Bass hits, voltage drops, how much is ok

[scottrc5391]

I am running a PA [email protected] ohm amp on a Alpine type-R 15" sub at 1 ohm and hardly have the gain up half way so I am using probably like 1500W max. The sub is new. My car has a 110 amp alternator and an Optima yellowtop battery. Most people with my car say it is good (on stock alt.) for around 2000W and can hold up well under that load. My voltage guage is conveniently located so I can see the voltage when I have the system on and bass hitting. Most hard hits the needle jumps from 14V to about 13.5V. The lowest I have seen it is under long hard bass at like 13V. I know this doesn't seem like a big deal (or is it) but I want to be sure it is ok to have a little voltage drop when bass hits and not hurt alternator, etc. I haven't noticed much (if at all) light dimming or anything but I don't drive at night much. OK, another thing is that my stock door, dash, and rear speakers have tiny wires (prolly like 20 awg) and that even without the sub on the needle moves slightly. It's not quite as bad at cruise speed, but bad at idle naturally. So would running new bigger wires to the regular speakers and running 2 awg to the amp make a big difference? I thought running at 1 ohm would decrease the power draw but it seems to be the same as when I ran a RF 15" at 2 ohm. Let me know what you think. Thanks.

[yayopwr]

bro your fine...my **** used to bounce around like there was no tomorrow didnt have any effect on my car but after a while it did take its toll on the stock battery

[scottrc5391]

Cool, ok, thought it was ok. Just checking. Anybody else?

[Eddieca85]

Haha you should be cool bro. I used to rock a 1000watt system in my 83 ford fairmont with some sick *** infinitys rears, bazooka subs, and profile fronts on a stock battery and a stock alternater. Sometimes my **** would dim hardcore style. Like i would get around 11V haha. That stock alternater was like 60 watts tops. My **** was like a strobe light driving down the street at night.

[Bavarian3]

a power acoustic amp? it must put out no where near 2400 watts cuz if u had ur gain almost half way up ur sub would not be alive still.

[scottrc5391]

a power acoustic amp? it must put out no where near 2400 watts cuz if u had ur gain almost half way up ur sub would not be alive still.

No, a Planet Audio Big Bang amp. I got it off a guy who used to use it in competition and it could easily slam 2 or more 15" subs. So just so you know it does put out all 2400Wrms. Not exactly sure where I put my gain and level knobs but now that I think of it I think my gain is up only 1/3 the way and the level knob is up 3/4 the way. I'm not sure what exactly the diff. is between the two but I know that too high a gain would cause distortion (amplify weak signal) so it's better to keep it down and level up. I have been told to do this. The gain controls how "easily" the amp can get loud, and the level I believe is just like another level knob like a remote bass knob is, which increases/decreases signal strength into the amp from HU. On top of those adjustments, I also use my Alpine's built in subwoofer level control a lot, so believe me I am not going to blow this sub. Yeah and I know this sub can handle 500Wrms and 1500W max so I am fine. Thanks for the replies so far.

[forbidden]

This amp should use a unregulated power supply, this means that it will produce it's rated power at 12 volts and more power above that. I would think that if the amp is supplied with proper wiring, you have a good battery and a OK alternator, you should be fine. Down the road you may want to consider a high output alternator should the circumstances warrant it. If you notice your voltage dropping right down, this is notice that the battery is being discharged excessively and the alternator cannot deliver the needed current to replenish and operate the system, this is time for a new alternator.

[helotaxi]

I'm not sure what exactly the diff. is between the two but I know that too high a gain would cause distortion (amplify weak signal) so it's better to keep it down and level up. I have been told to do this.

The "gain" is a level matching tool only. Since there is no standard for the voltage of preamp outputs in the car audio industry, some adjustability is needed at the input of every component to keep the component form exceeding its capabilites and clipping the signal, potentially damaging everything downstream in the signal path.

The gain controls how "easily" the amp can get loud, and the level I believe is just like another level knob like a remote bass knob is, which increases/decreases signal strength into the amp from HU.

The gain as described above should only be used to match the preamp level of the input to the input stage of the amp. It control the voltage required to get maximum power out of the amp. Set it to high and the amp clips, set it to low and the amp doesn't make as much power. If your Alpine deck has 4V preouts (most that have a sub level control do) then 1/3 is probably a bit high and with the sub level control set flat and the bass boost up, that amp is probably making close to if not its max power with the volume turned up.

The "level" control is probably a bass boost. If the gain is set properly, the addition of bass boost will cause the amp to clip when it wouldn't ordinarily. For every 3dB of boost the amp will attempt to double its power output. If the gain is set properly to produce maximum power with no bass boost, adding boost will cause the amp to try to do more than it can.

On top of those adjustments, I also use my Alpine's built in subwoofer level control a lot, so believe me I am not going to blow this sub. Yeah and I know this sub can handle 500Wrms and 1500W max so I am fine. Thanks for the replies so far.

Depending on the enclosure that you have that sub in, you are probably closer to blowing it than you know.

To comment on your original post...Running the amp at 1 ohm will increase current draw over any other configuration. Twice the current draw compared to 2 ohms, and four times the current draw compared to 4 ohms. You can help yourself out on a lot of fronts by rewiring your sub to 4 ohms and properly setting the gain on the amp. The amp will make close to the rated power of the sub and will run cooler and draw less current while doing it.

[scottrc5391]

thanks for the reply forbidden.
Helotaxi, I really appreciate your help and clearing some things up for me. Yeah, I know all about clipping and whatnot, but I DON'T have the gain set to produce maximum power, I am using the gain to limit power (and like you said, it makes the voltage that the amp produces the most power at a higher value). This said, I use the "level" knob (which I think you are correct, is a bass boost like the sub level on HU) to add a little boost and well, because I don't think it will work right with it all the way down. I don't understand why they would put a level control on there if they didn't intend for you to use it too (maybe for real weak HU signal voltage?). But what I think you meant was to set the gain so that it produces around the max 1500W needed (with volume a sub level on HU up) and then keep the level on amp all the way down. I know this is confusing, sorry, it's rather confusing to me too but I think I understand what I'm doing enough to not blow out the sub, especially by clipping the amp. You are a really smart guy and know exactly what you are doing, but I don't think I am close to max power by any means. Yes, I have 4V preouts. I don't really see any problem with setting the gain AND level to an intelligient position to prevent both clipping amp and overpowering sub, which I see no evidence of. Plus, I don't want to turn the gain up and level down (to compensate) because I know that this would cause high amplication of a weak signal and maybe distortion. It seems that the way I am doing it is fine, and not everything has to be done perfectly, as long as you use common sense.
And, as for the 1 ohm vs. 2 ohm or 4 ohm thing, I had always thought (logically), that if you have smaller resistance, you have less current and power draw (to produce same amount of power) because the amp doesn't need as much current to be able to produce what you need. Say you need 1500W and you run 4 ohms: well, the amp needs more current because the resistance in the sub is higher and it has to create a higher voltage than would be needed with 1ohm sub to overcome the extra resistance. I have always heard that it is more efficient to run at the lowest ohms possible because of this fact. I know that if you max the amp out it will definately produce more power and draw more current in a 1ohm configuration than in a 2 or 4ohm because of less resistance. That is if you MAX it out, meaning you are getting as much power as possible. I am NOT doing that, just wanting a little wattage (1500W about), and it seems that it should do this with more efficiency than getting 1500W out of a 4ohm configuration. I agree that it may not run as cool as it would with more resistance (more current going through output transistors), but I figure if it is 1ohm stable I am going to take advantage of it. So are you saying that I should rewire to 4 ohm? I simply don't understand why that would help. Maybe I should just try it and see what it does but I think it would be worse. I am NOT by any means questioning your knowledge, just asking for some explanation on what you are saying, and maybe I will learn a little more in the process. Oh yeah, sub box is about 2.2 cu ft, within recommended sealed box volume as Alpine suggests. Sorry for the long post, thanks.

[scottrc5391]

OK, disregard my second paragraph I just typed; I just read this page about high current amps and it told me what I was looking for: http://www.bcae1.com/hcvsnohc.htm
Basically it confirms what you said about resistance and current draw. 1 ohm load draws twice as much current as 2 ohm, 4 times as much as 4 ohm, so I will rewire to 4 ohm. High current amps are designed to put out a lot of power at low impedence but aren't as efficient as amps running higher impedence subs for some reason. It seems that amps aren't quite as simple as ohm's law. I don't completely understand amplifier circuits but from what I gather, in order to have higher power output by using 1 ohm, more current is drawn, rail voltage (and output V) is limited so less current flows through the transistors (high current caused by low resistance), and you end up getting the same power as with higher resistance but with more current draw too. I don't see why they don't just make it run more efficiently at lower impedence and have the transistors be able to handle this extra current without limiting voltage, but they don't, and that is why you are correct that higher impedence=more efficiency, but in return, lower max wattage.
AND, if I wire to 4 ohm, I should STILL be getting around 800Wrms according to the specs of the amp, so that is more than enough, just hope it won't ever clip at higher volume. I was fine with 2 ohms though, and if I ever get another sub, I will wire both subs in parallel for 2 ohm total so I get all the power I need. Once again, thanks for your help, and I will try to set the gain right for this new arrangement.

[scottrc5391]

OK, I wired it to 4 ohm. Needle doesn't hardly budge under hardest bass hits now. Thanks for the suggestion. I didn't even have to readjust the gain.

[helotaxi]

You have the basic ideas down but are still a bit fuzzy on the details.

First, do you know the input voltage range of that amp? Second, what method did you use to set the gain? Like I was saying, with most amps a 4v input and 1/3 gain is probably a bit too high and it is probably making full power. Figure out how much power your want the amp to produce. For that sub in a sealed enclosure I would stick right around rated RMS (for displacement limited power handling purposes) with a ported box you could probably get away with more. Now we get to play with a little math. P=V^2/R. P is the power that you want. R is the impedance that you have the sub wired to. V is what you want to solve for. If for example you want 500 watts to a 4 ohm sub, solving that equation for V would give 44.7v. What does this mean? Well, this is the output voltage that will give you that power to the sub. How do you use that? Connect your amp and headunit; set amp gain to minimum; turn up the head unit to where it clips (32 on that Alpine IIRC); with the sub disconnected, measure the voltage across the outputs of the amp while play a 0dB down test tone with the multimeter in RMS mode; slowly increase the gain until you get the voltage you are looking for. Now your gain is set properly. If you ever use the bass boost circuits, set them to max before you do the above.

Amps follow Ohms Law just like every other electrical circuit. Ohms law is what allows them to make more power into a lower impedance. The max output voltage on an amp is determined by the max rail voltage that can be provided by the amp's power supply. With that voltage and the final impedance you can determine the ammount of current that must flow through the output stage of the amp. P=V*I and that give you your power. Due to inefficiencies, power into the amp must exceed power out. So basically a 400 watt amp must draw at least 400 watts (usually more like 500-600 watts) from the car's electrical system. It doesn't matter what impedance the amp is running at, 400 watts is 400 watts and the amp must draw more than that. Example: I own two amps that will produce 400 watts, one at 4 ohms and one at 1 ohm (I do own these amps BTW). The one that does it at 4 ohms has an output voltage of 40V and output current of 10A. It draws about 40 amps from the car. The 1 ohm version puts out 20 amps and 20 volts and draws a bit more than 40 amps. Because more current is flowing through the output stage, it will generate more heat than if it was making the same power at 4 ohms and will be less efficient.

Now lets look at the same amp with different loads. Take the 1 Ohm stable amp from above. Its voltage is set at 20V. At 4 Ohms it flows 5A for 100W. At 2 10A for 200W and @ 1 20A for 400W. As you can see you are better off running at the highest impedance that will give you the power that you need.

Hope all that made things clearer for you.

[Bavarian3]

OK, disregard my second paragraph I just typed; I just read this page about high current amps and it told me what I was looking for: http://www.bcae1.com/hcvsnohc.htm
Basically it confirms what you said about resistance and current draw. 1 ohm load draws twice as much current as 2 ohm, 4 times as much as 4 ohm, so I will rewire to 4 ohm. High current amps are designed to put out a lot of power at low impedence but aren't as efficient as amps running higher impedence subs for some reason. .

my JBL 1200.1 puts out 1200 watts at 1 ohm and 2 ohms. Many other amps put out the same power at 1 ohms through 4 ohms. Like the JL 1000/1 or phoenix gold tantrum 1200.1

[Bavarian3]

)
AND, if I wire to 4 ohm, I should STILL be getting around 800Wrms according to the specs of the amp, so that is more than enough, just hope it won't ever clip at higher volume. I was fine with 2 ohms though, and if I ever get another sub, I will wire both subs in parallel for 2 ohm total so I get all the power I need. Once again, thanks for your help, and I will try to set the gain right for this new arrangement.

u shouldnt clip it at all considering ur still well overpowering it.

here is my post from another thread

To tune and amp....
1. Set HU setting how u like them and how u would listen to them.
2. Make sure gain and bass boost is all the way down.
3. Turn the volume up on ur HU as high as u would listen to it
4. Start turning up the gain until u hear the subs distort or when u know its too much and theyr not getting any louder.
5. turn it bak down a bit
6. Set ur Xover(LowPass) how u like it, turned the Xover up too much will cause the subs to sound messy.

Dont use Bass boost it causes uneeded distortion but if u want to use a little bit if u feel it makes them sound better then use only 2+-4+db and ull need to turn the gain down a bit more.


that should yeild u the best sound out of the sub. good luck

[helotaxi]

my JBL 1200.1 puts out 1200 watts at 1 ohm and 2 ohms. Many other amps put out the same power at 1 ohms through 4 ohms. Like the JL 1000/1 or phoenix gold tantrum 1200.1

And to make that power at the lower impedances, it will draw just a bit more current because it is creating more heat at the lower impedance. What those amps do, unlike the older cheater amps, is step down the rail voltage at lower impedances so the current is not huge and the output stage can still handle it, but it still flows more current and creates more heat at the lower impedance.

The original PG MS series amps had a selector switch that changed the rail voltage for running lower impedance loads. The original SS Reference amps had the same type switch. On the new REF and RUB amps there is a micro computer that analyzes the final impedance and does the switching automatically. The JLs do the same thing but with a floating rail rather than a high/low switch like all the others.