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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

Please share your thoughts below.

  • 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.

    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.
  • John from Austin, TX

    Posted on 8/19/2020

    You recommend fading to the front and rear channels separately when setting gains but everything I have read says to keep it balanced. To me, it makes sense to isolate each channel. I am setting them on a Harley bagger, 4ch. Please advise why you would fade when setting gains. Thank you.

    Buck Pomerantz from Crutchfield

    on 8/20/2020

    John, You'll want to quiet the rear speakers when setting the gain for the front channels and quiet the front speakers when setting the gain for the rear channels because you'll want to hear what's going on clearly.
  • Robert Hague from Deltona

    Posted on 7/31/2020

    I have a old pioneer avic u310bt HU, running factory bose speakers in my avalanche, i hooked a rockford fosgate punch 250a2 to it for a 600w 4ohm speaker.(all i had at the time), i now have a cerwin vega cvp 16004d to push 2 600w 4 ohm speakers, but im getting no sound with the new amp, remote has 12+, power has 12+, the speakers play through my phone an a y jack but not the rcas from the HU to the amp, i checked 4 brand new pairs an nothing, everything worked with the old amp, but nothing with the new amp except through my phone. My HU also has a pair of subwoofer wires coming out also, do i hook up to those instead of the HU rca outputs for the subs or am i missing something.

    Buck Pomerantz from Crutchfield

    on 8/3/2020

    Robert, If you bought your gear from Crutchfield, you could call Tech Support for free help troubleshooting your system. Their toll-free number is on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Click on this link for details.
  • Billy from Savannah

    Posted on 6/18/2020

    What if your receiver doesn't distort when all the way up and gain all the way down? Do you keep receiver all the way up and start increasing the gains until distort or stick to the 3/4 rule on receiver?

    Buck Pomerantz from Crutchfield

    on 6/19/2020

    Billy, If you know for a fact that the receiver doesn't distort at full volume - like you measured it with an oscilloscope - you can go ahead and set amp gain with the receiver on full. The 3/4 recommendation plays it safe and allows headroom when you want to make it loud later.
  • Donald Zauner from East Norwich

    Posted on 5/25/2020

    I have a pac lp7-4 and just bought the Rockford Fosgate M400 from Crutchfield. How do I adjust the gain on the Pac Lp7-4 and the the Amp? Where do you start? I would think you want the amp to be the main adjuster? Can you clear this up for me? Thank you

    Buck Pomerantz from Crutchfield

    on 5/26/2020

    Donald, The gains of both devices need to get set to prevent distortion. I recommend starting the line output converter's gains at 50% and then set the amp gain according to the steps outlined in this article.
  • Forrest from Traveres City

    Posted on 5/23/2020

    quick question, why do you set the gains for speakers with HPF off instead of turning on the high pass filter first and then setting gains? Everything I read says to set gains with all filter off, but I came across 1 article that said to set the HPF on and crossover frequency between 120 and 150, then turn up head unit volume to just below distortion and then turn gain up to just below distortion. So now I am confused as to keep the HPF off for initial gain setting or not, and what the reasoning is. thanks, learning is fun!

    Buck Pomerantz from Crutchfield

    on 5/25/2020

    Forrest, There are a few different ways to set amp gain. This article assumes you have no test equipment, like a tone generator or oscilloscope, and so describes gain-setting using music. You'll want to hear the unfiltered response to catch any distortion caused by clipping. Engaging a high-pass filter later will not hurt the gain setting. However, adding any EQ or bass boost will necessitate re-setting the gain.
  • Gaetan Cochet from London

    Posted on 4/28/2020

    Very interesting article! I am using a 4 channel-amp but it does not have the gain for the subwoofer. The subs are linked to the front speaker with a crossover (the car is a BMW 1 series convertible). On the amp, for the front speakers, I can select full or hpf. Which one would be best to get some bass to the subs? Thank you for your time, Gaetan

    Buck Pomerantz from Crutchfield

    on 4/30/2020

    Gaetan, It's not at all clear what your system consists of or how it's connected, but generally speaking, you should engage an amplifier's high-pass filter when powering speakers so they won't distort trying to play low notes. A subwoofer needs to be crossed over with a low-pass filter, for efficient, clean bass.
  • Dan Charlong from Coral Springs

    Posted on 4/12/2020

    Hello team, Thank you for your tutorial. I have 2 X CT Sounds Meso 6's and 2 X CT Sounds Meso 6x9 with the CT T-60.4 amplifier. After reading your reviews on them, I just had to have them. They really are nice. I have my EQ set to flat and no boosters from the stereo. The speakers sound really good, but I'm not really getting any bass from the 6X9's. I've spent a ton of time trying to tune them so that they sound good all the way around. The subs that I'm using sound awesome, but I'm actually turning those off so I can try to get the best sound out of the components. I don't really have any depth, I hear very clear highs, but for some reason I cant get these four speakers to sound "great". I have the amps setting on "High Pass" for the front and the rear. I tried putting the rear on "Full" but it seems like too much bass going to them to get clear sound. Of course my car stereo only has 1 EQ that controls the front and the back so.. How can I leave the rear on "Full" The front on "High" and still get good sound. I'm kinda going nuts trying to figure it out. Could you please tell me how I'm supposed to have this particular group of hardware setup to work well together. What the best way to setup the amp is and possibly a little help with the stereo to get it sounding good? I would really appreciate it. Please, if you can email me??? Thank you so much.

    Buck Pomerantz from Crutchfield

    on 4/13/2020

    Dan, Edgar, Check out this article for tuning advice.
  • Tony

    Posted on 2/5/2020

    im using two 4 channel amps and a dsp. 3 component system and a sub. One amp for tweeters and midranges and the other for mid bass and bridged amp.Can you please tell in detail 1-HPF or LPF ,should be engaged on amps ?? 2-what basic frequencies should i set on dsp for each channel. chers

    Buck Pomerantz from Crutchfield

    on 2/5/2020

    Tony, Without knowing precisely what equipment you're referring to, we can't help you with 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 correct information to you.
  • Raymond Stroud from Winona

    Posted on 1/21/2020

    I'm using a 4 channel JBL GX 604. I the rear channels on 2 4 ohm 10 inch subs. It sounds great but I don't know if I have the gains set to optimize the amp. The subs are not wired together. Should I use 3 channels and wire my subs together ?

    Buck Pomerantz from Crutchfield

    on 1/23/2020

    Raymond, If your system sounds good now, I see no reason to rewire it.
  • OSCAR HARDING from Houston

    Posted on 8/20/2019

    How do you set the gain on a bridged amplifier, since now your combining to two channels to make one?

    Buck Pomerantz from Crutchfield

    on 8/22/2019

    Oscar, Each gain control on a 4-channel amplifier works for a pair of channels. Those two channels are the pair that get bridged together, so the one gain still works for them both.
  • Mike from PA from Monanca, PA

    Posted on 7/29/2019

    How would you tune a system that has crossovers in the receiver, crossovers that come with components, AND hi/low pass filters that are on the amp?

    Buck Pomerantz from Crutchfield

    on 8/1/2019

    Mike, Use the filters of one device only. If you use more than one, they'll interact disruptively causing distortion.
  • Robert Buckingham from Augusta

    Posted on 5/6/2019

    Is this the best process to tune a new system that has one 4-channel amp going to the front and rear doors plus a mono amp powering one sub box?

    Buck Pomerantz from Crutchfield

    on 5/6/2019

    Robert, This article should help with your 4-channel amp. For your sub amp, check out Tuning your subs.
  • Ghazi from Beirut

    Posted on 2/10/2019

    Thank you Mr. Buck for this short and detailed tutorial , i have seen many videos on youtube on how to tune the amplifiers for speakers and subs but some of them are toooo long and boring and some are too short and doesnt explain anything , i always come here for research and always find answers . Best regards.