Loudspeaker with circular radiation. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Loudspeaker with circular radiation. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Speakers

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Regular readers of our magazine have certainly noted the article by V. Shorov and V. Yankov ("Radio" 1997, No. 4, p. 12-14) about a similar acoustic system. We present a more complex design, on the implementation of which its author, the German engineer Hans Burk, worked for about a year. Currently, such acoustic systems are quite widespread.

This loudspeaker "Omnisono" ("all-encompassing sound") is defined by the developer as a "point emitter". A point source of sound can be considered such an emitter, the geometric dimensions of which are small compared to the length of the excited sound wave. In the low-frequency region, all loudspeakers are point-like, but as the signal frequency increases, when the dimensions of the emitter become commensurate with the wavelength, their directivity becomes sharper. Depending on the design at high frequencies, its diagram can be in the form of a narrow beam (in the worst case) or a hemisphere (ideally).

The radiation of the "Omnisono" loudspeaker covers most of the full sphere, and remains omnidirectional over the entire frequency band. It has a rated power of 120 watts, short-term (musical) power is higher - 200 watts. The phase response of the loudspeaker has a phase shift of about 90° in each of the four frequency bands, in the entire band the phase shift reaches 360°.

The four-way speaker system has an asymmetrical design. The dynamic heads are placed one above the other so that their axes are vertical, as shown in the figure.

Loudspeaker with circular radiation

The woofer head with a diffuser diameter of 245 mm, placed in a closed cylindrical wooden case (350 mm in diameter and 850 mm high), faces the diffuser bell downwards, to a diffuser of complex configuration. The sound is emitted through an annular acoustically transparent slot. The body (useful volume 62,5 l) is filled with sound-absorbing material.

The top cover of the housing is formed by the box of another woofer-midrange head (diffuser diameter 160 mm), also filled with sound-absorbing material. Above it, in a mini-box, a midrange dome head (dome diameter 50 mm) is placed, also with damping from the magnetic system. At the top is a dome-horn head HF. The diameter of the dome of the latter is only 25 mm, which gives a good approximation to a point radiator: the length of sound waves in the allotted frequency range is from 8,5 to 1,7 cm.

To create the effect of a uniform sound field in a real listening room, it is most important to ensure a uniform sound pressure in the horizontal plane, which is achieved by installing a diffusing cone above the HF head. On the base of the cone there is a ring made of sound-absorbing material protruding beyond its edges. This dampens the natural oscillations of the diffuser and prevents the occurrence of unfavorable interference phenomena. Similar phenomena are also initiated by the housings of the HF and MF heads, but in practice their influence is negligible due to the small geometric dimensions compared to the wavelengths emitted by the underlying heads. The choice of heads (and their radiating surfaces) of a relatively small diameter is due to the desire for "pointiness". Based on the condition d/l<1, the upper heads are placed quite close to each other, on four bearing racks with stepped cutouts, to which the flanges of these heads are screwed from below.

Together with the editors of the magazine "Funkschau" comprehensive tests of the AC "Omnisono" were carried out. Due to the relatively high impedance (12 ohms), the loudspeaker is noticeably inferior to the majority in terms of characteristic sensitivity, which is partly offset by its low distortion (Kg < 1% at 10 W). However, in a real listening room with standard furnishings at a power of 2,5 W at a distance of 3 m from the speakers, a volume level of 86 phon is provided with a wide directivity pattern. The sound pressure is exceptionally uniform and independent of frequency.

The sound of the speakers is completely devoid of color at all frequencies, it is completely clear, without highlighting any frequencies, and neutral in the best sense of the word. Own resonances (including the main bass head) are not heard, at least they are very well damped.

This speaker is not intended for "disco" and other pop styles - such installations require emphasized, "brilliant" high frequencies and bass. The absolute neutrality of the sound is more of interest to discerning music lovers who prefer the fidelity and accuracy of sound reproduction without superficial showiness. Low frequencies (double bass, timpani) are spatial and not squeezed, in other words, these are not virtual, but "real" basses. When playing Bach's D minor organ toccata, there are no overtones that usually accompany the deepest tone of an organ point. The piano sounds natural, the winds (especially the horns) are very good, the strings are more "restrained" than "sparkling". Pulse signals are reproduced particularly cleanly.

To achieve the maximum effect, such loudspeakers must be located at a considerable distance from the walls, which to some extent limits their scope as front speakers.

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