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How to: Set gain correctly with a digital volt meter...

XonDubs

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not sure if this is posted yet or not but ill post it up incase you guys need help. remember your gain setting is to match the power of the head unit.the gain is NOT a bass volume.
items needed:
1.digital volt meter
2.cd with a 50hz test tone(or if this is for components 1khz)both must be recorded in 0db reference level in the frequency range.
3.beer
---
the formula for this that i am going to use is watts X impedence= sq rt.
disconnect your subroofers(or components) set all your bass and treble at flat.turn your gains all the way down. pop in your cd with your test tone. pop open your beer and take a swig. now connect the digital volt meter your amp, +to + and - to -.
make sure the volt meter is set on AC VOLTS, and everything is connected correctly.now find out the wattage on your amp, for example if your amp is a 1000 watt amp youll take 1000 and multiply it by the impedence of the speakers. so take 1000 X 4 and that will be 4000, then you find the square root of that. which in this case would be 63.25 volts, so there you go. if its a 2 channel amp then you take and divide that by 2. so we will need to see 31.6 volts per channel. so now you turn up your cd player to the absolute loudest you will be listening to it(up to 3/4 of the way up MAX)
now adjust your gain until you see the amount of voltage you came up with before, in our case it was 31.6 volts. now take out the digital volt meter and put it on the other channel and repeat what you just did. now hook your subwoofers or speakers back up and back the gain down a smudge so you have some room to mess with it. now slam your beer and your done, congradulations. if you got this far you have done something most audio install places dont know how to do. pat yourself on the back.
 



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XonDubs

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now to find the wattage your amplifier is throwing out= youll need that same volt meter with a digital display and test cd.
you disconnect subwoofers(or speakers) and hook up the volt meter to the amp + to + and - to -. and ill use the same ratings as previous.
so say i got 31.6 volts out of each channel you will take that and times it by 2 for bridged mode, so now you have 63.25....now you take and times that by itself. 63.25 X 63.25= 4000.5625 then you will divide that by the impedence of the speaker....so 4000.5625 divided by 4 = 1000.14...there we go we found out we are using a 1000 watt amplifier.
good luck on this guys, if you have any more questions you can PM me, or post in here.
 






XonDubs

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for a good tone generator free click here
 






Nick26

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cool thanks for the tips! I think I have mine pretty well balanced but this is a good technical way to know for sure... when you say 1000 watt amp though are you talking RMS, MAX? and how would you account for a JL watt vs say a Sony watt?
 






snocross1985

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Sounds like some great stuff you have here! Same questions as Nick, though.
 






XonDubs

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this would be max wattage....as what the amplifier is capable of putting out according to on the box, or booklet for the amplifier.
and as far as JL watt vs. sony watt, there shouldnt be a difference when setting your gains based on the specified maximum wattage output of the amplifier.
ide reccomend this way for everyone, adjusting gains by ear is like playing craps, its like a 1 in 20 chance its close to right.
 






snocross1985

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Thanks for the answers.
 






XonDubs

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no problem
 






full foot notch

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so what if your speakers are 8 ohm, or at least the amp sees an 8 ohm load, would ya still calc it with a 4 ohm load, or change it and calc it with a 8 ohm load, which, if my mind serves me correct, would be half(double resistance of 4 ohm load, ie half of 63.25, so 31.625)
 






XonDubs

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full foot notch said:
so what if your speakers are 8 ohm, or at least the amp sees an 8 ohm load, would ya still calc it with a 4 ohm load, or change it and calc it with a 8 ohm load, which, if my mind serves me correct, would be half(double resistance of 4 ohm load, ie half of 63.25, so 31.625)
if they were 8 ohm speakers then youde have to calculate 8 instead of 4....
example:
1000 X 8 = 8000 = 89.44 volts
 






Nick26

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XonDubs said:
this would be max wattage....as what the amplifier is capable of putting out according to on the box, or booklet for the amplifier.
and as far as JL watt vs. sony watt, there shouldnt be a difference when setting your gains based on the specified maximum wattage output of the amplifier.
ide reccomend this way for everyone, adjusting gains by ear is like playing craps, its like a 1 in 20 chance its close to right.

real quality amplifiers like JL though don't even list a maximum cause they know that doesn't even mean anything useful... http://www.jlaudio.com/amps/5001.html RMS is what's important

and to say there shouldn't be a difference between a JL watt and a inflated Sony watt is a joke... ive heard a 250 watt JL amp that sounds much much louder than a 1000 watt sony amp on the same subs.
 






XonDubs

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so one watt in JL is better then one watt in sony? i dunno man, a watt is a watt.
 






davesexplorer

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Yeah not watt ratings, actual wattage output.
 






Nick26

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davesexplorer said:
Yeah not watt ratings, actual wattage output.
not sure what you were trying to say with that...

all I'm saying is the only problem with this method is relying on what the manufacturers say for the wattage... now if there were a way to safely measure or calculate the max wattage for a specific amp and we used that number then I think that'd be more reliable...
 






Jefe

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I'm not sure what this is sopposed to get you. Yes, you would be matching the head unit to the amplifier which is important (especially since head unit line output levels are so varied in car audio). But every sub is going to have a different efficiency so you're not balancing the system by doing this.
Not to mention that the output of an amp is going to change between running with and without a load.

In pro audio we make sure that every component in the system is receiving the same level of line level signal (0dB). However, once we get to the amp, the gain on the amp is the volume control for the components attached to the amp. This way all line level signal is running at the optimum level to reduce the signal to noise ratio and eliminate clipping.
 






Nick26

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Jefe said:
I'm not sure what this is sopposed to get you. Yes, you would be matching the head unit to the amplifier which is important (especially since head unit line output levels are so varied in car audio). But every sub is going to have a different efficiency so you're not balancing the system by doing this.
Not to mention that the output of an amp is going to change between running with and without a load.

In pro audio we make sure that every component in the system is receiving the same level of line level signal (0dB). However, once we get to the amp, the gain on the amp is the volume control for the components attached to the amp. This way all line level signal is running at the optimum level to reduce the signal to noise ratio and eliminate clipping.


yeah exactly... typically you really shouldn't ever turn the gain below 1 anyway cause you'll just cause more heat and with that comes distortion as well...
 






XonDubs

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i should clear things up, i may have been a bit vague with what i was saying. no this wont be a "perfect" setting, but it will get you alot closer then just guessing. and since most people dont have an o-scope, so this is just another way of getting kind of an idea. btw i posted in here how to find out how many watts your throwing out....
but, in what you said...a JL watt being better then a sony watt....what you must be thinking of is efficiency(sp?) and less distortion, plus JL is more "true to theyr word" when doing power ratings, as sony inflates it more. now im not stupid i know JL is better then sony, but when i said using this formula you go by what is stated on the box, in your case if its a JL then use RMS rating....
btw if you didnt know a watt is....
n. Electricity Abbr. W

An International System unit of power equal to one joule per second
 






Nick26

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XonDubs said:
i should clear things up, i may have been a bit vague with what i was saying. no this wont be a "perfect" setting, but it will get you alot closer then just guessing. and since most people dont have an o-scope, so this is just another way of getting kind of an idea. btw i posted in here how to find out how many watts your throwing out....
sorry never noticed the thread on finding wattage but I imagine that too would have the same downfalls as Jefe pointed out with this procedure, such as load readings vs no load.

XonDubs said:
but, in what you said...a JL watt being better then a sony watt....what you must be thinking of is efficiency(sp?) and less distortion, plus JL is more "true to theyr word" when doing power ratings, as sony inflates it more. now im not stupid i know JL is better then sony, but when i said using this formula you go by what is stated on the box, in your case if its a JL then use RMS rating....
Thats what I was getting at... with quality equipment and setup your system can sound seemingly so much louder (because its clearer) for the same amount of power... but then you take into account speakers too..

XonDubs said:
btw if you didnt know a watt is....
n. Electricity Abbr. W

An International System unit of power equal to one joule per second
Trust me I know what a watt is as a unit of power, being a software engineer with an electrical engineering backgound I've had my fair share of physics courses...
 






XonDubs

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Nick26 said:
sorry never noticed the thread on finding wattage but I imagine that too would have the same downfalls as Jefe pointed out with this procedure, such as load readings vs no load.


Thats what I was getting at... with quality equipment and setup your system can sound seemingly so much louder (because its clearer) for the same amount of power... but then you take into account speakers too..


Trust me I know what a watt is as a unit of power, being a software engineer with an electrical engineering backgound I've had my fair share of physics courses...
your a software engineer? i kind of wanted to get into that field, what company are you with?
 



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Nick26

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XonDubs said:
your a software engineer? i kind of wanted to get into that field, what company are you with?

yeah its a really interesting and challenging field... theres just so much you can learn, and so many directiosn to go with it... I work for a relatively small company named astro-med. They have a few different product areas and I work with the medical software.
 






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