How To Hook Up A 4 Channel Amp To Front And Rear Speakers

Adding a 4 channel amp is a great idea. I’ve enjoyed powerful, crystal-clear sound in my vehicles for years using my own 4 channel amps.

But how do you hook them up?

In this guide I’ll show you how to hook up a 4 channel amp to front and rear speakers. After installing hundreds of amps in vehicles just like yours I’ll share with you the fundamental tips you need for great results.

And hey – don’t worry…in most cases you can do it yourself and get professional results on a budget!

Infographic – How to hook up a 4 channel amp (tips and general guide)

Hook up amp 4 channel amp front rear speakers infographic diagram

Basics first

If you’re reading this there’s a good chance you’re not familiar with installing an amp, connecting wiring, and other details related to hooking up a 4 channel amp in a vehicle.

Not everyone has installed car stereo equipment before so I’m going to be as thorough as possible and avoid making any assumptions about how much you know.

What is a 4 channel amp?

Holding Alpine MRV-F300 amp in my hand

Today’s 4 channel amps offer newer technology, better sound, and more compact size than in the old days. An excellent example is the Alpine MRV-F300 50W x 4 model. It uses Class D technology to run extremely cool and yet it’s small enough to fit under a car or truck seat. Very nice!

What a 4 channel car amplifier is may seem obvious at first but there’s a bit more to know Additionally, there are some interesting (and good) ways they differ from 2-channel amps.

In fact, there are actually a few benefits you’ll get using one 4 channel amp instead of 2 stereo ones to power your front and rear speakers.

A 4 channel amplifier is a stereo amplifier with 2 more channels built in to boost (amplify) weak input signals to a higher voltage signal. This drives speaker voice coils to move the speaker cone and produce sound.

4 channel amplifiers add more channels into a more compact and efficient design than separate amplifiers would have.

Additionally, they offer more flexibility, as most can be configured for “bridged” operation which can give more power when you don’t need all 4 channels.

What is “bridging” an amp?

Bridged mode capability is a special design feature in which a “push-pull” set up is created: one channel (normally used for the left speaker) produces a signal that’s the opposite of the second channel (normally used for the right speaker).

This causes the speaker to receive a voltage audio waveform that is the difference between the two channels – resulting in more available power to speakers.

Essentially, bridged mode is a flexible way to get more power if you’re not driving 4 speakers. It means 2 channels are sharing the workload of one speaker between them and therefore and drive it with more power.

2 channel vs 4 channel amp diagram

2 channel vs 4 channel amp diagram

A 4 channel car amp is basically an expanded version of a 2-channel amp. However, because they’re built together and not 2 separate 2-channel amps, they’re more compact. This saves installation space and makes it easier too. Additionally, most can be bridged to use 2 channels (or 3, depending on your needs) so you’re not restricted to using them with only 4 speakers.

The benefits of using an amp to drive speakers

Whether you have a factory stereo or a great aftermarket (non-factory) one, adding an amplifier is one of the best decisions you can make.

In-dash stereos are very limited in how much power they can produce. They can’t drive speakers with the same clarity and low distortion as a good amplifier can.

The maximum volume you’ll be able to get from your speakers will be pretty low, too.

There’s simply no way around it – most in-dash stereos are limited to about 15W-18W RMS of power for each speaker channel. That’s because they’re running directly from the +12V supply. Amplifiers are unique in that they take the +12V electrical supply and boost it to a higher voltage.

When a signal is boosted and sent out to your car’s speakers the voltage is much higher and the speaker can receive much more power.

That’s why tiny amplifiers are rarely worth bothering with – if there’s no special power supply inside, it’s simply not capable of producing much power.

Getting great sound

Powering speakers from an amp makes a big difference, and I’ve enjoyed excellent sound for years this way.

When an amplifier drives your vehicle’s speakers it’s often not even pushed to its limits. The sound produced at the speaker has lower distortion, doesn’t “bottom out” when heavy bass is played, and you can get a lot more volume, too!

Additionally, using an amplifier with built-in high-pass crossovers means you can block out lower-end bass that causes your speakers to distort and attempt to play music tones they’re not suited for.

The result is cleaner sound, less distortion, and great volume – you can crank your music even higher!

Just imagine driving down the road with the windows open and finally being able to blast the music you love. I’m confident you’ll love it as much as I do.

Things to know before you start

Clip art image of a face thinking - Things to know content image

It only takes a few minutes to make a list of the parts, wire, tools, and other bits and pieces you’ll need. Planning ahead can mean the difference between getting your system going without major problems or having a frustrating time – or complete failure! I always get organized and get my items together before I start a job.

Planning ahead is very important. You don’t want to run out of wire or discover you don’t have the rights parts, for example. That will mean you can’t finish your project.

It’s even worse when you have to drive around town searching for items or you’re not able to do anything after the stores close. Believe me, I’ve been there, and it’s terrible!

Notes about wire, tools, and a few other things

When it comes to installations, always plan to have more, rather than not enough, wire. This goes for speaker wire as well as RCA cables.

The amplifier kits I recommend have the right length for your amp installation, but speaker wire & RCA cables are another matter in this case.

What length and size speaker wire do I need?

wire of 16 ga speaker wire

There’s no need to spend an excessive amount of money on speaker wire. 18 gauge is enough for many installations, but 16 gauge is a great choice too if the price is right. A great example is this AmazonBasics 100 foot roll. I recommend a 100 foot roll for many installations with a 4 channel amp (see why below).

Here’s an estimate of the worst-case scenario for the length of speaker wire required. I’ll use the example of installing an amp using speaker-level inputs, with the following typical installation:

  • Amp is located in the trunk
  • Speaker level signal connections near the radio (center console)

Let’s use roughly a 15′ length of distance from the radio to the amp. That’s a good estimate in my experience.

So we have:

  • Wire from the radio to amp (signal wire): 4 channels x 15′ = 60 feet
  • Wire from the amp to speaker wiring near radio: 4 channels x 15′ = 60 feet

Total estimated wire required: 120 feet.

That means you need 2 100 ft rolls of wire. Or at the least, 1 100 ft roll and 1 50 ft roll. If you’re planning to use a line-level adapter, expect to pick up a 100′ roll.

If your installation is using RCA jacks, expect a 100 ft roll also (4 channels x 15′ length estimate for the speaker wire from the amp).

What about RCA cables?

KNU Conceptz KCA-K4 4 gauge amp wiring kit RCA cables imageIf you’re installing a 4 channel amplifier and using RCA cable connections, you’ll need to buy a 2nd pair along with your amp wiring kit, as most only include a 2-channel cable.

For most installations, I recommend 18′ length cables. That’s usually long enough for most vehicles and you should usually have enough length to hide the cables inside the interior and under the rear seat, etc.

There’s no reason to spend an excessive amount of money. Just pick up some good quality, well-made cables. Even a pair like these value-priced ones will be fine in most cases.

Tools you’ll need.

Image showing example crimp tool and crimp connectorsCrimp tools are great for installing your amp and speaker wiring with professional results. If you’re doing your own installation, you can get by with an inexpensive tool like this Pros'Kit crimp tool. Crimp connectors are sold separately in many automotive parts stores or general stores and are very affordable.

I recommend a few tools. If you shop carefully, you can avoid getting ripped off on tool prices. When connecting speaker wiring to factory wiring, it’s easier to use crimp connectors than solder.

Never simply twist the wire together and wrap it in electrical tape. Always use a reliable connection.

During warm weather, electrical tape adhesive can fail and the tape can come off of the wire. This exposes it to possible short circuits and potential damage to your radio or amp.

If you have access to a cordless drill, that’s fantastic! They’re great for drilling holes in the vehicle’s metal for mounting your amplifier or connecting the ground wire to bare metal.

I also recommend the following:

  • Wire cutters (some crimp tools have this built-in)
  • Roll of quality electrical tape
  • Wire ties (“zip ties”), 6″ length, bag of 100
  • A digital test meter for voltage measurement

Etekcity MSR-R500 digital test meter example

A test meter is often incredibly helpful when installing an amplifier. However, you don’t need to spend much money! A basic but good budget model like this one at Amazon will work great.

I recommend getting an affordable but good digital test meter to find a switched +12V wire for getting a remote-on signal to the amp.

They’re also extremely helpful when troubleshooting power problems when something isn’t working.

Get your installation shopping list together

Image of a paper checklist being prepared with a marker

Here’s a general but pretty accurate list of what you’ll need for connecting a 4 channel amp to front and rear speakers.

Installation types 1 or 2: Factory radio or no RCA connections

  1. 4 channel amplifier with speaker level inputs or amp and line-level adapter
  2. 120 feet or more speaker wire, 18 gauge or larger
  3. Amp wiring kit
  4. Crimp tool and butt (wire crimp) connectors (25 or more at least)
  5. Cutting pliers
  6. Electrical tape
  7. Wire ties, 6″, bag of 100
  8. Test meter

Installation type 3: RCA connections

  1. 4 channel amplifier with speaker level inputs or amp and line-level adapter
  2. 100 feet roll speaker wire, 18 gauge or larger
  3. Amp wiring kit
  4. Additional RCA cables, 18′ minimum
  5. Crimp tool and butt (wire crimp) connectors (25 or more at least)
  6. Cutting pliers
  7. Electrical tape
  8. Wire ties, 6″, bag of 100
  9. Test meter

Be sure to plan well and estimate the amount of speaker wire you’ll need. For the amp installation itself, I strongly recommend using a pre-made amp wiring kit like you’ll find here in my amp kit buyer’s guide.

You’ll also need to get a 2nd pair of RCA cables. I recommend 18 ft length or more. Don’t spend too much money, but do get decent quality ones.

How to get a signal to your amp

Example of the rear of a car stereo installation closeup

Image of an aftermarket (non-factory) stereo showing the RCA jacks and speaker output wiring. Either one can be used for getting a signal to an amp, but RCA jacks offer a better option. They’re normally lower distortion and allow using plug-in RCA cables. If those aren’t available, either an amp with speaker-level inputs or a line level (speaker level) adapter can be used.

In order to install a 4 channel amp and drive all 4 speakers, in many cases, the biggest obstacle is getting a signal to the amp. Once that’s done, the rest is usually a standard amp installation.

There are 3 basic ways to get a signal to your 4 channel amplifier:

  1. Connect speaker outputs to your amp’s speaker level inputs
  2. Connect a line-level adapter to the radio then use RCA cables to the amp
  3. Connect your radio to the amp using RCA cables directly
NOTE: I won’t be covering factory sound systems that are “premium” and have a factory amplifier. Those such as Bose, JBL, and Mark Levinson, often found in luxury vehicles or special-edition models, are much more complex and harder to deal with.

In that case, my advice is to speak with a good installation shop first and do your research.

If you feel that factory amplified systems should be here as well, send me a message or comment and let me know

In a few cases, adapters are available to connect an amp to a factory amplified system’s audio wiring, but it’s often difficult or there are obstacles you won’t find until you get started.

One of the reasons why is that factory amplified systems often have non-standard wiring connections for the audio path and are prone to bad noise problems if you connect an amplifier without the proper adapter or wiring.

Which type of connection do I need?

If you have a radio with RCA jacks, skip on down to the next section.

However, if you have a stereo with no RCA jacks (which is always the case for factory-installed stereos) you’ll have to buy one of the following:

  • A “line level” converter
  • An amplifier with speaker-level (“high level”) inputs

1. Line level converters

PAC LP7-4 4 channel line level converter

Line-level converters like this PAC LP7-4 4-channel model are designed to take speaker-outputs from a stereo with no RCA jacks and adapt them to RCA jacks. Using this, you can run RCA cables to your amplifier.

Line level converters are designed to allow connecting to an amplifier’s RCA inputs by converting speaker outputs from a stereo to a low-level signal an amp can use.

It’s very important to buy a quality, well-designed line-level adapter to avoid noise, poor sound quality, and other problems. Don’t get the cheapest – instead, get a name brand model you can rely on (like the one above).

2. Speaker level inputs

Car amplifier speaker level input example
Amplifiers with high-level (speaker-level) inputs like this one allow connecting to speaker wiring for a signal source. This avoids having to buy a separate adapter.

Speaker level inputs are common on many 4 channel amplifiers. These amps contain electronics that scale down speaker wiring signals to a lower signal safe for the amplifier’s input circuitry.

They’re simple to connect: normally it’s just a matter of connecting both positive (+) and negative (-) wiring for each speaker channel on a small wiring harness included. This then plugs into the speaker level input connector.

4 channel amp speaker level harness example

A typical speaker-level input harness for a 4 channel amp. The wires are color-coded to make installation easier. White = left front, gray = right front, green = left rear, and purple = right rear.

While it can save money (you won’t need a line-level adapter in this case) I often recommend that people consider buying a line-level converter anyway.

This allows an easier upgrade for your stereo later, which is very common for people to do. Using the line-level converter now will allow you to run RCA cables to your 4 channel amp to be used later if you buy a better stereo (which will include RCA jacks, almost always).

3. RCA jack (line-level) connections

RCA jacks offer a clean, lower-noise connection than speaker-level adapters do, but honestly, it’s not noticeable to the average person. RCA cables (line-level connections) are the preferred way to connect a signal to your amp if you have that option.

RCA jacks on the rear of a Pioneer head unit. This is the ideal way to connect your amplifier’s signal inputs, if available. For a 4 channel amplifier, you’ll need 2 stereo RCA cables to do so. White represents the left channel white red represents the right. These are standard colors for audio outputs for both car and home stereo.

If your stereo has RCA jacks, then congratulations. Things just got a bit easier – and potentially better sounding, too!

You’ll need 2 stereo RCA male-to-male cables (4 audio channels total) to run from the radio to your 4 channel amp. That’s 4 signal channels: left & right front and left & right rear.

4 channel amp signal connection diagram

Here’s a helpful diagram showing the most common connections you’ll need to make one of the 3 most common cases I mentioned earlier:

  1. Connecting to your amp’s speaker level inputs
  2. Using a line-level converter
  3. Connecting your amp to the radio’s RCA jacks

4 channel amp signal connection diagram
You can also click here to view the .pdf document for print or download.

Connecting and running signal wiring

Speaker-level connections

As mentioned above and as shown in the diagrams, if you’re using speaker-level outputs to get a signal from the radio, you’ll need to connect wire. Ideally, you’ll do so near close to the radio, then run the wire together as a bundle.

You can bundle speaker wire together with wire ties to keep it neat and make the installation easier.

Estimate the length of speaker wire you need to reach the amp (or line level converter) for each audio channel. To do so, run a length of wire from the radio to where the amp will be installed, then allow a little extra and enough length to run around curves and interior parts.

Cut 7 more lengths of wire, for a total of 8:

  • 4 channels (4 pairs of wire) going to the amp’s speaker level inputs
  • 4 channels from the amp to the radio’s factory speaker wiring

Image of car stereo wires crimped

I recommend connecting to speaker-level outputs using crimp connectors and a crimp tool for a reliable, solid connection. Blue connectors are normally the right size for 18-16 gauge wire.

Factory stereo color codes

If you have a factory stereo, you’ll need to find the wiring colors for the speaker wiring.

A great resource for that is, where you’ll find wiring diagrams for your vehicle and color codes listed.

Making connections

Image of factory stereo wiring harness

After removing the radio you’ll find connectors like this for the factory stereo wiring harness. You’ll need to separate the speaker wires, cut them, and attach wiring to run to the amp.

Remove the radio and disconnect the factory wiring plugs or aftermarket radio’s wiring harness.

Cut the speaker wires, leaving enough length to move the wire and to have enough length to connect to the wire freely.

Strip a small part on both the stereo’s speaker wire and your amp speaker wiring. If using a line-level adapter, connect to the stereo’s speaker output side. Then connect the 4 pairs of wire to the speaker wiring in the harness.

Insert the stripped wire (about 1/4″ of bare wire) into the connectors and crimp them carefully using a crimp tool if you have one. Alternately, you can twist together wire, solder it, and carefully wrap it with electrical tape or use heat shrink tubing for insulation.

If using speaker level inputs on your amp, also connect 4 pairs of wire to the output of the stereo.

Wire bundle with zip ties example

To make a neater, more professional installation, bundle the speaker wiring similar to this using wire (“zip”) ties. I recommend using 6″ ties which often are sold in packs of 100.

Once all wiring is connected, bundle it up using wire ties or, optionally, a little bit of electrical tape wrapped around. In both cases spacing out wire ties or tape about every 1″ or 1.5″ along the length of the wire works well.

Connecting RCA cables

Example of connecting RCA cables to rear of a car stereo

Connecting RCA cables to an aftermarket (non-original) stereo for running to an amplifier.

If you’re using a line-level converter or have a stereo with RCA jacks, connect all 4 cables plugs to the front and rear outputs.

RCA cables are sometimes marked with left and right symbols (“L” and “R”). In some cases, white, clear, or some lighter color can be used to represent the left channel.

Connect the cables consistently so you’ll be able to recognize which one is which. If the front and rear RCA cables are the same, you might want to mark front and rear using some masking tape and a marker or pen.

Connect the remote-on amp wire

Don’t forget the remote wire! Amp wiring kits include a small wire that’s used to connect the amp so that it switches on and off with the accessory position of the ignition switch.

Locate a +12V wire that has power when the ignition is switched to “ACC” or similar but turns off with the key. You may also have good luck finding an existing wire color from vehicle wiring diagrams I mentioned earlier or from a Google search.

I recommend checking the wiring even if you have already located it online, just to be sure.

Before re-installing the radio connect this wire and run it alongside the speaker wiring.

How to connect a 2 ch. car stereo to a 4 channel amp

Diagram showing a 2 channel car stereo connected to a 4 channel amp

You can connect a head unit car stereo with only 2 channels (left and right) to a 4 channel amp easily. Ordinarily, all you need is 2 RCA Y adapter cables. The head unit’s left channel RCA jack should be connected to the left front and left rear amp inputs. Likewise for the right channel. If using speaker level inputs on the amp, use the connections shown above. NOTE: Use only ONE of the two connections above! Never connect both types at the same time! Speaker-level outputs will damage RCA connections.

If your head unit (car stereo) only has 2 RCA jacks or two pairs of speaker outputs, that’s not a problem.

As shown in the above diagram, you can connect 2 channels to a 4 channel amp using either the speaker level inputs wired in parallel or by using simple RCA adapter cables.

RCA y adapter cable image

All you need is a decent pair (a total of 2) female to male RCA “Y” adapters like these low-cost ones from Amazon.

The sound quality will be exactly the same. Today’s amps are designed in such a way that there’s no harm in using a Y adapter to connect the amp. The amplifier will receive exactly the same signal, with the same quality, in the front channels as well as the rear.

The only drawback is there won’t be a front to rear fader control like with head units with 4 channels of outputs.

After connecting the stereo to the amp, you’ll need to adjust the rear gain to set the volume level for the rear speakers as needed for the proper volume depending on the stereo’s signal strength.

Installing the amp

Product image of Belva BAK82 amp wiring kitAn amp wiring kit like this one will make installing your 4 channel amp much easier. A good-quality one like this Belva 8-gauge complete kit includes not just wiring but much more. You’ll also need to pick up a 2nd pair of RCA cables (if using them) and enough speaker wire.

Your amplifier needs a good solid metal connection to ground and you’ll need to run the positive battery wire to the engine compartment. Your amp wiring kit will also include a fuse holder that should be installed near the battery as well (most kits include instructions, by the way).

You’ll also need to connect the amp’s speaker outputs to the wire you ran from the radio.

As it also applies to 4 channels amps, for the amplifier installation you can follow my guides here:

Here’s a basic diagram as well to help:

How to install a 4 channel amp diagram

Setting up your amp

Alpine MRV-F300 4 channel amp end viewOnce installed, you should set up your amp’s gain levels and crossovers for the best sound. In this image, you can see the adjustable crossovers for both front and rear channels. Turn on the high-pass crossovers and adjust to a setting close to 50-60Hz, to allow good bass for music but block low-end bass that distorts.

Once installed, you’ll need to set up your amp’s gain levels and crossovers, if available. Most sold today have that. (See my recommendations at the end for some great models)

Gain control is the amount of signal amplification the amplifier performs. Ideally, with a good input signal, it can be kept low to reduce any hiss or noise that can appear when it’s turned up high.

Here’s a great rule of thumb for how to adjust the gain for this type of system:

  1. Turn down gain controls on the amp
  2. Turn the stereo’s volume to 2/3 of maximum
  3. Slowly raise the gain controls until the volume is enough

When finished you should have enough volume available from the stereo but noise should be minimal. You’ll still need to tweak it a bit if the volume is too high or too low.

Setting the crossover

As I mentioned at the beginning of this guide, using high-pass crossovers will allow more volume with less distortion and will help protect the speakers from heavy bass.

For both front and rear channels turn on the high-pass feature and, if an adjustable dial is available, set it near 50 to 60Hz. Some models don’t offer an adjustable frequency for the cutoff but are likely preset to a good level.

Test and tweak

Once installed, test and tweak your amplifier as needed. A great way to mount your 4 channel amp is by using a board mounted to the car, covered with speaker box carpet or other material.

Play some music you’re very familiar with and adjust things like bass, treble, and the fader as needed. Using music you’re very familiar with (of high quality) means you’ll be able to notice any problems with the sound fairly easily.

If you don’t already have one, you might consider later upgrading to a head unit with built-in equalizer (EQ) functions to help tailor the sound.

Summary and recommended products

Hopefully you’ve found this post useful. Hooking up a 4 channel amp to your front and rear speakers takes some work and time, but it’s a great way to get sound you’ll love.

Considering buying an amplifier? You can find some great 4 channel amps (including the Alpine MRV-F300 pictured here) in my 4 channel amp buyer’s guide.

You’ll also need a good amp wiring kit – I’ve got a good amp kit buyer’s guide here.

Your comments are welcome!

  1. Hi Steven, I had an alpine 4 channel amp hooked up to all 4 door speakers. When I turn up the gain on channel 3&4 which should be the rear speakers, the right side front and back turn up. Im guessing the speaker outputs are backwards. Thanks

  2. Hi Marty,

    Happy New Year! Great article and information. Quick question…

    Info: 2010 Chevy Camaro SS with Boston Acoustic(blown speakers, stock head unit is horrible), replacing with Kenwood DDX9907XR, JL JD400/4 Amp, Kicker 46CSS654(Front Doors), Kicker 46CSC6934(Rear Deck) and single Kicker 47KSC2704(Front Center). I’m following your System 3: RCA Cable Connections diagram and other recommendations in this article.

    Left Front Door to Amp Channel 1, Right Front Door to Amp Channel 2, Left Rear Deck to Amp Channel 3 and Right Rear Deck to Amp Channel 4.

    Question: Regarding hooking up the Kicker 47KSC2704(Front Center) speaker to the Amp, should I connect that via a bridged connection to the Amp Channel 1(positive) and Channel 2(negative)?

    Thanks in advance!

    • Hi Farrell & Happy New Year to you, too! I appreciate your feedback as I work quite hard to put out helpful articles. :D

      I assume you’re going to connect the center speaker in tri-mode? (Connected in bridged mode while also using left and right speakers, one per channel, for the front). If so, you’ll typically end up with the center speaker having a higher volume than the left & right speakers, but it will work.

      Alternately you can use a very small bridgeable 2-channel amp or older mono/center channel amp to do the same thing. I’ve done this for my in-car 5.1 systems as it allows you to adjust the center output separately. Any bridgeable, lower-power 2ch. channel amp would work or you can also use some special amps like the one included with the Alpine SBS-0715 set. You can get those for a good price used on eBay or also some similar Pioneer models.

      Do be aware that combining the left + right channels is not a true center channel. A center channel is normally derived from the stereo signal for the front channels rather than just adding them together which can mess up the front staging.

      To be honest, you’re likely better off in this case just skipping adding a center speaker.

      Best regards.

      • Hi Marty, thanks for the info, that is very helpful! If at all possible, I would really like to keep the front center mid as it does enhance the overall sound.

        Currently I have the new head unit still connected to the OEM amp via the head unit speaker outputs so that it powers the OEM Front Center Speaker(Boston 2 Ohm Mid). However when connected that way the front center speaker is louder than the door and rear deck speakers.

        I really want optimal sound so I want to replace the OEM Front Center Speaker(Boston 2 Ohm Mid) with a Kicker 47KSC2704 4 Ohm Mid and I want that to be a true Front Center speaker.

        The Kenwood DDX9907XR Head unit is also connected using the RCA Front and Rear Audio Preouts to the JL Audio JD400/4 RCA Inputs CH. 1&2 and CH. 3&4 and the Kicker 46CSS654 left & right front door speakers connected to the Speaker Outputs(CH. 1&2) and the Kicker 46CSC6934 left & right rear deck speakers connected to the Speaker Outputs(CH. 3&4). And this is working and sounding very good when I unplug the OEM Front Center Speaker(Boston 2 Ohm Mid).

        I don’t think I can replace the OEM Front Center Speaker(Boston 2 Ohm Mid) with the Kicker 47KSC2704 4 Ohm Mid and leave it connected to the OEM Amp front speaker output because the OEM is 2 Ohm output. To your point above, I think that is why it is louder when it is plugged in.

        From additional research(, it looks like…
        Option 1… I can put a speaker L-Pad Attenuator on the positive speaker wire between the OEM Amp and the new Kicker 47KSC2704 4 Ohm Mid and use the attenuator to match the volume with the front door speakers
        Option 2… add a signal processor into the system, this seems best but I don’t fully understand what else I need to get and how to hook it all up.
        Option 3… purchase a different Amp that supports the 5 speaker setup I have. Does one even exist since the front center speaker is a mid range speaker.
        Option 4… something else.

        Thanks again for your advice!

        Question… What other options do I have for connecting the Kicker 47KSC2704 4 Ohm Mid into the new system without using the OEM Amp?

        • Hello there Farrell. I like to be very careful with terminology as otherwise it can create confusion or give ideas that aren’t quite accurate. In this case, it’s important to be aware that there’s no such thing as a “true” center speaker unless you’re using a signal processor or audio sound medium that provides an independent center channel signal source.

          For example, in car audio processors Dolby Pro Logic II can emulate a real center channel [deriving center from stereo, not just L+R mono]) when a DTS or Dolby Digital signal is not present. That’s how I used a center channel myself.

          What you’re wanting to do in your setup is create a “center fill” or “pseudo-center/mono” mono speaker configuration. The article you linked to didn’t quite explain it the way I would have hoped, as they’re mainly concerned with how to connect it. AudioControl used to have a very good white paper explaining why L+R is actually bad for stereo imaging but I can’t find it, unfortunately.

          At any rate, for your setup there’s a lot going on. So to get to the “meat and potatoes” of it all:

          • You can use a 4Ω speaker with the OEM 2Ω. It’ll work ok, with 1/2 the power of a 2Ω speaker.
          • You are using both RCA and speaker-level signals which means the volume may not be correctly proportional at times. It’s best to use just one or or the other, not both signal types.
          • The JL amp is bridgeable, and what could be done is use tri-mode as it used to be called back in the day. That’s simply wiring one speaker in bridged mode while 2 stereo speakers are also wired one per channel as normal.

          The issue here is the center speaker will have more volume and power to it than each speaker, meaning you’ll have to drop a fair amount of power across a resistor to get the volume down. I figure *at least* -15dB is a good start, which means you’ll need a some power resistors of fairly large power rating. Not practical, and they’ll get hot at high power output also. (Based on what I get checking with my speaker L-pad calculator here.)

          Trying to derive a center speaker without a dedicated amp channel isn’t easy as you can see. You can make it work, but personally I wouldn’t recommend it.

          My suggestion would be to get a small bridgeable 2-channel budget amp, connect it to the front RCA channels, wire it to the center speaker in mono/bridged mode, and turn the gain down as needed to deal with the volume mismatch problem.

          You’ll save yourself a fair amount of grief by doing so. You could use one of today’s ultra-compact mini amps and install it in or near the dashboard possibly, with minimal wiring requirements. Hopefully this helps.

  3. Hi Marty, what about adding a subwoofer into the mix? I have a multi channel amp, but my head unit only has front and rear. The amp has a sub channel, will this automatically filter out the non bass tones? Thank you for the great article.

    • Hi, if the amp has a built-in low pass crossover then yes. I assume you mean you have a 5 channel amp?

      If you need to add a second amp you can split off of the rear RCA outputs using “Y” adapters and jumper over to another amp. Or some amps also have pass-through RCA jacks to do the same. Thanks & glad you like the article. :)

  4. Thank you for the article.
    I have a 4 channel amp and I’m connecting and after market head to it that only has 2 channels. I bought a set of RCA Y-splitters. When I connect the splitters and plug into all 4 input channels I have no sound. If I remove the splitters and only connect to 2 channel inputs I am able to hear sound from 2 speakers. Am I missing something? How do I get all 4 speakers to work with a 2 channel head? Any help or insight is appreciated

    • Hello Karl. That is a very, very unusual problem. Something sounds very “off.” You should be able to use “Y” adapters with no problems because car amps just take a signal via the RCA inputs.

      It’s hard to say more without information, but does it have a 2/4 channel input switch on amp? If so I’d use that instead (not many amps do, but it’s handy). The only other thing I can think of without more info is that somehow the input signals are getting shorted or “zeroed” before going into the amp.

      Alternatively, you can try using a 4-channel speaker level to RCA adapter but that’s not the 1st choice, obviously. If it were me I’d see if there’s an issue with the amp itself or the connections you’re making.

  5. Hi I am using a spl 15004 and I’m getting mono audio and not stereo. Does this amp even have that I just assumed all 4 channel amps are… wow! I’m only using the front two (ch1 and ch2)

    • Hi, yes when I checked the SPL-15004 features it should be stereo. So my first thought is that you’re using two channels from the same side and not L & R. I would check to be sure.

        • Hi Adrian. PAC makes some very good stuff so I’d be surprised if that’s the issue. I’ve used several of there line output converters (LOCs) for installations. However, anything is possible as we say.

          If it were me, I’d do few things to narrow it down if possible:

          – Use a smartphone or media/MP3 player etc. to directly connect to the amp’s RCA inputs using an RCA adapter and be 100% sure whether or not the amp is functioning correctly (stereo sound). This is fairly easy to do and it’s easy to find a good test track for this purpose.

          – If the amp appears to be ok, I would try one channel by itself to the LOC then the amp and test using only left channel audio, then similar for the right.

          That might help you get a better feel for what’s going on. You can definitely try using a different LOC, but I usually prefer to start at the amp to eliminate that as a problem just in case something funny is going on there. (Sometimes weird defects happen in electronics!)

  6. Hie Marty, Please help me out, l removed my Car Amplifier because it was nolonger going out of protection mode. So please help me out how do l reconnect the speakers?

    • Hi, well it depends on how it was installed. If the wire was run from the amp to factory wiring, you’ll need to follow the wire (formerly connected to the amp) back to the original wiring connections and reconnect it there.

      Normally it would be cutting off the amp speaker wiring and just strip & reconnect the original wiring with crimp connectors. If a wiring harness adapter was used it could possibly be easier but that’s less likely to be the case.

      If the speaker wiring was run from the amp directly to each speaker (less likely to be the case) then it’ll be more work. You could run additional speaker wiring from the ends originally connected to amp to the radio’s speaker wiring.

    • Hello Hector. What type of stuff are you dealing with? You may not need to, but I’ll need some more info to try and help.

      A lot of amps (2 ohm stable) can power both tweeters and the front door speakers from just 2 channels. If you mean that you’re not getting good power from the radio you currently have then yes an amp will be the next step.

  7. Hi, Marty having read many of your articles after I stumbled across your site via a google search looking into crossover settings, I must say they are extremely detailed well written visually informative and most of all very helpful. My set-up consists of an Alpine MRV 450 V12 (5 channel) and then a JL Audio C3 525 set in the component mode for the front & C5 650X rear fill all with adjustable passive crossovers’ JL Audio 8W3v3-4 sub discretely hidden in a custom box OEM Audi Concert head unit. My questions are any idea what voltage output would the head unit be to the amp I know it is very low! Also, should I keep the high pass for channels 1-4 on and do any further adjustments via the passives’ thank you for taking the time to read and hopefully reply looking forward to any advice you may have to offer in respect of the questions I have put forward many thanks for all your great articles kind regards Mark

    • Hello there. Well if you’re using a factory head unit it depends on how it’s connected to the amplifier. As I think this amp does not offer speaker level inputs, I’m assuming you’re using a line-level adapter which is likely 1V max but possibly 2V or so (it depends on the particular adapter as well as the signal source).

      So probably about the same as an average aftermarket head unit. Adjustable line level adapters allow you to increase that if needed.

      You don’t *have* to use the built-in high pass filters, but in the case where you have a subwoofer doing so will alow you to block distortion-causing bass from the front & rear speakers. This means if you really crank it up you can drive them with more volume and clarity. Blocking subwoofer bass prevents the small speakers from distorting heavily (they almost always cannot handle low bass well).

      Even inexpensive speakers can be driven to their limit and excellent volume if the high-pass filters are used. I don’t think you’ll need to do anything with the passive crossovers unless they have a tweeter reduction feature and you feel the tweeters are too “bright.”

      You might find this helpful:

      Thanks for your kinds words regarding my site! Best regards. :)

  8. Many thanks for your reply information and link! the audi concert head unit has a line pre out via a mini iso to rca, adapter connected so no line converter were used. I do intend to keep the subsonic filter at 15Hz as that is sounding great for an 8 inch I was just curious about the head unit voltage the unit is 25 years old this year model number 4B0 035 186 made in Japan assembly by matsushita communication Germany thanks again Mark.

    • Understood Mark. Yeah I think it’s likely in the range I mentioned in my previous comment.

      If you ever have a very weak signal from a head unit that requires you to turn the amp gain up very high to hear it, there are ways to boost the signal before the amp.

      Best regards.

  9. Thank you for all the information, however, I do need a little more assistance. I am installing an aftermarket stereo and an external 4-channel amp with 4 speakers. I make all connections from my aftermarket wire harness (power, ground, remote, illumination, etc.) to the stereo’s harness, but I do not connect the after market harness speaker leads to the speaker leads to the stereo harness, correct? The speaker leads on the aftermarket harness ( I want use the factory wiring for the speakers) go the the speaker leads coming coming from my amp which then connects to my trucks harness giving power to the speakers…..the RCA’s from my amp connect to the stereo giving the signal. or do I directly connect the 4 speakers to my amp by-passing the harness and connect RCA’s?

    • Hi Felix that’s correct, unless you had a reason for wiring to the speaker directly from the amp, you’ll run speaker wire from the amp to the harness adapter.

      Factory speaker wire is usually fine for those power levels & speaker size, saving the time/money/effort needed for adding new wire. Also it’s a huge pain to get through door jambs in most vehicles.

      If you have factory tweeters or component speakers it can be more complicated but most of the time it’s pretty straightforward. Best regards!

  10. Great Article Marty! I am in the throws of upgrading a project car and love to hear your thoughts.
    The car is a 2013 Miata with the Bose Audio. Each door has a woofer and tweeter, there are 2 small speakers in between the two seats, and a center channel speaker in the middle dash. In general it was pretty awful and plan to upgrade in waves. I started with a Sony HU and things were dramatically better. I bought the mini 4 channel Sony amp, and plan to do the swap out one day with better speakers, but here is my question. Do you think if I follow what most say is worth doing, a new amp with better 4 ohm door speakers, that I won’t feel a void where my unused center and rear channels were? I appreciate your feedback. – Austin

    • Hi Ausin. You might feel a void in the sense that the center channel is “missing” but that would be because factory systems often use built-in processing to get the center “channel” (not a real center channel like found in surround sound, and definitely not the same as L + R channels). For a good stereo setup however I doubt you’ll miss the center.

      You can fix that but to do it right you’ll need a sound processor to re-create a center channel else it muddies up the left to right stereo image, unless that’s not a problem, when in that case you can just run a little bitty amp/amp channel for a L+R signal to that speaker.

      The rears? Probably won’t notice a lot, but yes a little bit. You can always add that later though. The main thing would be getting the front speakers sound good as the factory ones usually aren’t very good quality. Factory systems sometimes used built-in EQing to make up for poor speaker performance. Better speakers resolve a lot of that (especially better tweeters).

      Most of the customers I did installations for wanted at least some sound from the rear but didn’t always add it right away. You could also consider getting an amp with more channels as there are some out there with 6+ channels that would make it easier. Or get a mini amp to drive the rears since you don’t need much power or sound quality for those, just adequate.

      Hope that helps!

      • Great info. Thanks for your words of experience! One last question as I start my preparations…
        As each door has a spot for a woofer and a tweeter, should I run 1 channel to each door, or 2? Per your comment above, if I use 2 of the four channels for the doors, it would leave space for adding L and R 3.5″ speakers at a later time. (the Sony mini doesn’t bridge, but it does have 2 and 4 channel modes).
        Thanks again!

        • Hi, yes if they’re set up as component speakers (the speakers are wired to crossovers) you can just use one channel per door. There’s not really any good reason to use 2 separate channels unless you’re bi-amping the speakers (separate channels).

          It depends on how they’re wired from the factory by ideally they’re wired similarly already (one channel to each pair, with crossovers in use). Best regards.

  11. Question: I purchased new speakers with tweeters and crossovers. Then I purchased a 4 channel amp and a wiring kit. Found out that the RCA cable couldn’t go on the 2015 Kia Soul factory radio. Then I had to purchase a Concept LC-3 stereo Line Output Converter that I have to also wire,somehow on the radio. Now. I never wired this before. Will the 2 crossovers help? All the video’s don’t show much if you can wire all this together.

    Do I have to purchase anything else? How do I connect all of this to work? Please help.

    • Hi the crossovers are for the speakers only and don’t have anything to do with the signal input to the amp. You’ll need to find the speaker wiring colors for the Soul and tap off of those to connect the line level converter. Then run the RCA cables to the amp.

      You should be able to find the factory wiring colors online and perhaps in a Kia owner’s forum or search for them. You’ll need an amp wiring kit but that should be about it as far as what you need to buy.

      However, if I’m not mistaken the LC-3 is 2 channels only, not front & rear. So if you want to be able to use a fader you’ll need either a 2nd line level converter or swap it for a 4 channel one. (and an additional stereo RCA cable) Best regards.

  12. Great diagrams and you have a great way of breaking down what you’re explaining to make it simple thank you for that.
    I have four channel amp and I’m trying to hook up a second amp. How to hook up a second amp to the one existing one. Thank you in advance for any help.
    Backroad Mike

    • Hi Mike glad you like my site & info. You can use RCA “Y” adapters to get signal inputs to the second amp if the first amp doesn’t have RCA passthrough jacks (not many amps have those).

  13. Hey Marty,

    Is it possible to install an amp to a factory unit without connecting to the back of the unit? I want to prevent pulling my dash apart. Are there pros and cons? Just weighing my options…Thanks in advance!

    • Hi, sometimes it is but you’d have to find a way to get access to the speaker wiring and then run wire from each pair to a line level converter for the amp. You’d still have to find wiring to tap off of for a remote wire to the amp as well.

      It’s (usually) better to do it at the head unit if possible. It would generally be easier, faster, and definitely save wiring.

  14. I’ve been pulling my little hair out for the past month+. I know your not disgusting the Bose system but maybe you could help of which I’d appreciate it advance! I have a Tahoe that I had a local shop create a custom factory amp bypass connector. Pulling 8 pin speaker connector from factory amp wired all 4 doors then ran to amp. I have rca’s coming from head unit, but when I connect to amp I have some mids not working very faint but tweeter is very loud or vise versa trying different connections I can only get two sets working extremely well, fronts or rears at a time only..
    •Image dinamics ctx65cs 6.5 components in all four doors with crossover set to 0dbs with •skar RP-150.4ab amp head unit •pioneer avh 2400nex 7″..
    All speakers are wired correctly via location LF, RF,LR,RR I just don’t understand.. everything is new! Door wiring rechecked and retested. I’m lost!

    • Hi has the speaker Ohms been checked for the door speakers at the speaker wire crossover connection side with the wire disconencted there? That’s the first thing I’d do.

      If it’s as expected/normal (should be close to the Ohms expected for the component woofers in the doors) then they should be ok.

      If the tweeters are too bright, there’s a very big difference in noticeable volume between them and the woofers – especially if they’re mounted in the doors. If the crossovers have a tweeter attenuation feature you should definitely set it to -3dB or even -6dB if possible.

      But the first thing I’d do is 1) check the door speaker/wire Ohms using a test meter, and 2) use tweeter attenuation. It’s possible there’s an issue in the factory wiring to the door speakers but the only way to know is by troubleshooting and finding out. You could also temporarily run new speaker wire to one/both door speakers from the crossovers to verify that too.

      Best regards.

      EDIT: If it turns out it’s because the tweeter is too “bright”, you can reduce the volume yourself and set the crossover att. to 0dB. I’d probably use at least -9dB if the tweeter is really bright. More on that here:

  15. 2 4 ohm speakers bridged in rear. channel 1-2, channel 3-4. how would rcas be ran? rear left to channel 1-2 on y splitter? rear right on channel 3-4 with y splitter?

    • Hi, use the Y adapters like this: Ch. 1, 3: Left output from the head unit. Ch. 2, 4: Right output from the head unit. (Note: I assume you have the rear speakers in series because almost all amps cannot handle below 4Ω om bridged mode; 4Ω in parallel would be too low.)

      • i have my stock speakers in the rear then i added 2 marine speakers in the back to a amp. yes bridged they’re 800 watt at 4ohms

      • i have my stock speakers in the rear then i added 2 marine speakers in the back to a amp. yes bridged they’re 800 watt at 4ohms. also would you run y splitters out the head unit for front and rear rcas or just run into the rear rca input

        • Hi Robby if you’re using Y adapters it won’t matter if it’s front or rear, but I generally use rear just as a matter of practice. If your head unit has 4 RCA outputs however you might consider running a 2nd pair of RCA cables to you can adjust front/rear or subwoofer output (if the head unit offers it).

          Best regards.

  16. I have memohis 400.4 with pioneer next 440 focal mids/tweeters in front doors with crossovers and focal 2way in rear doors. I wired channel 1 to left crossover and 2 to right crossover then channel 3 to rear left and 4 to rear right. Is that correct the fader doesn’t work. I have 2 sets of RCAs front and rear going to head unit to Amp.
    Why doesn’t fader work and do I have correct channel going to correct crossover or rear speaker?

    • Hi Chris what is the model number of the Pioneer? At any rate, it’s *possible* the Pioneer’s outputs (if using a built-in crossover or other sound options) are not set up right. A normal front/rear output RCA setup should not be a problem, should be simple.

      I see there’s also a 2/4 channel input switch on the amp.* It needs to be in 4 channel mode, so I’d check that first.

      *(Assumes I have the right model number: Memphis VIV400.4)

  17. Motorcycle Stereo: Aquatic AV : AQ-MP-5UBT-HS
    2 Front Speakers are Hertz MPX 165.3 Pro mille Pro Series 6-1/2 2-way speakers.
    Amp is Kenwood KAC-M5014 4 Channel Marine Amplifier

    I am wanting to bridge the two-front speaker to my new Kenwood amp, can’t really find any good information on installing the amp properly and how to bridge the two speakers to get the best performance possible from them. Once bridged do you place the amp in 2 channel or 4 channel mode. My stereo has a series of rca wires factory installed. And an extra remote wire and a brown dc12v_2 wire.
    Not really sure on how to wire the speakers up to the amp and stereo and not sure what mode to have the amp in once bridged.
    Thanks for any help or advice you can give.


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