Influences of Speaker Cables
Purpose of the Speaker Cable
Often radiofrequency features are attached to audio cables. This is not to be recommended, as the length of the cable itself is very small compared to the wavelength of the signal. The wavelength is proportional to the speed of the signal (in the cable it’s a bit less than the speed of light) and vice versa proportional to the frequency of the signal. When examining the radiofrequency disturbances the aforementioned features will become significant amongst the audio cables too.
Picture 1. The simple electrical circuit of the twisted pair cable.
The conductance of the cable G can be deleted when working with audio frequencies. It is replaced by the load of the speaker ZKAIUTIN. After that one can examine the connection mathematically. The impedance of the speaker consists of two components: a real component RKAIUTIN and an imaginary component XKAIUTIN. The impedance of the speaker varies a lot in the area of the audio frequencies and the load is sometimes capacitive and sometimes inductive.
The resistance (R) of the cable depends on the resistivity, the length of the conductor and the conducting area of the conductor.
Often, especially in the cheaper cables, the value of the resistance changes remarkably when moving from lower to higher frequencies. The change of the value may be tens of percents.
The serial inductance makes the cable act as a low pass filter. So, it may cause fading in the treble and causes positive voltage phase shifting when compared to the phase of the current. The serial inductance creates a component called inductive reactance XL in the cable.
The serial inductance decreases when the conductor’s width increases. So, the conductor with the greater diameter normally has lower inductance than in the one with a smaller diameter. Naturally those cables must have been twisted in equal tightness.
The parallel capacitance works as a low pass filter too, but it causes negative voltage phase shifting when compared to the phase of the current. It creates a component called capacitive reactance XC.
Both the serial inductance and parallel capacitance increase with cable length.
When the influences of the twisted pair cable are examined as a part of the audio system one must also pay attention to the output impedance of the amplifier. If the amplifier’s output impedance is less than around 0,1 ohm and the output filtration effects of the amplifier begin far away from the audio frequencies, the influence of the output impedance is next to nothing.
The parallel capacitance creates a parallel resonance circuit when the speaker load is on the inductive side. The resonance point is achieved when Xc - XKAIUTIN = 0. The serial inductance, the parallel capacitance and the speaker impedance create a serial resonance circuit. The resonance point is achieved when XL - XcIIXKAIUTIN=0. There may be several resonance points in the total circuit because of the speaker impedance variation, often in the area of the RF too. The same kind of examination should also be done with the admittances. The examinations we have done are based on the assumption where the output impedance of the amplifier is a real one (no reactance exists). This constitutes a slight simplification of the process. Normally the output impedance has also an impact on resonances.
One can calculate the absolute values of the parameters by the formulas mentioned before. If one also wants to calculate the phases of the voltages and currents one must take the phase angles of the resistance and reactance into account. R has a phase angle of 0 degrees, XL has a +90 degrees phase angle and the Xc has a -90 degrees phase angle. It is rather easy to calculate the values but it is not reasonable to add the formula examinations here. When one wants to make no compromise in calculation of the reactances of the amplifiers output impedance must be taken into account.
of the Electrical Parameters
The pure serial resistance of the cable attenuates the signal equally throughout the frequency scale. No other influences exist. When the pure cable resistance is noticed as a part of the circuit the situation may become different. In this case the amplifier’s output impedance and the cable resistance must be relatively high, in the class of the several decimals of 1 ohm. Normally these values are achieved easily. Normally a slight amount of resistance (not more than hundredth parts of the speaker’s minimum impedance) is not crucial in the audio cable. The cable resistance must be equal throughout the audio frequency area. Bigger cable resistance naturally causes bigger power losses in the cable and thereby adversely affecting the damping factor.
The parallel capacitance is normally insignificantly small. But the serial inductance may affect the treble if its magnitude is more than couple of ’s. Anyway, it is better to examine the influences of the cable reactances with the aid of the resonances present. As said before the cable reactances cause resonances with the amplifiers output reactances and speaker reactances. The magnitude of the resonance is normally clearly below 1 dB, but it has audible influences because the attenuation lies over a wide spectrum of the audio frequencies. For example, an attenuation of 0,5dB over a wide frequency range is rather easy to notice by listening. When planning the cable it is possible to try to move the resonance point as low as possible. This may help in achieving a fuller sound and the listenable influences are even less critical because the ears are not so sensitive for the slight resonance in the lower frequencies.
It would be better investigate resonances with the aid of the spectral and the pulse distortion information than by looking at the influences on the frequency response. Then one can notice that a pulse may be distorted and there may be distortion components in the spectrum. The level of the distortion component may even be as high as - 40 db. Even more important is that the distortion component’s phase shifting moves the component into the area of the lower harmonics of the signal. This causes losses of the lower level details or at least distortion for the lower level details. Often some of the resonances lie in the area of the radio frequencies. This makes the speaker cable work as an antenna for radio disturbances. This problem will be handled in the latter part of this article.
What kind of influence
the speaker cable has on the over all phase response
An often discussed feature of cables is skin effect or internal impedance. During this phenomenon, electron flow at high frequencies is supposedly concentrated on the surface of the conductor. So the internal impedance’s influence is lower in the high frequencies than in the lower frequencies. Because of this phenomenon the highest audio frequencies may become attenuated a couple of decimals of one decibel.
Group delay describes the flow of different frequency components on the scale of time. It is caused by the internal impedance of the cable and it causes an effect comparable to the phase shifting of the signal components. Anyway, it is more comfortable to examine it with the scale of time. One knows that even one music instrument’s long basic tone consists of numerous sine wave components (the Fourier theorem). When those components leave the source, the time difference between them is 0 or they can actually be heard in the same actual moment, if it would be possible to listen to them. Those sine wave components do not flow simultaneously through the speaker cable which causes distortion of the signal. The highest frequency components are the first ones at the destination. The time difference between the lowest and the highest components may be, for example, in the range of 50 ns. Some subjective experiences suggest that in this case the signal sounds brighter, but the “official”, fact-based standpoint is either vague or non-existent.
As a summary one can say that the impedances of the circuit causes losses and phase shifting as well as charging and discharging of energy, which further causes the signal to become distorted.
Speaker Cable Construction
By altering the geometry of the cable one can affect the interference suppression and reactances. The low inductance is achieved by flat cable construction, but the capacitance and interference suppression may be a bit problematic. A cable consisting of numerous, separately isolated conductors, is usually referred to as a “Litz-cable”. Low inductance and enough big conducting area for the high currents can be achieved by this one. The mutual distance of twisted conductors influence the amount of inductance as well. More tightly twisted pairs have lower inductance and usually a better high frequency response than in the case of looser ones. Because the interference suppression is a very large issue it will be handled later under its own title.
Cable materials are also important to a certain extent. High quality oxygen free copper conductors are normally more than good enough for audio purposes. Gold and silver does not have any advantage elsewhere than as a coating of the conductors and connectors. Carbon fibre has its own advantages when compared to traditional conducting materials, but the cables are extremely expensive and the availability is very limited. Of course the isolation materials have their effects too. When one is using Teflon or polypropylene the results are good enough. Those materials give some mechanical robustness for the cable too.
There are a lot of connectors available which will not fit very well in the speaker or amplifier terminals. Anyway, when the price of the cable is high, the connectors are usually very high quality. The coating of the connectors is normally gold which gives better cover for the conductor than copper does. Also, it is easier to match the connector to the terminal when the coating is made of a softer metal. There is a lot of diversity in the quality of the soldered joints used in the speaker cables. The high quality cables use pure silver tin for the soldering joints. The quality evaluation of the connectors and soldered joints is a bit difficult. In there one can use the help of the electronic specialists. It may even be necessary to use a microscope when one wants to be absolutely sure about the quality of the joint. As the whole, bad contacts may in the worst case cause attenuation, distortion and lack of dynamics for the sound.
The cable materials
and construction will naturally attenuate the mechanical resonances
as well. The mechanical resonances may exist in the cable because of
the currents flowing in the cable and because of the audio waves existing
in the listening room. The influences of those resonances are a bit
hard to evaluate but at least in theory they can cause distortion (audible
When audio enthusiasts talk about speaker cables, interferences are usually underrated. From the technical side there are reasons for that: The level of the signal is tens of decibels higher than before amplification and therefore the information will not be lost so easily than in the case of the interconnects. But often people forget for example the following facts:
There is no perfect
geometry construction available.
I don’t know any official investigations or public measurements about the RFI or EMI influences in the audio systems. The reasons can be only be hinted at. Anyway, the problems are known by some audio enthusiasts and there is a lot of theory information available as well The most serious enthusiasts try the filtration solutions themselves and have their own subjective knowledge of the results. There is quite a lot of knowledge available on the suppression of the RFI, like Tomi Engdahl’s article http://www.hut.fi/~then/mytexts/radiohairiot.html (only in Finnish).
The interference protection is handled by high quality geometry, the cable jacket, ferrites and integrated filters in the cable. The twisted pair cable geometry is the most common and technically appropriate solution. Some vendors have even developed their own and more complex geometries (Matrixes). The cable jacket works as an effective shield against ESD (Faradays’ cage) and also gives protection from the capacitive and inductive interferences, but adds some capacitance. The ferrite filtration works rather well in the area of the RFI.
A filter-equipped cable with shielded, twisted pair construction is naturally the most effective when correctly built. In this case the manufacturer has a possibility to more easily affect the frequency of the electrical resonance. When we are dealing with filters one must be very careful with the group delay and the steepness and linearity of the filtration. One must be careful with the quality of the electronics and the mechanical construction too. Naturally all of this, including measurements and quality control, will cost a lot. Unfortunately the customer usually has to carry this cost. The amount of the components is not the target but the quality is.
In the worst case the EMI and RFI disturbances are easily audible from the speakers when the equipment is powered on. There are cases where even the ferrites cannot filter enough. When the worst cases are on that level, how much EMI and RFI is there really present in the lower level of the audio band! Even though RFI and EMI-noise are normally present at relatively low levels, they may confuse at least the lower level audio information like tones, slight echoes and the details of the soundstaging.
the Speaker Cables
In my opinion today’s measurement technology gives a possibility to measure very large amounts (the most?) of the audio parameters. For this one needs very much money, the latest technology and the right methods. In this case one needs at least a modern signal generator, oscilloscope, spectrum analyzer and maybe a special device for the investigation of the group delay.
Some of the vendors have taken measurements for their marketing. At least when one looks at the Cardas homepages the results seems to be reliable (http://www.cardas.com – Insights - Measuring Cable Resonance). The other vendors, like Transparent, give more or less general information. There is some other audio information available on those pages too.
Importance of Listening
The audio system used and its quality become crucial when one is evaluating cables. The audio signal may be so distorted even before the speaker cable that there are no more discernible differences in details In that case the purchase of better cables makes no sense. Experience confirms that one needs a very high quality audio system to hear remarkable differences between speaker cables
One can use audio cables for finding a specific “coloration” of the sound like warmth and richness. Some of the enthusiasts will not want too much resolution; some want a little more treble with a more forward-sounding cable. Anyway, interconnects will affect the sound more than speaker cables do.
The sense of cable listening is dependent on the several things, especially on the attitude and preferences of the enthusiasts. If the attitude is already very negative there is no sense in listening. Besides, if the results are already classified as insignificant, the listening gives added value. One must also consider the impact of an active imagination. A little part of the subjective listening experience is very likely imagined, but if there are many independent and identical experiences, it is more likely that they are real and one can trust them. As a summary, one can say that the importance of listening cannot be overemphasized.
Importance of Speaker Cables