RMS Question
 

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.

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

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

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.

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?

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?

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

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.

where can i find a cheap upgraded alternator?

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.

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

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

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/

Hell I learned something there

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

RMS values NEVER change due to wiring configuration.


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.


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 :eek: ) 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.


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


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! :)

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.

it will fit. the 18" box that im still *****ing waiting on full specs is a little over 7 cubic feet. and thats with the sub firing upwards so it cant be too close to that metal that separates trunk from backseats. ull be fine if u measure right

What do you need 6.5ft^3 for man? You could fit two of those subs in there?

My box took up 8.1 cubes and is 140 lbs without the speakers in it. If you're worried about it, before you build the box make a cardboard mock up of how big the box will be.

Its a competition sub

Figured id post some pics of current system while im at it :P

You're really dropping it into a competition setup and tuning to 55Hz? You do know that you should NOT play music through those boxes right?

even the soundstream xxx 10,000RMS 15 needs a max enclosure of 6 cubes with a 3 minimum. i think with the 800rms sub 6.5 would be overkill. unless it has a crazy soft spider. ive had two different 12"s in a single 3.9 cubic foot box. now due to the boxes design it did pretty well but it made my first 12 (Fi BL 12) extremely soft. moving it back and forth was pretty funny. second sub was a lot stiffer but i still think it would have sounded a lot better in a 2.25 cubic ft box. u should run the specs of the sub through one of those box design software programs

i saw that and i thought hmm that doesnt look right. maybe its wrong or some asian diagram with a misprint. now it all makes sense :lol:

k well ill upload all diagrams of boxes you guys tell me which is best for SPL but can still be used regularly.

this one . it says inside has 1inch of fiber glass. thats some pretty thick fiberglass there. or does it mean a total of 1" from the 3/4 MDF and 1/4 of fiberglass


if youre a g at making boxes do the bandpass

1 inch "fiberglass" insulation / damping material, but I'd use a different type....

recommendations?

I'd design your own ported box based upon online specs and recommendations. With this, you can decide what your goals are for this subwoofer application. Whether it may be rock music, hip-hop, c&s, or just overall musically sound. The design you were originally looking at was that of what many refer to as a "burp box." A design made to match the subwoofers specs in which you would, simply put, be able to play a VERY limited range of notes and be able to achieve a greater level of sound pressure than you would in a typical application. Music would sound horrible and with the lack of cone control on music as opposed to the tones that it was developed for, it would suffer form mechanical failure quite easily...

What music do you listen to? Are you looking to play any chopped and screwed/ LOW music? Are you looking to compete?

If you can answer a few questions I wouldn't mind getting some box dimensions for you. :) And for a first box of the sort, I would recommend a regular slot port made from the mdf itself. Those design plans implement the use of round ports. (pvc, aero)

I've even used the commercial Johns Manville wall insulation for some projects, more user-friendly than the old type itchy pink fiberglass. Its mainly to damp out higher frequencies that reflect and bounce around inside the box, but if it's a subwoofer, most of that is filtered out anyway with a low-pass filter.

More important is that the box not flex, and have proper bracing. If you tap on the box, or rap it with a stick, hammer, etc. and it makes a ringing sound, that's not solid enough, and needs more bracing or damping.

An exception might be that if the box rings at a very low frequency, it can add to the output and even sound pleasant. In general, though, ringing is not desirable.

Well i listen to mostly Rap, Hip Hop, CnS, and a bit of techno.
oh and some of that "Bass test" music ex. DJ Billy E.
and not sure what LOW music is exactly.

The misinformation runs deep on the previous page.

Why? I'd really like to hear why a box tuned to 55hz should not play music!


Just forget about ALL of those misleading box diagrams. Just tell us what sub it is and the specs or do your own math http://www.carstereo.com/help/Articles.cfm and tell us what you come up with.

What took you so long?

Okay I will re-word it. Bigshot44, you will not be happy with what your 55Hz box would do on music. Playing the music that you listed will be mostly peaking 20Hz below the tuning of your box. At 6.5ft^3 you will have little to no control over the cone of your subwoofer resulting in not only bottoming the driver out, but also more than likely leading to total mechanical failure.

"Burp" boxes sound horrible on music. (Trying to pick my words carefully so they don't continue to get picked apart, I am defining music as songs with basslines between 30-50 Hz. The reason why most people online hop on to get some quick audio advice and add some "booooooooom" to their trunks and leave.) They are a "burp" box for a reason.

Nothing wrong with a box thats tuned to 55hz, as long as its tuned with a flat response. Really I don't like to knock a box until its properly metered, by smaart or even term.

Are you building a box so you can do comps or you just want to be loud?

The size of the box has nothing to do with it bottoming out.

Haven't you heard my car? Tuned to 40hz, sounds great to untrained ear but missing out on 60hz to 125hz sucks. Thinking that a 6.5" or a 6x9" will produce that range efficiently without allot of work is madding.

Just think how shity this song would be with out 60 to 125hz http://www.youtube.com/watch?v=auDv6cf2PBM.

And I hope Ryan corrects me on this but for some reason building a box that fires into a trunk should be NO bigger then half the air space in the trunk, because having your subs firing into the trunk turns the trunk into a 6th order bandpass.