How To Wire a 4 Channel Amp To 6 Speakers
By Robert Jones · 2020-08-17
You can wire a 4 channel amp to 6 speakers in many
Right, so you've got a 4-channel amplifier and you're scratching your head, wondering how on earth you're going to get six speakers hooked up to it. Happens to the best of us. Many moons ago, I remember a mate of mine, Geoff – lovely bloke, always tinkering with his old Ford Cortina – tried something similar. Ended up blowing a fuse and smelling a bit of burning plastic. Not ideal. But don't fret, it is absolutely doable, you just need to know how to set about it. We're going to talk about doing this safely and effectively. ### Why Four Channels for Six Speakers? It might seem a bit counter-intuitive, doesn't it? Four inputs, six outputs. But quite often, you'll find yourself in this situation. Maybe you've got a decent 4-channel amp already, and you've just picked up a couple of extra speakers for the rear doors or the parcel shelf, or perhaps you're building out a more immersive soundstage. Whatever the reason, you're trying to make do with what you've got, and that's smart. Buying a new amp entirely just for two extra speakers can be a daft waste of money if you don't have to. ### The Basics: Understanding Impedance and Power Before we get stuck into the wiring itself, we need to quickly touch on impedance and power. These are key. Think of impedance (measured in Ohms, Ω) like resistance to the flow of electricity. Most car speakers are 4 Ohms. Your amplifier is designed to work with a certain range of impedance. If you wire speakers incorrectly, you could present too low an impedance to the amp, making it work too hard, overheat, and eventually pack up. Trust me, I've seen it happen more times than I care to mention. Power (measured in Watts) is also important. Each speaker has a certain power handling capability, and your amp has a certain power output. You want to match these up as best you can. Overpowering a speaker can blow it, and underpowering it can lead to distortion, which actually sounds worse than it sounds. I’ve gone through countless speakers in my early days by being a bit too ambitious with the volume knob and not paying attention to these things. ### Wiring Configurations: Series vs. Parallel There are two main ways to wire multiple speakers: series and parallel. Understanding these is key to getting this job done right. * **Series Wiring**: This is where you connect the positive terminal of one speaker to the negative terminal of the next. It adds up the impedance. So, two 4-Ohm speakers in series become 8 Ohms. Good for increasing impedance, which can be useful if your amp can't handle low loads. * **Parallel Wiring**: Here, you connect all the positive terminals together and all the negative terminals together. This halves the impedance. So, two 4-Ohm speakers in parallel become 2 Ohms. This is where you need to be careful, as going too low can damage your amp. ### The Challenge: How to Get Six from Four The trick here is to pair up speakers on certain channels to manage the impedance. You'll essentially be running two speakers off a single amplifier channel. This means you'll be doing a bit of parallel wiring, so pay close attention to the impedance. Most car amplifiers are stable down to 2 Ohms per channel. If you go lower than that, you're asking for trouble. ### Method 1: Connecting Two Speakers in Parallel to Two Channels (Then Two More Pairs) This is probably the most common and safest way to do it. You turn your six speakers into three pairs. Each pair then connects to a single channel on your amplifier. 1. **Identify Your Speakers:** Let's say you have six 4-Ohm speakers. You want to end up with a combined impedance that your amp can happily drive. 2. **Pair Them Up:** Take two of your 4-Ohm speakers. Wire them in parallel. Connect the positive terminals of both speakers together, and connect the negative terminals of both speakers together. * *Result:* Two 4-Ohm speakers wired in parallel will give you a combined impedance of 2 Ohms (4 Ohms / 2 speakers = 2 Ohms). Most 4-channel amps can handle 2 Ohms per channel, but **always check your amplifier's manual** to be absolutely sure. If it can't, you'll have issues. 3. **Repeat for Remaining Speakers:** Do this same parallel wiring for the next two speakers to create your second pair, and then again for the last two to create your third pair. Now you have three pairs, each presenting a 2-Ohm load. 4. **Connect to Amplifier:** Now you have three 2-Ohm pairs. What do you do? Well, your 4-channel amp has four channels. This means you can connect one pair to channel 1, one pair to channel 2, and one pair to channel 3. * *What about channel 4?* You'll have one channel left over. You can either leave it unused, or you could, for instance, connect a small subwoofer to it if your amp is stable for that. Or, if you wanted true stereo separation for all six speakers, you'd need a 6-channel amp or an additional 2-channel amp. **Pros:** * Relatively straightforward. * Good power distribution if your amp is 2-Ohm stable. * Maintains stereo imaging for the paired channels. **Cons:** * Requires your amp to be 2-Ohm stable. * Leaves one channel unused on the amp, or requires compromises. * Not true individual speaker control for all six. ### Method 2: Running Front/Rear in Parallel, Leaving a Single Speaker for the Other Two Channels This method is a bit more of a compromise and can be a bit trickier to balance, but it's an option if you want to power two "front" pairs and then have individual speakers for "rear" or "fill" on their own channels. 1. **Front Pair (Channel 1&2):** Take two 4-Ohm speakers (say, your front-door speakers) and wire them in parallel to Channel 1. This gives you 2 Ohms. Take another two 4-Ohm speakers (perhaps rear-door) and wire them in parallel to Channel 2. Another 2 Ohms. 2. **Individual Speakers (Channel 3&4):** Now you have two remaining 4-Ohm speakers. Connect one of these directly to Channel 3 and the other directly to Channel 4. This will give you 4 Ohms on those channels. This setup means you have two channels seeing a 2-Ohm load and two channels seeing a 4-Ohm load. Your amplifier needs to be able to handle both. It also means the speakers on channels 3 and 4 will likely be quite a bit louder than the paired speakers if the amplifier's gain for each channel isn't carefully adjusted. You'd need to balance the levels carefully with the gain controls on the amp itself. **Pros:** * Uses all four channels of the amp. * Some flexibility in speaker placement. **Cons:** * Requires careful gain matching to balance speaker levels. * Potential for inconsistent sound levels without proper tuning. * Still not individual control for all six speakers. ### Important Considerations and My Advice * **Check Your Amplifier Manual:** I can't stress this enough. Every amp is different. Some might be 2-Ohm stable, others might only be happy at 4 Ohms. Pushing an amp beyond its limits is a quick way to buy a new one. * **Speaker Polarity:** Always, always, always connect positive to positive and negative to negative within your parallel wiring. Incorrect polarity will cause the speakers to be out of phase, making the sound thin and weak, and cancelling out bass frequencies. It'll sound truly awful, trust me. * **Wire Gauge:** Don't skimp on your speaker wire. Use a decent gauge, especially for longer runs and higher power applications. I usually recommend at least 16 gauge for most car audio setups, sometimes thicker if you're pushing some serious wattage or have really long cable runs. Anything too thin will restrict current and lose power, affecting your sound. * **Gain Matching:** Once everything's wired up, you'll need to set your amplifier's gain properly. This isn't a volume control; it's about matching the output of your head unit to the input sensitivity of your amplifier. Do it wrong, and you'll either have distortion or not enough power. There are plenty of guides online, but the basic idea is to turn your head unit up to about 75% of max volume, then slowly raise the amp gain until you hear distortion, then back it off just a touch. * **Listen to Your System:** After you've wired everything, play some music you know well. Listen for any strange noises, distortion, or channels that are significantly louder or quieter than others. If something sounds off, go back and double-check your wiring. * **Fuses and Protection:** Make sure your amplifier has the correct fuse in place. If something does go wrong, you want that fuse to blow, not your amp. Honestly, for most folks, Method 1 is the way to go, especially if your amplifier manual confirms 2-Ohm stability. It's simpler, more predictable, and less likely to give you headaches with sound balancing. I've wired up countless setups using variations of this method over the years, from my own classic car projects to helping out mates with their vans, and it generally just works. If you're really stuck, or if your amplifier isn't 2-Ohm stable, it might be worth considering a dedicated 6-channel amplifier or even adding a small, separate 2-channel amp for those extra speakers. Sometimes trying to make one amp do too much ends up costing more in the long run if you damage equipment. ### FAQ **Q: Will wiring six speakers to a 4-channel amp reduce the overall volume?** A: Not necessarily. If wired correctly (like in parallel, as discussed), the impedance load on the amplifier can actually increase the power delivered *per channel*, potentially making the speakers louder. However, each individual speaker might get less power than if it were the only speaker on that channel. It's about how the power is shared. **Q: Can I mix speaker sizes or brands when wiring them in parallel?** A: You can, but it's generally not recommended for optimal sound quality. Different speakers will have different sensitivities and tonal characteristics. If you mix and match too much, you might get an uneven soundstage. Try to keep pairs of speakers (e.g., your front pair, your rear pair) consistent. **Q: My amplifier gets hot after wiring six speakers. Is this normal?** A: A little warmth is normal, but if your amplifier is getting excessively hot to the touch or going into 'protect mode' and shutting off, it's a big red flag. This almost certainly means you've presented too low an impedance load to it. Double-check your wiring and your amplifier's minimum impedance rating immediately. Continuing to run it hot like that will kill the amp.