AutoTips Speaker Wiring Tips
Connecting some speakers in your car? Here are some basics: Speakers place a load on your car stereo. An impedance rating (measured in Ohms) is a measure of the resistance of the speaker to electricity. A lower impedance will allow more current (and power) to flow into the speaker. Amplifiers are rated as to the lowest impedance they can handle. You might see speakers rated at 8 ohms or 4 ohms, and your stereo may be rated to drive 8 ohm or 4 ohm speakers. Note this is not the same as a power rating. You can use a higher impedance speaker than the amplifier calls for.
Q: My car stereo amplifier says it can drive 4 ohm speakers, can I use 8 ohm or 16 ohm speakers?
A: Yes, as long as the total impedance to the amplifier is not less than 4 ohms (See below for multiple speakers)
Q: My speakers do not have an impedance rating. How can I tell what they are?
A: You can use an ohm meter or multi-meter (available at Radio Shack or other stores) to measure the resistance. The impedance is a more complex measurement than resistance, but for practicle purposes, the resistance measurements of a speaker should be close enough for the purposes of this article. Connect an ohm-meter to the speaker terminals, and read the number.
Click here for sketch of speaker wiring. If the speakers are wired in series, the impedances will add. If they are wired in parallel, the total impedance will be less than for one alone. The formula for resistances in parallel is:
Total Resistance = 1/ ( (1/R1) + (1/R2))
As an example if we had a pair of 8 ohm speakers, the resistance in parallel would be: 1/( (1/8) + (1/8)) = 4 ohms You could wire a pair of 8 ohm speakers in parallel, if your amplifier was rated good for 4 ohms. If it were rated for 8 ohms, your only choice if you wanted to connect the speakers together would be to wire them in series. Then the total resistance would be 8 + 8 = 16 ohms, which should not be any problem.
Also be sure the power output of the amplifier does not exceed the power rating of the speakers.
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