I started to type out a very long explanation of voltage, current, inductance, reactance, impedance, etc... It is hard to explain exactly what Impedance (Z) is without knowing what the various factors that go into making it up really consist of. Needless to say, after typing up what would have been the longest post in the history of Agon, i stopped.
Resistance is but one simple part of Impedance. Impedance is a complex combination of Resistance, Inductance and Capacitance summed into one simple to navigate figure. Even though resistance and impedance are used interchangeably in many situations, they really have different meanings.
Resistance is the opposition to signal flow. Think of it as kind of an "amperage restrictor". Depending on the level of resistance involved, the amount of current flow ( amperage ) will vary according. More resistance equals less amperage in the circuit and vice-versa.
On the other hand, Impedance may actually oppose current flow in a much more active manner. This is because Impedance factors in both capacitive and inductive reactance of the circuit along with the simple opposition to signal flow that resistance by itself generates.
Think of "reactance" as the equivalent of "resistance" going through an alley and running into combatative thugs. Not only is it a lot trickier for the signal to push its way through the circuit, those "shady characters" won't let the signal pass without a major fight.
This is not to say that all "complex" impedances are "tough" to deal with, but when a circuit has a high level of reactance, the subsitution of the words "resistance" for "impedance" becomes more and more meaningless and less accurate of a description. This is why we say that some speakers that are tough to drive are "reactive" ( lot of "fighting" with the amp to deliver the signal to the speakers ). Easy to drive speakers offer a "resistive load" i.e. "non-reactive" because they don't put up much of a fight.
Having said that, it is quite possible for a low impedance load to be easy to drive. That is, so long as the amp can pass enough current on a steady state basis to keep up with the amount of signal flow required. When a speaker has both high levels of reactance AND a low impedance, it can be VERY tough to deal with. This is because the amp has to be able to provide gobs of power AND "fight" the reactance as it does so.
As far as the "Z" of a cable goes, it depends on what spec "Z" is being quoted for. A low "nominal impedance" with a speaker cable is a great thing. That's because the output of an amplifier has a very low impedance and the input impedance of most speakers is also quite low. Sticking with a speaker cable that has a very low "nominal impedance" has great benefits as far as i'm concerned.
The same may not be true for an interconnect, depending on the components being connected. As previously discussed, due to various input and output impedances on gear, the "nominal impedance" of a cable can act as somewhat of a "buffer" or "impedance transformer" between the components. What "nominal impedance" works best will depend on how stable the output circuit of the source component is and how reactive the input of the load component is. If all of this gear was properly designed, we would want to have the output impedance of the souce matching the input impedance of the load component with a cable of the same "nominal impedance" connecting them. Since we don't have this type of situation taking place in audio today, we've ended up in the situation that we have where cables do affect the sonics of a system. Rather than just being a passive device to carry signal from one active device to another active device, they become an active part of the complex impedances that the signal sees as it travels through-out the entire system. By changing the complex impedances ( inductance, capacitance and resistance ) that the signal sees, we change voltage to current ratios, loading characteristics, etc... This effects the linearity of the system as a whole. Sean
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Resistance is but one simple part of Impedance. Impedance is a complex combination of Resistance, Inductance and Capacitance summed into one simple to navigate figure. Even though resistance and impedance are used interchangeably in many situations, they really have different meanings.
Resistance is the opposition to signal flow. Think of it as kind of an "amperage restrictor". Depending on the level of resistance involved, the amount of current flow ( amperage ) will vary according. More resistance equals less amperage in the circuit and vice-versa.
On the other hand, Impedance may actually oppose current flow in a much more active manner. This is because Impedance factors in both capacitive and inductive reactance of the circuit along with the simple opposition to signal flow that resistance by itself generates.
Think of "reactance" as the equivalent of "resistance" going through an alley and running into combatative thugs. Not only is it a lot trickier for the signal to push its way through the circuit, those "shady characters" won't let the signal pass without a major fight.
This is not to say that all "complex" impedances are "tough" to deal with, but when a circuit has a high level of reactance, the subsitution of the words "resistance" for "impedance" becomes more and more meaningless and less accurate of a description. This is why we say that some speakers that are tough to drive are "reactive" ( lot of "fighting" with the amp to deliver the signal to the speakers ). Easy to drive speakers offer a "resistive load" i.e. "non-reactive" because they don't put up much of a fight.
Having said that, it is quite possible for a low impedance load to be easy to drive. That is, so long as the amp can pass enough current on a steady state basis to keep up with the amount of signal flow required. When a speaker has both high levels of reactance AND a low impedance, it can be VERY tough to deal with. This is because the amp has to be able to provide gobs of power AND "fight" the reactance as it does so.
As far as the "Z" of a cable goes, it depends on what spec "Z" is being quoted for. A low "nominal impedance" with a speaker cable is a great thing. That's because the output of an amplifier has a very low impedance and the input impedance of most speakers is also quite low. Sticking with a speaker cable that has a very low "nominal impedance" has great benefits as far as i'm concerned.
The same may not be true for an interconnect, depending on the components being connected. As previously discussed, due to various input and output impedances on gear, the "nominal impedance" of a cable can act as somewhat of a "buffer" or "impedance transformer" between the components. What "nominal impedance" works best will depend on how stable the output circuit of the source component is and how reactive the input of the load component is. If all of this gear was properly designed, we would want to have the output impedance of the souce matching the input impedance of the load component with a cable of the same "nominal impedance" connecting them. Since we don't have this type of situation taking place in audio today, we've ended up in the situation that we have where cables do affect the sonics of a system. Rather than just being a passive device to carry signal from one active device to another active device, they become an active part of the complex impedances that the signal sees as it travels through-out the entire system. By changing the complex impedances ( inductance, capacitance and resistance ) that the signal sees, we change voltage to current ratios, loading characteristics, etc... This effects the linearity of the system as a whole. Sean
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