Setting gains with dmm

[McIntosh 10+ year member]

Like JimJ mentioned Ohms law.
Its a very simple equation. Power (watts) = Current x Voltage.

Just measure the voltage with a dmm and the current with a clamp meter. Multiply those together and you will get the answer of how many watts you are putting out. (+/- the tolerances of the meters you are using)

All of those input variables such as varying battery voltage, rca voltage, amp efficiency, load impedance, etc. will be too complex for the average enthusiast to use to calculate the output from (at least without adequate test equipment and strong electronics background.) But all of those input variables can be used to get more power out of your amp but you have to be careful about clipping and distortion.

If you get more watts than your amp is rated, then you're likely getting distortion which I believe can be measured with an oscilloscope (never tried it). Its also called THD (total harmonic distortion), most amps can output much more than they are rated but the THD % would be unacceptable to consumers. I think most amps are rated for output at 1% THD iirc.

Also you said you have a 1 ohm load. Usually subs are not that accurate in their impedance and you most likely are in the 0.8 to 1.2 ohm range, but you can check that with your meter also.

Its AC, Ohm's law doesn't work so well. Impedance isn't resistance and is largely frequency dependent (among other things in audio). Clipping is not THD either. Different animal altogether. Harmonic distortion will always be present, clipping is appraoching square waves (not good). There's a LOT of VERY inaccurate info floating around this site (not meaning just this thread, but in general). I guess if all you're after is loud (as opposed to clear) its a moot point. Rattle your lugnuts loose if that's all you're after. Who cares if it sounds like **** so long as its loud, **** the torpedoes!

 

[mud 10+ year member]

Like McIntosh said, the DC resistance might be 1 ohm, but the actual impedance that your amp sees isn't. It looks more like this:

This is for my Mag in 2 cubes tuned to 27 Hz. I'm not sure how accurate it is, but you can see that it sure isn't constant.

 

[JimJ 5,000+ posts]

Its AC, Ohm's law doesn't work so well. Impedance isn't resistance and is largely frequency dependent (among other things in audio).

I had assumed he was talking about measuring at a specific frequency.

 

[Unfortunate 10+ year member]

so how do u properly measure by ear?

just play a song or use lets say the usual 50hz test tone?

 

[SomeDonnieDude 10+ year member]

57v x 57v=3249w @ 1 ohm...but you are probably not even close to 1 ohm after rise so this is pointless.

3249/ 3ohm (after imp rise)= 1083w...this would be a little more like it.

^^^Not sure how accurate or if I'm forgetting something.

Setting your gain with a DMM on an amp with unregulated output is near pointless IMO.

 

[smoka 10+ year member]

Its AC, Ohm's law doesn't work so well. Impedance isn't resistance and is largely frequency dependent (among other things in audio). Clipping is not THD either. Different animal altogether. Harmonic distortion will always be present, clipping is appraoching square waves (not good). I guess if all you're after is loud (as opposed to clear) its a moot point. Rattle your lugnuts loose if that's all you're after. Who cares if it sounds like **** so long as its loud, **** the torpedoes!

Well you're a real douchebag. You love to rant about how smart and great you are but you contribute 0 to the post. Why don't you post something helpful? Or do you just like to talk about yourself?? How does your post contribute to the OP??? Btw, being an electrician is nothing to brag about. I have several electricians that work for me, they are good guys, but I doubt many of them graduated high school.

Techncally power equations are not part of Ohms law. They are so similar I always call it all Ohms law and most people do aswell. (especially since you use Ohms law in many of the power equations).

So looks like I'm a little dusty on my circuit theory.

Impedance = Voltage/Current = Resistance in DC

Impedance = Phasor Voltage/Phasor Current in AC

First off, the OP said he was using test tones and trying to find the output at only one frequency. I'll admit I was wrong when I thought I was calculating Real power, and instead it looks like the equation I gave was to calculate Apparent power (Vrms x Irms), measured in VA (not watts).

And I never said clipping = thd. I just said that they both can occur when trying to get the most power out of your amp.

There's a LOT of VERY inaccurate info floating around this site (not meaning just this thread, but in general).

It will affect voltage drop, however. Not an issue in car audio.

Your inaccuracies are so bad they are quotable.

 

[McIntosh 10+ year member]

Well you're a real douchebag. You love to rant about how smart and great you are but you contribute 0 to the post. Why don't you post something helpful? Or do you just like to talk about yourself?? How does your post contribute to the OP??? Btw, being an electrician is nothing to brag about. I have several electricians that work for me, they are good guys, but I doubt many of them graduated high school.Techncally power equations are not part of Ohms law. They are so similar I always call it all Ohms law and most people do aswell. (especially since you use Ohms law in many of the power equations).

So looks like I'm a little dusty on my circuit theory.

Impedance = Voltage/Current = Resistance in DC

Impedance = Phasor Voltage/Phasor Current in AC

First off, the OP said he was using test tones and trying to find the output at only one frequency. I'll admit I was wrong when I thought I was calculating Real power, and instead it looks like the equation I gave was to calculate Apparent power (Vrms x Irms), measured in VA (not watts).

And I never said clipping = thd. I just said that they both can occur when trying to get the most power out of your amp.

Your inaccuracies are so bad they are quotable.

Those that work for you are certainly not electricians (defined as one who has completed an nationally accredited apprenticeship program). Five years of school and OJT make you a Journeyman, not Sally Struther's home study program. You're not qualified to carry my tools. An Associates degree is the minimum requirement, not graduating HS is out of the question. Dusty my ass. You've never been through any kind of training and are at best a "shadetree electrician". The kind that burn houses down and kill people. People on this forum seem to think a short piece of wire can carry more current than a long piece. They're ignorant. Ignorant as opposed to stupid. They know no better, that doesn't make them stupid, rather ignorant. Totally unqualified people like you perpetuate the myths. Of course you're all smarter than your fathers (or me) will ever be. I was too at your age. I now know much better. You will too at some point. I hope you don't get hurt learning life's basic lessons. Someone's been there and done that (and has a tee shirt to prove it) long before you were born. You're blazing a trail that has been trodden many times before.

 

[smoka 10+ year member]

Those that work for you are certainly not electricians (defined as one who has completed an nationally accredited apprenticeship program). Five years of school and OJT make you a Journeyman, not Sally Struther's home study program. You're not qualified to carry my tools. An Associates degree is the minimum requirement, not graduating HS is out of the question. Dusty my ass. You've never been through any kind of training and are at best a "shadetree electrician".

Lol, so 2 yrs of community college and working in the field for 3-4 years is something to brag about? You may know something about Power/electricity but what do you know about electronics from being an electrician?

I graduated with a BSEE 3 years ago so I guess that would make me somewhat qualified to try to answer peoples questions here. Since graduating and working for past 2.5 yrs (company is in top 100 of fortune 500) I've mostly focused on control systems and machine design/improvements so I'll be the first to admit that my circuit analysis skills are rusty (use it or lose it).

Since your job over the past xx years deals with electricity I'm sure you know much more about several subjects than my few semesters learning in theory and labs. I don't claim to know everything, but that won't stop me or others from arguing with you and making you prove me/us wrong //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Totally unqualified people like you perpetuate the myths.

You forget that this is a Forum (and a fairly large one). If someone posts the wrong info there will be more people along to correct it. There are many times I've corrected someones bad/wrong/misleading info and I fully expect that someone will correct me if I am wrong (like you did with the power equation above). This is a community of enthusiasts were everyone has the chance to help out no matter what skill level, its up to the post readers to decide what they want to do.

Of course you're all smarter than your fathers (or me) will ever be. I was too at your age. I now know much better. You will too at some point. I hope you don't get hurt learning life's basic lessons. Someone's been there and done that (and has a tee shirt to prove it) long before you were born. You're blazing a trail that has been trodden many times before.

I don't think I'm smarter than my dad, but I definitely have more knowledge about electronics. Considering he can barely send a text msg and I can modify the SDK of his phone its easy to see how the younger generation of today can feel like 'know-it-alls' when it comes to electronics with older generations. Probably most people on this forum are the local go-to guys when their friends have audio problems which with some people might lead to an inflated car audio ego?

McIntosh, your problem is that your posting style is to attack posters. That tends to start the flaming and nothing gets accomplished. You might want to try to 'correct' all the wrong info you see in a more mature and friendly way. That way people can learn from you and respect you. Unless you like the flame wars, in which case you have made a good start.......

 

[McIntosh 10+ year member]

Lol, so 2 yrs of community college and working in the field for 3-4 years is something to brag about? You may know something about Power/electricity but what do you know about electronics from being an electrician?
I graduated with a BSEE 3 years ago so I guess that would make me somewhat qualified to try to answer peoples questions here. Since graduating and working for past 2.5 yrs (company is in top 100 of fortune 500) I've mostly focused on control systems and machine design/improvements so I'll be the first to admit that my circuit analysis skills are rusty (use it or lose it).

Since your job over the past xx years deals with electricity I'm sure you know much more about several subjects than my few semesters learning in theory and labs. I don't claim to know everything, but that won't stop me or others from arguing with you and making you prove me/us wrong //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

In a word no. I too was enrolled to get my BSEE at Drexel in Philly, PA. Financial problems cause me to drop out after only two years. I only got the basic Engineering classes in (back when we used pencils in Engineering Drawing, and computer cards to program in FORTRAN). That was 1978. I took the IBEW oath in 1979, probably before you were born. An electrician's training does certainly include a great deal of electronics (unless you take the Sally Struthers course). Variable frequency drives, distributed control systems, etc. tend to be electronic in nature. Who do you think installs/troubleshoots these? I certainly don't know everything either. I always say if you can't learn SOMETHING from an apprentice, you're just too stubborn. Most everyone knows something I don't. To assume otherwise is arrogant and most always wrong. I'm sure you know a few things I don't but to assume I don't know more than a few things you don't is borderline foolish.

You forget that this is a Forum (and a fairly large one). If someone posts the wrong info there will be more people along to correct it. There are many times I've corrected someones bad/wrong/misleading info and I fully expect that someone will correct me if I am wrong (like you did with the power equation above). This is a community of enthusiasts were everyone has the chance to help out no matter what skill level, its up to the post readers to decide what they want to do.

I don't think I'm smarter than my dad, but I definitely have more knowledge about electronics. Considering he can barely send a text msg and I can modify the SDK of his phone its easy to see how the younger generation of today can feel like 'know-it-alls' when it comes to electronics with older generations. Probably most people on this forum are the local go-to guys when their friends have audio problems which with some people might lead to an inflated car audio ego?

I certainly don't know how to text. I'm sure my phone is capable, but I fail to see the point in it at all. If I want to talk, I call. We used to have pay phones for this purpose. Now you can't even find one. I do have a cell phone, but it gets used every few months at best. I have an answering machine if I'm not home. I've seen too many broads on their cells nearly crash me on the road...bad idea. I use mine for emergency only.

McIntosh, your problem is that your posting style is to attack posters. That tends to start the flaming and nothing gets accomplished. You might want to try to 'correct' all the wrong info you see in a more mature and friendly way. That way people can learn from you and respect you. Unless you like the flame wars, in which case you have made a good start.......

Its not my intent to "attack" posters. Some info by "experts" is so far from the truth it irks me. People who emphatically state a short piece of wire can carry more current than a long piece of wire comes to mind. The AWG determines the ampacity (I'm pretty sure you know that). WTF kind of moron tells people a short piece of #8 can carry 200 amps? If their car burns down in their driveway, no prob for me. With my luck I'll be stuck next to them at a stoplight and I'll get caught up in it.

It surely seems this forum is all about quantity and not quality, which I also don't understand. SPL is the goal. Lets say I just bought a new plasma TV. 80" (who cares, just an example). I say "this is really bright". Lets have a contest! Mine's brighter you say. Lets turn them on. They're both so bright you can't possibly look at them, but one is certainly brighter. There's a winner? I guess there is when you compare brightness, but neither are viewable without sunglasses. Not a very useful TV and the picture quality ***** on both. But they sure are bright. I hear people most every day driving by with woofer excursion slapping the stops. Nice. I know it sounds like **** outside the car, how good can it sound inside? I really don't wanna know.

FWIW, my "system" is 1984 Alpine amps (100W/ch rear and 40W/ch front) that STILL crank. I have 3-way "home speakers" in the back with only 8" woofs that render the rear view mirror useless. Its louder than any human can stand for any period of time, trust me. Is it 140+dB? Surely not. Can you stand it for an hour? Not without permanent hearing damage. More than overkill and 25 years later still working just fine. 280 watts of yesteryear. Are there better out there? Naturally. My Nephew's 146 dB system sounds like ****. Subwoofers and crap increase SPL, but not necessarily in a good way.

 

[McIntosh 10+ year member]

Lol, so 2 yrs of community college and working in the field for 3-4 years is something to brag about? You may know something about Power/electricity but what do you know about electronics from being an electrician?

I graduated with a BSEE 3 years ago so I guess that would make me somewhat qualified to try to answer peoples questions here. Since graduating and working for past 2.5 yrs (company is in top 100 of fortune 500) I've mostly focused on control systems and machine design/improvements so I'll be the first to admit that my circuit analysis skills are rusty (use it or lose it).

Since your job over the past xx years deals with electricity I'm sure you know much more about several subjects than my few semesters learning in theory and labs. I don't claim to know everything, but that won't stop me or others from arguing with you and making you prove me/us wrong //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

You forget that this is a Forum (and a fairly large one). If someone posts the wrong info there will be more people along to correct it. There are many times I've corrected someones bad/wrong/misleading info and I fully expect that someone will correct me if I am wrong (like you did with the power equation above). This is a community of enthusiasts were everyone has the chance to help out no matter what skill level, its up to the post readers to decide what they want to do.

I don't think I'm smarter than my dad, but I definitely have more knowledge about electronics. Considering he can barely send a text msg and I can modify the SDK of his phone its easy to see how the younger generation of today can feel like 'know-it-alls' when it comes to electronics with older generations. Probably most people on this forum are the local go-to guys when their friends have audio problems which with some people might lead to an inflated car audio ego?

McIntosh, your problem is that your posting style is to attack posters. That tends to start the flaming and nothing gets accomplished. You might want to try to 'correct' all the wrong info you see in a more mature and friendly way. That way people can learn from you and respect you. Unless you like the flame wars, in which case you have made a good start.......

2 years of community college? Where did that come from? I attended Drexel University in Philly, FWIW. Working in the field for 3-4 years? I took the IBEW oath in 1979 (likely about the time you were born). We get a pretty substantial amount of electronic training as well. Variable frequency drives, distributed control systems, etc. are not simply house wiring. With 3 years under your belt I'm sure you've seen everything from behind that desk. I'm not qualified at all compared to you. I've neither seen nor learned anything in 30 years. There were those before me that forgot more than I now know. I have respect for them. I know better.

 

[Buck 5,000+ posts]

****, I'm going to do it by ear it's so much easier.

 

[bustaplz 10+ year member]

****, I'm going to do it by ear it's so much easier.

LOL. This thread was really interesting until the penis measuring started.

 

[BigJoker 10+ year member]

QUOTE=McIntosh;6007235]Its not my intent to "attack" posters. Some info by "experts" is so far from the truth it irks me. People who emphatically state a short piece of wire can carry more current than a long piece of wire comes to mind. The AWG determines the ampacity (I'm pretty sure you know that). WTF kind of moron tells people a short piece of #8 can carry 200 amps? If their car burns down in their driveway, no prob for me. With my luck I'll be stuck next to them at a stoplight and I'll get caught up in it.

It surely seems this forum is all about quantity and not quality, which I also don't understand. SPL is the goal. Lets say I just bought a new plasma TV. 80" (who cares, just an example). I say "this is really bright". Lets have a contest! Mine's brighter you say. Lets turn them on. They're both so bright you can't possibly look at them, but one is certainly brighter. There's a winner? I guess there is when you compare brightness, but neither are viewable without sunglasses. Not a very useful TV and the picture quality ***** on both. But they sure are bright. I hear people most every day driving by with woofer excursion slapping the stops. Nice. I know it sounds like **** outside the car, how good can it sound inside? I really don't wanna know.

FWIW, my "system" is 1984 Alpine amps (100W/ch rear and 40W/ch front) that STILL crank. I have 3-way "home speakers" in the back with only 8" woofs that render the rear view mirror useless. Its louder than any human can stand for any period of time, trust me. Is it 140+dB? Surely not. Can you stand it for an hour? Not without permanent hearing damage. More than overkill and 25 years later still working just fine. 280 watts of yesteryear. Are there better out there? Naturally. My Nephew's 146 dB system sounds like ****. Subwoofers and crap increase SPL, but not necessarily in a good way.

//content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif:laugh:

why does your old ass come on here and argue with everyone? don't you have anything better to do then argue with us whipper snappers?

 

[Buck 5,000+ posts]

LOL. This thread was really interesting until the penis measuring started.

//content.invisioncic.com/y282845/emoticons/eek.gif.771b7a90cf45cabdc554ff1121c21c4a.gif

I didn't even read that **** I just saw some argument going between the guys and got lost in what they were talking about.

 

[smoka 10+ year member]