How To Hook Up Subwoofer To Stock Radio

So, you're looking to add some serious thump to your ride by installing a subwoofer, but you want to keep that factory head unit? Excellent choice! It's a common upgrade and definitely doable. While aftermarket head units often simplify the process, integrating a sub with your stock radio requires a bit more planning and finesse. This guide will walk you through the different methods, potential challenges, and everything you need to know to get that bass booming without butchering your dashboard.

Understanding the Challenge: No RCA Outputs

The biggest hurdle when hooking up a subwoofer to a stock radio is usually the absence of RCA (Radio Corporation of America) outputs. These are the standard connectors (typically red and white) found on aftermarket head units specifically designed to send a low-level audio signal to an amplifier. Stock radios, on the other hand, generally only output amplified signals designed to drive speakers directly.

This means we need a way to convert the amplified speaker signal into a low-level signal that an amplifier can use. This is where a crucial piece of equipment comes into play: a Line Output Converter (LOC).

Method 1: Line Output Converter (LOC) – The Most Common Approach

What is a Line Output Converter (LOC)?

A Line Output Converter, as its name suggests, converts a high-level (speaker) signal into a low-level (RCA) signal suitable for an amplifier. Think of it as a translator between your stock radio and your subwoofer amplifier.

How to Choose the Right LOC:

LOCs come in varying qualities and feature sets. Here's what to look for:

Number of Channels: Choose an LOC with the appropriate number of channels for your subwoofer setup. For a single subwoofer, a 2-channel LOC is usually sufficient (one channel for each voice coil on the sub, if dual voice coil).
Adjustable Gain: An adjustable gain allows you to fine-tune the signal strength being sent to the amplifier. This is crucial for matching the output of your stock radio to the input sensitivity of your amplifier and avoiding clipping (distortion).
Quality: A higher-quality LOC will typically offer better signal clarity and less noise. While budget-friendly options exist, investing in a decent LOC can significantly improve your sound quality. Brands like AudioControl, PAC, and NVX are generally well-regarded.
Remote Turn-On: Some LOCs feature a remote turn-on wire. This wire senses when the stock radio is powered on and sends a 12V signal to your amplifier, turning it on as well. This eliminates the need to find a separate switched power source. If your LOC doesn't have this, you'll need to find an alternate solution, which we'll discuss later.

Wiring the LOC: Step-by-Step

Identify Speaker Wires: This is arguably the most important step. You need to tap into the speaker wires coming from your stock radio. You can usually find wiring diagrams online for your specific vehicle model. Look for resources like Crutchfield's vehicle database or online car audio forums. The diagrams will tell you the color code of each speaker wire (left front +, left front -, right rear +, right rear -, etc.).
Choose Speaker Location: Decide which speaker wires you'll tap into. Rear speakers are often preferred, as they generally carry a full range signal (including bass frequencies). Tapping into front speakers might require a more sophisticated LOC that can sum multiple channels to create a full-range signal.
Connect the LOC: Use wire strippers and connectors (crimp connectors or soldering are both good options) to connect the speaker wires to the corresponding input wires on the LOC. Pay close attention to polarity (+ and -). Getting this wrong can result in phase cancellation and reduced bass response.
Run RCA Cables: Connect RCA cables from the output of the LOC to the input of your subwoofer amplifier.
Ground the LOC: Connect the ground wire of the LOC to a solid chassis ground in your vehicle. Ensure the ground connection is clean and secure.

Finding a Remote Turn-On Signal (If Needed):

If your LOC doesn't have a remote turn-on wire, you'll need to find a separate 12V switched power source in your vehicle. This is a circuit that only receives power when the ignition is turned on. Common sources include:

Accessory Power: Often found in the fuse box and labeled "ACC" or "Accessory."
Cigarette Lighter: The power wire to the cigarette lighter socket.

Use a multimeter to verify that the circuit you choose only receives power when the ignition is on. Connect a wire from this circuit to the remote turn-on terminal on your amplifier.

Method 2: Amplifiers with High-Level Inputs

Some subwoofer amplifiers have high-level inputs, also known as speaker-level inputs. These inputs are designed to accept the amplified speaker signal directly from your stock radio, eliminating the need for a separate LOC. While seemingly simpler, this method still requires careful consideration.

Advantages and Disadvantages:

Advantage: Fewer components (no LOC needed).
Disadvantage: Not all amplifiers have high-level inputs. The quality of the high-level input circuitry can vary significantly, impacting sound quality. Some cheaper amplifiers might introduce noise or distortion.

Wiring with High-Level Inputs:

Identify Speaker Wires: Same as with the LOC method, you need to identify the speaker wires coming from your stock radio.
Connect Speaker Wires to Amplifier: Connect the speaker wires directly to the high-level inputs on your amplifier. Again, pay close attention to polarity (+ and -).
Remote Turn-On: You'll likely still need a remote turn-on signal for the amplifier. Many amplifiers with high-level inputs have an auto-sense turn-on feature. This feature detects the audio signal on the speaker wires and automatically turns on the amplifier. However, this feature can be unreliable in some vehicles, so a dedicated remote turn-on wire is often preferred.
Ground the Amplifier: Ensure the amplifier is properly grounded to a solid chassis ground.

Important Considerations and Troubleshooting:

Grounding:

A poor ground is the bane of car audio installations. Ensure your LOC, amplifier, and head unit (if applicable) all have solid, clean grounds. Scrape away paint and corrosion from the grounding point and use a star washer to ensure a good connection.

Gain Staging:

Proper gain staging is crucial for optimal sound quality and preventing distortion. Start with the gain on your amplifier turned all the way down. Slowly increase the gain until you reach the desired volume level without introducing distortion. Listen carefully for clipping (a harsh, crackling sound). If you hear clipping, reduce the gain. It's better to have the gain too low than too high.

Noise:

If you hear engine noise or alternator whine in your subwoofer, it's likely a grounding issue or a problem with the RCA cables. Try rerouting the RCA cables away from power wires and ensuring all ground connections are clean and secure. A ground loop isolator can sometimes help, but it's usually better to address the root cause of the noise.

Factory Amplifier Integration:

If your vehicle has a factory amplifier, the process becomes more complex. You'll need to identify the output wires from the factory amplifier that feed the speakers. Tapping into the speaker wires before the factory amplifier will likely result in a weak signal and poor performance. Consult a wiring diagram specific to your vehicle's audio system to identify the correct wires.

DSP Integration:

Some newer vehicles have complex digital signal processing (DSP) systems integrated into the factory head unit. These systems can apply equalization and other processing that can negatively impact subwoofer performance. In these cases, a more sophisticated LOC or DSP interface might be required to bypass the factory processing and obtain a clean, full-range signal.

Safety First:

Always disconnect the negative terminal of your car battery before working on any electrical components in your vehicle. This will prevent accidental shorts and electrical damage.

Conclusion

Adding a subwoofer to your stock radio takes a little more effort than with an aftermarket unit, but it's certainly achievable. By understanding the principles of signal conversion, choosing the right equipment, and paying attention to details like grounding and gain staging, you can enjoy powerful, clean bass without sacrificing the functionality of your factory head unit. Remember to consult your vehicle's wiring diagram and take your time to ensure a proper installation. Happy listening!