SO YOUR SPEAKERS SOUND | MODEL CONSTRUCTION

High-quality sound speakers for home sound equipment to reproduce low-frequency signals with a frequency of 30-50 Hz, which corresponds to the length of the sound waves 7-10 m. in Order to efficiently radiate such fluctuations, we need a dynamic head with a large diameter of the diffuser (there are instances d of 400 mm). However, in practice most commonly used “dynamics” with the size from 200 to 300 mm. Their own resonant frequency in the range of 15-30 Hz.

When the head beep, her mobile system oscillates, radiating to both sides equal in strength but opposite phase sound waves, which are omnidirectional in nature. Body dynamics is not able to isolate one from another region of compression and rarefaction of the air. The result at the point of hearing sound pressure is low. This phenomenon is known in the art as an acoustic short circuit. Eliminate it by placing an acoustic radiator in a sealed box (Fig. 1). (Symbols in the figures denote: a — width B — depth C — height of the box, x is the material thickness, (1 — thickness of plate). Often it makes one or even several holes, positioning them in certain places of the body (Fig. 2). These holes are called patinir meters, or backreflection. Their kind — passive radiator (Fig. 3), which is an offline dynamic head. The location of the holes on the front panel speakers are selected in such a way that back radiation coincided with the front, thereby increasing the low frequency sound pressure.

Important for speakers, have their size, shape and materials from which they are made, the internal “stuffing” and design of the front panel. Thus, the body affects the technical parameters established in this dynamic heads and primarily on enhancing its own resonant frequency. An important role is played by the diameter of the diffuser and “displacement” hull. With the increase and decrease in the size of the moving system resonance frequency varies slightly. If the head with a large diffuser to install in a relatively small box, the resonance frequency will change markedly — low frequency “cut off”, and as a result the effective frequency range of speakers is shrinking. In other words, incorrectly matched by the volume of the housing can degrade the playback quality even very good drivers.

For effective head at low frequencies, the Bulgarian radio Amateurs are recommended to choose the volume columns based on the data in table.

If you use a phase inverter you must also meet certain requirements. The hole for it should be located at a minimum distance of 60-80 mm from the bass head and 40-50 mm from the rear wall of the housing. At the same distance from the hole and placed the sound-absorbing material. It is better if the phase inverter is located under the bass head.

Recommended dimensions for vented enclosures depend on the “displacement” of the column and the diameter of the diffuser head. So, head d 125 mm, mounted in the housing having an internal volume In dm3, the pipe of the phase inverter is d 50 (46) mm and B=60 mm. For loudspeaker volume 16 dm3, the diameter of which is equal to 160 mm, the desired pipe d 50 mm and a length of 100 mm. Respectively for head d 200 mm at a volume=30 dm3 dimensions of the pipe will be d 75 mm S = 100 mm From loudspeaker d 300 mm, N4 = 60 dm3 pipe should be 75 mm and d L = = 220 mm.

The shape of the body, both internal and external, also affects the frequency response of the loudspeaker. The most acceptable is spherical, and the wrong cube when dynamic head located in the geometric center of one of its sides. In the cylindrical case the most favourable location of the head — transverse (Fig. 4A) and not longitudinal (figure 46), although to mount it in the latter case, much about TSE.

If the housing is the most common form of a parallelepiped, low-frequency dinamik it is best to set asymmetrically relative to the sides of the reflective Board (Fig. 1).

The kind column in the form of a parallelepiped shown in figure 5.

Good acoustic data from the speaker housing in the form of a triangular prism (Fig. 6) or a truncated pyramid (Fig 7, 8).

Usually the case for columns made from wood: plywood, drevesnostruzhechnyh plates (DSP), oak, stained beech or pine, having significant acoustic losses. The thicker the material, the stronger the wall and the possibility of occurrence of resonance oscillations decreases. These parasitic oscillations are usually out of phase with the direct radiated signal, lead to unpleasant changes of timbre of the loudspeaker.

For volumes 5-10 dm3 and power dynamics, 6-10 W the thickness of the walls of the box 8 to 10 mm, and V =” 40-60 dm3 and power 40-100 watts — the rest is made of plywood or chipboard. However, for large dimensions and large capacity dynamic head it can still cause undesirable vibrations. To avoid such problems, the wall of the column, tightening the wooden slats section 40 X40 mm or metal bars d 6— 10 mm (Fig. 10).

The vented enclosures are made of plastic or metal (e.g., aluminum) pipe with a wall thickness of at least 2 mm.

Minerals also are used as material for the construction of columns. In the first place is marble. Due to the layered structure it well absorbs sound, and therefore it does not occur resonant vibrations. Marble is easy to process, but as a drawback it should be noted that it is heavy and fragile.

The walls of the body are interconnected using one of the methods shown in figure 11. Easier to manufacture a box with a removable front and rear panels.

First cut out the side walls. Before Assembly it is necessary to glue and then nail small nails restrictive mounting rail size 15X15 or 20X20 mm and length specified in figure 12.

The housing wall glue glue Universal or C-200 and every 15-20 mm hammered thin nails for greater reliability of fastening. The box will be even stronger if the corners to attach the additional bars (Fig. 13). The free space is filled with epoxy. According to thus derived the slinky determine the dimensions of the front and rear panels. They are made of wood of coniferous breeds. Based on the available dynamic head, plan the location of the holes under them (Fig. 14).

Speakers are often adorned with decorative framework from wooden reek in the cross-section 15×15 mm Radiating pull on reflective Board and fix buttons or furniture with nails.

To reduce parasitic oscillations, trying to avoid direct connection of the base on which is mounted the head, with the rest of the body. The same applies to the fastening elements — bolts, nuts and washers.

The internal volume of the column is filled with some sound-absorbing material, for example glass wool. The number is determined by measuring the resonant frequency. The filling of the shell is considered normal if it fell 10-12%. Empirically established that this will take 30-40 g of glass wool or 10-15 g of poliestireno wool (jambolana) per 1 dm3. You can use rags. Sound-absorbing material placed in the cover of the dense tissue.

If the housings are properly selected and carefully sealed it, then carefully press on the diffuser of low-frequency drivers its mobile system gradually returns to its original position. The absence of such phenomena indicates the presence of acoustic losses that reduce the sound pressure at low frequencies of 1-2 dB.

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