Thursday, October 8, 2009

What is impedance and ohms.

Purchasing separate components for your whole house audio system may save you money and provide greater flexibility, but there are some basic concepts and terms you need to understand before buying. Impedance is one of the most important terms to understand when configuring your needs for a whole house audio system; and will ultimately lead to better system performance and less installation frustration. Trying to understand impedance can be an intimidating process, but it was explained to me using a very simple analogy and I will do the same for you. First things first, the impedance value of a loudspeaker is more commonly expressed in Ohms. Most home speakers are 8 Ohm, but do not work under this assumption, ask the dealer or look on the box [All of Theater-Solutions are 8 Ohm].

Think of your water pipes and pump at home. The pipe diameter represents the impedance of your loudspeaker; the water flowing through it is power, and the water pump is the amplifier (or receiver). Now, if you have a pipe large in diameter, it allows a large amount of water to flow through it, but requires the pump to work extremely hard to keep up the pressure, this would be considered a “low impedance” situation, the large pipe does not lighten or impede the large flow of water. Likewise, if the pipe were small in diameter, it would allow less water to flow, we will call that “high impedance”, because the smallness of the pipe is impeding or slowing the flow of water, or electricity. Let’s recap: Low impedance equals large flow: High impedance equals slow or low flow.

Using this same analogy let’s consider voltage and current; voltage (water pressure) and current (water flow) together create power. Now, if your pipes at home were suddenly to widen in diameter the pump would still pump the same or voltage doesn’t change, but the flow (current) would; and therefore you would receive less water flow. The pump would have to provide more power to keep up the flow, therefore lower impedance (large pipes) requires a stronger amplifier (water pump). Now reverse that theory for high impedance, and remember if the pipe is small it is restricting the flow or impeding it and pressure can build up and flow becomes more difficult. Impedance is not difficult to define, it’s more defining the actual application of impedance that is challenging. So before we proceed, let’s review what we know from our previous analogy.

  • Low Impedance equals large or free flow of power, but requires the amp to work harder to drive enough current to maintain flow. This added demand can be too much for an amplifier and cause it to over heat and shut down.·

  • High Impedance equals slow or low flow of power, and can cause restricted flow of current. The level of current influences the volume at which the speaker plays; low current equals low volume.

The optimal range for most amplifiers, receivers, and speakers to work between is 4 to 8 Ohm. This is generally easy to maintain if you are just directly hooking up speakers to a receiver or amp, but when considering multiple rooms and speakers it quickly becomes increasingly difficult to identify the overall resistance. This is important because that will identify your receiver/amplifier needs. As you wire speakers either in series or parallel, or a combination of both the resistance either increases or decreases, therefore changing the loudspeakers Ohm. In the end multiple speakers should not be hooked up directly to a standard audio amplifier. The best solution is to use either an impedance matching speaker selector box with the protection enabled, or impedance matching in wall volume controls; "impedance matching" is underlined because not all volume controls are impedance matching. Using this speaker selector boxes and volume controls it is possible to wire your entire house using a single receiver/amp as long as your receiver/amp has the needed power.

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