a few questions about gain settings

[stalephotograph 10+ year member]

ok so i just read through the gain setting tutorial nd just have a few questions to ask and some things to get cleared up.

so i know sqrt(ohmxrms) = voltage and read w/ ac.

i just bought a dmm this morning and i notice it has a selection of 200 and 600 ac v~ im not sure which i would use to read.

my amp is a direct 1500d and sub is a 12" re se. running the sub at 2ohms and recieving 800wrms from the sub i get the following answer from the formula.

sqrt(2x800) = 40volts

my amp has has the following settings on it

gain, freq 30Hz-250Hz, bass eq on/off, subsonic on/off, and phase 0/180

my guess would be that i adjust those until the dmm reads the 40volts needed from above?

i may also add that my box is a 2.3cuft tuned to 32Hz.

also one more thing. how would i got about reading the actual load coming from the voice coils from the sub, just to be on the safe side that i havent burnt one up? if anything else is missing please let me know. im sorry for such the noobish questions.

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[FoxPro5 5,000+ posts]

If you follow the gain setting tutorial step by setp you will be fine. The easiest to use is on JL's website www.jlaudio.com

You will probably need to turn the DMM to 200 on the AC votage. At least that's what I used IIRC. Read the directions on the DMM to know for sure.

THe other settings on your amp have noting to do with the gain. Unless you low pass the sub on your headunit, then you will need to use the LP on the amp. Start low and play with it till you like it.

The voice coils have resestance which can be measured on your DMM too. Use the ohms setting (looks like omega). But you don't need to worry about it, just use the nominal impedance that RE says it is (dual 4 ohms).

 

[stalephotograph 10+ year member]

the amp is a mono block so im sure its already lowpass. but i was just wondering what the other settings should be set to as well. i just dont want to hurt anything. but thanks for the help so far.

 

[stalephotograph 10+ year member]

well i just got back in from doing some adjusting. i left all the settings on the amp the way they were, had my volume at the max i listen to, sub output on 15max and bass on 0. when i put the dmm to it i was shocked that i got a reading of almost 65volts. i turned it down to about 42volts thats the closest i could get it b/c the gain dial is a bit sensitive. i must say by doing just that it sounded as if it was more consistant and clearer than it was. hopefully wht ive done was right and works good. that 50hz sine is awesome!!!

 

[Scoobydoo 5,000+ posts]

what is sqrt?

my formula is sqrt(400*2) = volts

sqrt(800) = volts

but i have no idea what sqrt is or equals?

 

[2kchevy06civic 5,000+ posts]

it's square root.

 

[Scoobydoo 5,000+ posts]

it's square root.

ah that makes sense

i couldnt find the answer anywhere, thanks

 

[2kchevy06civic 5,000+ posts]

^_^

 

[Scoobydoo 5,000+ posts]

there should be a chart

28.3 volts = 800 watts

 

[stalephotograph 10+ year member]

there should be a chart
28.3 volts = 800 watts

28.3 volts would be for the 400wrms your amp produces at 2ohms.

sqrt(400wrms x 2ohms) = 28.3

 

[stalephotograph 10+ year member]

ok so i read in the tutorial about someone turning the gain up a little more than called for so they could actually get more sound for actual music. i have my gain set at about 40volts reading on the dmm. would it be ok if say i turned it up to about say 50volts since i listen to more music than actual test tones and things? i ask this b/c i love the double bass from rock/metal/hardcore music but since i set the gains w/ the dmm they seem to not be there. can anyone clear this up for me please?