How to Wire a 4 Channel Amp to 4 speakers and a Sub

One of the most common questions we get is “How do I wire my amplifier?” or “I have 4 speakers and a subwoofer, what do I need to wire?” While there are multiple ways to wire your amp, this is an article about how to properly connect 4 speakers and a subwoofer.

How to wire a 4 channel amp to 4 speakers and a sub is one of the most confusing topics in-car audio today. Thankfully, installing an amplifier in your car contains many more questions than you will find when connecting your speakers to the amp.

There are some general guidelines that are common across the board but it is best to consult with professionals for further instruction or ask on our forums at Caraudioplace.com.

Minimum Impedance (Ohms) Rating

mage showing a typical 4 channel amplifier’s minimum speaker load (Ohms) rating. Most car amps today have a minimum of 2 ohms per channel in standard (stereo) use and 4 ohms minimum when bridged. Never run an amplifier with a speaker load that’s lower than the rating! Your amp will run hot and possibly become damaged.

Today’s 4 channel (and other) car amplifiers have a minimum speaker load they can handle. The speaker impedance or “Ohms” rating of a speaker (also called the speaker load) is the resistance to the flow of electrical current that the amplifier sees at the speaker terminals.

Speaker Loads

Speakers are usually connected to subwoofer in series or parallel (well, really, most often in parallel) which affects the total resistance an amp will see. That’s important because amps are designed for a certain minimum speaker load (Ohms rating).

As I mentioned above, most car amps today can handle a 2-ohm load per stereo channel (left & right channels) and 4 ohms minimum when bridged to drive an amplifier (called “mono”).

The real answer, however, is that it depends on your amp’s ratings. Always be sure to check to be sure. To keep it simple, I’ll summarize what will work for almost all systems & amplifiers you’ll come across.

Wiring

In this post I’ll cover 3 types of systems that should cover almost all amps you’ll find:

  1. 4 channel amps with a minimum speaker load of 2 ohms in stereo, 4 ohms bridged (for the subwoofer)
  2. 4 channel amps with a minimum speaker load of 2 ohms in either stereo or bridged
  3. 4 channel amps with a minimum speaker load of 4 ohms

#3 is less common but it’s one you’ll run across. Maybe you’ve got an older amp that’s been sitting around unused. If so, you’ll be glad to know there’s a work-around that I’ve come up with that will let you wire your 4 speakers up without damaging your amp.

Testing with a Multimeter

Shown: An example of how to measure speaker impedance (Ohms) with a multimeter. It’s a great way to know for 100% sure what kind of speakers you’re dealing with to avoid problems with your 4 channel amp.

Car stereo and home speaker speakers are very similar except for the impedance rating they use. A speaker’s impedance value, measured in Ohms, is just the total measurement of electrical resistance the amp will see from the speaker’s voice coil.

Partly due to tradition in the electronics world and partly due to various other electrical reasons car stereos are commonly rated at 4 ohms and home stereo speakers around 8 ohms.

The good thing is that all you really need to know is roughly what the resistance of a speaker is. If you can measure that you can tell what Ohms rating to go by!

Measuring Speaker Ohms

To measure the Ohms (resistance) of a speaker’s voice coil, hold the meter probes to the speaker terminals, making sure to keep firm contact to bare metal Paint, insulation, dirt, and solder flux can mess up your reading otherwise.

For example, we usually have a label on a speaker telling us if it’s 2 ohms or 4 ohms and so forth. However, as crazy as it sounds, some speakers don’t!

Things like the following can cause problems (I have seen this happen many times!):

  • Leftover solder flux or solder coating from manufacturing
  • Heavy oxidation
  • Heavy dirt, dusty, or other contaminants that build up over time
  • Paint or other coatings that don’t conduct electricity

If in doubt, you can rub them gently with a bit of sandpaper or even scratch the meter probes against the terminals to make better electrical contact.

Speakers don’t measure exactly 4 or 8 ohms!

Car and home speakers are rated by their general Ohms (impedance) rating. For example, 2, 4, and 8-ohm speakers are never measured exactly with those Ohm measurements.

That’s because each speaker’s design is a bit different from the next. The resistance you measure from a speaker is due to the voice coil’s resistance thanks to the long wire it’s made of.

Conclusion

A 4 channel amplifier is split into two different connections, the “front” and the “rear” channels. The front channels are responsible for amplifying sound coming from the left and right of your vehicle. The rear channels are responsible for the amplification of sound coming from behind you. A subwoofer will not have its own designated channel but will be wired to either of your front or rear speakers depending on placement.

FAQ:

Q: How many speakers do I need for a 4 channel amp?

A: System 1: 2 speakers (parallel wiring) to each front channel = 2 Ohms x 2 + 1 subwoofer wired for 4 Ohms on the rear channels bridged for more power. This is the first and best choice for most modern 4 channel amps.

Q: What is the difference between a 2 channel and 4 channel amp?

A: Whereas a 2 channel amp can only support either two speakers or one subwoofer with the amp in “bridge” mode, a 4 channel amp supports either four speakers or two speakers and a subwoofer. Do You Need Two RCA Cables For A 4 Channel Amp?

Q: How do you wire a 2 ohm amp for 2 speakers?

A: System 2: 2 speakers in parallel to each front channel = 2 Ohms x 2 + 1 subwoofer wired for 4 or 2 Ohms on the rear channels bridged for more power. 4 channel amps that handle 2 ohms bridged are less common but they are out there.

Q: How to wire a subwoofer to a car AMP?

A: Once this is done, you can wire the subwoofer to the rear channels by connecting the negative end to the amp’s right terminal and the positive end to the amp’s left terminal. In system 2, the same wiring that is done in system 1 is done. You should make the connections by connecting the speakers in parallel combinations.