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Why do speakers appear to lose their power over distance?

Q: “I’ve heard that speaker will “lose” their power over distance. Why does this happen?”

A: The full depth of this question can’t really be covered in the confines of inSync, but there is a short, basic answer. For the most part, this is due to the fact that while copper is a very good conductor of electricity, it isn’t perfect. It has a certain amount of resistance, determined primarily on its cross-sectional area (but also by its purity and temperature). This wiring resistance is “seen” by the amplifier output as part of the load; if a cable with a resistance of one ohm is connected to an 8-ohm speaker, the load seen by the amplifier is 9 ohms. Since increasing the load impedance decreases current flow, decreasing power delivery, we have lost some of the amplifier’s power capability merely by adding the series resistance of the cable to the load. Furthermore, since the cable is seen as part of the load, part of the power that is delivered to the load is dissipated in the cable itself as heat. (This is the way electrical space heaters work!) Since Ohm’s Law allows us to calculate the current flow created by a given voltage across a given load impedance, it can also give us the voltage drop across the load, or part of the load, for a given current. If a given cable has a certain amount of resistance to current flow per foot (a common way for them to be rated) then naturally greater lengths are going to add to this, which is what causes the loss to accumulate over greater lengths of cable. The natural follow up to this question is how can this power loss be minimized, which we’ll cover in another inSync Tech Tip of the Day.

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