Running low impedances

[Full Tilt 10+ year member]

I was just curious as to why people give so many warnings about operating amps at low impedences when you can get anywhere from half to a whole ohm of rise while playing. I decided to go with D4 subs to run at 1 ohm, but after rise I'll probably be seeing between 1.5 and 2. Why don't more guys wire for .5 nominal so you'll actually sit at about 1 after rise?

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[T3mpest 10+ year member]

Because impedance doesn't always rise.. When you drop to .5 yes, some of the frequencies will end up being higher than .5, some can also end up lower, which can damage equipment. Second, when you drop impedence you also reduce effeciency of the amp, which can often strain your electrical which in turn strains the amp.

Third reason is a bit more complicated, but also VERY important to realize and most don't, it as I state time and time again comes from people applies what people to "in the lane: on "burps" and misapplying it. (as the case is with rise like I stated earler) Anyways, most coils are already into thermal compression by the time you send a sub a 1ohm load on most of these bigger amps that people love to wire down low. When a coil heats up, it's DCR actually increases. On a burp we don't have to worry about this, on music we do. Even though you've dropped your amp lower on music after you run it for a while extra heat inside the coil is not only not great for the driver, but ends up raising the impedance again, which while this thermally helps the driver, also defeated the purpose of the lower ohm load.

Lastly, going from 3500 watts to 4200 watts for example, isn't really an audible difference. In bass frequencies you really need to gain a good 2-3db before you've gained anything too meaningful on music and that's trying to get well over 50% more watts from the amp, AFTER it deals with all the things fighting against this that I mentioned. Generally wiring that last step down isn't giving you that once you factor in everything...

So if you've got crazy electrical, subs that can easily thermally handle the power your putting on them (by easy I mean your well under RMS still, like in multi sub walls builds) and still have mechanical throw left, sure wire it down to .25 ohm and get 25% more power from the amp if the amp has no issue with it assuming it has stable power source to draw from. If your planning on burping, again wire it down as low as you can with good voltage and "roll" it up so it doesn't go into protect.

If your just an average guy with "ok" electrical that is quite a bit of power considering the subs your using and aren't competing to see a number on a screen, it's generally safer for all the equipment if you stick to normal loads, even on the competition grade stuff.

Example Can a Sundown 1500d run at .5 daily? Sure. Is it a good idea when running a set of SA-12's with stock electrical except for the big 3 being done.. IMO, NO and that's a pretty common setup around here.. It's good for 25% more power so less than a DB in the real world minus the power compression, impedance rise that causes and the lowered voltage due to the amp efficiency dropping from 68-61% (random numbers, but probably ball-parking) Just some food for though.

Edit: One last thing. If you look at the impedance graph of any subwoofer box, you'll see right at tuning impedance SPIKES, sometimes 4-8x it's nominal load. You'll also easily realize from common experience that the sub doesn't tend to get much quieter at tuning (often it's the opposite) even though your sub is often seeing 4-8x less power at that frequency. That's due to increased efficiency of the port. Bigger boxes again, tend to have more rise, but on a daily setup you'll often find bigger boxes tend to be louder, again especially near tuning. Power is far from everything, it SHOULD be a means to an end, no more no less.

 

[ciaonzo 5,000+ posts]

Because impedance doesn't always rise.. When you drop to .5 yes, some of the frequencies will end up being higher than .5, some can also end up lower, which can damage equipment. Second, when you drop impedence you also reduce effeciency of the amp, which can often strain your electrical which in turn strains the amp.
Third reason is a bit more complicated, but also VERY important to realize and most don't, it as I state time and time again comes from people applies what people to "in the lane: on "burps" and misapplying it. (as the case is with rise like I stated earler) Anyways, most coils are already into thermal compression by the time you send a sub a 1ohm load on most of these bigger amps that people love to wire down low. When a coil heats up, it's DCR actually increases. On a burp we don't have to worry about this, on music we do. Even though you've dropped your amp lower on music after you run it for a while extra heat inside the coil is not only not great for the driver, but ends up raising the impedance again, which while this thermally helps the driver, also defeated the purpose of the lower ohm load.

Lastly, going from 3500 watts to 4200 watts for example, isn't really an audible difference. In bass frequencies you really need to gain a good 2-3db before you've gained anything too meaningful on music and that's trying to get well over 50% more watts from the amp, AFTER it deals with all the things fighting against this that I mentioned. Generally wiring that last step down isn't giving you that once you factor in everything...

So if you've got crazy electrical, subs that can easily thermally handle the power your putting on them (by easy I mean your well under RMS still, like in multi sub walls builds) and still have mechanical throw left, sure wire it down to .25 ohm and get 25% more power from the amp if the amp has no issue with it assuming it has stable power source to draw from. If your planning on burping, again wire it down as low as you can with good voltage and "roll" it up so it doesn't go into protect.

If your just an average guy with "ok" electrical that is quite a bit of power considering the subs your using and aren't competing to see a number on a screen, it's generally safer for all the equipment if you stick to normal loads, even on the competition grade stuff.

Example Can a Sundown 1500d run at .5 daily? Sure. Is it a good idea when running a set of SA-12's with stock electrical except for the big 3 being done.. IMO, NO and that's a pretty common setup around here.. It's good for 25% more power so less than a DB in the real world minus the power compression, impedance rise that causes and the lowered voltage due to the amp efficiency dropping from 68-61% (random numbers, but probably ball-parking) Just some food for though.

Edit: One last thing. If you look at the impedance graph of any subwoofer box, you'll see right at tuning impedance SPIKES, sometimes 4-8x it's nominal load. You'll also easily realize from common experience that the sub doesn't tend to get much quieter at tuning (often it's the opposite) even though your sub is often seeing 4-8x less power at that frequency. That's due to increased efficiency of the port. Bigger boxes again, tend to have more rise, but on a daily setup you'll often find bigger boxes tend to be louder, again especially near tuning. Power is far from everything, it SHOULD be a means to an end, no more no less.

Thanks for typing all that out, man.
//content.invisioncic.com/y282845/emoticons/handclap.gif.0c301076f534e244f0460706894f19e0.gif

 

[Timmy13091 10+ year member]

I was just curious as to why people give so many warnings about operating amps at low impedences when you can get anywhere from half to a whole ohm of rise while playing. I decided to go with D4 subs to run at 1 ohm, but after rise I'll probably be seeing between 1.5 and 2. Why don't more guys wire for .5 nominal so you'll actually sit at about 1 after rise?

Most of us who wire low throw so much money into are electric that efficiency doesn't matter .. And just try to squeeze the most possible out our amp's .. Not the smartest thing but it works

 

[UsAmpsFreak]

Most of us who wire low throw so much money into are electric that efficiency doesn't matter .. And just try to squeeze the most possible out our amp's .. Not the smartest thing but it works

Yea, it's because you can get just as much dip and you do rise. You can easily measure 2.5-3 ohms with rise on a one ohm load. Certain frequencies will also dip down below .5 ohms at times.

 

[Full Tilt 10+ year member]

Thanks guys - especially you, T3mpest, the reply really clarified some things for me.

 

[SounDrive Pro Seller]

Because impedance doesn't always rise.. When you drop to .5 yes, some of the frequencies will end up being higher than .5, some can also end up lower, which can damage equipment. Second, when you drop impedence you also reduce effeciency of the amp, which can often strain your electrical which in turn strains the amp.
Third reason is a bit more complicated, but also VERY important to realize and most don't, it as I state time and time again comes from people applies what people to "in the lane: on "burps" and misapplying it. (as the case is with rise like I stated earler) Anyways, most coils are already into thermal compression by the time you send a sub a 1ohm load on most of these bigger amps that people love to wire down low. When a coil heats up, it's DCR actually increases. On a burp we don't have to worry about this, on music we do. Even though you've dropped your amp lower on music after you run it for a while extra heat inside the coil is not only not great for the driver, but ends up raising the impedance again, which while this thermally helps the driver, also defeated the purpose of the lower ohm load.

Lastly, going from 3500 watts to 4200 watts for example, isn't really an audible difference. In bass frequencies you really need to gain a good 2-3db before you've gained anything too meaningful on music and that's trying to get well over 50% more watts from the amp, AFTER it deals with all the things fighting against this that I mentioned. Generally wiring that last step down isn't giving you that once you factor in everything...

So if you've got crazy electrical, subs that can easily thermally handle the power your putting on them (by easy I mean your well under RMS still, like in multi sub walls builds) and still have mechanical throw left, sure wire it down to .25 ohm and get 25% more power from the amp if the amp has no issue with it assuming it has stable power source to draw from. If your planning on burping, again wire it down as low as you can with good voltage and "roll" it up so it doesn't go into protect.

If your just an average guy with "ok" electrical that is quite a bit of power considering the subs your using and aren't competing to see a number on a screen, it's generally safer for all the equipment if you stick to normal loads, even on the competition grade stuff.

Example Can a Sundown 1500d run at .5 daily? Sure. Is it a good idea when running a set of SA-12's with stock electrical except for the big 3 being done.. IMO, NO and that's a pretty common setup around here.. It's good for 25% more power so less than a DB in the real world minus the power compression, impedance rise that causes and the lowered voltage due to the amp efficiency dropping from 68-61% (random numbers, but probably ball-parking) Just some food for though.

Edit: One last thing. If you look at the impedance graph of any subwoofer box, you'll see right at tuning impedance SPIKES, sometimes 4-8x it's nominal load. You'll also easily realize from common experience that the sub doesn't tend to get much quieter at tuning (often it's the opposite) even though your sub is often seeing 4-8x less power at that frequency. That's due to increased efficiency of the port. Bigger boxes again, tend to have more rise, but on a daily setup you'll often find bigger boxes tend to be louder, again especially near tuning. Power is far from everything, it SHOULD be a means to an end, no more no less.

I've actually been reading up on a LOT of this stuff lately and you hit the nail right on the head. Lots of this information is very good to know for MECA where you pretty much try to get as loud as possible with the least power draw possible