If we use the single voice coil subwoofer, the amplifier will not make full power in the 4 ohm load. We have a small car and want to use a single 12 inch subwoofer in a large vented enclosure to get maximum low-frequency output. To complete this fictional example, we have an amplifier that will produce 400 watts into a 4 ohm load and 700 watts into a 2 ohm load. The dual voice coil subwoofer can have its coils wired in series to produce an 8 ohm load, or in parallel to produce a 2 ohm load. The other subwoofer has dual 4 ohm voice coils. One subwoofer has a single 4 ohm voice coil. We have the option of two different fictional subwoofers, each rated for 750 watts of continuous power handling. You want to choose a combination of subwoofers that will let you wire the voice coils together to an impedance that will allow the amp to make the power you want. What About These Subs?ĭeciding which subwoofers to buy depends on the amp you are using and the number of subwoofers you are going to use. In most cases, unless the voltage of the power supply in the amplifier is adjustable, amplifiers will make more power as the load impedance decreases. If you look at the specifications for an amplifier, especially a subwoofer amplifier, you will see power ratings at different load impedances. If we change the impedance of the load to 2 ohms, we double the current to 10 amps, for a resulting power level of 200 watts. Using the equation P (Power) = Voltage x Current, we get 20 x 5, or 100 watts of power. Ohm’s law states that a potential of 20 volts applied across a resistance of 4 ohms will result in 5 amp of current to flow. With 20 V applied to our voice coil, let’s say we have a 4 ohm impedance on this coil. We don’t need to worry about the fact that this is an alternating current signal – we will examine this at a single point in time. (OK, maybe this didn’t stay as simple as originally planned.)Īmplifier Load Determines Amplifier Power Ohm’s Law Pie ChartLet’s use an example of an amplifier that has a peak output voltage of 20 V. This current flow causes a magnetic field and, subsequently, the voice coil moves toward or away from the magnetic field created by the stationary magnet on the speaker. This low impedance, combined with the increased voltage of the audio signal in the amplifier, causes relatively large amounts of current to flow through the voice coil of the speaker. In car audio, we typically see loads between 1 and 4 ohms. You may (logically) be asking yourself, “Why do we call it a power amplifier?” We get an increase in power because the speakers we connect to the outputs of the amplifier have a low impedance. How an Amplifier WorksĪn amplifier is a simple device that takes an audio signal (from your radio, for example) and increases the voltage.
Understanding the differences between them requires a slightly enhanced understanding of how an amplifier works. When it comes to buying subwoofers, a lot of people have questions or make assumptions about the benefits and drawbacks of single voice coil and dual voice coil versions.