What is the relationship between Voltage, Current, Resistance and Power in Audio Circuitry?
A voltage is a measurement which is determined by one point having an excess of electrons while the other point has an absence of electrons. A battery for example, has a positive (excess of electrons) and negative (absence of electrons) terminal. Voltage is also like an electrical pressure, like the pressure in a water tap. So a volt is a measure of the difference in electrons between 2 points. Voltage is measured in volts.
An electrical conductor is something which allows electrons to easily pass through it. It does not resist them. When such a conductor connects between 2 points with voltage, a current is passed between them. So current is the amount of electrons passing through the conductor. With a battery, when there is the same amount of electrons in both positive and negative terminals, it is discharged or dead. Current is measured in amperes or amps.
Understanding resistance means that one must understand Ohms law along with it. Resistance is measured in Ohms. Current flow is determined by the resistor's resistance and the voltage. The higher the resistance, the less the current flow. But at the same time, the higher the voltage, the higher the current flow. Ohms law states: E = I x R. E is Electromotive force (voltage) I is for Intensity (current) and R is for resistance. If one knows either of the 2 values, you can find out the third value. For example, R = E/I.
Now that the basic electronic terms are out of the way, there is another term which is more commonly used in audio: Power. We all want to know how powerful our amplifier will be, for example. Determining the amount of power a piece of sound equipment has helps us determine whether it is suited to our needs or not.
In Ohms law, P (power) = I x E. A resistor is also known as a load, and when power is dissipated in the resistor, it comes out as heat. Power is measured in watts. To measure power: if the voltage across the resistor is 20V for example, and the current through the resistor is 0.1A, then the power dissipated will be 2W.
One's first logical thought would be to think that if one were to halve the resistance, the voltage would remain the same and the current would double. This however, is not the case, as this not actually possible. Every power source and therefore amplifier will eventually run out of voltage and current.
Series and parallel circuits
Possibly the single most important factor bringing all the other terms stipulated above, together, is running an amplifier or loudspeakers in series or parallel. Basically, when 2 loudspeakers for example, are connected to an amplifier in series, the load (resistance) doubles as both resistances are added together. This means that the loudspeakers and amplifier will have to work harder in order to produce the required wattage. This also means that the amplifier will not be able to produce as much wattage. In fact, it will be approximately half, due to the doubled resistance. The one benefit of higher resistance is that, in general, the sound quality produced will be of higher quality.
When 2 loudspeakers are connected in parallel, the opposite occurs. When 2 loudspeakers are connected to an amplifier in parallel, the resistance gets halved. This means, theoretically, that the wattage produced will double, but as explained earlier this is not exactly so. However, one can still enjoy the benefit of having more wattage, and if the loudspeakers and amp can handle more wattage, you will get louder volume to suit your needs. The downside of this is that the sound quality decreases with less resistance.
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Edited by: Rajesh Bihani ( Find me on Google+ )