ohm’s law question
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=45636
Printed Date: July 18, 2025 at 4:07 PM
Topic: ohm’s law question
Posted By: djdaveoc
Subject: ohm’s law question
Date Posted: December 20, 2004 at 6:56 PM
I have a sub with 2 4-ohm voice coils. If I want to run a sub amp in mono, how many ohms load with the sub be? I'm asking because I'm trying to pair up a sub with an amp that will be a good fit power wise. Thanks for any help. I'm a brand newbie to car audio! ------------- }:) Plan, Research, Do
Replies:
Posted By: Lizardking
Date Posted: December 20, 2004 at 7:33 PM
Wired in parallel that would be a 2ohm load to your amp...If you run in series I believe that would be a 8ohm load to your amp.. ------------- Eclipse "Approaching Perfection"
Posted By: darthness
Date Posted: December 20, 2004 at 7:37 PM
and in case you didnt know, you'll want run a 2ohm load, not 8ohm.
contrary to most things, smaller amount of ohms = better. i forgot why though :))
Posted By: 12v.boogie
Date Posted: December 20, 2004 at 7:40 PM
wired in parrell its 2 ohm but if you monoout an amp it cuts it down to a 1 ohm.
Posted By: Lizardking
Date Posted: December 20, 2004 at 7:43 PM
Lower the ohm the better unless you push your amp to it's limits then it's not.. ------------- Eclipse "Approaching Perfection"
Posted By: pneise
Date Posted: December 20, 2004 at 8:21 PM
darthness wrote:
and in case you didnt know, you'll want run a 2ohm load, not 8ohm.
contrary to most things, smaller amount of ohms = better. i forgot why though :))
lower resistance means more current for a given voltage=more power to speaker :)
Posted By: stevdart
Date Posted: December 20, 2004 at 8:24 PM
Shop for a mono class D amp with ratings that include wattage at a 2 ohm load impedance.
Posted By: djdaveoc
Date Posted: December 20, 2004 at 8:49 PM
I know I mentioned the dual VC sub but now I'm thinking of getting a JL Audio 12W7 since I already have the subzone box for it. Any suggestions on the amp brand and model? I'm thinking maybe a PPI but if there is an amp that would be a good fit for a 12W7 that costs less than PPI but is almost as good, I'm open to ideas. I just want to make sure and power the sub to it's full RMS capacity which I believe is 750 watts RMS into one 3-ohm voice coil. Thanks again! -------------  Plan, Research, Do
Posted By: djdaveoc
Date Posted: December 21, 2004 at 6:01 PM
Lizardking what is the difference between wiring in parallel and wiring in series? Thanks. ------------- Plan, Research, Do
Posted By: stevdart
Date Posted: December 21, 2004 at 8:30 PM
Incredible what you find out with a Google search! 288,000 results in a quarter second....but you'll find all you need on the first page.
Posted By: KarTuneMan
Date Posted: December 22, 2004 at 1:11 AM
The second post in this , and on this topic.....should have been "what make and model amp" are ya using for your sub(s). You need to get the subs and the amp together so you don't waste money and time
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Posted By: djdaveoc
Date Posted: December 22, 2004 at 1:43 AM
stevdart, I found the information online, thanks. Hopefully I'll understand it. I guess some of the people on here have an engineering or electronics background, but I have none of either. So reading things that are written by advanced engineers is a real nightmare for me. I know because my father is one of them. They use technical terms that a newbie does not understand, so really, I feel like a need a translator. I was hoping to get a very brief answer in plain English that anyone could understand. And Kartuneman, thanks for your reply I think. I didn't really understand what you said. In my last post I stated that I might get a JL Audio 12W7 sub which I think is one 3-ohm voice coil and takes 750 watts RMS. I asked what amp someone would recommend that would put out the right amount of power for this sub. I think that JL Audio says that 1,000 watts RMS is too much and 500 is too little. ------------- Plan, Research, Do
Posted By: DYohn
Date Posted: December 22, 2004 at 8:49 AM
darthness wrote:
and in case you didnt know, you'll want run a 2ohm load, not 8ohm.
contrary to most things, smaller amount of ohms = better. i forgot why though :))
That's just plain wrong. Ohms are ohms and low is not better than high or vice versa. Lower ohm load on an amp will cause it to push more current and result in more power output, but at the cost of SQ, noise, heat generation, power load on your system, etc. Too low an ohm load will blow fuses and can fry your amp. Higher ohm loads sound much cleaner and allow your amp to function with less power draw and less heat and more safely. Matching the ohms load of your loudspeakers to the best operating characteristics of your amp is the "better" thing to do. ------------- Support the12volt.com
Posted By: djdaveoc
Date Posted: December 22, 2004 at 11:13 AM
So I guess for the JL Audio 12W7 I will have to look for a class D mono sub amp that puts out 1,000 watts RMS into 2-ohm or 500 watts RMS into 4-ohm. That would mean it would put out about 750 watts RMS into a single 3-ohm voice coil of the sum, correct? ------------- Plan, Research, Do
Posted By: dedlyjedly
Date Posted: December 22, 2004 at 5:23 PM
12v.boogie wrote:
wired in parrell its 2 ohm but if you monoout an amp it cuts it down to a 1 ohm.
NOPE, even if i could monoout anything, joining the output of two channels into one, sometimes affectionately referred to as bridging, has no affect on impedance!!! i repeat, no affect that said, the impedance presented to the amp does greatly affect output performance, but has no change on impedance. of course you must disregard all of this when wiring up the flux capacitor ------------- MECP certified, 5yrs experience, you probably otta listen bitch!!
Posted By: djdaveoc
Date Posted: December 22, 2004 at 9:29 PM
I meant of the sub. oops ------------- Plan, Research, Do
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