8 Steps to Connect a Subwoofer to the Rear Speakers

Ensure That You Have These Things:

Before we dig further, you just need to make sure that you have the following items:

• External amp
• Subwoofer
• Amplifier wiring kit
• Screws
• Torch
• Connectors
• Soldering gun
• Speaker wire cutter

8 Easy Steps to Connect a Subwoofer to Rear Speakers:

Now that you have everything you need to make a successful connection. Follow these simple steps:

1. Find a Suitable Place for Your Car Subwoofer:

First and foremost, you need to find a suitable placement for your subwoofer box. I suggest you place it in the trunk or the back seat area so that your subwoofer is close to the rear speakers. For a vehicle with a hatchback, you can mount your subwoofer behind one of the back seats for a more discreet installation.

But if you can’t afford to put it in the trunk, you can choose under the seat spot. If you are still confused about finding the best place for your subwoofer in the car, you can read our guide. When you decide where to install your car subwoofer, ensure it is securely mounted and that the mounting surface is flat and level.

Such a placement will help keep the vibrations from the subwoofer to a minimum and ensure that the sound produced is accurately reproduced. Additionally, provide enough space around the subwoofer for air to move freely. This will help to eliminate any distortion caused by the subwoofer’s vibrations. If you place it close to the objects, it can cause them to vibrate, making a distorted sound as a result.

2. Turn off the Car Ignition:

Many beginners make the mistake of not turning off the car before connecting the subwoofer. Whether you are just making changes to your audio system or any other car electrical components, it is best to turn off your car ignition and remove the power terminals from the battery. Removing the terminals will ensure that you prevent any damage to your rear speakers or subwoofer.

3. Connect an External Amp to the Car’s Battery:

When wiring an amplifier, it is necessary to use a fuse on the wire between the battery and the amplifier. This will help protect both the amplifier and the battery if there is an electrical surge. Ensure you use a fuse near the battery area in the car’s bonnet. To properly connect a fuse to the power cable, here’s what you need to do:

1. Cut a length of wire that is long enough to reach from the battery terminal to the amplifier.
2. Strip off about 3/4 inch of insulation from each end of the wire.
3. Connect one end of the wire to the battery’s positive (+) terminal and the other to an appropriately sized fuse holder.
4. Place the appropriate fuse size into the fuse holder and ensure it’s securely in place.
5. Connect the other end of the wire to the amplifier’s positive (+) terminal and ensure all connections are secure and tight, with no exposed speaker wires or metal parts.

3.1 Pass the Wire Through Beneath the Car’s Carpet:

Now that we have prepared all the necessary things for the amp and battery connection. It’s time to take the power wire from the battery to the car’s rear part ⁽¹⁾, where you have placed the amplifier and subwoofer.

You can use the torch light to see under the dashboard to look for any holes that you can use to insert the wire from the battery area to the inside of the car. Now follow the simple steps:

1. First, use the flathead screwdriver to carefully pry up one corner of the carpet in your vehicle. Use only a little force since you want to protect the carpet. Once you lift one corner of the rug, continue using the screwdriver to work around the edges until you can fit a hand underneath the carpet.
2.  Now that access is underneath your car’s carpet. You can begin threading the wire through. Insert one wire end into the opening and slowly pull it through, using your hand to guide it as necessary. Ensure that you follow an appropriate route for the wires so that they don’t interfere with any other components or move too close to any moving parts.

4. Ground the Amp:

Now that everything is in the line. Ensure you ground your amplifier to connect your subwoofer with the rear speakers. Follow these simple steps:

1. Start by connecting the amplifier’s ground wire to a metal part of the car’s chassis or frame. Make sure this contact point is not painted over or covered with plastic or rubber.
2. Once the ground wire is secured, connect the positive lead from the amp to the car battery terminal using an 8-gauge wire (Where you’ve attached your fuse). Make sure the connection is tightened securely.

5. Ensure Remote Turn-on Connection:

In this step, you have to make the remote turn-on connection. This will help you turn the car stereo system on and off with the ignition key. Follow these simple steps:

1. Start by running a single-stranded, shielded wire from the amplifier’s remote terminal to an unused fuse slot in the fuse panel located in the engine bay.
2. Connect one end of the wire to the fuse slot, and secure it with a plastic connector. Once that is done, proceed to the battery terminal, which is also located in the engine bay.
3. Attach one end of a fused power cable to the battery’s positive (+) terminal and then connect the other end of this same cable to an unused fuse slot in the fuse panel.
4. Finally, connect the other end of the single-stranded wire from the amplifier’s remote terminal to this same power cable using a plastic connector.

6. Find the Rear Speakers’ Wiring:

Finally, we are close to connecting the sub and rear speakers. Just follow the simple steps to trace the rear speakers’ wiring:

1. The rear speaker wires may be behind an access panel if your car has a trunk. To locate this panel, carefully examine both sides of the trunk and look for screws, locks, or clips that hold it in place. 
2. If your car does not have a trunk and the rear speakers are in the back seat area, you may need to pull up or remove some of the interior trim to gain access to the wiring. Look for screws, clips, or locks that hold various panels in place, and carefully remove the necessary trim to gain access.

7. Connect the Rear Speaker Wires to Subwoofer:

You can easily tap the audio signal once you have located the rear speaker wiring. Now strip the speaker wires and attach them to the subwoofer. You can use crimp connectors for a safe connection. You can also use the soldering method for a firm connection and to prevent damage.

8. Ensure All Connections Are Properly Made:

Once you have made all the connections, recheck them for stability. Ensure that the speaker cables used in the connection are correctly connected, as loose rear speaker wires can interrupt the audio signal. Additionally, ensure that all speaker cables are securely linked with their respective ports on the subwoofer and speakers.

Turn on the Car Audio System and Test:

At last, you have to ensure that you successfully connected the sub with the rear speakers. You need to turn on your stereo system.

If all connections are properly secured, the sound produced by your system should be clear and crisp. To test the functionality of your setup, play some music with heavy bass and note if there is a difference in sound quality from one speaker to another. If everything sounds good, you’re ready to enjoy your car sound system!

Connect a Subwoofer to the Rear Speakers Without an Amplifier:

You can also connect a subwoofer to the rear speakers without using an external amplifier. However, I will strongly recommend you use an amp because subwoofers require amplifiers to work correctly. Anyway, follow the steps:

1. As told earlier, you must turn off the car ignition and remove the battery terminal before making any changes to your car’s electrical components.
2. Now, connect the subwoofer to the battery to provide it power. You must use a fuse to create a safe connection. Using a compatible fuse can save both the battery and subwoofer.
3. Now, you’ll have to access the rear speakers’ wiring area. For this, remove the speakers from their spot carefully without breaking the speaker wires.
4. Finally, use an adapter to connect the subwoofer to the rear speakers’ wiring. You should use the jack connection to ensure connectivity between the subwoofer and speakers.
5. Now that you have connected the sub with the rear speakers, test the subwoofer to ensure you get the sound output.

You Can Also Use a Line Output Converter to Tap Rear Speakers for Sub – How?

1. Install a line output converter in the rear speaker wires, which connect to an amplifier’s input or a power wire.
2. Connect the two internal subwoofer outputs from the amplifier to each L/R speaker channel on the line output converter.
3. Connect your subwoofer’s RCA cables to one of the L/R outputs on the line output converter.
4. Set the gain and crossover settings on the amp and subwoofer to deliver a balanced sound in the listening area.
5. Turn up the gain of both amps until you hear clear, strong bass from your subwoofer, then reduce it slightly to avoid distortion or clipping.

Connect a Subwoofer to Car Stereo Without an Amp:

However, if you don’t have an amplifier, you can connect the subwoofer to the car stereo without it. Follow these steps:

1. Determine if your car stereo has pre-amp outputs. If it does, you’ll need to purchase an RCA Y adapter cable with one plug at each end and a splitter in the middle.
2. Connect the adapter cable’s two plugs into the two pre-amp output jacks on the stereo’s back.
3. Connect one end of a single RCA patch cable to the splitter in the adapter cable’s middle. 
4. Connect the other end of this same RCA patch cable to your subwoofer’s input jack. It should be labeled “Input” or “Line In”.
5. Connect the other end of this same RCA patch cable to the input jack on your car’s amplifier, if applicable.
6. Turn your car stereo on and adjust the subwoofer’s level, usually through its volume control knob.
7. Make sure that you set the amplifier gain correctly. If there is no amplifier involved, then you are done! Enjoy the improved sound quality of your car stereo system with added bass (low frequencies)!