Circular-pattern tweeter speaker

A big disadvantage of modern dynamic loudspeakers is the sharp directivity in the high frequency region, which creates certain inconveniences when listening to monophonic programs and narrows the stereo effect zone when using conventional speaker systems in stereo.

In various domestic and foreign literature, a figure has been repeatedly presented (Fig. 1), illustrating the influence of the location of the loudspeakers on the stereo effect zone.

To expand the stereo effect zone, many fans of stereo sound reproduction use one or two closed-type loudspeakers in each channel, placing them in the corners of the room, as shown in Fig. 2.

High-frequency acoustic units produced by a number of foreign companies are made in the form of a cube, on the inner side of each face of which there is a loudspeaker (6 in total).

The use of omnidirectional emitters not only expands the area of ​​the stereo effect, but also significantly reduces the required area of ​​the room from 18–20 to 12–15 sq. M. In the materials of foreign advertising press, there are reports that the use of omnidirectional emitters makes it possible to obtain a satisfactory stereo effect even in the passenger compartment of a passenger car.

The author of the article proposes a design of a high-frequency acoustic system with a circular directivity characteristic in the horizontal plane with an operating range from 5–6 to 18–20 kHz.

The design uses domestic loudspeakers 1GD-3 RRR with the following main parameters: average standard sound pressure 0.3 N / m², natural frequency of mechanical resonance 4.5 ± 1 kHz, module of total electrical resistance at frequency frequency 630 Hz – 12.5 Ohm, rated power 1 W, operating frequency range 5–18 kHz.

A general view of the acoustics is shown in Fig. 3. The spherical front of the sound wave from the loudspeaker 1 (the figure shows a section of the loudspeaker diffuser) falls on the diffusing lens 2. The sound vibrations reflected from the lens have a circular directivity in the horizontal plane. The forming lens is designed in such a way that the directional characteristic of the loudspeaker also appears in the vertical plane. The unit uses two loudspeakers to increase the sound pressure and expand the directivity.

When assembling a counter-aperture acoustic system, a loudspeaker with a nylon mesh, which protects it from dust, is glued to plate 4 and a ring pressed into it 5. Then the entire assembly is attached to the body 3. The posts 7 also hold the base 8 with the lenses glued to it. 2.

Sketches of the speaker system parts are shown in Fig. 4. The body 3 and the base are veneered, you can use plastic with a pattern imitating valuable wood species. The rest of the parts are made of D16 duralumin. The outer surfaces of these parts are polished.

The electrical activation of the acoustics loudspeakers is determined by the parameters of the amplifier and subwoofers. For single-band amplifiers with a nominal output power of 5-10 W, we can recommend the option of switching on the unit, shown in Fig. 5, a.

For stereo amplifiers with a single subwoofer, the circuit is simplified. In fig. 5, b, for example, a diagram of the connection of the unit to the audio column of the Yauza-10 tape recorder is shown. The chokes are wound on plastic frames with a diameter of 25 mm. Winding width 30 mm. Choke Dr1 (Fig. 5, a) contain 150, and Dr1 (Fig. 5, b) – 100 turns of wire PEV-2 1.04.

And in conclusion, I would like to warn radio amateurs that the use of the described counter-aperture acoustics is advisable only if the amplifier operating frequency band exceeds 8-10 kHz. With a lower bandwidth, its use becomes unjustified and ineffective.

Radio, pp. 39-40, No. 4, 1973