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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

  • 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.
  • Cheobrean Onordo Goodlitt from Orlando

    Posted on 6/25/2021

    These instructions have been so good..thanks a crutchfield we trust!!

  • Gary Murphy from Lake Stevens

    Posted on 3/29/2021

    Thanks guys for leaving this guide. I like to do the installs myself, hard to find someone to just do the tune. I followed these directions and have much better performance first try. Now that I know what to do, I'll keep tweaking.

  • Will from Roanoke

    Posted on 3/8/2021

    I have a simple question that I am having a time finding an answer, I have a punch 300x2 and I am running it to 2 Fosgate T1693's. Built-in high-pass 12dB/octave Butterworth tweeter crossover 50Hz - 22kHz frequency response with 90dB sensitivity 200 watts maximum power handling (100 watts RMS) Should I set the AMP to AP and adjust the AMP crossover from like 80 to 100 hz so it does not let lower bass tones through? I have a 12" P3 sub for my bass... Or should I set it to HP and if so what would I set my AMP crossover to? I know the 6x9's can handle a little bass, but I get plenty of bass from my 12" sub, I mainly want to get good mid and highs from my 6x9's.. I'll be setting gains with the AMP setup CD, and I'll be adding a 5db Overlap Gain, also using the CD to be sure there is no clipping.. My front speakers are 5 & 1/4" Fosgate Punch's, I am letting my Aftermarket Kenwood Excelon DDX6906S push those, for now anyway... The AMP has an EQ setting, after tuning I always set the EQ from my deck, but I am guessing this can be turned up and adjusted by ear to what sounds best?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/26/2021

    Will, Your component speakers should be run using the high-pass filter (HPF) to remove the bass tones. The subwoofer should use a low-pass filter (LPF) to remove high-frequency content from the bass. Set both to around 80 to 100 Hz to start, and then tweak to taste.
  • Tim from Tacoma

    Posted on 2/15/2021

    Bought the 10TW3-D4 10" sub in a Stealthbox to add bass to factory radio (head unit [HU]) plus JVC KS-DR3005D 5-channel amp. Factory HU does not have RCA sound outputs nor separate subwoofer outputs. The JVC amp has a 4-channel high-level input, which I am using. I have the input mode selector switch set to 4-channel. Everything works, except the bass is not as bouncy/boomy as I thought it would be from a 10" sub. I have the amp's bass boost set to max (18db) and it's okay but it really should be way too much bass at that setting. I have played with the crossover frequency dial and it doesn't really make much difference (I can hear a slight lessening/increasing of bass at both ends.) Is this setup simply not going to have crazy window-rattling bass? If so, why? Is it because it is only a 4-chan high-level speaker input? Or is it because the sub needs more RMS power, since the amp is rated at 350 watts RMS into 2 ohms?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/25/2021

    Tim, Tim, Check to see if the sub is wired to 2 ohms, like this. Then check the amp's gain adjustment - it may be set too low. The subwoofer output channel of that amplifier is actually rated at 300 watts RMS through 2 ohms, so maybe you just need a heftier amp for your sub.
  • John from Bradenton

    Posted on 1/23/2021

    What is the fader button ? And input level buttons do ?? Also i have the kicker cxa360.4 amp and im getting alot of highs but no bass how should i tune amp to get better midbass need help

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/25/2021

    John, From the Owner's Manual: Fader Switch: Depress the fader switch if you are running two sets of inputs (front and rear for example) to the amplifier. Leave the fader switch OFF if you want to drive all channels from a single stereo input. Input Level: The RCA inputs on KICKER CX amplifiers are capable of receiving either Hi or Low-level signals from your source unit. If the only output available from your source unit is a Hi-Level signal, simply press in the Input Level switch on the amplifier. Refer to the wiring section of this manual for additional instructions. For your bass issues, see my answer to your previous question.
  • John Hand from Bradenton

    Posted on 1/21/2021

    Hello i just had installed a kicker 360.4 channel amp on kicker ks 4x6 in front and kicker ks 6x9 today the highs are there but no bass how do i increase this ?? My old stock speakers had more bass lol on my amp what do i need to do im confused thank you

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/25/2021

    John, You can start by making sure the amp 1 and amp 2 high-pass crossovers are turned off. Then, you can add even more bass using the bass tone controls in your receiver or the bass boosts on the amplifier.
  • John from Austin, TX

    Posted on 8/22/2020

    Buck, thank you for the response. My last question when setting gains has to do with whether or not the vehicle (Motorcycle in my case) should be running or the ignition in ACC. I have read a lot of posts that say the gains can be set with the ignition in ACC initially but to dial them in it should be running. I believe the reason for it running might be voltage drops? I can't recall. Thoughts? Thank you.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/24/2020

    John, Setting gain is matching the input sensitivity of the amp to the output level of the receiver, whether the engine is running or not. I've never heard of anyone setting amp gain while the engine is running - too much noise and fumes. Besides, bumping the voltage from 12V while off to 13.8V while running has no effect on the receiver's output or amp's input sensitivity, only the amp's output level.

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