setting gains (Voltage)

**mattman** · 06-19-2008, 06:08 AM

I have read a couple of pages about setting gains and what i'm a little confused about is do i set the gain to the voltage my sub can handleEG- 500w rms sub = (square root of 500 x 2 ohms) is around about 31-32 volts OR do i set the gain to what my head unit dishes out (4volts). Im not sure wether the two are different readings or what. i got the info from these two sites
http://www.mobileelectronics.com.au/...howtopic=35875
http://www.icixsound.com/vb/showthre...=gain+settings
Additional iformation
my question is a little odd so ill explain abit.
My head unit is an alpine with 4v preouts. the mono block powering the sub is 600 rms and the sub is 500 rms. does turning the gain down lower the rms power or just the sensitivity. i want to match the power to avoid under or overpowering the speaker so do i do the voltage calculations and tune to the sub or lower voltage to 4 volt sensitivity.( it is my understanding that the power is still going to be 600 rms at 4 volts gain but then the 2 websites contradict each other.

**FusionFanatic** · 06-22-2008, 10:14 PM

Originally Posted by mattman

I have read a couple of pages about setting gains and what i'm a little confused about is do i set the gain to the voltage my sub can handleEG- 500w rms sub = (square root of 500 x 2 ohms) is around about 31-32 volts OR do i set the gain to what my head unit dishes out (4volts).

normally the "gain" should be set to the highest level you desire before clipping occurs. but in your case you are using an amplifier that can output more power than your subwoofer can handle, so your gain should be set to limit the amplifier output to less than 500w.

Originally Posted by mattman

Im not sure wether the two are different readings or what.

they are very different readings. one is the pre-amp (input) voltage, and one is the speaker (output) voltage.

Originally Posted by mattman

My head unit is an alpine with 4v preouts

remember, that 4v rating is not what the HU will put out when listing to music. depending on how alpine rates that pre-amp (RCA) output, that 4v rating is either it's 'peak' output or 'RMS' output. if it's an RMS rating, then it will only output 4v when listening to a constant tone at full volume. if it's a peak rating, then it will only output 4v during musical 'peaks' at full volume. either way it will never output 4v at normal listening levels.

Originally Posted by mattman

does turning the gain down lower the rms power or just the sensitivity.

both... in most amps; the "gain" control is a potentiometer, which limits the voltage going into the amplifier. the amplifier itself can reach full volume at a lower input voltage than your HU can output. the purpose of the gain is to limit the input voltage to avoid overdriving the amp (or in your case, to limit the output power of the amp by limiting the input voltage even more).

**mattman** · 06-23-2008, 02:26 AM

thanks for your reply I think i am going to try and get my hands on an oscillope and just test the max volume on head unit without clpping then set the gains to match the rms of the speakers with a mulitmetre and then test with osc to see if they clip.(:

**FusionFanatic** · 06-23-2008, 12:32 PM

you don't need an oscilloscope. you can set your gains "by ear" and by output voltage...

according to your first post, your amp will produce ~500w RMS when the output voltage is around ~31v. you can set your gains "by ear" to the level you desire, while watching the meter to make sure the output voltage doesn't go above ~31v.