Phoenix Gold Phorum

So this is probably a dumb question, but I want to know the answer and I have not been able to find anything...

So if I have a amp that does 500x1 RMS @4ohm (it draws 11.18amps and produces 44.7 volts), and I put a 2ohm load on it and set the gains so that the amp is producing 500 watts according to the voltage (this draws 15.81 amps and produces 31.6 volts), really whats the difference between these except for the extra 5amp draw, and how much heat will be added by that extra 5amps?

My concern is that I will overheat the amp. Here's my setup. I have an XS2500 that I have running a 2ohm Solobaric 8" L7. I have a 2 high CFM server grade fans in the compartment with the amp, one of the fans is blowing directly on the amp and I have a cap as well. I have set my gains using a DMM to about 31v, which is around 500watts @2ohm according to the math. I think that setup will be ok, since I am not doubling the power when using a 2 ohm load. I ran this for about 15 min, and the amp didn't get that hot... But I really don't know how much more heat will be generated by that extra 5 amps of power. I think my fans should be good enough (You should hear them when they come on I really need to make a heat sensing/voltage control circuit for my fans to keep them quite).

Thanks all!

The amp will get hotter for one, but you've addressed that issue w/the fans. The dampening factor will change along w/the THD- which you'll probably never hear.

The AC voltage is less because your resistance is less. Less resistance = more power. It's all in the math, but you seem to know that too.

I guess I should explain where my thinking is on this as well. In all the reading I did researching this question, all I could find about running a 2ohm load was how much power you CAN get out of your amp, if it's 2ohm stable, compared to running a 4ohm load. They then go on to talk about how much hotter the amp gets and all that jazz. Well I don't want more power out of my amp, 500watts is good enough for me! My XS2500 is rated at 500x1 RMS @4ohms, and that makes it perfect for my needs. So what the difference between 500watts @4ohms, and 500watts @2ohm to my ears/equipment? Will that make the amp that much hotter for it to cause a problem? That's all I really want know.

Also the only reason I am running this sub is because I have it, and it would just be collecting dust right now, so that's why I am using it. I plan on getting a new sub and running a 4ohm load on the amp by the end of the year, so this is only a temporary situation. I really like this amp so far, and I want to keep it for a long time, so I don't want to blow it by running a crazy watt 2ohm load on it. That and my sub is only rated for 450watts RMS, so I don't want that guy to go out either.

If i recall, and i might be wrong, but 500W RMS @ 4ohm or 500W RMS @ 2 ohm is supposed to be the same thing to your ears. If you have an amp that is stable at 2ohm, and provide 500w rms at 2 ohm with a 2ohm sub, or an amp that provide 500w rms at 4 ohm with the same sub but 4ohm version, there should be no difference...

At least that's the comprehension i have to it, i may be wrong tho...

str3atwarrior wrote:If i recall, and i might be wrong, but 500W RMS @ 4ohm or 500W RMS @ 2 ohm is supposed to be the same thing to your ears. If you have an amp that is stable at 2ohm, and provide 500w rms at 2 ohm with a 2ohm sub, or an amp that provide 500w rms at 4 ohm with the same sub but 4ohm version, there should be no difference...

At least that's the comprehension i have to it, i may be wrong tho...

Thanks for proving why I needed to ask the question, I am confused about this as well! There IS a difference in power draw @2ohms compared to 4ohms, 5amps, but I don't know if that's a big difference or not, hence the question

I kinda figured 500watts is 500watts to my ears, but...

I'd have to ask my boss about this, he will know for sure. Will try to get to him today and come back with an answer

500 watts, weather at 2 ohms or 4 ohms will still draw the same current. It's the input voltage that matters.

Example: 500 watts divided by 13.8 volts = 36.23 amperes. Take into account that that is also at a, say 60% efficiency. So now we need to take 36.23 amperes X 100% = 3623, divide that by the 60% efficiency rate and you get 60.3 amperes of total current.

At what volume you did the tests, or did you, IDK, but the math is wrong.
500 watts is the AC output of the amp to drive the speaker, that we know.
But you're dividing the wattage (500) by the AC voltage of the amp which is the same thing. What you need to divide the watts by is the voltage FEEDING the amp, ie the vehicles electrical system, 12-14.4 volts.

Do you understand it any better?

smgreen20 wrote:500 watts, weather at 2 ohms or 4 ohms will still draw the same current. It's the input voltage that matters.

Example: 500 watts divided by 13.8 volts = 36.23 amperes. Take into account that that is also at a, say 60% efficiency. So now we need to take 36.23 amperes X 100% = 3623, divide that by the 60% efficiency rate and you get 60.3 amperes of total current.

At what volume you did the tests, or did you, IDK, but the math is wrong.
500 watts is the AC output of the amp to drive the speaker, that we know.
But you're dividing the wattage (500) by the AC voltage of the amp which is the same thing. What you need to divide the watts by is the voltage FEEDING the amp, ie the vehicles electrical system, 12-14.4 volts.

Do you understand it any better?

Ok, so I measured it with the car running (13.x volts, my charging system is fine) and my stereo 3/4 of the way turned up, like I am supposed to when setting the gains with a DMM (I followed all the instructions), and my gains are set so the output of the amp is 31.4v or something very close. It doesn't really matter what the input voltage is, because either way I believe the XS has a regulated power supply, I think, (because they can limit the current produced by the amp, I don't think you can do that with an unregulated power supply, but I could be wrong on this, so correct me if I am wrong) so the amp will only see a constant voltage anyways, really making this a moot point...

Either way at 31.x volts @2ohm, it's still making 500watts correct? My math should be correct on that. So this really doesn't answer my question, unless I am totally missing something here…

I want to know if there is going to be a big difference to my amp between a 500watt load @2ohm, compared to a 500watt load @4ohms. It's going to get hotter because it pulls more current, I get that, but how much? Am I going to damage anything by running this amp with ample cooling and power with a 500watt 2ohm load, as opposed to a 500watt 4ohm load?

Nobody talks about running a 2ohm load at the same wattage as a 4ohm load, all they talk about is the increase in wattage when running a lower resistance and what to do to protect your amp for more watts! I don't want more watts, same watts, different resistance. How's that going to effect me, if at all?

Am I being clear on what I am asking?

31.x IS 500 watts. They are one in the same. You're just reading them differently. To get 500 watts at 2 ohms, you'll set the amps output to read the 31.6 vac that you're talking about.

The math is as follows: 500 watts at 2 ohms (500 x 2) = 1000. To get the AC number you need, you have to square root the 1000 which equals 31.6

So do you see how 500 watts is the SAME as 31.6 vac?

The XS2500 is regulated, but not very tightly so if the voltage the amp sees changes, it will still change the power output.

The amps power is supplied by the vehicles electrical system, on avg. 13.8 vdc while running. It's that voltage you need to input into the formula. If the wattage is to remain the same (500) and you change the voltage to the amp, then you will also change the amperage the amp will draw. If you were able to (as in if the amp could handle it) give the amp 24 vdc, then the amp would draw ~35 amperes at 60% efficiency VS the 60 amperes at 12 vdc.

Did I loose you yet?

smgreen20 wrote:31.x IS 500 watts. They are one in the same. You're just reading them differently. To get 500 watts at 2 ohms, you'll set the amps output to read the 31.6 vac that you're talking about.

The math is as follows: 500 watts at 2 ohms (500 x 2) = 1000. To get the AC number you need, you have to square root the 1000 which equals 31.6

So do you see how 500 watts is the SAME as 31.6 vac?

The XS2500 is regulated, but not very tightly so if the voltage the amp sees changes, it will still change the power output.

The amps power is supplied by the vehicles electrical system, on avg. 13.8 vdc while running. It's that voltage you need to input into the formula. If the wattage is to remain the same (500) and you change the voltage to the amp, then you will also change the amperage the amp will draw. If you were able to (as in if the amp could handle it) give the amp 24 vdc, then the amp would draw ~35 amperes at 60% efficiency VS the 60 amperes at 12 vdc.

Did I loose you yet?

I totally understand that concept, I don't think we are reading the same book, so no way are we on the same page I think you are correcting my statment on the amps being drawn, not my question, so I think that's where I am lost. You are correct, my amperage fiugres were wrong, that's what I get for trusting a website to do my math

I guess I am confused because when adjusting the gains with a DMM, input voltage was never mentioned, (I guess assumed at 13.8??) so ya. How will this effect me, that's where I am lost. That's all fine and dandy, but when I did my test/config, is my amp producing WAY MORE POWER than I intended? It doesn't sound bad/distorted/clipped, and right now I get 31.5vac out of the amp with the car running playing a test tone...

At 2 ohms it might lower the dampening factor of the amp and raise the THD, which you probably wont hear, and at 2 or 4 ohms, with the total output being 500 watts, the amperage will stay the same and the amp wont work any harder or be stressed any more then it would be at 4 ohms.

Does that get it done for you?

smgreen20 wrote:At 2 ohms it might lower the dampening factor of the amp and raise the THD, which you probably wont hear, and at 2 or 4 ohms, with the total output being 500 watts, the amperage will stay the same and the amp wont work any harder or be stressed any more then it would be at 4 ohms.

Does that get it done for you?

Perfect!! This was my thinking, but I am fairly new to this car stereo stuff, at least actually caring about what I am doing , so I just wanted to verify, and nothing I found could do that for me. All the math seemed to add up right, but math was never my strong suit, so I asked the stupid question

I now see where your previous comments tie into this all, and it makes sense. Because the amp will only draw 60amps running 500watts @2ohm, this is fine because it is what it is designed for, just like if it was a 4ohm load. I get it

It seems that whenever someone wants to run a 2ohm load, they want to blow their amp, instead of keeping it within it's designed limitations, so this info really wasn't out there.

Thanks for bearing with my noobishness

No problem. We all have to learn it from somewhere. Thank you for bearing w/my way of explaining.

It's when people try to get more/double the power at the 2 ohms is when they get into trouble. I see no reason why the amp would have issues running 2 ohms as opposed to 4 ohms as long as it's kept at the 4 ohm power output level AND as long as the amp is rated to handle the lower impedance.

Eric D could simplify and elaborate further on this topic.