RMS Question

[Bigshot44]

I have an above average understanding of car audio, but ive never had a dual vc sub. its a dual 6 ohm that can be wired in parallel to 3 ohms or series to 12. im going to wire to 3 ohms and my question is does the rms change at all depending on how you wire it?

its a JBL W15GTi MKII
800rms, 5000w peak.

[scott192]

the rms will be the same its just how the amp will produce the power, a higher ohm load will cause less power from the amp where as at 3 ohm you will get more.. you should be good depending on your amp

my amp at 4 ohm makes around 1600wrms or at 2 ohm its 2000wrms so look at your amp specs and it will tell you what its putting out at the ohm you set it too

[Bigshot44]

K Thanks.
What would be better?

Alpine MRP-M1000
600 watts RMS x 1 at 4 ohms
1,000 watts RMS x 1 at 2 ohms

or

Clarion DPX11551
850 watts RMS x 1 at 4 ohms
1,550 watts RMS x 1 at 2 ohms

[scott192]

id go with the alpine cause i know there good amps and looking at your subs rms rating it will be getting around 800wrms so perfect match! make sure you use 1/0g wire or your amp will not like you lol

[Bigshot44]

Originally Posted by scott192

id go with the alpine cause i know there good amps and looking at your subs rms rating it will be getting around 800wrms so perfect match! make sure you use 1/0g wire or your amp will not like you lol

k lol. what size fuse will i need? And would i be able to get away with 2 gauge? or is 1/0 a definite.

[scott192]

well you might want a second battery down the line or a second sub and amp so getting the big stuff now is best!! and dont do what i did and buy it from visions or places like that go to princess auto and get welding cable much cheaper and just as good if not better so theres my 2 cents on that lol and youll want to run around a 150 amp fuse

[Bigshot44]

Originally Posted by scott192

well you might want a second battery down the line or a second sub and amp so getting the big stuff now is best!! and dont do what i did and buy it from visions or places like that go to princess auto and get welding cable much cheaper and just as good if not better so theres my 2 cents on that lol and youll want to run around a 150 amp fuse

ya i was going to go to princess. Visions is good for me though cause i can get 50% discounts cause i know the manager. Also i do have a second Battery. ive heard i should make a vent for it, is that true?

[scott192]

yea if its not a sealed battery you should have a battery box and a vent tube

[Bigshot44]

Originally Posted by scott192

yea if its not a sealed battery you should have a battery box and a vent tube

what if i make a small box and and cut 2 holes for wires and seal completely. would that be good enough?

[JLw7123]

just get a red top or XS power battery then u will not have to worry about venting the battery.

[Afugy]

Don't waste your money on a second battery, you're far better off getting a better alternator. I feel as if we've gone over this before like 100 time. Adding a second battery to the car puts to much stress on the stock alternator and not only that but unless both batteries are the same you could have problems with one battery draining out the other battery.

[Bigshot44]

where can i find a cheap upgraded alternator?

[Afugy]

Well eBay or summit racing is where I got my'n for 250$, it's a powermaster, been working great for 2 years. http://www.powermastermotorsports.com/index.html I was unable to find the correct alternator on their web site, you will have to contact them.

And don't for get to upgrade your Big 3 as well.

[scott192]

when you get into the serious power you cant just get away with a better alt because your voltage will drop super low b4 the alt engages and starts making more power need both.. i have 2000rms and the second battery kept my voltage from dipping to low im hittin 12v vs 9v with one battery

[Afugy]

Then get a better alternator Scott, because I run 2000rms all day and don't drop below 13.6 volts on one battery. You don't need a second battery! Maybe a better battery, as in a yellow top optima. A second battery is just a waste, batteries do NOT make power! Batteries only store power!

http://www.aleromod.com/forums/showt...t=32776&page=3

Originally Posted by Ryan from Ohio

It all starts with the alternator. If you dont have a proper charging system your shit is going to fail- its only a matter of time. Thats the bottom line.

Deeper you say? Fine.

Now once you are drawing over 125% of your rated alternator the brushes in the alternator start to burn. What this means is that if you voltage rail is sagging bellow battery voltage you will be burning up alternators. Adding more batteries only makes the demand on the alternator more. Adding more capacitors is almost worse...

More more more??? OK baby...

Capacitors... Well its short term storage. In what a capacitor can output in one second it takes 5 seconds to fully recharge. What does this mean you ask? Well it means if you have a demand that forces a draw from the capacitor then and the cap becomes depleted during this draw or one close by, the voltage will sag. It will make it worse because not only is the amplifier consuming power, the capacitor is recharging also. So its a double whammy.

Bottom line is alternator #1. Extra batteries help, but its a band aide. Capacitors- good when you have the proper charging system to back them. Ideally you would have all three. proper alternator, extra batteries and a nice cap bank for the transients.

[JLw7123]

well the question is has he done the big three upgrade. I would also do the big three upgrade. here is a great alternator.
http://iraggi-alternator.com/

[Stickybuddz420]

Originally Posted by Afugy

Then get a better alternator Scott, because I run 2000rms all day and don't drop below 13.6 volts on one battery. You don't need a second battery! Maybe a better battery, as in a yellow top optima. A second battery is just a waste, batteries do NOT make power! Batteries only store power!

http://www.aleromod.com/forums/showt...t=32776&page=3

Hell I learned something there

[scott192]

im not saying that you dont need a h/o altenator but the second batter helps bigtime once you have both! causes less stress on the one battery and alternator = longer battery life and alternator life!

and as long as both batterys are the same amperage, age and resting voltage they should be fine together... once a battery is sulfated it will start draining the other battery so replace in pairs

[Cashdollar2009]

Originally Posted by Bigshot44

I have an above average understanding of car audio, but ive never had a dual vc sub. its a dual 6 ohm that can be wired in parallel to 3 ohms or series to 12. im going to wire to 3 ohms and my question is does the rms change at all depending on how you wire it?

its a JBL W15GTi MKII
800rms, 5000w peak.

RMS values NEVER change due to wiring configuration.

Originally Posted by Bigshot44

K Thanks.
What would be better?

Alpine MRP-M1000
600 watts RMS x 1 at 4 ohms
1,000 watts RMS x 1 at 2 ohms

or

Clarion DPX11551
850 watts RMS x 1 at 4 ohms
1,550 watts RMS x 1 at 2 ohms

I would personally go Alpine here if money was not an issue. They are better known in my opinion for their current product lines. After efficiency, impedance rise, etc you will be fine with your power @ 3-ohms.

Originally Posted by Bigshot44

k lol. what size fuse will i need? And would i be able to get away with 2 gauge? or is 1/0 a definite.

Fusing depends on both wire size as well as your power. You need to draw enough amperage through your power cable to produce this power. Too much amperage will heat up and possibly melt the insulation off of your power wire causing a short. (BAD ) To prevent this, larger power wire is recommended, as well as correct fusing. A good rule of thumb is to divide your desired rms by 10. (P=VI) or (watts=volts*amps). By using 10, you are again accounting for voltage drop, amplifier efficiency, etc. In your case, for around 500-800rms, 2 gauge will be more than efficient. (Can handle up to ~180A) I recommend fusing around 100 amps. This will be more than efficient in your case.

Originally Posted by Bigshot44

what if i make a small box and and cut 2 holes for wires and seal completely. would that be good enough?

If you are looking for a second battery, look into something car audio specific. You will be better off in the long run.

Originally Posted by Bigshot44

where can i find a cheap upgraded alternator?

And not trying to burst your bubble, there is no such thing that you are looking for. Either look to pay for something or you won't get your "moneys-worth."

I can't really come in and hop on the battery vs. alternator war, but I will say this; I have ran two Deka 9a31 group 31 batteries in my car for close to 6 months now. I have two runs of 2/0 from front to back. And my big three done in 2/0. My amplifier is more than capable of producing 3,500+ watts on the correct voltage. I have been consistently running "3k" (after impedance rise, no one is getting their amplifiers rms here) the entire time on my stock alternator, dipping into the 13.XX's at full tilt, nothing lower. Though I have placed my electrical system on the battery charger 3 times throughout this period. If you are serious about it, it will be a trade-off.

I am planning to sell my car here in a few years and can still not justify spending $300-$500 on a good alternator. I crept the classified sections of several of my forums until I got the right deal on my batteries. (<$300.)

BATTERIES ARE INTERCHANGEABLE.

ALTERNATORS ARE NOT INTERCHANGEABLE.

I plan to take my batteries with me, so personally, this was the better decision on my part. Honestly, there is too much to get into Battery VS Alternator as it is not necessarily a "black and white" issue. Both have there place. Both are required. If you are still unsure, do a little research and make up your own mind.

P.S. Make sure you post everything up once you get it in!

[Bigshot44]

Thanks everyone for all the info. Now all I got to do is figure out how the hell I'm going to fit a 6.5 cubic foot box in my trunk.