What is a parallel speaker cable or parallel power cable ?
A parallel cable is made up of two multi-core conductors, consisting of several individual wires or strands that are grouped together in a group and surrounded by an insulator.
The filaments or strands may be made of copper, aluminum or other conductive material. As they are sets made up of multi-core cables, the formed cable is flexible.
Multi-core cables are more flexible and less likely to break when bent or handled due to their multiple conductor strands, making them ideal for applications where mobility or repeated bending is needed. In addition, they are more durable than single-wire cables due to their resistance to mechanical fatigue. They also provide more secure connections on plug and connector terminals due to their larger electrical contact area. For all this, the parallel cables that we normally use are multi-wire. Furthermore, these cables are almost always made up of a pair of parallel cables, in this case also being a bipolar cable.
Types of parallel cables
- Polarized parallels: In direct current applications where respect for polarity is necessary, such as the power supply of a direct current circuit or the connection of a speaker that requires a certain polarity, we need to use a polarized cable that guarantees that we do not make a mistake in the connection and that we respect each of the connection poles.
- Two-Color Parallel: In order to identify each of the cables, different colors are used on each of the individual cables. The most common being the two-color red and black parallel cable. There are other combinations that are also frequently used, such as the combination formed by black and white or black-yellow. Other times a single color prevails, but one of the conductors has been marked with a stripe or dash to continue identifying the cable, such as white with a black or gray stripe and black with a white stripe, among others.
- Non-bicolor polarized parallel: Other times the cable is not colored and what the cable manufacturer chooses is to make each of the cable's insulators different. In this way, at first glance, the two cables are the same in terms of color, but seen in detail they are different. The figure below shows different ways of making a polarized cable in which each of the two cables can be identified without the use of a measuring device.
- Non-polarized parallels: For low voltage alternating current or direct current applications when a polarity distinction is not necessary, we can use unpolarized cables.
How is the resistance of a cable calculated?
The resistance of the conductive cable is calculated with the formula: R = ρ x L/S Where ρ (ro) is the resistivity of the material, which is also something that also depends on the temperature. So for a driver
copper and by doing the calculations we can make the following resistance table in a copper conductor.
| Section (mm²) |
Maximum conductor diameter (mm) |
Resistance (20ºC) Ω/Km |
Resistance (70ºC) Ω/Km |
| 0.5 |
1.2 |
39 |
49.73 |
| 0.75 |
1.3 |
26 |
33.15 |
| 1 |
1.5 |
19.5 |
24.86 |
| 1.5 |
1.8 |
13.3 |
16.96 |
| 2.5 |
2.4 |
7.98 |
10.18 |
| 4 |
3 |
4.95 |
6.31 |
| 6 |
3.9 |
3.3 |
4.21 |
| 10 |
5.1 |
1.91 |
2.44 |
| 16 |
6.3 |
1.21 |
1.54 |
In the case of a parallel cable we have to consider the resistance of 2 cables, so the total resistance would be exactly double.
Why is the section important in a speaker cable? Signal loss depending on the cable section
Sectioning in speaker wiring is important for several reasons:
- Signal loss: The longer the cable and the lower its section, the greater the signal loss that the audio signal traveling through it will experience. Too small a section can cause a drop in sound quality, especially at high frequencies. If we look at the previous table of the resistance of a cable, the smaller the section, the greater the resistance for the same distance. Furthermore, the losses are greater the lower the speaker impedance is, because the resistance of the cable is comparatively high in relation to the speaker impedance.
Example: To calculate the losses in 4 ohm and 8 ohm speakers across different cable sections and lengths, we will first need to obtain the resistance of the different cables per meter. To do this we will use the resistance formula depending on the length and resistivity of the material and...
For 0.25mm²: R= 0.094 Ω/m
For 0.5mm²: R= 0.052 Ω/m
For 0.75mm²: R= 0.043 Ω/m
For 1.5mm²: R= 0.026 Ω/m
For 2.5mm²: R= 0.019 Ω/m
For 4mm²: R= 0.012 Ω/m
And by creating a table we will have the different resistances due to the cable:
| Length (m) |
section: 0.25mm²
(Ω)
|
section: 0.5mm²
(Ω)
|
section: 0.75mm²
(Ω)
|
section: 1.5mm²
(Ω)
|
section: 2.5mm²
(Ω)
|
section: 4mm²
(Ω)
|
| 10 |
0,94 |
0,52 |
0,43 |
0,26 |
0,19 |
0,12 |
| 15 |
1,41 |
0,78 |
0,645 |
0,39 |
0,285 |
0,18 |
| 30 |
2,82 |
1,56 |
1,29 |
0,78 |
0,57 |
0,36 |
| 50 |
4,7 |
2,6 |
2,15 |
1,3 |
0,95 |
0,6 |
| 100 |
9,4 |
5,2 |
4,3 |
2,6 |
1,9 |
1,2 |
We can observe, for example, that for a cable with a section of 0.5mm² if we have a cable length of 100 meters, the resistance of the cable is 5.2 ohms. If the speaker to be connected has an impedance of 4 ohms, the power it will dissipate in the cable is 30% higher than what is translated into sound in the speaker itself. This effect is smaller, as we can see if the speaker is 8 ohms, or if the cable section is larger.
- Impedance: The section of the cable affects the impedance of the circuit. Impedance is the resistance that the circuit presents to the alternating current of the audio signal. If the cable cross-section is too small, the impedance may increase, which will negatively affect the sound quality and may damage the amplifier and speakers.
- Current Capacity: An adequate wire section ensures that it can handle the amount of current needed to power the speakers without becoming too hot or causing a significant voltage drop.
- Safety: Using an inappropriate section of cable may represent a safety risk. For example, if the cable cannot handle the current being applied to it, it can become overheated and cause a fire.
In summary, the speaker wiring section is important to ensure efficient audio signal transmission, maintain sound quality, protect equipment and ensure safety.
