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Old 12-23-2015, 04:46 AM   #1
Coryf

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Need some advice regarding wiring patterns, and amp wattage. easy stuff.

Hey guys. I fried my 10" sub last night so I just bought two 12s from a guy online.

few questions regarding the wiring pattern (ohms) and my current amp strength (is it gonna work nicely, or damage the subs)

subs I bought are Rockford fosgate power 3112 12".DVC 2ohm

http://www.crutchfield.com/S-fnH5LXW...2-RFR3112.html



amp I have is Kenwood KAC 8105D

http://www.kenwood.ca/Car_Entertainm...ment/KAC-8105D


is this wiring right?

I choose 2 ohm to play it safe.. middle of the range. from the rockford rosgate wiring wizard (option #2)

http://www.rockfordfosgate.com/rftec...2&woofer_imp=3


does this all look right?
did I do anything wrong?

I have a feeling that my amp is underpowered. I believe my amp is 300 RMS and the subs are capable of 1000 RMS.

sounds like I need a stronger amp or what? if so, what do you guys recommend?

how about my wiring and ohm selection? is that properly done, and the right choice?

I know the basics... maybe. but this has got me confused.

any help and advice would be greatly appreciated.

thanks!
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Old 12-23-2015, 11:36 AM   #2
diceen

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What you want to do is wire up each sub in series. That is, positive from amp to voice coil positive #1, negative #1 to positive #2, negative #2 to amp. Do this for both subs and plug them both in to the amp.

The sub only offers 500 rms of the total 2000 your subs can take. That's not going to be an issue if you play it smart with the volume, but I'd look into an amp with a bit more power.
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Old 12-23-2015, 11:43 AM   #3
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To clarify, you're wiring up each sub this way to be a 4-ohm load on their own. Once you connect both 4-ohm subs into the amp, you create a parallel circuit with both 4-ohm loads, presenting a 2-ohm load to the amp.
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Old 12-23-2015, 01:45 PM   #4
Coryf

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so wire them like this you mean?




when you say play it safe with the volume, whats the worst that can happen?


I definitely need a stronger amp. what would you recommend? and then is it just the amp I need? or is there other stuff that I should be looking to also like bigger wires, capacitor, etc..? anything else im missing.

or is it as simple as buying an amp, plugging it in and running it.

the car used to have a 10" sub and all the wiring is already ready to go. will that be sufficient?

thanks for the help.
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Old 12-23-2015, 03:06 PM   #5
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Yeah, wire them up just like the picture.

As for going to high on the volume with that amp, your amp is going to be struggling really hard to give the power your subs want, if you turn the volume too high. Your amp will be operarting at max, and that's bad for the amp. You could burn up your amp.

As for amp recommendations, I'd say a Rockford Power series, but there are many people on this forum who could undoubtedly offer higher-value, quality recommendations.

As for your wiring, I'd recommend 1/0. More than enough for 2000 watts rms with ampacity to spare
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Old 12-23-2015, 03:14 PM   #6
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Also, assuming you stick with a Class D amp for those subs (you should), you'll be pulling 180 amps out of your vehicles electrical system. This exceeds the ratings of most vehicle alternators. You will need to buy a high output alternator.
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Old 12-23-2015, 04:04 PM   #7
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what you did looks correct. depending on enclosure you may be able to send those subs more power. i'm guessing that kenwood is around 800 watts at 2 and 1 ohm, i know kenwoods don't generally give a lot more power at 1 vs 2 ohm. a nice ported enclosure would do those subs justice and probably lower the power handling a little so your current amp would work a little better.
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Old 12-23-2015, 08:09 PM   #8
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No problem cranking the volume as long as you set the amp gains properly.
And in your case 'properly' means setting the clipping point based on max rms power the amp can deliver, not max power the subs can take.
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Old 12-24-2015, 03:07 AM   #9
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awesome, you guys are very helpful. although im still unfamiliar with some of the terminology im sure ill figure it all out eventually.

I got it hooked up today and it pounds nicely, even with that underpowered amp. its about 50% more than my 10". id still like a little more though.. I mean I used to have a single 10, now ive got 2 12s so I figured it should be 2.5x as much "pounding" going on but not quite, im pretty sure thats due to the underpowered amp.

ive looked into getting a 2000W amp but now the alternator thing is scaring me. how critical is that? what if I didnt get a stronger alternator? would a capacitor help me?

I noticed tonight when the bass pounded hard it would dim the headlights a noticeable amount. (2004 Jetta TDI)

theyre in a ported box. I believe the amp is 1000 watt. 300 RMS I believe.

how do I go about adjusting the gain?

what do you guys do about rattles? seems like theyre never ending. even with the small amp ive got now ive noticed a few small rattles. not sure how exactly I go about finding them, and when I do, whats the proper way to fix them? stuff some sponge in the rattling part sorta deal?

thanks a lot guys, the info/help here is awesome! really appreciate it.
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Old 12-24-2015, 04:27 AM   #10
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Quote:
Originally Posted by Coryf View Post
awesome, you guys are very helpful. although im still unfamiliar with some of the terminology im sure ill figure it all out eventually.

I got it hooked up today and it pounds nicely, even with that underpowered amp. its about 50% more than my 10". id still like a little more though.. I mean I used to have a single 10, now ive got 2 12s so I figured it should be 2.5x as much "pounding" going on but not quite, im pretty sure thats due to the underpowered amp.
If you're running the same amp as you had with the 10-inch sub, the difference will be noticeable but maybe not mind-blowing. RMS Watts, sub size, make/model, and enclosure all factor into it. The difference between a 600 Watt RMS 10-inch sealed enclosure sub from some no-name brand, and two 600 Watt RMS 12-inch subs in a ported enclosure from a respected brand will be much more pronounced.

Quote:
ive looked into getting a 2000W amp but now the alternator thing is scaring me. how critical is that? what if I didnt get a stronger alternator? would a capacitor help me?
Very critical. Do not under any circumstances run an audio system over 75% of your alternator amperage. Most people will tell you even less, like 50%. Your alternator will be destroyed, your battery will take a beating unless it's a deep cycle/starter hybrid like a Yellow Top, and your system will sound like garbage. Expect the music to crackle and distort every time you lower the windows.

A capacitor will not help you. It's just another load on an already taxed electrical system.

You can look into getting a battery system hooked up, but it's honestly just easier to buy an HO alternator.

Quote:
I noticed tonight when the bass pounded hard it would dim the headlights a noticeable amount. (2004 Jetta TDI)

theyre in a ported box. I believe the amp is 1000 watt. 300 RMS I believe.
Check your amplifier ground #1. Make sure it's shiny bare metal with a good contact, no paint or dirt where the contact point is. Check out "The Big 3". I'd be shocked if a 2004 Volkswagen needed it with 500 RMS Watts (you should be at 500 RMS Watts if you wired it up like you said), but look into it.


Quote:
how do I go about adjusting the gain?
I use a multimeter. I turn my head unit volume to 75% of max, then adjust the gain until my subwoofer is receiving max rms wattage. (Keeping in mind that any subwoofer worth its salt can handle more than it is rated for).

In your case, where your subwoofers can handle more than your amp can put out, I would test for max output of the amp, and back off of that a bit.

Quote:

hat do you guys do about rattles? seems like theyre never ending. even with the small amp ive got now ive noticed a few small rattles. not sure how exactly I go about finding them, and when I do, whats the proper way to fix them? stuff some sponge in the rattling part sorta deal?
I use a lot of dynamat in my doors and on the rear decks. That might help. I've honestly never run in to too many rattle problems. If I have any, the music is too loud to notice.

Last edited by diceen; 12-24-2015 at 04:47 AM.
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Old 12-24-2015, 10:17 PM   #11
Coryf

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awesome man, youre very helpful and seem to know what youre doing.

that seems like a lot of work though (bigger amp and alternator) for something that really isnt needed and will be used much.

it already pounds pretty damn good. too much for the gf, but id like just a tiny bit more. maybe I should just leave it as is and call it a day and hope to not blow my amp. id like maybe another 25% more, but its already got quite the thump. maybe leaving it as it would not only help my wallet, but my ears when im older too! on some beats it already rattles me to the point where it makes my nose tickle... very annoying!! haha

otherwise it looks like id probably be spending about 700$ on a huge amp and a bigger alternator.

all the grounds are perfectly clean, its all new wires that had the rubber stripped off a month or 2 ago.

ive asked on TDI club what the alternator specs are, how much a bigger one is, and how hard they are to install. its still something I may consider. seems like itll be never ending though, once I get this all set up ill have to figure out the rattles. then upgrade door speakers. then buy a 2nd amp to run the door speakers... sounds like itll get expensive quick! im a gearhead so I like doing stuff like this.. nothing of mine ever remains stock, its always modded to the max.


where would I touch the 2 multimeter points for that?

that dynamat sounds like a lot of work, I think ill just live with the rattles, and either turn it up more or less to avoid them!

thanks a lot for all the help diceen, I definitely owe ya a beer

Last edited by Coryf; 12-24-2015 at 10:22 PM.
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Old 12-24-2015, 10:38 PM   #12
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Quote:
Originally Posted by Coryf View Post
awesome man, youre very helpful and seem to know what youre doing.

that seems like a lot of work though (bigger amp and alternator) for something that really isnt needed and will be used much.

it already pounds pretty damn good. too much for the gf, but id like just a tiny bit more. maybe I should just leave it as is and call it a day and hope to now blow my amp.

otherwise it looks like id probably be spending about 700$ on a huge amp and a bigger alternator.
If you're happy with the sound, then by all means stop here. I was under the impression you wanted to fully realize those subs' potential, but that was just an assumption. You can go a little bigger on the amp if you want, but that may require bigger wiring depending on what you have. I still don't know what gauge wiring you have right now, so you may need a wiring upgrade and don't even know it.

Quote:
all the grounds are perfectly clean, its all new wires that had the rubber stripped off a month or 2 ago.

ive asked on TDI club what the alternator specs are, how much a bigger one is, and how hard they are to install. its still something I may consider. seems like itll be never ending though, once I get this all set up ill have to figure out the rattles. then upgrade door speakers. then buy a 2nd amp to run the door speakers... sounds like itll get expensive quick! im a gearhead so I like doing stuff like this.. nothing of mine ever remains stock, its always modded to the max.


where would I touch the 2 multimeter points for that?

that dynamat sounds like a lot of work, I think ill just live with the rattles, and either turn it up more or less to avoid them!

thanks a lot for all the help diceen, I definitely owe ya a beer
Set multimeter for AC Voltage, then stick the red wire to the positive speaker terminal of your amp, and the black to the negative. Some multimeters require that the prongs be plugged into the appropriate jacks on the multimeter; check that they are.

For 500 Watts RMS into a 2 ohm load, your max voltage will be 31.6 volts. When your multimeter reads 31.6 volts when you are turning the gain on the amp up (and HU at 75%), that is your amp's max output. It may go higher, but it's not rated for higher, so that's bad.

It's no problem about offering help. I'm really interested in the technical details about car audio, but I'm still pretty green. I know that more than a few people on this forum have the credentials and experience to really lay down some information.

Last edited by diceen; 12-24-2015 at 10:48 PM.
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Old 12-25-2015, 02:27 PM   #13
Coryf

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I do wanna see what these two 12s will do, but not if it requires 700$ in parts. maybe in the summer ill upgrade it.. I always want more than what I go, no matter what!!

my wiring is junk, cheap thin stuff no doubt. I can get a picture later today after supper.

guys on the Jetta forum said my car has a 120A alternator.

also said this:

"Amps = Wattage/Voltage

Add up the wattage per channel and divide by 12v.

if suggested max is 75% of alternator output then max available amperage would be: .75 x 120A = 90 Amps

Max wattage, therefore, would be: 90A = W/12V -> W = 90A x 12v -> W = 1092"


if I were to get a 2000W amp.... 2000/12 = 167 amps. so id need a 160-170 amp alternator. is that right math? or do I go via the RMS watts?

I think we have a multimeter at home, ill give that a try. 75% of my head unit is damn loud though.. probably too much. I only run it at 16-20 / 50 which is max I believe.
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Old 12-25-2015, 04:16 PM   #14
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To figure out the amperage that an amp will draw, you multiply the RMS watts by the inverse of the amp efficiency, then divide by 13.8. You divide by 13.8 because when the car is running, you'll be receiving about this.

The inverse of efficiency of a Class D amp is around 1.25, though this can vary slightly.

Therefore, (2000*1.25)/13.8 = 181 amps

You'll want an alternator with at least 25% headroom, but again, that's cutting it close; go for higher if you can. Try to find a 240 amp alternator.


With your head unit at 75% and your amp gain all the way down, it won't be loud. It will only become loud once you start turning the gain on the amp up.

Last edited by diceen; 12-25-2015 at 04:47 PM.
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Old 12-26-2015, 11:41 PM   #15
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wow that sounds like a lot!

why wouldnt a capacitor work for me? how much "juice" does a capacitor store? Id rather bag on the capacitor than my alternator it seems like? the guys on the jetta forum are recommending a capacitor, why do you recommend against it? especially for my current setup where it already dims the lights.

im not 100% sure if im gonna go for a bigger amp. the 1000 watt one that I have now is plenty, ill only let the bass pound for 1 song, maybe 2 max. then my head/ears cant handle it anymore so I turn it down a lot. just really dont wanna fry my alternator.

I figure even if I discharge the capacitor faster than it charges, thats not a big deal is it? it depends on how much the capacitor can hold before its "empty"

sorry for all the dumb questions. electrical is my major major weak point. I can rebuild a 4 stroke dirtbike engine, or a 800hp cummins in my sleep, but throw me an electrical wire and a battery and my heads spinning!!! sad, I know.
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