Impedence's effect on the electrical system? + HU/Amp gain question

[SomeGuyDude 10+ year member]

I'm just gonna throw it out there because too much explanation is pointless. I'd heard somewhere that higher impedences means it's easier on the electrical system (i.e. 1200@2 is preferable to 1200@1). Is this at all true?

I've got Wikipedia open and a few other pages but I haven't figured out what the heck the impedence has to do with the amount of stress it puts on the car's electric.

2nd Q: My understanding of "gain" is basic. From what I got, the gain setting is the voltage at which the amp pushes fully, or something like that? Meaning you want your amp and HU to line up, that's why the knob seems backwards, because with a weaker HU the amp should push fill power at much lower voltage.

My amp only goes from 250mV to 4V (turned all the way down is 4), so does that mean for my amp and subs' safety I should only look at HU's that have a pre-amp of 4 and then put the gain all the way down?

If the above is totally retarded, please feel free to write TOTALLY RETARDED and then explain WTF is going on with that.

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[fuggles 10+ year member]

to first order the load on your cars electrical system is the same if your amplifier output is 1200W. it does not matter whether the amp is driving a 1ohm load or a 2ohm [given your constraint that both are 1200W]. the amp is pushing twice the current into a 1 ohm load vs a 2 ohm load. most amps will actually push more power into a 1 ohm load vs a 2 ohm load. this depends on the amp.

gain is how much the amplifier increases the signal voltage. gain = Vout/Vin. with low input voltage the amplifier needs more gain for a given output voltage.

the reason the amps 4v setting is low gain is because the input signal is higher voltage so the amp does not need to amplify the signal as much. if the input signal is 250mV the amplifier needs more gain to create to proper output signal level.

hope this helps.

Kent

 

[SomeGuyDude 10+ year member]

\Yeah, I've got a JBL amp that's rated 1200RMS at both 1 and 2 ohms, so I was just trying to figure out if it'd be better to get a DVC2 or DVC4 to ease up on my electrical system, but if it doesn't matter then it doesn't matter, good to know.

The gain question was more along the mathematical lines. I mean is there any way to go "well my HU is 4V so I should set my gains to 4V" or something like that?

 

[DammitJames 10+ year member]

the only way to truely set your gain right is with a ocsilliscope usally u can set the gain by ear by telling when it starts to distort my rule of thumb has always been not to go over 3/4 gain and ur amp isnt going to put out the same at 1 and 2 ohms its going to be more at 1 ohm seeing thats there is less resistance meaning more current can flow through it

 

[SomeGuyDude 10+ year member]

Yeah I know that's how it usually works, but the JBL bp1200.1 is rated at 1200RMS at 1 and 2 ohms both, which I admit confuses the hell outta me (and I know it's been benched at slightly more at 1ohm).

 

[haloweenhamster 10+ year member]

half the resistance - double the current

double the current - double the power

i dont know about in the US but in the UK JBL is crap and the specs mean nothin

they sell a 1KW sub over hear that cant handle 400w

and as fuggles said the 250mV to 4V knob sets the input sensetivity(gain)

with the gain set to a 250mV input the amp will amplify the the input the most as it only needs an input of 250mV peak-peak of give full output power ie 1200w

with the gain set to a 4V input the amp will amplify the input the least as it needs an input of 4V peak-peak to give full output power ie 1200w

 

[SomeGuyDude 10+ year member]

JBL's turned to crap from what I understand. The old BP line absolutely put out its rated power and then some. Now, power aside, is it still true that ohms are irrelevant on electrical strain? That's good news.

As for the gain, like I said, I know HOW it works, but there's always this "put it at 3/4" common-knowledge law, but that doesn't make sense to me. If my HU is 4V and I have an amp with 4V to 250mV on the gain, 3/4 of the way would be around 1V and that seems like it'd be way too high, no? So aside from using a Voltmeter, is there any way to sort of ballpark the math?

 

[haloweenhamster 10+ year member]

i have my amp gain set to half way and my remote set between 0-25%(music dependant) on full volume on hu and remote 25-50% on lower volume with 50% more playing room if i want to showoff my bass with low mids&tops

but my amp has an input sensativity of 200mV-5V

ajusted by speaker as the speaker bottoms out before the amp clips(distorts)

the gain is more critical on some amps dependant on how the gain/attenuation control is wired as

u can clip the input if set incorrectly but others u will drive the amp to hard and clip the output if set incorrectly

 

[haloweenhamster 10+ year member]

speaker impeadance only affect the strain on the amp not ur electrical system

if u r running ur system at 1.5KW output thats 108A + losses in ur amp from ur supply as most class D are 80% efficient thats 120Aish

as high powered amps stepup the voltage the output can be

60v 25A = 2.4ohm

50v 30A = 1.67ohm

40v 37.5A = 1.07ohm