Loudspeaker with VIFA drivers. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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In the construction of amateur loudspeakers, two types of acoustic design of low-frequency heads are used: a closed case and a phase inverter.

A phase inverter is a more complex acoustic design compared to a closed cabinet. The closed case adds additional rigidity to the dynamic head, while the bass reflex itself is an oscillatory system. The dynamic head and such an acoustic design are two connected oscillatory systems that exchange energy during operation. Sound emission occurs from the front surface of the diffuser and through the opening of the phase inverter, which effectively radiates only in the frequency range located near its resonance. This radiation at different frequencies has a different phase shift relative to the radiation of the dynamic head diffuser. The resulting sound pressure of the loudspeaker is obtained by adding in space the direct radiation of the head and the outlet of the phase inverter. The addition of sound pressure takes place taking into account the phase. With a certain selection of the parameters of the dynamic head and phase inverter, it is possible to obtain an acceptable frequency response in terms of sound pressure.

To calculate such an acoustic design, it is necessary to know as accurately as possible the TS parameters of the head (Thiel-Small): Fs, Vas, Qts. Based on these parameters, the volume of the case Vb, the tuning frequency of the phase inverter Fb and the lower cut-off frequency Fz are calculated, at which the sound pressure is reduced by 3 dB. It is convenient to calculate such an acoustic design using computer programs; in the literature there are tables and nomograms for calculating phase inverters.

When designing the V2 loudspeaker, the goal was to create a floorstanding loudspeaker with a low cost, focused on working with transistor amplifiers.

The V2 loudspeaker uses VIFA drivers: LF-MF - M18WO-08-08 and HF - D27TG-45-06.

The loudspeaker body with a useful volume of 22 liters is made of furniture plywood 18 mm thick; its drawing is shown in Fig. 1. The case has two partitions with holes dividing the volume into three compartments.

(click to enlarge)

The phase inverter pipe with an outer diameter of 60 mm, an inner diameter of 50 mm and a length of 73 mm is fixed on the rear wall so that it is located in the lower compartment. The top two compartments are filled with low-density padding polyester. The lower compartment is not filled with an absorber, but its inner surfaces are covered with artificial fur with a pile length of up to 15 mm.

On fig. 2 shows the frequency response for the sound pressure of the loudspeaker V2. The frequency response has a small smooth dip in the mid-range, which, together with the bass that is somewhat emphasized by the bass reflex, creates the illusion of a soft comfortable sound.

The V2 loudspeaker circuit is shown in fig. 3. Tonal balance can be adjusted by selecting the resistance of resistors R1 and R2. The nature of the bass sound can be changed by changing the filling density of the upper compartments of the case with synthetic winterizer.

To connect to the amplifier, a terminal is installed on the rear wall of the loudspeaker case, for which a hole with a diameter of 60 mm is provided. The terminal is a round cup made of insulating material, in which two terminals are fixed. Screw terminals or terminals can also be mounted on a round or square insulating panel on the inside of the back of the enclosure. The gaps between the panel and the terminal are sealed.

During the manufacture of the loudspeaker enclosure, it is necessary to ensure the strength of the connection and the rigidity of the walls so that air vibrations inside the enclosure do not cause its vibration. Vibrations transmitted to the body from the heads should be as strongly attenuated as possible so as not to introduce a noticeable coloration of the sound of the loudspeaker.

The walls are connected using PVA glue and screws. Pre-drilled panels at the joints are lubricated with glue and tightened with screws. Screws with a diameter of 3,5 ... 4 mm and a length of 40 ... 150 mm are well wrapped in the ends of plywood and MDF panels. It is advisable to sink the screw heads into cylindrical recesses, which are puttied and do not interfere with the decorative finish of the case.

Between the rear wall and the slats, a seal made of tape polyethylene foam is introduced, glued to the slats. Such a seal is sold in hardware stores for window insulation. These strips have an adhesive layer protected by an easily removable paper tape. The back walls are fixed with screws, which are wrapped in slats. The number of screws is determined by the size of the rear wall, the distance between the screws is 80...100 mm.

The loudspeaker crossover filters use 73 V K16-63 capacitors and 5 W ceramic resistors. You can also use capacitors from Solen and MBGO for a rated voltage of 250 V.

Filter inductors are wound on organic glass frames with a wire 1 mm in diameter. The active resistances of the filter coils in the loudspeaker V2 must not exceed 0,3 ohm (L1) and 0,5 ohm (L2).

When making separating filter coils on your own, you can use the information from the table, where the following designations are used: D1 - inner diameter of the frame, D2 - cheek diameter, H - winding width (distance between cheeks), N - number of turns.

The appearance of the loudspeaker V2 is shown in fig. four.

Author: S.Bat, Moscow

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