A cable is that conductor device which allows to transfer data, and then also audio signals, in our case in the form of electrical impulses continuous (sinusoidal) in the analog domain, in the form of electrical pulses alternating in digital field or light beams in the optical field.
For the moment let’s analyze the analog cables, inside of which passes an electric current in the form of continuous pulses.
Before going more specifically it is good to know that at the professional level using various types of conductors, they vary both in size, both for length and for that type of connector, according to the signal that should lead to their interior. A cable then, as seen looking in (fig.1) it has a generally PVC outer sheath (the most common) (fig. 2), that protects the actual conductors inside, in their turn with its protective sheath generally of the same material. The modern higher quality cables are non-plastic (fig. 3) such as natural fibers, rubber fibers, silicone, polypropylene, recognizable by the phrase Halogen Free or Not Halogen, therefore devoid of halogen elements (metals) believed to now responsible in the transfer of external interference to the internal conductors. Halogens which are present in the PVC sheath as part Molecular. Some manufacturers are able to create PVC membranes with minimal halogen components (these are the best).
Some manufacturers use PVC sheath (possibly with minimal halogen components) covered in a sheath of fibers in order to realize quality cables against the external interferences but with the elasticity and resistance of cables in PVC.
This outer sheath serves as protection against dirt, against water which may create a short circuit when in contact with the circulating electric signal in the load-bearing signal wires, against impact and cuts, but especially against the handling of the cable itself and against external interference, we do not know in what situation will pose the cable, could also be in the middle of the sand and coiled around itself, or even close to strong electromagnetic interference fields (to be avoided if possible). The outer sheath, just serves to handle the cable more easily, so that the breakage is less frequent, so that the cable being more elastic, because the strength of the handling is distributed more on the outer conductor with respect to the more interior, has more possibility of “change” due to the installation. An advice when you are connecting cables, is to lay more possibly the conductor, without making it strange turns, or roll it up in a circle clockwise and then counterclockwise, then you will see why.
The PVC cost much less than non-halogen and/or natural fibers and offer excellent sound quality and handling, why still the most used today, but suffice it to say that a built cable with outer sheath and sheath for the inner conductors in PVC without consider the effect of the shield and mass, has an attenuation from external electromagnetic interference by about 60 – 70%, while the Halogen Free up to 90%.
All cables used in audio have as a material in which the current circulates, copper, (today in some professional cables, silver, or even more platinum), as that copper is the best compromise between oxidation and resistivity.
The best cable is what he the copper conductors with the CU63 of the 100% since in the nature of copper is formed by two isotropic such as the CU63 (30%) and CU65 (70%), only that the CU65 is synthetic material for which not suitable to make the current to flow.
In the choice of the cable to ensure that it is a pure copper cable is required that there is marked LC, other indications UP or PC are poor quality.
As regards the cables in silver they have a better conductivity as compared to copper have a lower resistivity value, but that have a much faster process of oxidation (and for this as well as for the cost almost never used).
Conductivity : Silver: 0.0159 Copper: 0.0168 – 0.0179
It’s also important that the silver cord both LC.
Besides the isotropy other factors that determine a lack of efficiency of the element copper or silver that is in to make to pass audio signal without interposing resistance, they are other molecular elements that can be fused (in nature) together with the copper ingots or silver taken for being worked in the creation of the filaments that will go to compose the core of management of the cable (among which a fundamental isolator present cause of strong qualitative losses is the oxygen).
The more the ingot is pure (then devoid of other molecular elements) and much more quality will also be copper filaments that will result from its processing.
Poor quality cables are instead without wording or branded T.P.C. (Tough Pitch Copper), which indicates that the copper or silver have not been processed as in O.F.C. or O.C.C., but simply the ingot is melted, it is given the cylindrical form of the conductor and then engraved up to the desired section. A Poor quality cable present impurity including oxygen for around 300 – 500 ppm (parts for million).
Generally professional cables, are branded very often with the wording O.F.C (oxygen free copper), technology born inside the 1975, which allows a process of extrusion of the oxygen and molecular impurity from the copper, realized in controlled environments deprived of oxygen and various gases, with values of molecular impurity of about 10 ppms (parts for million) and an increase of the efficiency of transmission from 0,5 % to 2 % higher compared to T.P.C., this because by removing the oxygen from the copper, the cable becomes more elastic and better conductor, and then they last even longer. For which is important in phase of choice of the cable that there is also the writing O.F.C. The same thing for the silver O.F.S. (oxygen free silver).
The wording LC together with that O.F.C. or O.F.S. is indicative of a higher quality cable, as the cable once extruded by insulating elements and not being part of the molecular structure of the copper or silver, again comes heated allowing a further process of reduction of the external molecular parts, lengthening the crystalline veins that compose the same element, generally > 100 mm in comparison to the crystalline grid of a non-pure conductor (improving her quality of a conductor).
The quality of a conductor depends therefore from its purity, the more the molecular crystals that compose the element are connected, long and closer together with minimal presence of other molecular forms and much better the conductor it will be.
An evolution of the technology LC-O.F.C. is that O.C.C. (Ohno Continuous Casting), born around 1985, it is always a extrusion process but with repeated heating and cooling of the material such as to be determined a precise disposition and dimension of its crystalline structure and elimination of external molecular parts. The crystalline vein of a good cable O.C.C. it can get to be long (then pure) up to around 125 meters.
Below two comparative tables between the T.P.C. cables, O.F.C. and O.C.C .:
The values in Figure 4 are only a reference, they depend on the section of the conductor itself.
In figure 5 a crystalline comparison between conductors O.F.C. and O.C.C. (it is clearly seen as the processing O.C.C. allows a more homogeneous and ample crystalline structure).
As it regards the ingots of material used for the creation of the conductors of the audio cables, these are classified in base to the degree of purity, the more it’s pure and so the more the number next to the letter N will be elevated, and then 3N will be an ingot less pure (with more elevated presence of impurities) in comparison to an ingot 7N (generally the purest).
Bellow a representative tables of the impurities and their values, present generally in the ingots of Copper and Silver material (fig. 6).
Finally, the quality of performance of a cable also strongly depends on the temperature in which it is placed to work and the relative humidity, generally cables of professional level PVC, retain maximum performance as from the data sheet, from – 40 ° to about + 90 °. Therefore it can be considered a parameter of non-particular interest because it is very rare to be working in these conditions, but it is always advisable to pay attention because that most of the major limits to a cable, and more at the temperature equal work better.
The most commonly used cables are therefore those with the cores of conduction in copper, those of higher quality but also cost they are the cables in copper LC-O.F.C. silver plated or copper O.F.C. ultra-pure, the same for the silvered ones or even more those O.C.C.
Some manufacturers to improve the conduction capacity (speed of propagation) in the place of the PVC sheath that envelops the conduction filaments (as visible also in figure 7), they use material with dielectric property such as the teflon alone or together with other dielectric materials as polyethylene and natural fibers. These sheaths help the process of propagation of the electric signal for difference of charge. The PVC is an insulating material with the main objective to protect the inside filaments from the breakup, degradation and reduction in part of the external interferences, a dielectric material instead allows to create fields of electric charge inside the conductor when it passes the audio signal by difference of potential (rhyming for close examinations to studies in electrical and electrotechnical field), and also be used as shield for its charging capacity if opportunely connected then to mass.
The most used cables are therefore those with copper conducting cores, those of higher quality but also expensive are O.F.C. copper with silver plated cables or copper O.F.C. ultra pure.
For professional use is not advisable to use cables without outer sheath (fig. 4), precisely for the reasons just seen. Cables without outer sheath are often used in Hi-Fi contexts and internal wiring of electronic equipments in which the current flow is high enough to not load disturbances from external interference.
As mentioned before the sheath that protects the core of the inner conductor follows the same principles of the outer sheath, PVC popular, Not Halogens have more quality.
A cable, like any other tool in which electric current circles, it has an overall resistance at the time in which tension circulates and may vary depending on the interference generated, both inside and in proximity to it.
To calculate the resistance of a cable:
Where Z is the impedance, then the overall resistance of the cable. R is the resistance of the cable (it defines the dissipation energetic). Xc is the capacitive reactance. XL is the inductive reactance (Xc and Xl, defines the capacity of electromagnetic accumulation).
The resistance R of the cable can be calculated: R = ρ * l / s
On average, for commonly used cables we can say that: ( XLR balanced = < 100 Ω / Km)
( JACK unbalanced = < 50 Ω / Km) ( RCA unbalanced = 75 Ω / Km)
n.b. More details and information on these two types of cables, will be seen further up the treatment of the subject.
Where ρ (the Greek letter ro) indicates the value of resistivity of the conductive material, so in our case, copper has resistivity value 0.01 Ω, l is the length of the cable, s is the section of the cable.
From this formula, it’s understood as the length is inversely proportional to the section. So the more the cable we use is long, and the more it will have a larger cross-section, to send such a better audio signal possible without having eased much by the resistance of the cable itself.
Xc which is the capacitive reactance, comes into play, when you have two or more parallel cables between them, both between the bearing inner cores signal cable and between two places nearby, this involves dates the tensions that pass in the inner conductor, the capacitor effect mean as to her nature in charging phase, a natural low-pass filter, which exploits the circulating air as a dielectric between the two cables.
The cutoff frequency, can be thus calculated:
Ft = 1 / (2π x R x C) where R is precisely the cable resistance and C the capacitance of the capacitor.
The capacity cannot be calculated, but inferred, because that is generated when we put in parallel cables, (then variable), the resistance as seen can be calculated. So already choosing a good conductor, (with low resistance), you will get a gradually higher cutoff frequency, so as to bring it as much as possible out of the audible band. Another method is to twist the cables (stranding of the cables), so as to reduce the area of air between a cable and the other parallel, so as to decrease the capacitor effect. Usually if the cable is good it’s already done by the manufacturer. In fact, opening a professional cable, it can be noted that two or more internal cables to the sheath, are intertwined.
A great audio cable maintains a capacitance value within the 100 pF/m, the best cables on the market today are able to have a capacitive value within 50 pF/m.
The stranding’s are defined by a unit of measure, example 50 cmq stranding means that along the 50 cm cable have been turned of 360°, in professional audio cables generally the stranding is for the whole length of the cable.
There are 2 types of stranding effective:
- DM-Four (fig. 8)
- Star-quad (mostly used) (fig. 9)
Xl is the inductive reactance, is generated, when you have strong magnetic fields inside the conductor, then the problem may also come from outside the product from electromagnetic waves, in addition to that already present inside the cable, due to the voltage step. The magnetic field, also varies depending on the frequency, the more the frequency is high and of greater amplitude, and more self-induction will be high.
The inductive reactance can be calculated:
Xl = Δ Φc / Δ t
This audio level phenomenon, behaves exactly like the previous one, and that is, as a low-pass filter. It is also called skin effect, because the voltage across the conductor does not have a linear trend due the autoinduction, then the variable reactance, resulting in signal speed variation, phase and frequency response. The dispersion of the heat and voltage inductions rear driven car that go to create, and then generate a lowering of the dynamics and frequency response starting from the highest linear.
This phenomenon, as will be seen, is particularly generated in the power cables, (used to connect the output signal from the amplifier into the input of audio speaker), precisely because it is crossed by large voltages, and then large amplitudes of the frequencies.
From as it is noticed all these issues create greater resistance in the conductor, and therefore a lower quality. In power cables then, it’s not used to weave the wires to remove the capacitor effect, because along the cable passes already a fairly high voltage.
To minimize this value, at most you always try to use cables as short as possible, in order to reduce the self-inductance and resistance factor. What fundamental, for the correct operation and with the highest quality a loudspeaker, since the power cables as we will see are used to connect the amplifier to the speaker.
One way to reduce the inductive and capacitive effects can be also to wrap the cable first in one direction, then in the other so that, when generating strong self-inductance, (the cable to another induction heating transfers his near), adjacent the cable will be in antiphase and therefore cancels the effect. If instead too wrapped the spiral cable would be created in the form of a solenoid, which would give even more value to self-inductance.
In addition to these phenomena, and specifically left aside, because they are less considered because less known but always of extreme importance, also providing its own resistance to run, is the so called Maxwell effect, which identifies an electromagnetic phenomenon contrary to that inductive, such as to generate a high-pass filter, then attenuation in low frequency. It’s considered that, a thin section cable, has a better yield in the low compared to an equal distance large section cable covered as such effect is more limited. Even if it is right, it is also true that, a small section cable, in equal circulating current, obtains a higher resistance on the signal compared to a larger size. For this reason, they are springing special cables with flat conductors, thin and wide-lamination, so as to contain in part the resistance; others with particular conduction bundles, always for the same reasons.
In general the greater the distance traveled by the conductor and more increases the overall impedance. To attenuate the impedance value for long distance cables used cables of conductors section of successively larger.
Measured in dB/m and determines the level of attenuation of the signal voltage in relation to the distance traveled.
On average, for commonly used cables we can say that: ( XLR balanced = 0,4 to 0,5 dB/100m), ( JACK unbalanced = 5-6 dB/100m).
The more the section of the bearing signal cables is large and the less will be the attenuation.
Measured in volts, it determines the maximum voltage supported by the cable in order to obtain an efficiency of 100%, is a very variable factor as it strongly depends on the operating temperature, and from the associated resistance values.
Vp expressed in %, that is the voltage expressed as a percentage which determines the speed of propagation of the electrical signal in the conductor, and is the ratio between the speed of propagation in the conductor means and the speed that would have the same air. Even this parameter is variable according to the impedance and temperature parameters, on which also affect the resistance values of the circuits to which this cable is connected. In general, and of simplification, it can be said that, the lower is the total impedance and the faster the current will circulate, even if everything depends on the material used, it’s size in relation to the circulating current, the usual variations temperature and much more … it should be recalled that at the theoretical level, the speed of propagation in an ideal conductor (vacuum), is approximate to that of the electromagnetic field, then 300,000 km/s. In real context, the professional cables that reach higher speeds whereas a minimum applied load, are those of lower impedance such as power, in which the speed is approximately from 100,000 km/s to 280,000 km/s. Through studies plus the value of the propagation velocity is high and much more quality will be the conductor.
A less mentioned parameter, given its dependence on countless variables, is the phase error. The total resistance of the circuit, then the output and input impedance between two devices in communication, and impedance of the cable, determine the circulating wave phase shift.
Such distorting phenomenon, can be linear, so a simple time delay in which the phase shift follows the wave development between positive and negative values, only delayed (ms), compared for example to another conductor in lower impedance in which the propagation velocity is greater.
Or non-linear, for which the phase shift is made independently through the wave distortion, and much more onerous, since it cannot be corrected with the simple delay processors, useful for linearizing the time delay between more signals. The linear time shift, if the circuit is well constructed, is limited to a maximum of 9 ° – 10 ° for the power cables also beyond the 10 meters compared to other cables maybe of smaller sections, just listening if not relevant with large amounts of phase-shifted signals between them.
More serious however, are the non-linear phase shifts, with much higher values and very similar to the phase differences of the speakers.
The simplified formula, since it does not consider the resistors with variations in temperature, to find the linear phase shift considering the delay of the signal once crossed the conductor, is the following:
Φ = (t1 / t2) x 360
Φ = phase delay
t1 = time delay (considering: cable length (m) / propagation velocity (m/s))
t2 = time delay of a signal cycle (1/f (kHz))
To give an example, if a power cable that connects the output stage of an amplifier to the input stage of a speaker, has a length of 5 meters, and the inside of the wave propagation speed is 100.000 Km/s = 100,000,000 m/s, whereas the frequency of 100 kHz the phase delay will be:
t1 = (5/100000000) = 5 ηs
t2 = (1/100000) = 1 s
Φ = (0.00000005 / 0.000001) x 360 = 18 °
While in the case in which the frequency is 10 Khz:
Φ = 0.18 °
The phase delay as is known, varies with the frequency, at equal length and speed, the more the frequency is high and the greater will be its phase shift. And that’s why in the audio band, the phase shifts along the conductors are limited to a few degrees even at great distances.
At constant frequency and length, but varying the speed of propagation eg. 50,000,000 m/s, then assuming a load with a higher impedance we will have that:
Φ = 0.36 °
There is a higher phase shift.
In conclusion, then returns to the principle of seeking to minimize the total impedance of the cable, by means of the expedients previously seen, while the load impedance between the input stages and output is a much more problematic factor, since it is already fixed by the manufacturer .
Reaction to interference:
Even the cable as any other audio device has its own dynamic based on the noise produced along the line, from the impedance factors, capacitance, inductive and external electromagnetic and electrostatic interference. A great cable must have a reaction value against external interference > 70 dB.
A cable in good condition, then without oxidations and breakups considering the audio band can last 50 years with attenuation of approximately 2 dB signal.
Other qualitative factors:
Calibration: the common thread that makes up the cable must have constant section so that all parameters are seen previously observed.
Centering: The copper wire must be perfectly centered inside the insulating sheath. Unlike the thinner parts can break due to continuous bending. For the realization is necessary a special machine. Be wary that by handmade cables.
Crimping: The end of the cable is crimped to secure the connector. Crimping must be circular (and not square) for not introducing bottlenecks in the conductor.
Drawing: The outer jacket should fit snugly to the inner sheath or conductor. Any bubbles help increase the noise. The casing must also be able to prevent the cable from vibrating.
n.b. It’s also important that the cable is flame retardant and meets the safety standard IEC 60332.
Another indication that you can find is LSF (low smoke and fume) and LSHF (low smoke halogen free), the first indicates that the cable does not generate or generates little smoke and dust when heated, which could be harmful if you breathe, the second indicates that the outer sheath but can also be internal ones does not generate or generates little smoke and is free of halogen elements (thus improving also the quality of the sound), so theoretically the cable has been stripped from the metal molecules. This is obtained by molecularly modifying the sheath, although in reality in PVC jackets this is not possible to 100% as is in natural fibers.
Whereas a PVC cable, the LSHF have production values of hydrochloric acid below 0,5%, while the upper LSF.
Special cables made of natural fibers allow to further reduce these values.
Cables with soft sheaths if not specially treated to allow the presence of oxygen molecules, then the highest values of reaction to fire and flame.
A video comparison between LSF and LSHF cable:
For those who want to deepen the discussion on the PVC cables and their regulations:
Among the various indications, there is also a value referred to as AWG (American standard for the size and structure of the wires), (fig. 7). It incorporates in a single number, section and diameter of the cable, the overall strength and weight. Then there are the tables so you can make the relevant conversions, then the AWG value, find the parameters of interest.
The shielding of the cable is made of conductors that carry low voltage values as line cables and even more microphone cables in order to avoid phenomena such as electromagnetic interference present in the air, and the cross-talk (voltage that passes on another cable place near derived from heating of a cable given from the tension by circulating inside it in relation to its impedance which generates phenomena of self-induction, creating phase opposition, interference and crosstalk), this phenomenon is much more present in power cables, having much more tension current assets and as we shall see without shielding. The shielding differs from the mass since the mass has the task of transferring to the ground all the charged electrostatic interference from devices where the cable and circulating on the same cable, while the shield is attached has the task of transferring to the mass which in turn he moved to land all electromagnetic interference so that they will not cause disturbances on the signal.
The shields can be of 3 basic types, from which one also sees the quality of the cable. Obviously better shielding provides a greater cable purchase price.
Types of shielding:
The materials generally used to create the shields are aluminum, mylar, copper, natural fibers (the best are aluminum and mylar and possibly natural fibers if properly constructed).
Starting from the bottom, the shield Spiral (fig. 11), is that of lesser quality. It has a greater resistance to breakage of the other two, but has a shielding power much lower.
Braided shielding (fig. 12), it’s better than the worst of the Spiral Foil, has good elasticity, an average shielding. It is generally a knitted conductor, envelops the cables carrying the signal and is made of copper.
The Foil (fig.13) is the best of shields, generally of copper or aluminum (best) or in some professional cables in particular natural fibers (best if quality), is a conductor foil which fully envelops the two signal cables. But unlike the other two, it is easier to break.
The shielding at times, may be used as a real conductor, both of the signal transport, both as a return to the balanced cables that mass. It, is attached to the mass at the two ends so as to transfer all interference on the ground that would otherwise remain in the conductor. The mass of the conductor in turn, when the cable is connected to the device, transfers all interference along the mass of the devices, up to download everything to the ground.
The modern professional cables with the major shielding powers, generally have a double or triple shielding (fig. 14), composed of braided or spiral and foil together, and very often especially the more expensive ones may have both the shielding that the plated copper conductor or silver tin-coated.
n.b. Sometimes as a material for the creation of the shield Mylars are also used, Teflon or hybrid among different materials.
The power cables are unshielded, because, owing to their strong self-induction, it would create a cross-talk of this shield, which would become a real conductor more. This phenomenon would lead to an even greater increase self-induction, and then the resistance.
Very often with the shield inserted inside the conductor also the cloth to further increase the insulating power and impact protection and the handling and for Drain Wire, then absorb any moisture that passes through the outer sheath and protect the internal conductors.
n.b. A trick that is good practice whenever you connect microphone signals, line and power is to never place mic and line level signals close to those in power and even more so even those close to power cables and connections that carry the electrical supply line.
Some manufacturers of high performance cables and therefore high costs, are customized cables (especially in the materials used) and designed to have unmatchable performance than to its consumer cables.
An example can be cables realized with independent shielding for each single conductor shielding wrapped to the copper wire or silver before the covering sheath of the conductive core or the use of an only solid conductor then separated in extremity in the number of necessary poles rather than the use of a conductor for each pole, reducing so the capacitive interferences (minimizing the presence of oxygen present instead if realized of independent copper filaments that would go to compose one or more cables), or still in the realization of different section of filaments, for example those central with large section, improving the speed of propagation and decreasing the error of phase in as the audio signal tends to move to symmetrical and linear measure toward the filaments of large section decreasing so the area of propagation (we will see then in other articles the typologies of connections and conductors in base to the number of considered poles).
In figure 15 a graphic representation of comparison between conductors with filaments of same section and those with different section.
It must be said, however, that the shield is a conductor in more that increases the capacitive effect of the interference, so that in situations of little external interference is definitely better to use single shield rather than multiple. Even more in the recording studio where if well constructed, the interference are minimal and it is helpful to have unshielded cables hand. Unshielded cable in the absence of electromagnetic interference sounds better than a shielding one.
An excellent shield as also seen in the explanation of the technical characteristics must have a higher power insulation to 70 dB.
n.b. It’s important to be careful to not crush the cable because in addition to risk damaging it will also induce different values on the technical characteristics of the cable itself (generally in worse).
Cables with separate mass
There are some cable models that are offered with separate and external ground to the cable itself (fig. 16), so separate cables must be provided to connect the ground to external ground transfer devices, such as figure 16, connect them to the earth terminal of an audio pre-amplifier. This method is often considered to be more effective than ordinary common-wire cables in reducing interference.
Section of audio cables
It’s possible to buy already grafted cables (pre-wired with connectors) (fig. 17) by the manufacturer, or you buy it separately the reel (fig. 18) and then pre-wiring it by your self at home using connectors at will (saving on the total expenditure) these already include the core conductor, shield, etc .. made by the cable manufacturer with certain values of the section and specifications.
When you buy a cable reel it can be found in two types, already tinned cable from the factory (tinned copper) or cable non tinned copper (bar copper). Buy an already tinned cable is more qualitative because the soldering allows you to better protect the conductor (usually copper) from weathering, but then you will have to remove the old soldering pre-entered by the manufacturer and to place of it a new one so as to regain the right qualitative properties lost by the old soldering in the time being also subject from the atmospheric weather.
n.b. A pre-wired cable or reel is always good to put them in a climatically controlled environment (ideal temperature 10° – 20°, not to speed up the amount of wear.
Choosing the right section to the audio signal transport is a key factor and must be optimized between the right power to carry and the total impedance, also considering the possible phase shift induced.
In generic more the power and the impedance of the circuit it is high and more the section must be large with the minimum impedance values, as the impedance of the cable would add to that circuit by creating greater attenuation.
The impedance factor as seen is a complex value dependent from the constructive methods used, omitting for which this value and the value of the phase shift that depends also on the length of the cable and the type of impedance and phase of the input and output circuits to which will be connected the cable, taking as reference the fact that the same section is a better conductor with less impedance, you can come to understand through a formula which section must have the audio cable according to the circulating power.
The formula most used for this calculation is:
Where S is the section of the conductor, L is the cable length, P is the power circulating in the conductor, V is the working voltage in high conductor squared.
n.b. Increasing the section of a cable, but also adding shielding or increasing the cross section of the shield, as well as to create greater phase problems as that the audio signal must pass through a larger section of filament, also it increases the value of the capacity, then larger impedance and the low pass filter with lower cut-off frequency. If you increase the section or the number of shielding is necessary to have conductors with the lower section to offset the increased impedance and capacity.
In the choice of cable it is good so always choose the best compromise between cable diameters, lengths ahead, impedance factor and capacity.
n.b. Generally within the value of impedance as seen in the previously indicated formula is included also the value of the capacity.
As we shall see in future articles for a line signal is in the order of 1 volt and the section of conducting cores most used is 0.20 mm2 – 0.22 mm2 (also considering the sheath of conducting cores), Sections of 0.75 mm2 are the best in order to maintain a low resistive level at the expense of a slight increase in the capacitive effect, especially for long distances.
A good resistance that is less than 110 Ω/Km for sections of 0.18 mm2
90 Ohm/Km for 0.22 mm2 sections.
30 Ohm/Km for 0.75 mm2 sections.
A good capacity (considering the conductors and shield) is less than 80 pF/m to 0.18 mm2 sections.
90 pF/m to 0.22 mm2 sections.
100 pF/m to 0.75 mm2 sections.
For microphone cables in which the signal circulating is in the order of mV, the section most used also considering the cores is from 0.10 mm2 – 0.12 mm2 (for the transport of the lowest-level signals to short distance ) to 0, 30 mm2 – 0,35 mm2 (for the transport of more highest level to far distance), which generally also require the phantom 48 V power transportation as we will see when we talk about microphones, voltage necessary for the operation of condenser microphones). Most have used a section of 0.22 mm 2 an excellent compromise between the minimum and maximum values of section just analyzed.
Experiments have found that for the microphone signal being so low value it is possible to neglect the dispersion of energy into heat, then reduce the cable section can have a lower wave phase shift and provide more quality throughout the audio band. To this unless of not having to use a cable for connecting a microphone that requires an external power supply it is good to use cables with the lower sections. A small section for the same working voltage, also captures less interference.
A good resistance is less than 100 Ω/Km for sections of 0.18 mm2
75 Ω/Km for sections of 0.22 mm2.
30 Ω/Km for sections of 0.75 mm2.
A good capacity (considering the conductors and shield) is less than 80 pF/m for sections of 0.18 mm2 .
100 pF/m for sections 0.22 mm2.
250 pF/m for sections 0.75 mm2.
n.b. Some manufacturers also highlight the ability of only the conduction cables without considering the shield, generally a value close to half the capacity considering the conductors and shield.
The signal that circulates in the power cables is in the order of volts. The section of the souls of audio power cables generally goes from 2.5 mm2 up dependent on the electric voltage that will bring the conductor. It’s good to be aware of the maximum power and working voltage, usually one takes into account the power and peak voltage (we’ll see in other arguments the interface optimization between a power generator (power amplifier) and an audio speaker) .
A good resistance that is lower than 15 Ω/Km for sections from 1.5 mm2 up.
Over the section will be great and will lower the impedance at equal distance.
n.b. The power cable has capacitive effects negligible as massless and shield.
Typically the value of the section of the ground conductor is a few millimeters larger than the section of the cables carrying signal (0,1 – 0,2 – 0,3 mm more), this is because the conductor impedance is necessary mass is lower than that of the conductors of the signals in order to properly bring to the ground all the electrostatic interference.
The section of the shield is generally a factor tests and tests by the manufacturer, typically the most used sections that bring greater benefits against electromagnetic interference minimizing any capacitive effects due to the presence of the shield are from 0.10 to 0.12 mm.
A shield that provides more coverage and therefore protection, however, also cause an increase in the capacitive factor, for which the foil is the one with the higher capacitive value, then there is the braided and finally the spiral with the least capacitive value, but also the least protection against interference.
n.b. Regarding the audio cable length, we shall see in the next articles as also in this case the value strongly depends on the type of audio signal.
Environments of use
As it has been said and will be repeated several times along the discussion of this issue, depending on the type of installation that you will have will be more useful to use a cable with certain characteristics rather than others.
To live is good to use shielded cables with single foil or spiral shield, but also take some cable with double or triple shielded in case you are in environments and situations that create a lot of interference. The use of a single shield promotes the attenuation of capacitive phenomena that should be to produce as there is the presence of an added conductor, though also well realized (the shield). The outer sheath possibly PVC LSHF as being live a nomadic environment, but not fixed, so he assembled and disassembled for each date of an event, then it also collects the cord over and over again, it is useful to use the robust cables and still manageable with minimal presence of halogens. For those who have the financial ability even some non-halogen cable, or PVC coated non-halogen to be used in situations where it is particularly required quality. There are several PVC coatings, use with a medium or slight ruggedness (contain less halogens).
- Recording Studio
If the recording studio is designed and built to DOC the electromagnetic and electrostatic interference problems are minimal so you can use cables with PVC coating with minimum strength possible, even better if not PVC but made with Natural Materials. Also useful the use of unshielded cables to optimize the quality of the audio signal or foil or spiral shielding.
- Fixed Installations
For fixed installations, it is required cables that last over time, even against bad weather, so it is good to use PVC cables LSHF with maximum strength possibly double or triple shielding (foil and mixed with the presence in each case of the foil, as you’re never sure what condition the cable will be laid) at the expense of a slight drop in audio quality.
For the installation of hi-fi systems and which are usually in a fixed installation once it thought that it was useful to use cables without sheath (fig. 4) so as to minimize interference effects of the sheaths PVC LSHF and capacitive by the presence of any shield, today however the best solution is to use non-halogen cables, because we live in a world where smartphone, TV, tablets and any electronic device generates electromagnetic interference.
More About Analog Audio Cables:
Analog Audio Cables – II (Types of Connectors and Connections, Unbalanced Connectors and Connections)
Analog Audio Cables – III (Balanced Connectors and Connections, Passive Balancing)
Analog Audio Cables – IV (Active balancing)
Analog Audio Cables – V (Differences between Jack and XLR, Bantam, Speakon, Powercon)
Analog Audio Cables – VI (RCA, MiniJack, BNC, Midi, Starquad, Edac, D-Sub, Socapex, Euroblock, Tipologie di Adattatori )
Analog Audio Cables – VII (Connection Types, Ground Loop, Solder A Cable, Acoustic Pollution)
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