Three-way surround sound speaker. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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The 1997-way surround speaker, described in the April 97 issue of Radio magazine, evoked a lively response from readers who appreciated its good sound quality. At the same time, many of them expressed a number of wishes, mainly related to the insufficient power of the speakers and the limitation of the reproducible range from the side of lower sound frequencies. The authors of the article decided to continue the topic and offer readers a more powerful and broadband three-way speaker for self-production. It is also produced by the Moscow plant "Yantar". This speaker was demonstrated at the exhibition "Russian HIGH END-XNUMX" held in Moscow.

Making a three-way speaker will require much more labor than a two-way speaker, but those who undertake it will be rewarded with improved sound quality in the middle and lower audio frequencies.

Before starting work, it is necessary to purchase two low-frequency (LF) heads 35GDN-1-8, two medium-frequency (MF) 20GDS-1-8 and two high-frequency (HF) 10GDV-2-16. For the manufacture of inductors, you will also need two magnetic circuits from horizontal output transformers from tube color TVs TVS-90-LTs-2 or LTs-5. It is important that their magnetic permeability is around 3000.

The design of one of the loudspeakers of a three-way speaker is shown in fig. 1. It consists of a closed case 13 with overall dimensions of 500x250x250mm. In it, through the sealing ring 10, with the help of nuts 11 and racks 8, a low-frequency head 12 is fixed. A separation filter 14 is installed in the lower part of the housing, and input sockets 15 are installed on one of its side walls. The entire internal volume of the housing is filled with cotton wool. It will take about 400 g. With this acoustic design, the resonant frequency of the woofer is about 50 Hz.

Above the upper part of the case, on four racks 8, a mid-frequency box 7 with dimensions of 200x200x90 mm is fixed. A midrange head 6 is installed in the opening of its top cover. The internal volume of the box is also filled with cotton wool (40 ... 50 g).

The improvement in the sound quality of mid frequencies is achieved by acoustic damping of the main resonance of the midrange head. For this purpose, the windows of its diffuser holder should be sealed with synthetic felt 3 ... 5 mm thick. First, you need to make a template from thick paper that matches the configuration of the window. Then cut blanks from felt along it and, having applied Moment glue on their edges, paste them into the windows of the diffuser holder. This operation is recommended to be done very carefully, avoiding the formation of cracks.

Above the midrange head on stands 5, a large sound-scattering cone 4 is fixed, and above it, on a bracket 2, a small cone 1. The HF head 3 is mounted in the cavity of the large cone.

From above, on the edges of the low-frequency cabinet, a protective volumetric frame 9, covered with an acoustically transparent fabric, is installed, covering the midrange box and sound-diffusing cones.

Sketches of panels for the manufacture of a low-frequency cabinet are shown in fig. 2. When cutting them, you need to make sure that the cut is perpendicular to the plane of the workpiece. Then, in larger panels, drill six 2mm holes for nails and four 5,2mm holes for screws. After that, having applied PVA glue to the end of a small and the edge of a large workpiece, they must be knocked down with nails at right angles to each other, leaving technological allowances for subsequent finishing of the corners of the body. Then the walls of the case must be fastened with screws with countersunk heads. Similarly, with the help of nails and screws, the bottom and upper wall of the case are fixed. Technological allowances of all panels are removed with a file and their perpendicularity to each other is checked using a carpenter's square.

In the same sequence, the mid-frequency box is assembled. Its details are shown in Fig. 3.

Sound-diffusing cones are made, guided by the instructions contained in the article "Acoustic system for self-production" ("Radio", 1997, No. 4, pp. 12-14).

All heads and sound-diffusing cones are fixed on the top panel of the speaker cabinet. moreover, the woofer is installed directly in its central hole, and the rest of the parts are fixed on metal racks, the sketches of which are shown in fig. 4 and 5. The lower parts of the posts (Fig. 4) with the M5 thread are screwed into the nuts pressed from the inside of the top panel and fix the bass head, and the upper ones with the M4 thread enter the holes in the bottom of the midrange box and are fixed in it with nuts with the same thread and washers.

The fastening nuts must be pressed in very accurately. The best way to do this is as follows. Lay the woofer in the hole in the top panel, placing the corners of its cone holder diagonally, and mark with a pencil the places of the four holes for the fixing nuts. Then drill holes with a diameter of 5,2 mm in the marked places and drill them from the underside with an 8 mm drill to a depth equal to the thickness of the nuts. Then apply PVA glue to the drilled part of the hole, put a nut on it and, holding it in this position, screw a rack with a washer into it from the opposite side of the panel. Rotating the rack with a wrench, tighten the nut until it stops. All of the above operations with the top panel should be performed before assembling the woofer cabinet.

After the manufacture of all parts of the speaker housing, they begin to install the separation filter. Its schematic diagram is shown in fig. 6.

The filter parts can be mounted on a board made of foil-coated getinaks (Fig. 7) or simply on a piece of chipboard using the surface mounting method. The filter uses a resistor C5-5 with a power of 8 W and capacitors K73-16 (C1-C3) and K73-11 (C4).

Coils L1, L2, connected in series with the LF head, are wound on open halves of the magnetic circuit of the horizontal transformer and contain, respectively, 161 and 90 turns of PEV-21,0 wire. The windings of the coils must be insulated from the magnetic circuit with one or two layers of insulating tape. Coils L3. L4 are wound on the cases of capacitors C3, C4, equipped with cheeks made of sheet insulating material. The distance between the cheeks of the first of the capacitors is 50. and the second is 35 mm. The dimensions of the cheeks are 50x50 and 35x35 mm, respectively. Coil L3 should contain 166, and L4 -158 turns of PEV-2 0.5 wire.

Four pairs of connecting wires about 1 m long should be soldered to the outputs of individual links and to the inputs of the filter. Moreover, it is desirable to color-code the wires for connecting the heads, since this will have to be done blindly during the assembly of the speakers.

Now you can start assembling the speakers. First, on one of the side walls of the case, you need to fix the input jacks. Then install a separation filter at the bottom of the housing and connect it to these sockets. The wires going to the MF and HF heads should be passed through the hole provided for this purpose in the top panel. Further, the internal volume of the body is filled with cotton wool and, observing the one indicated in Fig. 6 polarity, connect the outputs of the low-frequency head to the corresponding filter section.

Having placed a sealing gasket under the woofer (for example, from polypenourethane), with the help of racks (Fig. 4) fix it on the top panel of the case. The free ends of the posts are inserted into the corresponding holes in the bottom of the midrange box and, having put washers on them, they are screwed with M4 fixing nuts.

Now, through the hole in the bottom of the midrange box, the wires leading to the midrange and tweeters are passed. Under the nuts that secure the racks (Fig. 5) in the upper panel of the midrange box, you should put the petals and solder the wires leading to the HF head to them. The posts hold the sound-diffusing cone of the midrange head, and two of them also serve as conductors connecting the high-frequency head to the crossover filter.

After installing the racks, the midrange box is filled with cotton wool and, through the sealing gasket, the midrange head is fixed on its top panel with screws, having previously connected it to the corresponding filter terminals. About connecting the HF head and installing a sound-diffusing cone under it is described in detail in "Radio". 1997, no. 4, p. 12-14. It seems that we should not stop at the manufacture of a three-dimensional frame for a protective mesh. This job is easy to do on your own.

In conclusion, we will give only the main characteristics of the speakers described here: long-term (short-term) electric power - 60 (120) W: level of characteristic sensitivity - 86 dB / W / m; nominal electrical resistance - 8 ohms; effective range of reproducible frequencies -40...20000 Hz; dimensions - 790x250x250 mm, weight -15 kg. The frequency response of the speakers for sound pressure is shown in fig. 8.

Authors: V.Shorov, V.Yankov, Moscow

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