Originally Posted by Bill Fitzmaurice
The number one factor that determines cable performance is capacitance. There is virtually no correlation between capacitance and price. Some of the most expensive cables are also some of the worst with respect to capacitance.
There is no #1 factor that is universal. The weakest link is the most important.
What happens when the resistance gets too high? First, there is power lost in the wire and the speaker will not play as loud. More important, as the resistance in series with the speaker increases, it makes the amplifier look more like a current source. This means the speaker frequency response will tend to follow the rise and fall of its impedance curve. The greater the impedance variation, the more noticeable the response changes will be. If the speaker has constant impedance versus frequency, the only change will be reduced output.
The red (upper) curve is without any added series resistance. The green (middle) curve is with one ohm added in series with the speaker and the black (lower) curve is with 2 ohms in series. You can see there is an overall loss in output but it is not the same at all frequencies. For the green (middle) curve in the area of 125 and 2500Hz, where the impedance is high, there is only about 1/2dB of loss in output whereas at the area of lowest impedance, at 300 and 10 kHz, the loss is about 2dB. The larger 2 ohm resistance shows even greater changes.
The resistances used in this example are much larger than the recommended wire resistance of 0.2 ohms but they do show how impedance variations can influence response. Response changes this large can be easily heard in an A-B listening test.