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When I had hit upon a 3D spiral horn concept several years
ago, my intention had been to improve a folded rear horn. A rear horn utilizes the sound radiated from the back of driver to enhance effectively bass sound. A folded rear horn made of plywood is difficult to build because of its complicated structure. Moreover, its sound quality is degraded by unwanted resonance originated from its angular sound passage. I had thought a 3D spiral horn might solve these problems by its relatively simple structure and by its curved surface. After numerous trials, I have reached an understanding that the rule of thumb applicable to a rear horn had not stood up for a 3D spiral (horn.) My experiences have been a history of struggle for freeing myself from common senses about rear-loaded horn. This may imply that a 3D-spiral (horn) is a new type of loudspeaker, which belongs neither to a rear-loaded horn nor to a ordinary bass-reflex (vented box). A 3D spiral horn has a relatively short three-dimensional spiral sound passage that looks like a conch shell. Its structure is comparatively simple. It can be built using standard PVC pipes and fittings. Therefore, you do not need a high degree of technical skills to build. The most prominent peculiarity of 3D spiral (horn) is that its lower frequency region extends to 50 Hz using 3" full range driver without booming and without decline of SPL. (Please see frequency response of Helix-H75) Sound degenerations are minimal because a 3D spiral horn has a smoothly expanded sound passage and because there is no parallel plane, which may produce standing wave. Recent examination has indicated a constant pitch spiral gave an equivalent frequency response with an expanded spiral. (See VC75) If you bring the ear close to the horn mouth, you can hear very clear sounds although bass sounds are much emphasized. This means the distortion inflicted through a 3D spiral horn is minimal. |
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A Japanese conch shell is shown left, and here is a sound sample. Buddhist monk practicing asceticism in the mountains blows on a conch shell of the present age. |
