frequency range of a spherical horn. Since emission already comes from a spherically shaped surface at the horn throat, a wide and well-controlled directivity over the entire frequency spectrum is achieved. (See Figure 2.) |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Figure 2 -- Dispersion Characteristics of High Frequencies.In contrast to the exponential horn, beaming effects do not appear at high frequencies. This results in exceptional uniformity and integration at the off-axis response in the vertical and horizontal plane. Another difference of the spherical horn regarding the lower frequency range should be noted. The spherical horn shows a linear decline at its lower cut-off frequency point. The typical bumpy response of exponential horns does not occur. (See Figure 3: "Frequency Range in the 'Fo' Area.") |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Figure 3 -- Frequency Range in the 'Fo' Area. Frequency response of a spherical horn and an exponential horn at the lower cut-off frequency point. The symbolic frequency graphs show that the typical bumpy wave pattern due to reflection into the horn does not occur in a spherical design. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
The Right Shape The calculated values along the horn's axis are adaptable to whatever shape one wishes to obtain, be it square or rectangular, etc. Simply imagine a spotlight reflector. You'll find round and rectangular lamps and, depending on the design, you'll obtain a beam of light serving as a spot light or as a light illuminating the surrounding area. The same applies to a horn loudspeaker. Depending on the design of the horn, the sound waves can be shaped in order to accurately fulfill the specified requirements. This procedure -- used mostly in professional sound reinforcement -- has one crucial disadvantage. It alters the shape of the original sound wave. You'll obtain the same volume everywhere which is important for sound reinforcement. However, you won't hear the same music anymore. In terms of the spotlight, you'll obtain the same light intensity everywhere in the room, but overall it will have become darker. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Figure 4 -- The three-dimensional grid model of a spherical horn for calculation of the injection mold and the programming of the CAD/CAM machines.
Since we prefer it to be lighter, we are manufacturing our spherical horns simply according to nature's pattern, which means in circular, spherical shape. As long as the physical principles of the world remain unchanged, and the sound waves spread as they do now, our spherical horns are just right as they are. And it will be this way forever. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Since we prefer it to be lighter, we are manufacturing our spherical horns simply according to nature's pattern, which means in circular, spherical shape. As long as the physical principles of the world remain unchanged, and the sound waves spread as they do now, our spherical horns are just right as they are. And it will be this way forever. The Right Manufacturing Process Let's turn from theory to practice. How does Avantgarde Acoustic convert the right horn principle into an excellent product? There are various procedures available. The easiest way would be to manufacture the horn on a lathe, using wood as the basic material. However, wood tends to alter and change its shape. Depending on humidity, temperature and air pressure, wood expands or shrinks which would consequently alter the horn's curvature. A much better material is glass fibre reinforced plastic (GFP). This technique implies that the negative mold is covered with a mixture of epoxy resin and glass fibre. The surface structure, however, is of inferior quality. This is the reason why GFP horns have to be reworked manually. Herewith, the same problem arises as with wooden horns. The more the horn surface has to be manually smoothed, the less precise the horn shape curvature will be. Uncompromising product quality at a reasonable price cannot be realized that way. That's the reason why we took a new approach. As the very first manufacturer in the world to do so, Avantgarde Acoustic produces our spherical horns by using elaborate injection molding technology. Under a pressure of 2,500 tons, the molten resin is injected into a steel mold. These steel molds are manufactured with a tolerance of ± 0.002 inch, and a weight of more than 17,600 lbs. for the 37.4 inch low-midrange TRIO horn SH9504. This ensures a precision in horn manufacturing which had been impossible. It results in the unmatched long term stability and accuracy of our horns. On the one hand, this guarantees a very precise emission of the sound waves within the horn, due to the exact design of the horn shape curvature. On the other hand, it is possible to offer extremely high quality and product continuity in the series production process. Thus, one horn resembles the other, left and right channel are always 100% identical, which is absolutely indispensable for an exact stereo sound reproduction and imaging.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||