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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8841 Registered: Dec-03 | Ohm The ohm is the unit of measure of a device's opposition to the flow of current. One ohm of resistance will allow only one amp of current to flow through a circuit when one volt of electrical force is applied to the circuit. cited from: http://www.bcae1.com/ohm.htm Ohm: A measure of how much something resists (impedes) the flow of electricity. Larger numbers (more Ohms) mean more resistance. cited from: http://www.hometheatermag.com/glossary/ Impedance refers to AC voltage, wheras resistance refers to DC voltage. Amplifiers in the car audio realm are designed to operate within certain parameters. This means they have a range of input voltages, and a range of speaker impedances under which they're meant to operate. Usually, this is about 12-16 volts DC for input, and 2 to 8 ohms of speaker load. There are "high current" amplifiers which can operate to lower loads, some as low as 0.25 Ohms, but for this example we'll use the more common range of 2 to 8 ohms, as this range is the most common, and the components to build an amplifier to these specs are generally cheaper than the high current models. Often, people ask why the ohm ratings of speakers matters, or they ask how much power their amplifier will put into a certain speaker, or what amp goes with which subs. These are all answered by and large by Ohm's Law. Ohms law - The relationship between voltage, current and impedance. If two values are known the other can be calculated. This relationship is expressed many different ways. The basic relationship is voltage (V) is equal to current (I) times impedance (Z). the voltage input for a car audio amplifier with a PWM regulated power supply is a fixed value. That's 12VDC. The Impedance (Z) is based on the voice coils of the speakers connected to that amplifier and how they're wired together. The current draw (I) is determined by the Impedance of the speakers (Z) and how they're wired together, or as this is often called, the "final load" on the amplifier. In addition there is the efficiency of the amplifier which takes additional current due to losses attributed to heat and design efficiency, but for now, we'll just talk about Impedances, Every time you halve the load (Z) on the amplifier, you double the current required (I) and double the power output (theoretically.. in reality it's a bit less than double.) While this sounds great, getting more power, it comes at a price. Every time you get closer to the edge of teh amplifier's operating range, you lose the reserve power (headroom) the amplifier has for momentary peak demands, as well as increasing distortion levels, and reducing the signal to noise ratio. In addition to all of that, when dealing with subwoofers, you also decrease the damping factor of teh amplifier by reducing the load to gain more power. What this means to you is, while you get more power from an amplifier by running lower loads, you give up some sound quality to get that power. All of the above is also why, when quoting an amplifier's power output, you should always note the power at RMS values, not peak. You should also always mention the impedance at which the amplifier puts out the stated power. Some amplifiers are "100 watts" when at 4 ohms, but running the same amp at .5 ohms, it's now an "800 watt" amplifier. Which one it is to you, will entirely depend on the Impedance of the speakers you're using, and how you wire them. For more information on series and parallel wiring of speakers to get various loads, see www.bcae1.com |
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Silver Member Username: FfxdevilarmsDubuque, Iowa United States Post Number: 763 Registered: Jul-04 | Plus its what people say when the meditate. lol. |
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Gold Member Username: GlasswolfWisteria, Lane USA Post Number: 8847 Registered: Dec-03 | or the first syllable of Ohmygawd! |
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Silver Member Username: 54danny54Post Number: 821 Registered: Nov-04 | lol ha ha |