Simple speakers

In cases where the speaker with the desired characteristics to buy, it is not possible, it will have to make yourself. This will require one or more of the same type of dynamic heads and relatively simple acoustic arrangement - a wooden box. In Amateur conditions it is best to use wideband drivers. Speakers with wideband heads easier to manufacture than the loudspeakers, which use several different heads. However, the self-made loudspeakers based broadband heads have a working range of reproduced frequencies already, about 50-60 Hz 14 to 16 kHz.

Recently developed and commercially available broadband head on the basis of which it is possible to construct a single speaker with a very wide operating frequency range.

Externally, the loudspeakers as industrial manufacturing and improvised often make out in the form .parallelepiped. The front panel drape loose cotton or synthetic cloth. Box loudspeaker produce from boards or chipboard thickness of 15-20 mm.

For self-made loudspeakers, you can use dynamic head, the list and the characteristics of which are given in the table. The first digits in the designation of the head point to its rated power.

The choice of heads and the number of the loudspeaker is determined by its purpose and the required rated capacity. It should be borne in mind and the nominal resistance of the head, and the resistance of the loudspeaker as a whole. If you intend to use only one head, the rated capacity must be not less than the rated power bass amplifier with which the loudspeaker will work, and the resistance of the head shall not be less than the minimum load resistance of the amplifier. As practice shows, the best for this speaker fits chetyrehbalnoy head GD-4, GD-35 or HD-36. In a pinch you can use a head DDG E.

Loudspeakers
Table 1

It should be noted that the dynamic head can withstand significant overload on the input power. So, head of new developments DDG E, HD-35, HD-36 in the passport and have a parameter such as nameplate capacity. Passport power head DDG E - 5 W, and the heads HD-35 and GD-36 - In W. Abroad analogous to the nameplate capacity of heads is their maximum power.

But despite the available supply of mechanical strength, it is not necessary to overload the head, because the level of nonlinear distortion of the audio signal is significantly increased. Typically, the harmonic distortion of the head at rated power does not exceed 5-10%. Upon reaching the nameplate capacity of the non-linear distortion factor can reach values when they become noticeable to the ear.

In cases where you want to create a loudspeaker with a nominal capacity greater than one head, install several identical heads (usually two to four), electrically interconnected in series, parallel or mixed. The rated power of the speaker is equal to the sum of the rated capacity of heads.

It would be a mistake to assume that the presence of even the best of the head guarantees a high quality loudspeaker. For this it is necessary to choose the appropriate acoustic design, i.e. optimal for these heads design box speaker. In addition to the front panel, which is set on the head or multiple heads, side, rear, bottom and top panels, drawer design may include internal partitions, various absorbing coating and other details. There are several varieties of acoustic design speaker, with its features of construction, advantages and disadvantages.

First the overall design of the speaker is determined by the number of its heads. If heads, there are several and they are placed close to one another, such a loudspeaker group called the emitter. The name of this means that at low frequencies and partly on secondary diffusers heads oscillate almost in phase, causing the acoustic output of the loudspeaker is increased. At the lowest frequencies to improve the value is divisible by the number of heads.

This feature of the group of emitters for a long time and effectively used in professional sound reinforcement techniques, for example, in cinema installations, and more recently and in the Amateur designs. Operating range of frequency response of these speakers is extended from the bottom compared to speakers with one head. However, the efficiency of reproduction of the lower frequencies. Depends largely on the size and design of the box loudspeaker. On average, we can assume that for lowering lower operating frequency interval is necessary to increase the size of the box.

However, the known design speakers with a relatively small outer dimensions of the box have a very small value of the lowest reproducible frequency. In Fig.1 presents various options for the design of acoustic design for one head. Speakers with multiple heads can be arranged in a similar manner. The easiest option is a box without a back wall (Fig. 1,a). Head is mounted on the front panel of the drawer of the aperture of the diffuser forward toward the listener. Sound vibrations excited by the rear surface of the diffuser are in opposite phase with the vibrations from the front surface. For useful acoustic vibrations from the front surface of the diffuser were not suppressed as a result of the imposition on them of vibrations from the rear of the box should be deep enough so that the acoustic waves from the rear side of the diffuser reached the plane of the front panel with a certain delay compared to the direct waves, i.e. with a phase shift. At the lowest reproducible frequency of the shift must be 90°, for higher frequencies it will be great.

The speakers without the rear wall well implement energy capability of the head, but have one disadvantage: the quality of their work is influenced by the presence of walls and other objects near the rear of the drawer opening. Therefore, these speakers must be installed no closer than 30 - 40 cm from the wall.

From this drawback free speakers with the rear wall or enclosed speakers. The loudspeaker may be a sealed box, the front panel which has a dynamic head (Fig. 1,b). To avoid unwanted reflections from the inner surface of the box, it is covered with a thick layer of absorbent material (natural or mineral wool, wool, felt, etc.). But this loudspeaker another inherent disadvantage of increasing the resonant frequency about 2-3 times and the associated narrowing of the working frequency range. This disadvantage can be eliminated by using special compression heads with very low self-resonant frequency, only 15-25 Hz. Once installed in a closed box resonance frequency is increased to acceptable values: 50-60 H z.


Fig.1

Compression of the head, except that they are relatively expensive and scarce, have another big disadvantage is low efficiency. Best compression heads develop a standard sound pressure level of not more than 0.1 PA i.e. their efficiency is about 4 times less than conventional heads with standard pressure of 0.2 PA. For these speakers need large capacity, usually at least 10-20 W, and the volume will be not more than the loudspeaker 3-4 watts with conventional heads. But such a speaker will have a relatively small size.

Is it possible to make a speaker that is free of these disadvantages? You can! This is a speaker with bass reflex design, the device which is shown in Fig. 1,V. In the front panel of the loudspeaker, there is one hole cross-section close to the area of the aperture of the diffuser head or slightly smaller. The hole shape can be round or rectangular. The hole is the mouth of the tube-tunnel, attached from the inside of the box to the front panel.

The main advantage of the phase inverter is that acoustic oscillations excited by the rear surface of the diffuser at the exit of the hole at certain frequencies are in phase with the vibrations created by the front surface of the diffuser. As a result, the efficiency of the loudspeaker is substantially increased. Usually pick the dimensions of the box (or rather his internal volume), the cross section of the bass ports and the length of the tunnel so that the phase rotation of 180° of the rear radiation of the head consistent with the frequency close to the resonant frequency of the head. When this condition occurs the extension of the operational range of reproduced frequencies down.

Before the working length of the tunnel barrier was chosen equal to the thickness of the front panel of the drawer, so the dynamic head coordinated with bass reflex design choice square bass ports and external dimensions of the box. As a result, the speakers were very bulky. Now widely used in the bass reflex tunnel, lengthening the path of acoustic waves before leaving the box. Changing the length of the tunnel, it is quite possible to choose the parameters of a box loudspeaker in relation to a particular head even at relatively small sizes.

Should indicate that a precise calculation of the size of the box speaker with bass reflex design is very complicated. Therefore, in Amateur conditions convenient to use the nomogram, shown in Fig. 2. She clearly connects the internal volume of the box loudspeaker, the resonance frequency of the dynamic head, square bass ports and the length of the tunnel. How to use the nomogram, which will be explained below, when considering the designs of homemade speakers.


Fig.2

The most complex device loudspeakers with a maze (see Fig. 1,g) and the mouthpiece (see Fig. 1,d). Here also, as in the phase inverter, used the oscillations excited by the back of the diffuser for increasing returns at the lowest frequencies. The maze increases the length of the path, run through an acoustic wave inside the box. A characteristic feature of the maze is that the area of its cross section throughout the length remains almost constant. The total path length of the sound wave must be equal to a quarter wavelength at the lowest frequency of the working frequency range, usually equal to the frequency of self-resonance of the head. Calculation shows that at the resonance frequency of 80 Hz, the length of the labyrinth must be equal to 1 m, 40 Hz to 2 m, 20 Hz-4 m. Thus, at the lowest frequencies the length of the labyrinth is significant.

In the loudspeaker with horn has several partitions to increase the length of the path traversed by the acoustic wave excited by the rear surface of the diffuser, but the cross-section of the labyrinth has not remained constant, but increases as it approaches the outlet. This design of the maze makes it relatively smoothly to agree on a relatively high pressure over the head with atmospheric pressure on the output of the horn that gives increasing the efficiency of conversion of electrical power into acoustic at low frequencies. The length of the horn should be possible.

In Amateur literature one can find descriptions of the various structures of the speakers, but the vast majority of them are made in either the sealed box bass reflex or sealed box bass reflex, or a group of the radiator. Loudspeakers with a maze and a mouthpiece difficult to manufacture, require complex calculations under specific head, making them difficult to repeat in Amateur conditions. Below is described a self-made speakers with different number of heads that can leverage the power of bass amplifiers, descriptions of which were given above.

Loudspeakers with one head

In Fig. 3 shows two variants of the construction of the front panel speaker with bass reflex design, which used either head DDG E or GD-4 GD-35, HD-36 (the dimensions for this option are given in parentheses). In the first embodiment of the loudspeaker operating frequency range extends from 80 Hz to 12.5 kHz, and the resistance is 4 Ohms. In a second embodiment of the loudspeaker of the lower working frequency interval corresponds 35-60 Hz. The impedance of the loudspeaker is also equal 4 Ohms (some copies heads GD-36 resistance is 8 Ohms, as indicated in the passport, attached to the head).


Fig.3

It should be noted that here are guaranteed the borders of the frequency interval, in practice it is usually wider and reaches 14 and even 16 kHz.

The front panel of the loudspeaker can be made of plywood with a thickness of 12-15 mm or chipboard thickness of 18-20 mm. a Box made from the same material and collect on the screws with the mandatory gluing all joints. It is best to use casein or synthetic glue. The head is mounted on the inner surface of the front panel and fastened by screws. It is desirable for the head to enclose the ring of felt or thick cloth. The depth of the drawer is determined based on the desired volume of the loudspeaker, available material and aesthetic reasons. For the speaker head DDG E optimal depth is 200 mm, and for GD-4, GD-35 and GD-36 - 270 mm.

After assembling the box all seams must be sealed with putty and glue. From the inside to the walls need to glue a layer of absorbing material with a thickness of 3-5 cm from cotton or wool fabric, quilted with one or two layers of light cotton fabric, such as gauze, to fibers and yarns did not get the crown. The bass reflex tunnel can be run from plywood with a thickness of 5 mm or thick hard cardboard.

Knowing the dimensions of the box and the resonance frequency of the head, the nomogram Fig. 2 to determine the length of the tunnel so to ensure the best reproduction of the lower frequencies. Let us illustrate this with examples.

Let the inner volume of the box is $ 25 dm3, and the cross section of the bass port is 0.84 dm2. The resonant frequency of the head DDG E equal to 80 Hz. To find the length of the tunnel first, find the point of intersection between an inclined straight 80 Hz with a vertical line drawn through the mark 25 dm3. Then from a point corresponding to the cross section 0,84 dm2, drop a vertical line to the intersection with the horizontal line drawn through the previously obtained point. The point of their intersection in the area of the curve Length of the tunnel gives the desired value. According to the conducted constructions, tunnel length should be equal to 7 cm.

For the speaker chetyrehbalnoy head of internal loudspeaker volume equal to about 48 dm3, section bass ports 1,3 dm2, and the resonant frequency of the head close to 60 Hz. Similar plots on the nomogram shows that the tunnel length should be equal to 9 cm In cases where at first you don't succeed to find an acceptable result, you must change the volume or the cross-sectional area of the hole and repeat the build.

In practice, the speaker with bass reflex design provides an additional increase in the efficiency of conversion of electrical power into acoustic at low frequencies is about 3-4 times, i.e. on 5 - 6 dB. This increase is equivalent to a decrease in the lower bounds of the range of frequencies reproduced by approximately 20-30%.

Of course, achieving such results is contingent upon fulfilling all requirements, and in the Amateur conditions is difficult. Variation in size and resonant frequency can affect the final result. To some extent, the deviation can be accounted for in the selection of the length of the tunnel. This tunnel is made with an allowance of 1.5-2 cm in length, and then in establishing the allowance is cut to get the best sound, the lower frequencies. So that when the length of the tunnels every time not to disassemble the speaker, can be recommended to temporarily take the tunnel to the outside. However, it is somewhat changes the overall volume of the box, but it will allow you to quickly and easily find the optimal length of the tunnel. Then install it again inside the box and finally fixed with glue.

The front panel should drape outside thin cloth. Pre-washed, dyed a dark color (usually black or brown), smooth and pull the panel slightly damp. Fix the fabric on the back panel, small nails and glue. After drying, the fabric tightly and evenly covered panel.

The front panel should fit with no gaps to fit the edges of the box. Usually for this purpose to the inner surface of the walls of the box, attached the four Reiki section 20x20 mm of solid wood, and to them already screws attach the front panel.

Loudspeakers with two heads

Electrical characteristics of the loudspeaker with one dynamic head is completely determined by its properties. The increase in the number of heads gives the possibility to adjust these characteristics. You can change the impedance of the loudspeaker. If you connect the voice coil heads in-phase-connected in series, the resistance is doubled compared with the resistance of one head. When in-phase-parallel operation of heads impedance of the loudspeaker is reduced by half. In addition, in both cases, increases its rated power. For example, if you use two heads DDG E, rated power is 6 watts (passport 10 W), and the resistance may be equal to 2 or 8 Ohms. As shown above, the impedance of the loudspeaker is usually less than 4 Ohms't choose, so the best should be considered as an impedance of 8 Ohms. If you have two heads GD-35 rated power is 8 watts (passport 16 watts, 8 Ohms.

In Fig. 4 shows the layout of the front panel speaker with two heads DDG E and GD-35 or HD-36. In the first case (Fig. 4,a) width equal to 300 mm, for the option with chetyrehpolnye heads (Fig. 4,b) 200 mm bass ports in the selected loudspeaker round, and tunnels with a wall thickness of 3-4 mm is made in the form of a cylinder, made from heavy paper or cardboard. In the first loudspeaker four tunnels, two in the second. This is done to simplify the manufacture of the phase inverter. In the calculation take into account the total area of the holes. The nomogram length of each of the four tunnels of the first embodiment of the loudspeaker must be equal to 5 cm, and each of the two second-5.5 cm. Tunnels are glued on a cylindrical wooden discs with a diameter of 36 and 72 mm, respectively.


Fig.4

If necessary the front panel can be made of two pieces of plywood or particle Board. The possible place of junction of the two parts shown in Fig.4 by the dashed line. The inner side panel, the joint should be reinforced with a piece of plywood or particle Board of the same thickness 60-80 mm width or pine rail section H mm.

The size of the speakers allow you to place them in a bass amplifier and an Autonomous power source. To do this in the drawer compartment fence off the required size. The decrease in the volume of the speaker is compensated by a corresponding lengthening of the bass reflex tunnel. Such design of the loudspeaker is very convenient for various portable electro-acoustic installations. On the top of the box it is advisable to mount the handle for carrying the loudspeaker.

Loudspeakers with two heads are better reproduce the lower frequencies. This improvement to the above-described construction begins with chatty 800-1000 Hz and reaches a maximum (the return increases almost twice) at frequencies below 300 Hz. In turn, this expands the frequency band of about half an octave in the direction of lower frequencies.

As already mentioned above, the manufacture of the speaker patinvert is relatively difficult. Therefore, if you want to make a simple design loudspeaker with a relatively high rated power, it is advisable to choose one of the options loudspeaker type emitter group containing four or six heads of the same type. These speakers have considerable power, allow in a wide range to vary the resistance and well reproduce the lower frequencies when using a simple box without a back wall.

Group radiator with four heads

In Fig.5 shows the layout of the front panel of the loudspeaker, which has four of the same type chetyrehkantnyj head (GD-4, GD-35, HD-36). Its rated power-16 W (passport - up to 30 watts), the resistance depends on the type of heads and how to connect to their voice coils (it can be equal to 8 or 32 Ohm for GD-4 and 4 or 16 Ohms for the others). The speaker effectively reproduce frequencies between 45-50 12-14 Hz to kHz.


Fig.5

The rear wall of the box is missing. Its depth is 150 mm At the bottom of the box can be placed inside the bass amplifier and an Autonomous power source (or rectifier), and any baffles are not required. Dynamic heads of the loudspeaker may be connected in series or mixed (parallel-series), as shown in Fig. 6,a and b, respectively, in all cases necessarily common-mode enable heads that ensures the correct connection of the beginning and end of the voice coils. Modern heads on DiffuseMaterial have colored marker to indicate the beginning of the coil (Fig. 6 indicated by dots).


Fig.6

In the description of bass amplifiers, it was stated that their output depends on the load resistance. Therefore, using the various options to include heads, you can pick the desired characteristics of the amplifier. For example, in the case when the amplifier is powered by batteries of items, it is advisable to increase the load resistance and thereby reduce the consumed current. For this head include sequentially. If each head has a resistance of 4 Ohms, the speaker will be 16 Ohms. Parallel-serial connection heads preferably when the power from the powerful rectifier. In this case, the impedance of the loudspeaker will be equal to the resistance of one head. Described in this book bass amplifiers can operate as a standalone (battery) and with mains power supply. By simple switching of the voice coils heads switch Q1, as shown in the diagram Fig.7, it is possible to ensure better utilization of power sources. The toggle switch is put inside the box loudspeaker near the heads.


Fig.7

Group radiator with six heads

For vocal and instrumental ensembles, conducting dance evenings in the great hall right speakers with a rated capacity of not less than 20 watts. Clearly, with chetyrehpolnye heads, this loudspeaker can be collected only when there are five or six heads. With five heads, it is difficult to provide the same current through them in parallel-series connection, a serial connection is too large, the impedance of the loudspeaker. So it may be easier to install in the loudspeaker six heads, turning them three in series and both groups in parallel. The resistance of each head 4 Ohm impedance speaker will be equal to 6 Ohms, which is in good agreement with most bass amplifiers. Phasing heads in the loudspeaker is required.

In Fig.8 shows a sketch of a box loudspeaker with six four-watt heads GD-4, GD-35 or HD-36. The front panel is composed of two identical parts, made of chipboard. For each half-panel set with three heads and connect them together in series. This design of the front panel to increase its rigidity and to achieve a more uniform radiation in space. The latter is particularly desirable because of the increasing number of heads in the loudspeaker radiation is concentrated in the direction perpendicular to the plane of the front panel and the side radiation is significantly attenuated.


Fig.8

It should be noted that speakers type emitter group despite the simplicity of the design have a high rated capacity and wide frequency interval, a drawback common to all speakers without a back wall, the influence of the wall of a room, which includes a loudspeaker is practically not observed, if the sound amplifying unit operates on the club scene or outdoor.

We often hear the question: is it worthwhile to build a loudspeaker based on less powerful heads, for example, watt or dvuhletnih? Such questions arise in ham radio and in the absence of the required heads. I must say that the loudspeaker with a single head with a capacity of 1 or 2 watts ineffective. Satisfactory results can be obtained from emitter group of four or six thin heads with round or oval cone. Suitable head 2GD-3, GT-40 I GD-36 or better yet - modern head 2GD-40 with the coil 4 ohms of resistance.

Literature

  • V. A. Vasiliev. Hams - rural club. M. Radio and communications. 1983
  • Publication: N. Bolshakov, rf.atnn.ru

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