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How to set the gains on a 4-channel amplifier

A step-by-step way to tune your sound system

Rockford Fosgate Power T400X4ad

Rockford Fosgate Power T400X4ad 4-channel amplifier

Adding a 4-channel amp to your car stereo system — two channels to run the front speakers and two channels to run the rear speakers — not only raises the sound level, but also greatly increases the sound quality of your music. This is how I'd tune it up:

  1. Before turning on your system, make sure your amplifier's gains are set to their minimums, their high- and low-pass filters are off (set to "all pass" or flat), and that any bass and treble boosts are also off.
  2. Turn on all the units of your system. Set your receiver's tone or EQ controls, its balance, and its fade to their middle, off, or flat positions. Note where the settings were as you might want to restore them later. If you have a subwoofer in your system, turn its amp gain all the way down.
  3. Play your test music. That's a recording you are very familiar with and know what it's supposed to sound like. It has plenty of sonic variety: lots of very high notes like flutes, brass, and cymbals, lots of mid-range content like piano, guitar, and vocals, and lots of very low notes like bass and drums. And you will listen to it over and over again. (For steps 4 through 10, while you're setting the amplifier's gains, it is best to play the loudest passages of your song selection.)
  4. Set the receiver's fade control all the way to the front speakers.
  5. With your amplifier's gain controls still all the way down, turn the receiver's volume up to ¾ full, or until the music sounds distorted. (If you don't hear any music at all, try turning the amp's front gain control up slightly until you do.) If you hear distortion, turn down the receiver's volume until the distortion goes away and the music sounds clean.
  6. Now turn up the front gain control of your amp until the music distorts, then turn it down so it plays clean again.
  7. Turn the receiver volume down.
  8. Set the receiver's fade control all the way to the rear speakers.
  9. Again, turn the receiver's volume up to ¾ full and turn up the rear gain control of your amp until the music distorts, then turn it down so it plays clean again.
  10. Turn the receiver volume down.
  11. If you have no subwoofer in your system, restore your receiver's original tone, balance, and fade settings now. Or, you can refer to "How to Tune a Car Sound System: Part 1" for help in tuning your stereo to sound its best. Another tip is to engage the high-pass filter on the front channels of your 4-channel amp, and tune it to eliminate some of the low notes coming from the front speakers in order to bring extra clarity to your soundstage. (That's the ability of your stereo to sound like a band is playing in front of you, live in your car.)
  12. If you do have a subwoofer in your system, adjust the receiver's fade control to the front speakers only and turn up the volume until the music is loud, but not uncomfortable. Engage the high-pass filter of the amplifier's front channels and adjust it so the bass notes disappear. Fade the receiver to the rear speakers only and engage and adjust the rear channels' high-pass filter until the bass disappears there too. Return your receiver's fade control to its original position.
  13. Slowly turn up the gain of your subwoofer amplifier until the bass notes sound balanced and smoothly blended with the rest of the music. Your sub amp's low-pass filter should already be tuned to reproduce only the low notes. You can refer to Tuning Your Subs, for help in fine-tuning your subwoofer system.
  14. If your highs and lows seem balanced but the bass sounds like it's coming from the rear, adjust the sub amp's low-pass filter lower to "de-localize" it. Pay close attention to the "crossover area", the parts of the music played by both the full-range speakers and your subwoofer. Smooth any roughness by fine-tuning the filters. For instance, if the vocals sound tinny, you can adjust the high-pass filters on your 4-channel amp to include more low notes. If the vocals sound boomy, tune the high-pass filters higher.

Take your time and tune it all for your own ears and you will never go wrong.

Kicker 46CXA360.4T

Kicker 46CXA360.4T 4-channel amplifier

  • Kevin Peterson from Texas

    Posted on 6/13/2023

    I have 90 RMS speakers in my front doors and 60 RMS speakers in my rear doors. Will a 4 channel amp correctly power them with proper adjustment or do I need to source some 90 RMS rear speakers?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/14/2023

    Kevin, A speaker's RMS wattage rating tells you what amount of power is appropriate for the speaker to work well at its maximum volume without damage. You can certainly apply less power and still get good sound. In your case, a 50 or 60 watts RMS per channel amp will work great.
  • Gabriel from Farmerville

    Posted on 5/26/2023

    Are you supposed to use the bass boost settings when hooking up 4 channel to door speakers

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/26/2023

    Gabriel, Bass boosts augment the strength of frequencies around 40-50 Hz, which most door speakers cannot handle without distorting, so we don't recommend using one in that situation.
  • Ben

    Posted on 1/26/2023

    I prefer to set gains with test tones and a multimeter . It may mean using math, but it seems to be much easier and more accurate than using my ears to pick out distortion from heavy metal music at such a high volume setting. Doing this also seems to balance powered front and non-powered rear speakers much better than by using my ears. I remember a previous JL amp instructions actually included correct voltage output settings when setting gains. I've done it that way ever since. I also use Pioneer's auto-eq. For that, I'll set all the gains as normal, set my x-overs and other settings, and then run the auto eq. Every time, the auto eq has usually changed the output voltages even at baseline settings. After that's finished, I'll retest the output voltages and adjust the gains if needed. Any sound I don't like from this outcome is adjusted at the head unit.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/26/2023

    Ben, Multimeters are only accurate at 60Hz - so using one to set gain by the numbers will not result in an accurate setting. Check out How to set amplifier gain using test tones for better methods. You are correct about re-setting the gains after EQing.
  • Robert Peavy from Boiling Springs

    Posted on 12/20/2022

    I'm trying to understand what factors determine the amount of gain an amp is able to utilize before it clips or starts to induce RF engine noise? If my amp isn't able to be turned up to half way or more then shouldn't there be something wrong, as you're not using the amp to its full potential. Bad ground, ground wire too long, induced RF over power wire, RF contaminating RCA cables, or noisy alternator? It seems frustrating to have a 100 watt x 4 and have gain turned down to 3/8 th's.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/21/2022

    Robert, You are misunderstanding what a gain control does. It is not a volume or output power level control. It is an input sensitivity adjustment. You adjust an amplifier's gain so that it can achieve full output power, as well as without clipping the signal. If the gain is set properly - even if it's at its minimum setting - the amplifier will put out its maximum amount of clean power whenever the source unit plays at its maximum level.
  • Dan from Encinitas

    Posted on 8/7/2022

    I have a 4-channel amp for my door speakers, & a mono amp for my subwoofers. I've been reading over & over both articles on how to tune the amps. But which one should I tune 1st for the best outcome? Does it matter?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/9/2022

    Dan, It ultimately doesn't matter which amp you tune first, but most people start with the more-critically complicated 4-channel amp, then tune the bass amp to blend in well.
  • Moses from Malaysia

    Posted on 6/8/2022

    Hi Sir. Am using android HU without CD player. I try to use ISB drive to set the gain but cannot do so. I do not have scope to use. Any advise or suggestion?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/9/2022

    Moses, You can go online and download test tones to record on a USB drive, so you can use them to set an amplifier's gain. Just play a tone, turn up the gain until it distorts, then turn it down until it sounds right.
  • Steven Allen from Memphis

    Posted on 2/16/2022

    Most head units now controls your amp settings it's all about preference but good info

  • Mike M&M from Pensacola

    Posted on 1/22/2022

    I've installed maybe 20 stereo systems, vehicles as well as motorcycles. Not allot, compared to others here. But, they've always sounded "decent." I got a new 20 Electra Glide, with no head unit, cause I've just bluetooth my phone to the other head units and play music from my phone. So with this bike I installed a DS18 BT receiver, 2 amps, 8 speakers and a DSP. I've never had a setup with this many places to adjust the sound. So, my question is, where do I do my adjustments?... Amp?... DSP?... Phone?... All?... ??... I have no subs, just 4 6.5's and 4 6x9's. Do I leave my amps on HPF? FULL?... I'm so confused... LOL... Thanks for your help in advance

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/24/2022

    Mike, Your DSP has the most tuning power, so use that for all tuning and set everything else to bypass or flat. But without knowing precisely what gear you're referring to, we can't help you with more advice. If you want a question answered about a system, you must identify the gear by brand names and model numbers so we can get the right information to you.
  • Kambiz Khatami from Mesa

    Posted on 9/20/2021

    Just one observation. Shouldn't the procedure for setting up the rear speaker be identical to the front ones? If so, I believe it's missing turning up the volume on the receiver first in order to hear distortion and turning it down before adjusting the rear gain! Thanks

  • Shawn LoBello from Syracuse NY

    Posted on 7/27/2021

    What is the best software to buy to set up your Bike audio system

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/27/2021

    Shawn, With questions like that, it's always better to have a conversation with a real live human. Give us a call and talk to one of our Advisors. We can help you choose the right gear and give you the right advice on how to install it.
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