How to Tell Whether I Need 5-Ohm Speakers in My Car
Car stereos come in many different types. Depending on the output of your car stereo, the total input allowance of your speakers needs to add up to the output of the stereo. This interplay of input and output is a resistance to current called impedance. The unit of measurement for impedance is the ohm, and its distribution depends on the wiring. The total number of ohms the speakers can handle must equal the total number of ohms the stereo gives off.
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Instructions
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1
Take the stereo out of the car. Unscrew each of the radio's four attachment screws from the dash with a Phillips screwdriver. Slowly loosen the radio from the dash and gently pry it out, taking care not to disconnect the wires.
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2
Turn on the multimeter, and turn the selector dial to the "Volts DC" setting. Zero out, or "Reset," the multimeter.
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3
Check the stereo's impedance. Find the wiring terminals on the back of the stereo. Connect the red (positive) clip of the multimeter to the positive port on the stereo. Connect the black (negative) clip of the multimeter to a neutral piece of metal on the dash.
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4
Check each speaker's impedance. Connect the positive clip of the multimeter to the positive port of the speaker. Connect the negative clip in the same manner. Write down the reading as given by the digital or needle readout on the multimeter.
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5
Check the wiring. In series wiring, the wire goes from the positive port of the stereo to the positive port on the first speaker and continues from positive port to negative port from speaker to speaker. From the last speaker, the wire goes from the negative port on the speaker back to the negative port on the stereo. In parallel wiring, the wire goes from the positive port on the stereo and connects all of the positive speaker ports one after another. A wire links the negative ports in the same manner; the wiring never attaches a positive port to a negative port.
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6
Calculate the impedance distribution. If the speakers are wired in a series, the total impedance of the speakers must match up with the impedance of the stereo; with an 8-ohm stereo, you either need two 4-ohm or four 2-ohm speakers. For parallel wiring, calculate the impedance by dividing the impedance of one speaker by the number of speakers. Therefore, with an 8-ohm stereo, you need two 16-ohm speakers. For parallel wired speakers with different impedance, calculate the impedance of one speaker by using the inverse impedance (one/the impedance) and adding up the ohms of all the speakers.
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Check to ensure the total number of ohms the speakers can handle matches up with the total number of ohms given off by the stereo.
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Tips & Warnings
Unhook the battery before working on the radio.
Do not try to hook up the speakers without first calculating the impedance; you can blow the amp on your car stereo.
References
- Photo Credit autoradio 2 image by Nathalie P from Fotolia.com
