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Choosing the right caliber
The last step after purchasing and installing the audio complex is connecting the blocks and connecting the acoustics. Which cable to choose and how to connect? European speaker manufacturers rarely say anything about the requirements for the parameters and dimensions of the speaker cable. American ones, from the USA and Canada, whose acoustics are widely represented on the Russian market, usually indicate the size. However, it looks something like this: "use a 16 - 18 gauge cable to connect the acoustics, if the length is more than 3 meters." Sometimes the instructions are more specific: "we recommend using 18 gauge or thicker cable for lengths less than 8 meters and 16 gauge or thicker cable for lengths greater than 8 meters." In this case, the gauge refers to the size of the wire in accordance with AWG (American Wire Gauge). The smaller the AWG number, the thicker the wire. So how much will it be in the usual millimeters? We provide a comparison table for some of the most commonly used cables. All of you in each acoustics test have the opportunity to observe the frequency dependence of the speaker impedance. In fact, it is a resistance module, since the phase characteristic of the input impedance of a traditional speaker with crossover filters and dynamic heads also changes with frequency. It changes in such a way that at some frequencies the amplifier feels it as simple resistance, at others - as capacitance and resistance, and at third - as inductance and resistance. The most difficult part is low frequencies. For the vast majority of modern speakers, woofers operate by capturing the region of mechanical resonances (resistance at these frequencies increases on the frequency dependence), but the most dangerous next resonance is electromechanical, at which the impedance is minimal and almost equal to DC resistance. For some heads, its value may be less than 4 ohms. The lower the internal output impedance of the power amplifier, the more effectively the natural oscillations of the head at the resonance frequency are suppressed (damped). Perhaps you remember such an amplifier parameter as the damping factor. This is the ratio of the speaker's nominal impedance to the amplifier's output impedance, and therefore may vary for systems with different impedance ratings. According to some data, the value of the damping coefficient should be several tens. In such a popular publication as Howard Traman's Audio Cyclopedia, it is indicated that it must be at least 20. Now, if you look at the table and make a simple calculation for acoustics with a resistance of 4 ohms and an amplifier with a damping factor of 20, it becomes clear that even a half-meter speaker cable of 17 gauge (section 1 mm²) will worsen the damping factor by 10%. And the resistance of a frequently used three-meter segment of such a cable will already increase the resistance of the amplifier by a third and, with the values \uXNUMXb\uXNUMXbspecified in the example, will almost halve the damping factor. For an amplifier with a large damping factor, i.e. With a lower output impedance, the effect of a speaker cable of this caliber will be even greater. Also often "discussed" is the influence on the quality of sound reproduction of the surface effect, more often called the skin effect in audiophile circles. For most stranded speaker cables, this effect appears to be negligible. In general, cable losses determine its resistance, inductance and capacitance, and insulation leakage conductance (all per unit length). Therefore, the best of all options would be a short, thick, stranded (it is possible with insulated separate conductors) speaker cable. In any system, both interconnects and speaker cables are used. What should be the alignment between them? According to experts involved in the development and production of special audio cables, it is better to have a long interconnect cable and a short speaker cable. This, for example, involves the use in a high-quality stereo sound system of a preamplifier and two monoblock power amplifiers located in close proximity to the speakers. Here, the cardinal solution to the problem with speaker cables can be the use of active speaker systems. But back to the discussion of connectivity in simpler systems. Two-pin connectors for connecting acoustics, which were generally accepted twenty years ago, were not designed for high power. At the time of their development, 10 watts per channel was considered "normal" power for a stereo amplifier. Such connectors allowed the use of only ordinary electrical wires of the "noodle" type with a small cross section, and therefore have sunk into oblivion. The same fate befell the spring clips on the Japanese block equipment. Although in fairness it must be clarified that such clamps are used with might and main in music centers and for connecting additional channels (center and rear) in some AV receivers. Most modern devices are equipped with screw terminals that allow the connection of cables with a core of various diameters. Directly, without an adapter or a lug, you can connect a cable with a diameter of up to 3 mm. If you remove the plugs and use adapter single-pole plugs, then you can easily connect with a 6-mm wire. Skin effect The essence of the skin effect is that with increasing frequency, the current is displaced from the thickness of the conductor to its surface. By the way, this is where the name "skin" comes from: in a technical context, the meaning of the English word skin is the outer layer, the shell. The simplest parameter that characterizes the skin effect is the ratio of resistance per unit cable length for direct and alternating current (Rac/Rdc). The depth at which the current density is 1/e times less than at the surface is called the skin depth. Here, e is the base of the natural logarithm and is equal to approximately 2,72. At low frequencies, the skin depth is much greater than the radius, which means that the current is equal across the entire cross section of the conductor. The influence of the skin effect can become noticeable when the ratio becomes significantly higher than unity. We say "may" because it will only happen when the increase in resistance results in an audible change in sound. For frequencies above 15 kHz, Rac/Rdc becomes 1,1 using 15 gauge solid wire. For a stranded wire, and only such wires are used to connect acoustics, it is very difficult to talk about a specific value of the skin depth. Multiple weaves and contacts between individual conductors that form an electrically conductive core do not make it possible to accurately calculate and evaluate its value. To a lesser extent, the skin effect affects a multi-wire cable, each individual core conductor in which has an insulating layer, i.e., for a litz wire. With him, at least, it is theoretically possible to accurately calculate the value of the surface area, which will be larger in relation to a single-core with an equal cross-sectional area. By the way, the widespread use of such a wire in the inductors of radio receivers (i.e., at high frequencies) was determined precisely by the small skin effect.
Literature Stereo & Video. 9/September/1999
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Comments on the article: Vladimir Ilyin If you completely simplify the recommendations, then I will give this advice. The limit of visibility of improvements with an increase in the cross section of the type-setting conductor comes from 1,7 mm for copper to 2 mm. If you want damping guarantees, you can put a conductor up to 2,3 - 2,5 mm. A further increase in the cross section does not give a gain noticeable by ear at reasonable signal powers. Next comes the power range, in which heating the coil of the dynamic head destroys the integrity of the distinctness and intelligibility of the signal. For a better understanding - study the special literature on professional dynamic heads (compression effect).
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