Sub/amp wiring for resistance conundrum...

[Bellmeister]

Ive been running a 400watt RMS 8" SKAR SVR sub with a Skar rp 1200 watt amp at 4 ohms. The amp does 500 watts RMS at 4 ohms. 500 watts amp, 400 watts RMS sub, I thought was perfect ( i also have an LC2i that adds bass)
But Ive gotten advice from a couple people that I should wire it to run at 1 ohm, which the amp can do, and just turn the gain down. ??? Something about how Im pushing the amp too much at 4 ohms but I thought it was the opposite! I thought 1 ohm was running the amp wide open and hotter. 1200 watts with a 400 watt sub? Wonder why Im being told that, sounds way off to me. Thanks

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[tommydh 10+ year member]

It is way better to "over power" a sub than to "under power". As long as you properly set the gains and don't push a distorted signal that sub should be fine. I was running a single Sundown SD-2 10" off of a RF T1500 at 1 ohm. I never had an issue with the sub or the amp running too hot. Just think of it like you have 2 cars 1 has top speed of 100 MPH other has top speed of 160MPH which one will do 95 easier?

 

[ThatChevyGuy 5,000+ posts]

I'd swap for a 2ch class ab and bridge at 4ohms a decent 600rms rated or so you want more power for headroom if needed than sub rms rating

is your sub a dual 2 ohm ?

 

[Bellmeister]

I'd swap for a 2ch class ab and bridge at 4ohms a decent 600rms rated or so you want more power for headroom if needed than sub rms rating

is your sub a dual 2 ohm ?

yes dual 2 ohm

 

[mat3833 10+ year member]

It is way better to "over power" a sub than to "under power". As long as you properly set the gains and don't push a distorted signal that sub should be fine. I was running a single Sundown SD-2 10" off of a RF T1500 at 1 ohm. I never had an issue with the sub or the amp running too hot. Just think of it like you have 2 cars 1 has top speed of 100 MPH other has top speed of 160MPH which one will do 95 easier?

This really doesn't translate to amps. Running 1 ohm is alot harder on the amp than running 4 ohms.

A better automotive comparison would be a gearing difference. Car has a 7000 rpm Rev limit, in high gear 4 ohm would be like the car turning 2500RPM at 70mph while 1 ohm would be like the same engine turning 6000RPM to do the same 70mph.

"over powering" a speaker is not nessecarily good not bad. Sending lots of clean power to a speaker is fine, but a speaker can quickly fail on below "rated" power with a clipped signal.

Matt

 

[mat3833 10+ year member]

Ive been running a 400watt RMS 8" SKAR SVR sub with a Skar rp 1200 watt amp at 4 ohms. The amp does 500 watts RMS at 4 ohms. 500 watts amp, 400 watts RMS sub, I thought was perfect ( i also have an LC2i that adds bass)
But Ive gotten advice from a couple people that I should wire it to run at 1 ohm, which the amp can do, and just turn the gain down. ??? Something about how Im pushing the amp too much at 4 ohms but I thought it was the opposite! I thought 1 ohm was running the amp wide open and hotter. 1200 watts with a 400 watt sub? Wonder why Im being told that, sounds way off to me. Thanks

Running the sub at rated power isn't bad. Running your amp at 4 ohms isn't bad either. There is nothing wrong with how you have your sub/amp set. Wiring down to 1 ohm would give you the ability to send much more power to the sub if you wanted too, but you could easily blow it if you don't know what you are doing.

Wiring to 1 ohm and turning the gain down to match the same power as 4 ohm doesn't offer any real benefit or downside in this case. Personally, I'd run at 4 ohm, but it's really down to personal preference and who/what you believe.

Matt

 

[metalheadjoe 10+ year member]

This really doesn't translate to amps. Running 1 ohm is alot harder on the amp than running 4 ohms.

A better automotive comparison would be a gearing difference. Car has a 7000 rpm Rev limit, in high gear 4 ohm would be like the car turning 2500RPM at 70mph while 1 ohm would be like the same engine turning 6000RPM to do the same 70mph.

Matt

How and why? Lots of people toss this claim around but nobody can explain it.
Output power equals input power times efficiency.

Analogies are generally worthless and inaccurate, but I am an auto enthusiast, so I'll play along. Your amp is closest to a transmission in the drivetrain comparison. It takes the power from the engine and ultimately converts it to travel speed. A 4-ohm load might be a higher gear, and a 1-ohm load might be a lower gear, but the transmission doesn't care. Its only function is to take input power from the engine and convert it to usable output power for the rest of the drivetrain. This is obviously over-simplified, because engines have power-curves, and you don't want to over-rev them OR lug them, which is why comparisons like this are worthless.

 

[Dafaseles]

Here's a question...
We know an amp running at 4 ohm with the gain set right before the clipping point puts out X amount of watts and is, let's just say hypothetically, it's 90% efficient.
At 2 ohm, with the gains set the same, it puts out Y amount of watts and, again hypothetically, is 85% efficient.
Now at 1 ohm, it puts out Z amount of watts and is 80% efficient.
What if you ran at 1 ohm, but set the gain to put out X amount of watts (what the amplifier puts out at 4 ohm right before clipping). Would that make the amplifier more efficient than at 4 ohm, considering you don't have the gains set so high? Or would it still be the hypothetically 90% efficient? Or would the efficiency be lower than 90% because it's wired to a 1 ohm load?
This thread made me wonder if that's the case or not.

 

[mat3833 10+ year member]

How and why? Lots of people toss this claim around but nobody can explain it.
Output power equals input power times efficiency.

Analogies are generally worthless and inaccurate, but I am an auto enthusiast, so I'll play along. Your amp is closest to a transmission in the drivetrain comparison. It takes the power from the engine and ultimately converts it to travel speed. A 4-ohm load might be a higher gear, and a 1-ohm load might be a lower gear, but the transmission doesn't care. Its only function is to take input power from the engine and convert it to usable output power for the rest of the drivetrain. This is obviously over-simplified, because engines have power-curves, and you don't want to over-rev them OR lug them, which is why comparisons like this are worthless.

Comparisons always have a caveat, hence why I stuck to a same gear and changed the RPM. In this case RPM could equal power in or amps in or whatever metric you wish, but the comparison is the same.


Here is the over simple way of explaining an amp:

Amps make power in one simple way, they produce voltage. The DC voltage from the car powers a toroidal transformer that converts the DC to AC voltage, and powers the Mosfets. These Mosfets have a few different specifications, but the main concern would be their current capacity. Say we we have 40 amp capable Mosfets.

Running an amp at maximum possible output power in this case, the input signal is "boosted" to whatever the output voltage is, say 40v. This would be the rail voltage, going above this "rail voltage" would cause clipping. The caps in the amp have a capacitance and a voltage rating, in this case we could say this amp has 40v "rail caps". The capacitance value matters, but in this case we can ignore it for the most part.

So, 40v of possible rail voltage, 40 amps of current available at maximum. Here's the Kicker, voltage is MUCH eaiser to produce in an amp and contributes alot less heat. That's why most industrial high power motors use 240v or 480v or even higher voltage. The higher the voltage, the less current you need to flow and vice versa. Using the 40v and 40a numbers above the amp would theoretically put out the following numbers, efficiency is 100 percent in this example.

4 ohm load - 40v and 10 amps = 400w
2 ohm load - 40v and 20 amps = 800w
1 ohm load - 40v and 40 amps = 1600w

AAs you can see, halving the resistance doubles the amperage, and therefore doubles the power. BUT you are also at least doubling the heat created.

So, we want to make 400w at 1 ohm, we get the following:

1 ohm load - 20v and 20 amps = 400w

So 4 ohm load = 10 amps and a 1 ohm load = 20 amps.

These calculations are very basic until you take into account efficiency. If you take a basic 90 percent efficiency rating at 4 ohms, and a generous 70 percent efficiency rating at 1 ohm you get the following:

4 ohms requires 11 amps of input current
1 ohm requires 26 amps of input current.

Amps are much more efficient when fully loaded(as far as I know, could be wrong on this one), so calculating efficiency for the 1 ohm load would be difficult.


TLDR:

Lower ohm loads require alot more current. Current = heat
Voltage is eaiser on coils and your amp
Amps are generally at least 20 percent more efficient at 4 ohms than 1ohm


Matt

 

[metalheadjoe 10+ year member]

Here's a question...
We know an amp running at 4 ohm with the gain set right before the clipping point puts out X amount of watts and is, let's just say hypothetically, it's 90% efficient.
At 2 ohm, with the gains set the same, it puts out Y amount of watts and, again hypothetically, is 85% efficient.
Now at 1 ohm, it puts out Z amount of watts and is 80% efficient.
What if you ran at 1 ohm, but set the gain to put out X amount of watts (what the amplifier puts out at 4 ohm right before clipping). Would that make the amplifier more efficient than at 4 ohm, considering you don't have the gains set so high? Or would it still be the hypothetically 90% efficient? Or would the efficiency be lower than 90% because it's wired to a 1 ohm load?
This thread made me wonder if that's the case or not.

I bet you're better off running a smaller amp harder verses running a bigger amp easier (theoretically speaking), because each electronic component consumes a tiny amount of power, which decreases efficiency. Larger amps don't turn off components they don't need, which is why larger amps draw more idle current.

I know it's an indirect response. Listening habits play a huge role here.

 

[mat3833 10+ year member]

Here's a question...
We know an amp running at 4 ohm with the gain set right before the clipping point puts out X amount of watts and is, let's just say hypothetically, it's 90% efficient.
At 2 ohm, with the gains set the same, it puts out Y amount of watts and, again hypothetically, is 85% efficient.
Now at 1 ohm, it puts out Z amount of watts and is 80% efficient.
What if you ran at 1 ohm, but set the gain to put out X amount of watts (what the amplifier puts out at 4 ohm right before clipping). Would that make the amplifier more efficient than at 4 ohm, considering you don't have the gains set so high? Or would it still be the hypothetically 90% efficient? Or would the efficiency be lower than 90% because it's wired to a 1 ohm load?
This thread made me wonder if that's the case or not.

As far as I know, amps are most efficient when fully loaded so this idea doesn't track.

Matt

 

[Dafaseles]

I bet you're better off running a smaller amp harder verses running a bigger amp easier (theoretically speaking), because each electronic component consumes a tiny amount of power, which decreases efficiency. Larger amps don't turn off components they don't need, which is why larger amps draw more idle current.

I know it's an indirect response. Listening habits play a huge role here.

Yeah, I have to agree. Taking it a step further, you paid let's say $400 for a 1200 watt amp to get 500 watts out of it, when you could have bought a 500 watt amp for say $150 and all would have the same output and same end result running 1 ohm. 500 watts isn’t going to stress most people electrical out that much, I was just curious.

As far as I know, amps are most efficient when fully loaded so this idea doesn't track.

Matt

So then it would be more efficient at 4 ohm just under clipping than 1 ohm with the gain turned down. Interesting. I can see where that can be true. It's made to work a certain way. One day, I'll have to try it out.

 

[mat3833 10+ year member]

Yeah, I have to agree. Taking it a step further, you paid let's say $400 for a 1200 watt amp to get 500 watts out of it, when you could have bought a 500 watt amp for say $150 and all would have the same output and same end result running 1 ohm. 500 watts isn’t going to stress most people electrical out that much, I was just curious.


So then it would be more efficient at 4 ohm just under clipping than 1 ohm with the gain turned down. Interesting. I can see where that can be true. It's made to work a certain way. One day, I'll have to try it out.

I'm speaking for class D amps specifically. Idk about class A/B or any others. It shouldn't be too hard to test, but I don't have a reliable clamp.

Matt

 

[metalheadjoe 10+ year member]

Comparisons always have a caveat, hence why I stuck to a same gear and changed the RPM. In this case RPM could equal power in or amps in or whatever metric you wish, but the comparison is the same.


Here is the over simple way of explaining an amp:

Amps make power in one simple way, they produce voltage. The DC voltage from the car powers a toroidal transformer that converts the DC to AC voltage, and powers the Mosfets. These Mosfets have a few different specifications, but the main concern would be their current capacity. Say we we have 40 amp capable Mosfets.

Running an amp at maximum possible output power in this case, the input signal is "boosted" to whatever the output voltage is, say 40v. This would be the rail voltage, going above this "rail voltage" would cause clipping. The caps in the amp have a capacitance and a voltage rating, in this case we could say this amp has 40v "rail caps". The capacitance value matters, but in this case we can ignore it for the most part.

So, 40v of possible rail voltage, 40 amps of current available at maximum. Here's the Kicker, voltage is MUCH eaiser to produce in an amp and contributes alot less heat. That's why most industrial high power motors use 240v or 480v or even higher voltage. The higher the voltage, the less current you need to flow and vice versa. Using the 40v and 40a numbers above the amp would theoretically put out the following numbers, efficiency is 100 percent in this example.

4 ohm load - 40v and 10 amps = 400w
2 ohm load - 40v and 20 amps = 800w
1 ohm load - 40v and 40 amps = 1600w

AAs you can see, halving the resistance doubles the amperage, and therefore doubles the power. BUT you are also at least doubling the heat created.

So, we want to make 400w at 1 ohm, we get the following:

1 ohm load - 20v and 20 amps = 400w

So 4 ohm load = 10 amps and a 1 ohm load = 20 amps.

These calculations are very basic until you take into account efficiency. If you take a basic 90 percent efficiency rating at 4 ohms, and a generous 70 percent efficiency rating at 1 ohm you get the following:

4 ohms requires 11 amps of input current
1 ohm requires 26 amps of input current.

Amps are much more efficient when fully loaded(as far as I know, could be wrong on this one), so calculating efficiency for the 1 ohm load would be difficult.


TLDR:

Lower ohm loads require alot more current. Current = heat
Voltage is eaiser on coils and your amp
Amps are generally at least 20 percent more efficient at 4 ohms than 1ohm


Matt

Transformers do not invert DC into AC, no matter which fancy word you put before it.

Heat?? Seriously? You are grasping at straws if you bring heat effects into the equation. Do you want to introduce ambient temp as well? How about effectiveness of the thermal compound?

You could have said:
"I agree, 'output power equals input power times efficiency'", and left it at that.

 

[mat3833 10+ year member]

Transformers do not invert DC into AC, no matter which fancy word you put before it.

Heat?? Seriously? You are grasping at straws if you bring heat effects into the equation. Do you want to introduce ambient temp as well? How about effectiveness of the thermal compound?

You could have said:
"I agree, 'output power equals input power times efficiency'", and left it at that.

You are correct, the transformer(won't use the "fancy" word even if it's a descriptor and rather important in this case) steps up the voltage to the proper level for the rail caps, it's been a day. The 2 "rails" of mosfets actually "convert" the voltage by switching off and on making the signal. Either way, the example still stands, the transformer doesn't play any real part in the example.

I'm confused. How is heat grasping at straws? You do realize that heat is what kills amps most often right?

Driving amps too hard and blowing the mosfets - heat buildup caused their resistance to increase, which caused more heat to build up, which caused their resistance to increase, etc until POP!

Heat and moisture are the biggest issues in electronics. Heat reduces efficiency and/or melts things, and moisture allows things to corrode and either short to ground OR increases resistance and causes a component to blow.

Yea, "output power equals input power times efficiency", but you know what kills efficiency? HEAT! Amps run cooler at 4 ohm because they generate less heat because they pull less current! No matter how you look at it a 4 ohm load is eaiser on an amp. Current, aka heat generation, is the limiting factor in virtually all electronics.

There is a reason high power amps have big hunks of aluminum and/or fans to move air across those big ******* hunks of aluminum.

The same thing goes for the coil on your subwoofer. The coil needs to cool itself in some way or it will melt the epoxy and short out. Why would a coil generate heat? Oh yea, that's right current is flowing through a resistive load!

Cmon man, I'm not throwing ******** here. You asked a question, I gave the specific answer. If you want I'll dig up source material and some good-ol physics to prove my statements. Im deliberately keeping things simplified so it can be a general discussion.

Matt