# Amplifer power output myths exposed!



## 89grand (Nov 23, 2006)

*Amplifier power output myths exposed!*

OK, we've all heard that amplifiers double their power as impedance is reduced by 50%. Fact is, that's wrong, they don't. Most amplifiers with regulated power supplies, which seems to be nearly non-existent these days, do pretty good as impedance is cut in half, but even they don't do it either. I've known this not to be true for many years, but considering the amount of times I've seen it posted as fact here, I thought I'd share this information.

For those that don't know the difference (keeping this pretty simple), a regulated power supply amplifier will put out the same power from around 10 volts to the maximum voltage the electrical system will put out, You get no more power as voltage increases, but you don't get less as voltage decreases either, up to point, but you'll be below any normal operating voltage before that happens. Unregulated amplifiers power output is voltage input dependent. An unregulated amplifiers output typically increases by about 30% or so from 12.5 volts to 14.4 volts. And, as the tests will show, most unregulated amplifiers put out about the same amount of power into a 2 ohm load @ 12.5 volts as they do into a 4 ohm load @ 14.4 volts.

The closest amp to ever double its power as impedance was reduced by half, that I saw tests of was an old PPI ProMos50 and even it didn't totally double, but it was pretty close. I'm going to list the power tests of three old school amps with regulated power supplies, then 3 with unregulated power supplies.

*First up, the wonderful regulated PPI A600.2 *

Power output at 12.5 volts into 4 ohms = *176* watts per channel
Power output at 14.4 volts into 4 ohms = *176 *watts per channel
Power output at 12.5 volts into 2 ohms = *304* watts per channel 
Power output at 12.5 volts bridged into 4 ohms = *608* watts


*Second, the regulated Lanzar 2200*

Power output at 12.5 volts into 4 ohms = *130* watts per channel
Power output at 14.4 volts into 4 ohms = *131* watts per channel
Power output at 12.5 volts into 2 ohms = *219* watts per channel 
Power output at 12.5 volts bridged into 4 ohms = *438* watts


*Third, the regulated Ultimate Sound US2125 (this amp is regulated, but obviously not as tightly as the other 2)*

Power output at 12.5 volts into 4 ohms = *129* watts per channel
Power output at 14.4 volts into 4 ohms = *138* watts per channel
Power output at 12.5 volts into 2 ohms = *197* watts per channel 
Power output at 12.5 volts bridged into 4 ohms = *394* watts




Here's 3 unregulated 4 channel amps. (note, these amps were not tested into 2 ohms at 14.4 volts so I can't say for sure what they'd do, but probably similar to the regulated amps)

*First up, the unregulated Rockford Fosgate Punch 160x4*

Power output at 12.5 volts into 4 ohms = *40.5* watts per channel
Power output at 14.4 volts into 4 ohms = *56* watts per channel
Power output at 12.5 volts into 2 ohms = *57* watts per channel 
Power output at 12.5 volts bridged into 4 ohms = *114* watts

*Second, the unregulated Cadence CPA 4100XRi*

Power output at 12.5 volts into 4 ohms = *59.5* watts per channel
Power output at 14.4 volts into 4 ohms = *78* watts per channel
Power output at 12.5 volts into 2 ohms = *80* watts per channel 
Power output at 12.5 volts bridged into 4 ohms = *160* watts

*Third, the unregulated Jensen A432HLX*

Power output at 12.5 volts into 4 ohms = *60.7* watts per channel
Power output at 14.4 volts into 4 ohms = *81* watts per channel
Power output at 12.5 volts into 2 ohms = *74* watts per channel 
Power output at 12.5 volts bridged into 4 ohms = *148* watts

So...the next time you're told for instance that a PPI A600.2 will do 75 watts into 8 ohms (simply because it's rated to do 150 per channel into 4 ohms), take that with a grain of salt, because more than likely, it's more than 75 watts. First off because it did 176 into 4 ohms, secondly, power doesn't double, or get halved at impedance increases or decreases be 50% and these test, and many others I can post prove that.

I hope this post was enjoyed and informative!


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*

hmmmm....


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## chad (Jun 30, 2005)

*Re: Amplifier power output myths exposed!*

The doubling between 8 and 4 is more likely than between 4 and 2. between 8 and 16 it will be darn close to a double and the higher you go the better it (the mythological formula) works.

It's not only power supply sag but also semiconductor losses in the finals.


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## 89grand (Nov 23, 2006)

*Re: Amplifier power output myths exposed!*



chad said:


> The doubling between 8 and 4 is more likely than between 4 and 2. between 8 and 16 it will be darn close to a double and the higher you go the better it (the mythological formula) works.
> 
> It's not only power supply sag but also semiconductor losses in the finals.



Sure, that makes sense, but the whole idea of 25 watts at 8 ohms, 50 watts at 4 ohms 100 watts at 2 ohms is simply not the case.

That would also depend on what load the amp was designed for. I mean if I was designed to handle a 1/2 ohm load, well then that's probably different than an amp designed for 4 ohm loads.


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



chad said:


> The doubling between 8 and 4 is more likely than between 4 and 2. between 8 and 16 it will be darn close to a double and the higher you go the better it (the mythological formula) works.
> 
> It's not only power supply sag but also semiconductor losses in the finals.


hmmmmm.... again!

another thing kind of O/T but usually drivers with higher impedance's are more sensitive so it doesn't make a huge difference. i'll run a lower power more sensitive system over tons of power and low sensitivity anyday.


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



89grand said:


> Most amplifiers with regulated power supplies, which seems to be nearly non-existent these days,


aren't your/the pdx amps regulated? they claim to make the same power at 4 or 2 ohms don't they?


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## chad (Jun 30, 2005)

*Re: Amplifier power output myths exposed!*



89grand said:


> Sure, that makes sense, but the whole idea of 25 watts at 8 ohms, 50 watts at 4 ohms 100 watts at 2 ohms is simply not the case.
> 
> That would also depend on what load the amp was designed for. I mean if I was designed to handle a 1/2 ohm load, well then that's probably different than an amp designed for 4 ohm loads.


right, but you are WAY more likely to see the 25W gain between 4 and 8 then the 50W gain between 4 and 2.


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## 89grand (Nov 23, 2006)

*Re: Amplifier power output myths exposed!*



tcguy85 said:


> aren't your/the pdx amps regulated? they claim to make the same power at 4 or 2 ohms don't they?


The PDX amps have a totally different type of regulation going on. Not the same thing as the "regulated" amps I posted. I don't even think the PDX amps are regulated in that regard, they are only regulated in output, by sensing the load impedance, not a regulated power supply for input voltage.


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## 89grand (Nov 23, 2006)

*Re: Amplifier power output myths exposed!*



chad said:


> right, but you are WAY more likely to see the 25W gain between 4 and 8 then the 50W gain between 4 and 2.


Yeah, I'm not totally disputing that. Like I said, this post is disputing the notion that amps simply double power as impedance is halved. It probably gets closer to reducing by 50% as impedance is increased by 50%, but it still isn't that cut and dry.


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



89grand said:


> The PDX amps have a totally different type of regulation going on. Not the same thing as the "regulated" amps I posted. I don't even think the PDX amps are regulated in that regard, they are only regulated in output, by sensing the load impedance, not a regulated power supply for input voltage.


and how is that different?


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## chad (Jun 30, 2005)

*Re: Amplifier power output myths exposed!*



89grand said:


> Yeah, I'm not totally disputing that. Like I said, this post is disputing the notion that amps simply double power as impedance is halved. It probably gets closer to reducing by 50% as impedance is increased by 50%, but it still isn't that cut and dry.


Oh no joke. When I see people calculate their system power in their head via impedance, I hang my head in disgust


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



chad said:


> Oh no joke. When I see people calculate their system power in their head via impedance, I hand my head in disgust


impedance isn't constant anyway.....


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## 89grand (Nov 23, 2006)

*Re: Amplifier power output myths exposed!*



tcguy85 said:


> and how is that different?



A regulated amplifier simply draws more current to maintain output power as voltage input is decreased. Unregulated amps don't do that, that's why their power out drops as input voltage drops.

The PDX, like the JL Slash, PG Xenon etc, are regulating output power by sensing impedance. It has nothing to do with a regulated power supply that maintains output from input voltage.

I think the JL has a regulated power supply, whereas I don't think the Alpine does. Yet they both regulate output based of off load impedance.

In other words, the JL will maintain its power output from say 10.5 to 16 volts whereas the Alpine won't. They both regulate output power regardless of load impedance though.


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



89grand said:


> A regulated amplifier simply draws more current to maintain output power as voltage input is decreased. Unregulated amps don't do that, that's why their power out drops as input voltage drops.
> 
> The PDX, like the JL Slash, PG Xenon etc, are regulating output power by sensing impedance. It has nothing to do with a regulated power supply that maintains output from input voltage.
> 
> I think the JL has a regulated power supply, whereas I don't think the Alpine does. Yet they both regulate output based of off load impedance.


so the pdx is regulated by impedance, just not input voltage. so it's still regulated in a way.


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## FoxPro5 (Feb 14, 2006)

*Re: Amplifier power output myths exposed!*



tcguy85 said:


> impedance isn't constant anyway.....


Neither is power. Rated power is not average power. Music drives AC voltage and it's constantly changing as well. Anyone who thinks their amp puts out 100 watts to their speakers has done too many damn quaaludes.


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## 89grand (Nov 23, 2006)

*Re: Amplifier power output myths exposed!*



tcguy85 said:


> so the pdx is regulated by impedance, just not input voltage. so it's still regulated in a way.



No, that's not it.

You have regulated and unregulated power supplies in amplifiers. 

Then you have amps like the PDX, JL Slash and PG Xenons, that maintain the same out power regardless of load impedance (well to some degree).

The JL amp has a regulated power supply in addition to the regulated output. The Alpine has the regulated output regardless of load impedance, but it has an unregulated power supply.

Think of this as the same as the first post of unregulated vs regulated excpet the amps didn't produce more power as load impedance decreased.

In other words the JL amp may do this:
500 watts @ 2ohms with 12.5 volts
500 watts @ 4ohms with 12.5 volts
500 watts @ 2ohms with 14.4 volts
500 watts @ 4ohms with 14.4 volts

Where as the PDX may be like this: watts @ 2ohms with 12.5 volts
400 watts @ 2ohms with 12.5 volts
400 watts @ 4ohms with 12.5 volts
500 watts @ 2ohms with 14.4 volts
500 watts @ 4ohms with 14.4 volts


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



89grand said:


> No, that's not it.
> 
> You have regulated and unregulated power supplies in amplifiers.
> 
> ...


ok but it IS regulating the output based on impedance. might not technically be a regulated amp, but it is regulating something.  lol

i know what you're saying... it is pretty simple really.


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## tcguy85 (Oct 29, 2007)

*Re: Amplifier power output myths exposed!*



FoxPro5 said:


> Neither is power. Rated power is not average power. Music drives AC voltage and it's constantly changing as well. Anyone who thinks their amp puts out 100 watts to their speakers has done too many damn quaaludes.


yup! true true!

when somebody asks me how much power i am running i tell them i don't know, but i have so and so "on tap".


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## Oliver (Jun 25, 2007)

R.I.P.S.

http://mobile.jlaudio.com/products_amps_pages.php?page_id=228


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## tcguy85 (Oct 29, 2007)

right from jl from that page.... Conventional amplifiers are designed to produce optimum power at a particular impedance (2 ohm, for example). When asked to run above that impedance (say, 4 ohm), *these amplifiers lose power (half their power from 2 ohm to 4 ohm)*. hahah


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## ErinH (Feb 14, 2007)

89grand said:


> I think the JL has a regulated power supply, whereas I don't think the Alpine does. Yet they both regulate output based of off load impedance.


yes, it does. Not sure how practical it is though. I understand it, and while it's cool, what happens if you're not running a slash for your front stage and the voltage drops?... I would imagine the level matching just went out the window. *not sure how much that matters, but something I just thought about*



tcguy85 said:


> when somebody asks me how much power i am running i tell them i don't know, but i have so and so "on tap".


when someone asks me I tell them approximately what I set the gain for. and I almost always listen to it at that level.


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## Oliver (Jun 25, 2007)

Then there are people who get an amp modded so it kicks into 8 ohms


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## FoxPro5 (Feb 14, 2006)

The actual testing of a 500/1 should give some indication of what RIPS actually does:

Output Power (Resistive) (4 ohms @ 60 Hz to 1% THD+N): 
605 watts @ 14 volts; 
601 watts @ 12.8 volts; 
591 watts @ 10.5 volts
Output Power (Resistive) (2 ohms @ 60 Hz to 1% THD+N): 
620 watts @ 14 volts; 
604 watts @ 12.8 volts; 
598 watts @ 10.5 volts

Output Power (Reactive) (4-ohm IHF Load @ 60 Hz to 1% THD+N): 639 watts
Output Power (Reactive) (2-ohm IHF Load @ 60 Hz to 1% THD+N): 733 watts

http://www.carsound.com/reviews/amps/jl_5001.html


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## chad (Jun 30, 2005)

a$$hole said:


> R.I.P.S.
> 
> http://mobile.jlaudio.com/products_amps_pages.php?page_id=228


You should call them or e-mail them and have them explain to you how it senses the impedance for the presto changeo. it will be one of the most frustrating things in your life! because they dunno, and they won't let you talk to anyone that does know.


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## 89grand (Nov 23, 2006)

tcguy85 said:


> right from jl from that page.... Conventional amplifiers are designed to produce optimum power at a particular impedance (2 ohm, for example). When asked to run above that impedance (say, 4 ohm), *these amplifiers lose power (half their power from 2 ohm to 4 ohm)*. hahah


They may say that, but it's clearly false as the test reports indicated. 

I have no idea why everyone thinks they do, because they don't.


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## ErinH (Feb 14, 2007)

chad said:


> You should call them or e-mail them and have them explain to you how it senses the impedance for the presto changeo. it will be one of the most frustrating things in your life! because they dunno, and they won't let you talk to anyone that does know.


lmfao! 



89grand said:


> They may say that, but it's clearly false as the test reports indicated.
> 
> I have no idea why everyone thinks they do, because they don't.


Think he was agreeing with you and pointing out that JL is nuts.


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## 89grand (Nov 23, 2006)

bikinpunk said:


> yes, it does. Not sure how practical it is though. I understand it, and while it's cool, what happens if you're not running a slash for your front stage and the voltage drops?... I would imagine the level matching just went out the window. *not sure how much that matters, but something I just thought about*
> 
> 
> 
> when someone asks me I tell them approximately what I set the gain for. and I almost always listen to it at that level.


If the voltage drops from 14 to 12 volts, you're probably losing something like 1.something db's from the unregulated amp. Nothing insane, and probably not really enough to notice, but it will happen.

I've always thought regulated power supplies made the most sense. Unfortunately, they may be more expensive as they have become more and more rare.


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## chad (Jun 30, 2005)

bikinpunk said:


> yes, it does. Not sure how practical it is though. I understand it, and while it's cool, what happens if you're not running a slash for your front stage and the voltage drops?... I would imagine the level matching just went out the window. *not sure how much that matters, but something I just thought about*


No, No rail voltage drops, gain ALWAYS remains constant. So gain wilbe the same but available power does not (amp clips sooner)


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## 89grand (Nov 23, 2006)

FoxPro5 said:


> The actual testing of a 500/1 should give some indication of what RIPS actually does:
> 
> Output Power (Resistive) (4 ohms @ 60 Hz to 1% THD+N):
> 605 watts @ 14 volts;
> ...


Yeah, those numbers show it has a regulated power supply or pretty much so.


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## ErinH (Feb 14, 2007)

chad said:


> No, No rail voltage drops, gain ALWAYS remains constant. So gain wilbe the same but available power does not (amp clips sooner)


ahhh, gotcha. I wasn't thinking about clipping at all. 

I almost didn't type that original response but figured if I did I'd get a good answer. Sure enough...


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## tcguy85 (Oct 29, 2007)

bikinpunk said:


> lmfao!
> 
> 
> 
> *Think he was agreeing with you and pointing out that JL is nuts.*


you got it!


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## ErinH (Feb 14, 2007)

89grand said:


> I've always thought regulated power supplies made the most sense. Unfortunately, they may be more expensive as they have become more and more rare.


I'm still not sure how practical it is. At least for most of us guys who aren't running insane amounts of power. (keep in mind I have a 1000/1 and loves it!)


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## tcguy85 (Oct 29, 2007)

FoxPro5 said:


> The actual testing of a 500/1 should give some indication of what RIPS actually does:
> 
> Output Power (Resistive) (4 ohms @ 60 Hz to 1% THD+N):
> 605 watts @ 14 volts;
> ...


not really so regulated then huh?


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## t3sn4f2 (Jan 3, 2007)

Thankfully I'm not included in this since I always state in 4 to 8 ohms and say at least twice the power when moving up in ohms.


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## chad (Jun 30, 2005)

One more thing before bed....

Remember that amps take little voltage and make big voltage, that's it. take the numbers in the OP and convert them to voltage, you will see that output voltage decreases at lower impedances whereas if it were a true double output voltage would stay rock solid. this makes it MUCH easier to understand


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## ErinH (Feb 14, 2007)

tcguy85 said:


> not really so regulated then huh?


I dunno. Seems to be doing it's job pretty well. 14 watts is only 2% of the max rated power FoxPro posted.


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## 89grand (Nov 23, 2006)

tcguy85 said:


> not really so regulated then huh?


It's pretty close, which means the amp is pretty tightly regulated. The power differences between input voltages are next to nothing, a fraction of 1 dB.

Totally different from your run of the mill unregulated amp where power output is nearly 30% higher from 12.5 to 14.4 volts.


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## tcguy85 (Oct 29, 2007)

89grand said:


> It's pretty close, which means the amp is pretty tightly regulated. The power differences between input voltageS are next to nothing, a fraction of 1 dB.
> 
> Totally different from your run of the mill unregulated amp where power output is nearly 30% higher from 12.5 to 14.4 volts.


not sure i'd call an almost 100 watt difference that tightly regulated. probably wouldn't hear the difference between 6xx and 7xx but still a good difference anyway, it's not *that* close.


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## 89grand (Nov 23, 2006)

chad said:


> One more thing before bed....
> 
> Remember that amps take little voltage and make big voltage, that's it. take the numbers in the OP and convert them to voltage, you will see that output voltage decreases at lower impedances whereas if it were a true double output voltage would stay rock solid. this makes it MUCH easier to understand


True dat G!


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## tcguy85 (Oct 29, 2007)

bikinpunk said:


> I dunno. Seems to be doing it's job pretty well. 14 watts is only 2% of the max rated power FoxPro posted.


i was thinking more of the almost 100 watt difference in the reactive loads between 2 and 4 ohms. i wouldn't call 100 watts that close.


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## 89grand (Nov 23, 2006)

tcguy85 said:


> not sure i'd call an almost 100 watt difference that tightly regulated. probably wouldn't hear the difference between 6xx and 7xx but still a good difference anyway, it's not *that* close.



Where do you see a 100 watt difference between input voltages?

At 4 ohms, I'm seeing like 14 watts, and when you're dealing with nearly 600 watts, 14 is really nothing. And we're looking at the difference between 10.5 volts and 14.4. At 12.8 to 14.4 volts, there's only a 4 watt difference. In other words, this amp has a regulated power supply. 


Output Power (Resistive) (4 ohms @ 60 Hz to 1% THD+N):
*605* watts @ 14 volts;
601 watts @ 12.8 volts;
*591 *watts @ 10.5 volts


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## tcguy85 (Oct 29, 2007)

89grand said:


> Where do you see a 100 watt difference between input voltages?
> 
> At 4 ohms, I'm seeing like 14 watts, and when you're dealing with nearly 600 watts, 14 is really nothing.
> 
> ...


the reactive loads between 2 and 4 ohms. 639 and 733. almost 100 watts right there. so between ohm loads it's not THAT close. still closer than most but not that close.


here.... 
Output Power (Reactive) (4-ohm IHF Load @ 60 Hz to 1% THD+N): 639 watts
Output Power (Reactive) (2-ohm IHF Load @ 60 Hz to 1% THD+N): 733 watts

but yes... they did a good job at regulating power based on input voltage but not over ohm loads.


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## FoxPro5 (Feb 14, 2006)

In addition to what Chad said, all you have to do is take your favorite music track, put it in and crank it....and then watch for the highest AC voltage on a DMM. 

If we could somehow find the avg impedance of the VC as it changes over time (maybe you can? I don't know) then you can calculate both peak and average power:

VAC^2/impedance = power (watts)

Then take .707 of that to find the avg power output in watts.


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## 89grand (Nov 23, 2006)

tcguy85 said:


> the reactive loads between 2 and 4 ohms. 639 and 733. almost 100 watts right there. so between ohm loads it's not THAT close. still closer than most but not that close.
> 
> 
> here....
> ...


But see, that's good right there. That's not a negative as far as I'm concerned. 

It's an amp with a regulated power supply, so it delivers rated power down to 10.5 volts as promised and delivers, and it's supposed to regulate the output power into lower impedances, but it doesn't totally, and I like that.


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## tcguy85 (Oct 29, 2007)

89grand said:


> But see, that's good right there. That's not a negative as far as I'm concerned.
> 
> It's an amp with a regulated power supply, so it delivers rated power down to 10.5 volts as promised and delivers, and it's supposed to regulate the output power into lower impedances, but it doesn't totally, and I like that.


ok thats cool and all i just don't like this..

The remarkable R.I.P.S. System™ ensures *consistent* power delivery *over* a wide range of battery voltages and *load impedances*.

a 100 watt difference isn't very consistent imo. but whatever. it's all good.


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## ErinH (Feb 14, 2007)

Fox, do you care to explain to me what a 'reactive load' is, exactly? I've never heard that term before. Maybe it could clear up this small little debate.


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## tcguy85 (Oct 29, 2007)

bikinpunk said:


> Fox, do you care to explain to me what a 'reactive load' is, exactly? I've never heard that term before. Maybe it could clear up this small little debate.


well i think "resistive" means just off of a bank of resistors, so a constant impedance. maybe "reactive" means to an actual speaker where the impedance both increases and decreases. 

i might be way off, but thats what i am gathering from it.


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## ErinH (Feb 14, 2007)

tcguy85 said:


> well i think "resistive" means just off of a bank of resistors, so a constant impedance. maybe "reactive" means to an actual speaker where the impedance both increases and decreases.
> 
> i might be way off, but thats what i am gathering from it.


logical. I was thinking resistive as being tied to a speaker, but you could be correct.

Fox?....


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## FoxPro5 (Feb 14, 2006)

bikinpunk said:


> Fox, do you care to explain to me what a 'reactive load' is, exactly? I've never heard that term before. Maybe it could clear up this small little debate.


Premature ejaculation vs ultimate swimmer control.


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## ErinH (Feb 14, 2007)

FoxPro5 said:


> Premature ejaculation vs ultimate swimmer control.


I'm in the middle of that road...


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## tcguy85 (Oct 29, 2007)

FoxPro5 said:


> Premature ejaculation vs ultimate swimmer control.


huh? lol i don't get it.


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## thylantyr (Jan 21, 2008)

What is the load {physical device} used for testing these amps in post #1 ?
How long were the test tones played for ?


re: JL R.I.P.S

http://www.createforum.com/petereuro/viewtopic.php?t=342&mforum=petereuro


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## 89grand (Nov 23, 2006)

thylantyr said:


> What is the load {physical device} used for testing these amps in post #1 ?
> How long were the test tones played for ?
> 
> 
> ...


I don't know. Car Audio & Electronics tested them.


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## mtnickel (Mar 15, 2005)

FoxPro5 said:


> In addition to what Chad said, all you have to do is take your favorite music track, put it in and crank it....and then watch for the highest AC voltage on a DMM.
> 
> If we could somehow find the avg impedance of the VC as it changes over time (maybe you can? I don't know) then you can calculate both peak and average power:
> 
> ...


Well, what you see on a DMM is more likely to be the RMS value. The rms is usually done over some time interval, hence the mean. Your needle (or digital display) won't be nearly fast enough to show the transient of a waveform. That method would certainly work for finding the aprox RMS power (and using the nominal impedance would be a rough estimate).

To find peak power, you could perhaps just disconnect all the speakers (infinite impedance), and run a square wave output, to see what the rail voltages are. then do the calculation from there.

Just my 2 cents.


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## tcguy85 (Oct 29, 2007)

mtnickel said:


> Well, what you see on a DMM is more likely to be the RMS value. The rms is usually done over some time interval, hence the mean. Your needle (or digital display) won't be nearly fast enough to show the transient of a waveform. That method would certainly work for finding the aprox RMS power (and using the nominal impedance would be a rough estimate).


chad told me to throw my DMM away if i was going to use it to estimate actual wattage. personally i don't see why it won't get you a rough questimate. but i usually listen to chad. he was right about the dayton ho sub.


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## mtnickel (Mar 15, 2005)

tcguy85 said:


> chad told me to throw my DMM away if i was going to use it to estimate actual wattage. personally i don't see why it won't get you a rough questimate. but i usually listen to chad. he was right about the dayton ho sub.


Ya, for any true amplifier output test you should have load resistors and a scope (or very high quality DMM that can show wavefrom).

I just make sure i have much MORE than enough power for the drivers, then who cares about measuring. For me, my 150x2 @ 8 ohms mids (75x4 bridged), 150x2 @ 4 ohms tweets, and ~500x1 @ 4 bridged to sub seem to be plenty.


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## thylantyr (Jan 21, 2008)

89grand said:


> I don't know. Car Audio & Electronics tested them.


 

When you read amp tests and they say 8 ohm, 4 ohm, 2 ohm, 1 ohm,
do you ever wonder where they get these precision loads that
are 8.0 ohms, etal, not 8.2 ohm, not 3.8 ohm, not 4.5 ohm, not
2.2 ohm... lol

I've seen some bad test published because they used bad loads.


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## chad (Jun 30, 2005)

thylantyr said:


> What is the load {physical device} used for testing these amps in post #1 ?
> How long were the test tones played for ?
> 
> 
> ...


Thank you for posting that! After 4 years I finally have a decent answer as to how the power supply voltage is derived!!!!!!

WOOT!

Chad


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## thylantyr (Jan 21, 2008)

chad said:


> Thank you for posting that! After 4 years I finally have a decent answer as to how the power supply voltage is derived!!!!!!
> 
> WOOT!
> 
> Chad


Did you read about the 'latched' part ?  
I didn't know it 'latched', I thought the design was
dynamic.


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## chad (Jun 30, 2005)

thylantyr said:


> Did you read about the 'latched' part ?
> I didn't know it 'latched', I thought the design was
> dynamic.


Yeah, they told me it latched years ago when I enquired, what they could not tell me ws how the impedance was derived and what they did tell me was utterly wrong.


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## Dangerranger (Apr 12, 2006)

I think it's said that way more because most people could care less about trying to calculate a specific amplifier's output, take efficiency into account, etc. "x" amount of power multiplied/divided by two makes it pretty easy for the average joe to get a roundabout idea of how well an amplifier will meet his system requirements. Doubling the power nets a 3db increase, a few watts won't make a noticeable difference in most cases. Like the PPI A600.2 on the first page, making 176W at 4 ohm, and 304W at 2 ohm. That 304W vs the ~350W that it would be if the output truly doubled with halving impedance, looks like a big difference on paper but using 304W as the reference it would take 380W to net just a 1db increase, which is generally considered to be the threshold of a human's perception of volume increasing. 350 you're talking barely over half a decibel.


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## sqshoestring (Jun 19, 2007)

To test they should run the amp for a while into the load, then measure the load hot.

I have heard of some amps regulating the PS because of how they are made, the low voltage for op amps can go too high if the amp sees over 13v or something. So it is unregulated until it gets 13v or more, or where ever they set it at.

I also read another paper about amps talking about this doubling. I wish I could find it, but it (IIRC) said that depends on how the amp is designed. According to this place a better quality amp will not double, will not gain some huge amount at half the load when used within factory specs. But they said many makers want to advertise that so they make them differently to raise the power a lot bridged even though they rarely actually double.


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## chad (Jun 30, 2005)

An amplifier will NEVER really double wattage into half impedance given a constant voltage input, some get so close that it's splitting hairs but that's rare.


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## Oliver (Jun 25, 2007)

3 dB = raising your voice a little

10 dB = shouting or twice as loud as it sounded [add a zero to your amps rating, 100 watts ~ 1,000 watts ]

Classic post {should I buy this amp at 350 watts or this one at 425 watts}
to power my sub.


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## Diru (May 23, 2006)

chad said:


> An amplifier will NEVER really double wattage into half impedance given a constant voltage input, some get so close that it's splitting hairs but that's rare.


I can try


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## chad (Jun 30, 2005)

a$$hole said:


> 3 dB = raising your voice a little


And it takes a doubling of power to do that


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## envisionelec (Dec 14, 2005)

tcguy85 said:


> the reactive loads between 2 and 4 ohms. 639 and 733. almost 100 watts right there. so between ohm loads it's not THAT close. still closer than most but not that close.
> 
> 
> here....
> ...


An IHF reactive load is closer to a real speaker than resistive. But displaying a reactive load measurement does not tell the whole story about actual power output. That's because the load "reacts" to the input voltage. This is why you sometimes see a higher "power output" rating - it's power based on the reactance of the load. This can also work against the measurements, in cases where the phase angle is so steep (or shallow) that almost no work is being done by amplifier, or that nearly all the current is being sent back to the output transistors, respectively. The AudioGraph PowerCube technology is the only automatic measurement system that measures all these phase angles and reports them. Rockford Fosgate was one of the first companies to use the PowerCube - and had a big book of tested power amplifiers available to dealers in their training in the 1990s. Was amusing, to say the least - but it taught me a great deal about which amplifier designs actually perform and which do not.

The JL amplifier appears to do exactly what it's designed. PG did this with their M series amplifier - mainly to limit maximum power to keep the amplifier from destroying itself into low impedance loads; but many people misunderstood its intention.


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## Oliver (Jun 25, 2007)

envisionelec said:


> The JL amplifier appears to do exactly what it's designed.


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