Omnisono Circular Radiation Counterperture Speaker System

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Created on 03.19.

Last updated on 10.04.2020 09:57.

Author: Radio Magazine, P. Syke.

Regular readers of the Radio magazine certainly noticed an article by V. Shorov and A. Yankov (Radio, 1997, No. 4, pp. 12–14) about a similar counter-aperture acoustic system. We present a more complex design, on the implementation of which its author – German engineer Hans Brück – worked for about a year.

This loudspeaker “Omnisono” (“all-encompassing sound”) is defined by the developer as a “point radiator”. A point source of sound can be considered a radiator, 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 rises, when the dimensions of the emitter become commensurate with the wavelength, their directivity becomes sharper. Depending on the design at high frequencies, its pattern can be in the form of a narrow beam (worst case) or a hemisphere (ideally).

Omnisono loudspeaker radiation covers most of the full scope, and remains omnidirectional over the entire frequency band.

Rice. 1. Sound propagation of a counter-aperture speaker system in a room.

It has a nominal power of 120 W, short-term (music) power is higher than 200 W. The phase response of the loudspeaker has a phase incursion of about 90 ° in each of the four frequency bands, and the phase shift reaches 360 ° throughout the entire band.

The four-way speaker system is of an axisymmetric design. The dynamic heads are stacked on top of each other so that their axes are vertical, as shown in the figure. The woofer head with a diffuser diameter of 245 mm, placed in a closed cylindrical wooden case (350 mm in diameter and 850 mm in height), faces downward with the diffuser bell towards the diffuser of a complex configuration. Sound is emitted through an annular acoustically transparent slot. The body (useful volume 62.5 l) is filled with sound-absorbing material.

Rice. 2. Top box with Omnisono speakers

The top cover of the body is formed by the box of another bass-midrange head (diffuser diameter 160 mm), also filled with sound-absorbing material. Above it in a mini-box is a midrange dome head (dome diameter 50 mm), also with damping from the side of the magnetic system. The dome-horn head of the HF is located at the top. The diameter of the dome of the latter is only 25 mm, which gives a good approximation to a point emitter: the length of sound waves in the assigned frequency range is from 8.5 to 1.7 cm.

To create a uniform sound field effect 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 dispersion 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 vibrations of the diffuser and prevents the occurrence of adverse interference phenomena.

Similar phenomena are also initiated by the housings of the HF and MF heads, but in practice their effect is negligible due to the small geometric dimensions compared to the wavelengths emitted by the underlying heads. The choice of heads (and their emitting surfaces) of a relatively small diameter is due to the tendency to “point”. Based on the condition d / l <1, the upper heads are placed rather 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 Funkschau magazine, comprehensive tests of the Omnisono speaker system were carried out. Due to the relatively high impedance (12 Ohm), the loudspeaker is noticeably inferior to most in terms of characteristic sensitivity, which is partly compensated by its low distortion (Kg <1% at 10 W).

However, in a real listening room with standard furnishings at 2.5 W at a distance of 3 m from the speaker, a loudness level of 86 phon is provided with a wide radiation pattern. The sound pressure is extremely uniform and independent of frequency.

Rice. 3. The directional diagram of the Omnisono speaker.

The sound of a counter-aperture speaker system is completely devoid of coloration at all frequencies, it is completely clear, without emphasizing any frequencies, and neutral in the best sense of the word. Natural resonances (including those of the main woofer) are not audible, at least they are very well damped.

This counter-aperture speaker is not designed for disco and other pop styles – such setups require accentuated, shiny treble and bass. The absolute neutrality of sound is of interest rather to discerning music lovers who prefer fidelity and accuracy of sound reproduction without superficial showiness. Low frequencies (double bass, timpani) are spatial and not compressed, in other words, they are not virtual, but “real” bass.

When playing Bach’s D minor organ toccata, there are no overtones that usually accompany the deepest tone of the organ point. The grand piano sounds natural, the winds (especially the French horns) are very good, the strings are more “restrained” than “sparkling”. Impulse signals are reproduced especially cleanly.

Rice. 4. Construction of the counter-aperture acoustic system “Omnisono”. 1 – scattering cone; 2 – acoustic transparent cone; 3 – HF head (4–20 kHz); 4 – midrange head (0.8–4.0 kHz); 5 – head MF – LF (160–800 Hz); 6 – box for the MF – LF head; 7 – body; 8 – LF head (40-160 Hz); 9 – transparent mesh acoustics; 10 – base (deflector); 11 – support; 12 well separating filter.

To achieve the maximum effect, such loudspeakers must be located at a considerable distance from the walls, which to some extent limits their area of ​​application as frontal.

Omnisono Speaker Brochure

Omnisono counterperture speaker system

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