Cables are a highly controversial topic within the hi-fi hobby. And that is partly understandable… it’s rather intangible and difficult to prove that it does anything.
We made an attempt with a mass test of speaker cables. We listened to them blind and measured everything. Including practical measurements on a loudspeaker. These turned out to be the most interesting. But it is also interesting to combine the cable properties with these measurements to see if there is a relationship.
Practical measurements
Signal cables connect two devices. That can be a source to an amplifier, or of course a speaker to an amplifier. In the case of our first major investigation into the influence of speaker cables, we created a setup with an amplifier and a speaker. The only variable is the speaker cable.
You can see the results of this practical measurement above (the title of the graph is incorrect: this was measured at the speaker!). And you can see that not all cables are equal. There is almost 0.5 dB difference between the cables. And that difference showed up in a follow-up test we did where we tested different amplifiers on different speakers with different cables.
The graphs above are measurements with the Prism dScope. They are basically simple frequency response measurements where we measured the signal at the connection to the speaker. Through the graph we plotted the impedance and phase of the speaker to see how this affects the response.
These above graphs are a little crazy, though, since response is relative. Normally we plot it in absolute values, with decent dBs. That reads a little easier.
Below is a chart in absolute values. So just, nice dB’s. For each cable we have chosen a separate color. You can see that the differences between the cables remain constant. Of course the response changes per speaker and amplifier, but the influence of the cable remains the same. This means that a speaker cable does have a signature.
Other cables?
Now with speaker cables we have been able to establish a relationship between measuring and listening. The above measurements on a loudspeaker with only the cable as a variable, say something directly about the response of the changed cables. And in our blind test, this was also largely apparent.
Now we have also tried such a setup with other signal cables. However, different laws of physics apply there. With a loudspeaker cable, the resistance of the cable has a great influence because it is relatively high. A loudspeaker has an impedance of between 2 (very low, but some dip there) to, say, 40 Ohms. The nominal – average – impedance is 6 Ohms, for example. Then the resistance of a speaker cable suddenly plays a role! After all: 1 Ohm on top of 6 Ohm is significant.
With interlinks, this does not apply. An interlink has to deal with a – if correct – low output resistance (50 or say 100 Ohm. For example, from a CD player or d/a converter) to a high input resistance (10 or say 15 KOhm. For example, a preamplifier). Even though an interlink would have a resistance of 1 Ohm; on top of the 10 KOhm input impedance of a preamplifier, that’s nothing! It just doesn’t play a role.
That makes measuring these cables very difficult, because we just keep measuring straight lines. And that while we do observe differences. So a different approach is needed.
LCR properties
Now, ‘field’ measurements are actually much clearer than “synthetic” tests on, say, an LCR. However, we at Alpha Audio try to establish a relationship between the two. After all: they should say something about sound, right? We estimate that a relationship can be found. But to be fair: we have not yet been able to establish a direct relationship.
The cable properties:
- Inductance – voltage generated by the changing magnetic field in the cable (Henry)
- Capacitance – stored energy, capacitor action in the cable (Farad)
- Resistance – resistance of the cable (Ohm)
- Conductance – conduction of the cable (Siemens)
- Impedance – the complex resistance of the cable (Ohm)
Now manufacturers also use inductance, resistance and capacitance in speaker filters, for example. To explain it very briefly: a coil (inductance) often works as a high-pass filter. Capacitance works more like a low-pass filter. Perhaps to an extreme extent, this also works with cables, although the values are very small, as you can see in the graphs above. We are talking picofarads, micro-henries and mostly less than tenths of an Ohm.
Concluding
Measuring cables is extremely tricky. And the question remains whether we are measuring the right things. In the study of loudspeaker cables, practical measurements proved to provide the most insight. However, this measurement cannot be translated to interlinks. Let alone mains cabling. Different rules apply there.
The cable properties that we measure with the Sourcetronic mainly provide insight into the materials used, shielding and, for example, transition resistance. This cannot – yet – be translated directly into practice. But who knows… maybe we can in the future!