We have long been accustomed to the fact that the stereo units have at least two spaced loudspeaker. As already mentioned, to further improve performance, it is recommended to use four or more speakers. But, in practice, the presence of several spaced loudspeakers clutter the living room, entangles his wires, creates some inconvenience. So the hams and radiocontroller long ago there was a desire to create a monoblock stereo speakers, i.e. such constructions, and which the heads of both channels of the stereo system would be housed in a single housing.

It should be noted that monoblock stereo loudspeakers have long existed in the form of a so-called cantilever Radiola and radiocomando high class. Such installations in size sometimes surpass antique dressers. Attempts to reduce the dimensions of monoblock stereo speakers are faced with the difficulty of keeping the size of the stereo. The fact that the stereo effect is manifested .in the case where the distance between the speakers left and right channels is 1.5-2.5 m, and the listener is at an equal distance in front of the speakers (about 1-3 m). When placing the heads of both speakers in the same plane as the base stereo is approximately equal to the distance between the centers of the cones heads of various channels. Therefore reducing the size of the enclosure, we reduce the base stereo system and reduce the manifestation of the stereo effect.

Abroad there are several systems of stereo speakers with a reduced base. But before proceeding to consider the actual design, we will briefly review the principle of operation is illustrated in Fig.1,a-C.

Monoblock stereo speaker
Fig.1

In Fig.1,and schematically shows the placement of heads in a conventional monoblock speaker console radiograms. Base system, defined by the distance between the phase centers of the radiation heads left and right channels are marked with a double asterisk, somewhat less than the length of the loudspeaker. With this arrangement, heads the main direction of radiation at the frequencies of the signal coincides with the direction on the listener. To obtain a base of not less than 1.5 m hull length should be about 2 m. If we reduce this size to 1 m, the stereo effect will be manifested only in the vicinity of the loudspeaker at a distance of about 1 m. This is already uncomfortable.

The base may be extended, if the head be placed on the side walls of the speaker enclosure, as shown in Fig.1,b. But the main direction of radiation on the middle and especially at the highest frequencies will be oriented perpendicular to the direction of the listener. Obviously, the sound depleted medium-to-high frequencies, can not deliver to the listener a great pleasure.

To increase base monoblock stereo speaker, on the one hand, and preservation powerful enough radiation on secondary and higher frequencies towards the listener, on the other, it is necessary to place the head left and right channels in the end walls and partially deploy them in a horizontal plane at a certain angle in the direction of the listener. In most cases, exactly the way a lot of designers. Vary these speakers only the angles of rotation of the heads and geometric dimensions. But in Fig.1 shows a longitudinal section monoblock stereo speaker, which besides turning heads introduced improvements, greatly extending the base while keeping the radiation direction toward the listener in a wide band of frequencies.

The essence of the innovation is that before diffusers heads placed acoustic waveguides of a metal plate for changing the direction of propagation of the sound heads in the direction from the listener. Thus, there is the influence of two factors. First, turn of the head towards the listener improves the radiation pattern in the direction of the listener. Secondly, the deviation of the sound away from the listener increases the base system. When quite a certain ratio of the angles of rotation of the heads, and the directivity of the acoustic waveguides can achieve the expansion and preservation of the desired orientation of the sound. In this loudspeaker, with a length of speaker enclosure 750 mm possible base of about 1.5 m.

In Fig.2 shows sketches of the General appearance of the front panel and internal view Amateur loudspeaker, which implements the above-described principle of construction monoblock stereo speaker. Installation of two heads of different channels in a single package creates conditions for improving the acoustic bass reproduction due to the effect of group radiator and through the adoption of additional measures - use of the port with the pipe shown in Fig.2. The cardboard tube diameters and a length of 86 mm improves the uniformity of the amplitude-frequency characteristics of the installation in the lower frequencies, a wider bandwidth.


Fig.2

The effectiveness of the manifestations of the stereo Amateur monoblock speaker on the sketches of Fig.2 largely depends on the accuracy of the mounting heads in the housing and evenly spaced plates of the waveguides relative to each other. The body of the speaker is made of plywood or chipboard with a thickness of 20 mm External dimensions of the case H HH mm, i.e. the body of the speaker, the shape and the size of a wall-mounted bookshelf. To ensure proper repetition of its design, the author recommends the following sequence of manufacture.

On the sheet of graph paper builds life-size outline of the longitudinal section of the future speaker enclosure size Fig.2. Further, at a distance of 110 mm from the edge of the rear wall, the line going under fragile 11° to the contour of the side wall. From the point of intersection of this line with the contour of the outer perimeter of the front panel at an angle of 60° to the first line is a second line length 200 mm. Then, from the end of the second line at the angle of the ' 60s to her a third. When the build the third line should pass through the point from which were started geometric construction. In terms of the lines, intersecting, should form an equilateral triangle with sides of 200 mm. Then construct the contour of the inner perimeter of the housing, the holes are laid out under the head. A similar construction is carried out on the second end of the housing of the loudspeaker.

Plate acoustic waveguides made from a flat sheet of duralumin, 1.5 mm thick, height 266 mm When mounted in the grooves of the upper and lower lids, it is important to ensure their mutual parallel position and equal distances between them. Plastuny should be parallel to the far wall, set at an angle to the front panel. Heads mounted on the walls with a circular cutout with a diameter equal to the diameter of the diffuser along the border of bonding with DiffuseMaterial, Goram. The inner surface of the housing is covered with a layer of mineral wool with a thickness of 50-70 mm., the Author of the design was also used additional wall of cotton wool between each head and the total volume of air in the body of the speaker. Such measures will help to reduce the effect of sound reflections inside the enclosure and to prevent direct exposure heads at each other.

By repeating designs are encouraged to apply domestic broadband head high and normal sensitivity, for example, type GD-36, with the resistance of the voice coils 4 and 8 Ohms. Thus it is necessary to clarify the fitting dimensions and the diameter of the hole opening of the diffuser. For use in the design of the hull using fine radiating, which covered both end walls and the front panel (one piece). The upper and lower covers they veneer or cover simulating film.

According to the author of the design, the quality of the speaker is high. With a body length of about 1 m base is more than 1.7 m, i.e. this. monoblock speaker then its properties equivalent to two speakers spaced from each other a distance of about 2 m. to this we must add that the loudspeaker can be hung on the wall, put on him, as on a bookshelf, books and magazines. The quality of the speaker will not deteriorate.

Literature:

  • V. A. Vasiliev. Foreign Amateur radio construction. Moscow, Radio I Svyaz", 1982.
  • Publication: N. Bolshakov, rf.atnn.ru

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