Tehnium Magazine no. 4 - 2004

Tehnium Magazine no. 4 - 2004 - Sound system with coaxial speaker

Reading time: 4 minute

The main topics discussed

1. Mini-batteries: operation-maintenance

Although considerably more expensive, Ni-Cd mini-batteries (and more recently those Ni-MH and Ni-ion) have largely replaced batteries in the supply of portable electronic equipment, due to their clearly superior performance in terms of stored electricity and the intensity of the maximum allowable load current.

Of course, the most valuable advantage of mini-batteries is that they can be recharged, the number of charging cycles discharging "guaranteed" by the manufacturer for models up to 2004 of about 1000 or even more.

Charging Ni-Cd mini-batteries does not usually cause problems, the manufacturer specifying for each type the intensity of the charging current and the minimum duration for full charging. Dilemmas - or even problems - can occur when we have to charge several mini-batteries simultaneously (connected in series by mounting in a suitable socket).

New batteries it is stored and delivered "completely" unloaded. Under these conditions, they must have terminals o voltage of about 1 V, which is, however, good to check in advance for each specimen, using a DC voltmeter set to the range of 2 V or 3 V.

"Old" batteries removed from various devices for recharging - must also be briefly checked in advance (it also happens to give way one by one), after which the desired set is unloaded, considering the download "complete" when it reaches approx. 1 V / element. We must specify that, in this case, the individual check is indicated to be done not "empty", but having connected in parallel with the terminals of the voltmeter a load resistor, for example a 2.5 - 3.5 V / 0.2A -0.3A flashlight bulb.

2. Technical and practical considerations regarding the construction of Hi-Fi acoustic enclosures type TQWT

After the construction and experimentation of several pairs of enclosures TQWT - Voigt and after consulting some materials, but also of other builders who approached this type of enclosure, it was possible to synthesize some aspects that can be a good guide for those who practically approach these enclosures.

The material does not have an academic level and the theoretical aspects are strictly necessary for understanding the basic phenomena in the operation of acoustic enclosures.

3. Sound chamber with coaxial speaker

There is a type of enclosure for sounding large spaces (conference rooms, dance halls or discos, etc.), enclosures named in the specialized language enclosures PA (PA = public address, in English). These enclosures have as main technical characteristics an acoustic pressure (SPL) of high value, of over 95 dB / W / m, and a maximum allowed power of the order of hundreds of watts.

Obviously, these enclosures are equipped with transducers capable of satisfying these requirements in difficult operating conditions of the environment, time duration, complexity of the program, etc.

For this article, an interesting enclosure was chosen both from a constructive point of view and from the point of view of the translator used. The enclosure was made in several copies by SC Difuzoare SRL, a company specialized in sound systems, based in Turnu Severin, using a coaxial transducer type BM 12 - CXA, produced by P. Audio and having an excellent price for its performances.

The choice of the type of enclosure was based on some advantages generated by its structure, much more complex than the usual enclosures, but with superior acoustic qualities.

This type of enclosure is called "back loaded horn" - chimney with load on the back of the transducer, and also appeared in the '30s, when the performance of the transducers required a "help" as effective as possible from the acoustic enclosure.

This type of enclosure had a new period of glory in the 70's, thanks to the company JBL, but the more aboriginal construction excluded it from the production of PA or house premises. Currently, only a few companies approach this type of construction, and the prices are prohibitive.

4. High voltage source for the laboratory

For those attracted by the beautiful phenomena of electricity, there is an installation that can provide a high voltage DC voltage, fine adjustable at intervals such as 0-1000 V or 0-10 kV. With its help, a multitude of particularly instructive laboratory experiments can be performed.

5. A PC power supply

One of the components least considered by PC owners is the power supply itself. For many of us this is just a metal box, unimportant and taking up space in the housing of the central unit. In reality, this is not the case, and the proper functioning of a PC depends on its quality.

The problem often faced by those who change the hardware configuration of the PC themselves is the blocking of the computer after it runs for a shorter or longer period of time, with the new components, obviously more powerful in terms of performance, but also in terms of resource consumption. The explanation is based on the trivial power supply.

With the installation of the new components, the power demand is higher, and if it is at the limit or exceeds the nominal power of the source, it leads to an instability of the voltage parameters on different outputs, the result being easy to see.

6. Numeric clock

The assembly presented in the article is a numerical clock made with the integrated circuit LM 8560, product of the company "National Semiconductors" (or the equivalent "Texas Instruments" - TMS 3450 NL). It is noted the simplicity of the scheme, the small number of components, compared to other similar assemblies, and the ease of making the simple wiring plated.

The accuracy of the watch is very good, of course due to the outstanding performance of the IC, which contains in the capsule "almost everything" (oscillator, frequency dividers, minute and hour counters, decoders, display control logic).

In addition, the internal oscillator is synchronized with the network frequency (pin 25, R3) in order to avoid errors in the counting process.

Thus, for 50 Hz, the frequency of the network with us, pin 26 connects to the table (for 60 Hz is left "in the air"). The assembly is found in some schemes of so-called "clock radio", produced by some more or less known companies.

The integrated circuit can be purchased from such decommissioned devices, as the radio's performance is quite modest.

7. Electronic mixer for electric motors of two-propeller ship models

When building a navigating model, on a ladder, endowed with two axes (propellers), it is necessary to equip it with two almost identical engines.

In such a situation, the majority adopts as a governing solution the one that seems the simplest, namely: each sleeve (vertically) controls independent variators (in practice being similar to driving two-lane vehicles).

The solution is simple to achieve, but very complicated in steering the ship (engine synchronization).

The problem can be posed differently: isn't it easier to maneuver a ship in two planes to control the ship's movement in the desired direction? It is obvious that in this case the handling of the model is incomparably easier and more precise. This is a desideratum of any pilot.

The material aims to describe such a device, called an electronic mixer.




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