Correctly setting gains

[Chrisk13 10+ year member]

I've looked through some tutorials but i'm still slightly confused. I want to set up my amp gaisn correctly because when my friend first installed everything for me he did not explain things quite well and only guessed where they should be. I plan to set them with a DMM in a few days but what numbers should I be looking for exactly? My sub is a TS-SW2501S4, amp is a Rockford Fosgate R300-4, and 2 Pioneer TS-A6874R 350 Watts speakers. I have the sub bridged for the 2 rear channels.

Any help would be great, thank you.

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[accuab 10+ year member]

Easy way: play music and slowly turn gain up till distortion is heard. Then turn the gain down slightly.

Better way: How To: Set your Amplifier Gain - SSA Car Audio Forum

This is from SSA and people recommend their stuff all the time here. The information looks all correct.

Also, use this Google, it is your friend. Type questions in you have. Most of the time someone else has already asked it before.

Here's a link for test tones if needed http://www.realmofexcursion.com/downloads.htm

 

[Chrisk13 10+ year member]

Ok, thanks. I tried using the 50hz test tone and raising the gain till I head distortion but i'm not a prop at that so it's a little hard for me to tell exactly what the distortion should start sounding like.

 

[Z1NONLY 10+ year member]

You should be setting the gain for a particular voltage, not just listening for distortion.

 

[accuab 10+ year member]

^^^^^^^^ like he said. Use the link I gave you to ssa. Determine the voltage you should be looking for.

Voltage of the output = sqrt(RMS Power X impedance of the speaker) Plug the dmm into the amp speaker terminals and read ac voltage. Slowly turn the gain up until you see your calculated voltage on the meter.

 

[Z1NONLY 10+ year member]

Set the gains without the speakers connected. (Test tones can really heat them up)

 

[Chrisk13 10+ year member]

Thanks, this is all makes sence now lol. The last thing i'm wondering is the RMS i'm looking for. Do Iuse the amps RMS or do I have to do something to it since i'm bridging 2 channels?

EDIT: Nevermind, I think I found it looking through the manual and it says the rms for 4 ohms and a bridged channel is 150 watts. I have one last question though, what are the chances I may have caused damage to any of the equipment by running it improperly set?

 

[accuab 10+ year member]

JL Audio - Car Audio Systems

Look at that. Step five talks about which voltage to use for bridged channels. Click view example two. It actually says for a bridged channel to use half( ie 2 ohms) and then double the voltage. That site is for jl stuff so the info could vary some. On the damage, it would depend on just how wrong it was. Under is fine. Over can cause damage but it depends on how much and at what volume was used. If it still works just run with it.

Also, if your amp is more powerful than the sub can handle, set the amp for the sub - not the amps max.

 

[Chrisk13 10+ year member]

Ah ok. So my amp's manual says that for a 4 ohm load bridged channel the rms is 150 watts. My sub has a 4 ohm Impedance. So to figure out the voltage I want to be output from the amp I need to take the square root of 300 and then double it, correct? I got 34.64 volts, that sound right?

 

[Z1NONLY 10+ year member]

24.5 volts = 150w at 4 ohms.

Square root of P (150 watts) times ohms (4 ohms)

So 150 times 4 is 600.

The square root of 600 is 24.5

 

[Chrisk13 10+ year member]

If it is bridged though do the ohms need to be cut in half?

 

[Z1NONLY 10+ year member]

The amp has to put 24.5 volts across a 4 ohm coil to generate 150 watts of power. (bridged, monoblock, ti-mode...whatever) 24.5 volts into a 4 ohm load = 150 watts.

There is a remote possibility that the amp will cut the voltage in half when bridged an connected to a load, but I doubt it.

You could tune the amp to a very low wattage, (25 watts) and then run the test tone to the speaker without changing the settings, and reading the voltage under load. (to see if the amp does something strange when bridged into a 4 ohm load)

If the voltage stays relatively close with and without load, then simple ohms law is all you need.

24.5 volts is the number you want to make 150 watts at 4 ohms.

 

[Chrisk13 10+ year member]

Oh, thought the person posting up a bit said to halve the ohms when running it bridged. I'll use that number then when doing it.

 

[Z1NONLY 10+ year member]

There are a lot of variables when doing this. But the ohms law part is a constant. (The relationship between voltage, resistance and power)

The reason there's still room for well informed people to make slightly different recommendations is because music is much more of a "moving target" than a test tone.

Some people recommend setting gains with a -3db test tone because almost no music is recorded at 0db (full "volume" for a given type of media)

Some differ on the HU settings used when setting the gain. (3/4 volume, full sub volume etc.)

A lot of stuff will differ after your gains are set. You will adjust the volume and other settings on your HU. Some music will be recorded much lower than others and result in less output. The list is very long.

What I try to do when I set the gains on the amp is make sure that my worst possible moments of adolescent, bass-track volume-twisting, still result in a clean, un-clipped signal for my speakers.

Using a 0db test tone and high sub-out and volume settings (that don't result in clipping from the HU) when setting gains, help ensure that your speakers get clean power.

 

[LosIsATool 5,000+ posts]

Get a DD-1.. You will get the most out of you entire setup