How to Use 4-OHM Speakers in an 8-OHM Powered Sub

Woofer

8-Ohm-powered subs have amplifiers designed to work best with 8-Ohm speaker impedances, but in a pinch, you can get away with using 4-Ohm speakers. Any time you alter the design of a speaker box by using a driver in place of the one it was designed for, the results are acoustically and electrically unpredictable. You can use your sub's amplifier in a new cabinet built for your new speaker configuration. The trick is to end up with a total speaker impedance your sub amp can tolerate, without overheating.

Things You'll Need

• 18-gauge speaker wire
• Crimp-on speaker terminal connectors
• Wire cutters
• Wire strippers
• Connector crimper
• 18-gauge wire nuts

Instructions

8-Ohm sub with single 4-Ohm speaker

1. Connect existing woofer's wires to the new woofer, changing the connectors to ones that fit the new woofer, if needed. Observe (+ -) polarity.

2. Mount and seal the new woofer in the cabinet and test with music.

3. If the amplifier's heat sinks get hot after about 15 minutes, replace the woofer with a new or rebuilt 8-Ohm woofer to prevent amplifier damage.

8-Ohm sub with two 4-Ohm speakers

1. Wire the speakers in series as follows: cut the connectors off the existing speaker wire coming from the sub amp.

2. Cut a length of new speaker wire to reach from one speaker's terminals to the other, split the pair in two and strip 1/4-inch pieces of insulation off each wire end.

3. Using the appropriate sizes and types of connectors, attach the positive wire from the sub amp to the first speaker, and the positive (copper) lead of the new speaker wire to the negative terminal of the first speaker.

4. Connect the positive speaker wire lead from the first speaker wire's negative terminal to the positive terminal of the second speaker.

5. Connect the negative speaker wire lead to the negative terminal of the second speaker, and use a wire nut to connect the remaining end of that wire to the sub amp's negative return wire. Mount and seal both speakers, then test with music.

Tips & Warnings

• To change wire terminations, cut wire to remove old connectors, strip 1/4-inch of insulation, crimp on new connectors to fit the new speaker's terminals.

• If the new speakers have screw terminals, cut and strip the ends of the existing wire, insert and tighten down on the stripped ends.

• Two 4-Ohm speakers wired in series present a safe 8-Ohm load to the amplifier.

• Provided the sub amplifier does not overheat, a 4-Ohm speaker may be more efficient and play louder, since at lower impedance more current is transferred from the amplifier.

References

• Audioholics: "Loudspeaker Impedance, Series & Parallel Connection Basics"
• Basic Car Audio Electronics: "Series Connection"
• Shavano Music: "Basics of wiring Speakers: Loading, Phase and other tips"