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Look! Subs in parallel ohms formula

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=48298
Printed Date: May 15, 2025 at 3:06 PM


Topic: Look! Subs in parallel ohms formula

Posted By: audeogod
Subject: Look! Subs in parallel ohms formula
Date Posted: January 22, 2005 at 12:58 AM

I'm sure this is on this site somewhere but recently I've seen a few posts about subs in parallel and DVC's and all.  I thought this would help.

If you want to figure out what ohm load you will have when subs are wired in parallel, and assuming that all subs or voice coils(SVC's have one, DVC's have two each) are the same ohm load(when using two or more, they should be) then use this formula:

Resistance = R/n 

That is the resistance value of one voice coil divided by the total number of voice coils you have. 

Example 1.  two 4 ohm subs in parallel.  4 divided by 2 =2 so you have a 2 ohm load

Example 2. three 4 ohm subs in parallel.  4 divided by 3 = 1.33 so you have a 1.33 ohm load

Example 3. two DVC 4 ohm subs with all coils in parallel.  4 voice coils total so it's 4 divided by 4 = 1 so you have a 1 ohm load.

You could also wire the coils of each DVC in series, which is just one end of one wired straight to the end of the other one and make an 8 ohm sub out of each.  Then wire each woofer together in parallel and get a 4 ohm load total.  The math is the same.  In series you just add it all up so each sub is 4 ohm + 4 ohm = 8 ohms.  Then in parallel it's 8(ohms of one sub) divided by 2(two voice coils) = 4 ohms total.  There are really four coils, two on each sub, but we wired them in series making the two into one.  So we do the math as just two voice coils.

As for series wiring, it was already stated.  Simply just add them all together.  But in car audio, we don't do a lot of series wiring.  Mostly parallel.

I figure this post will last about a day or so until the ones that were asking are thru with their projects.  After that it will go on to page 2 and 3 and 4 and......forever.




Replies:

Posted By: kfr01
Date Posted: January 22, 2005 at 1:20 AM
Good post audeogod.  I'll /bump this once to delay the trip to forever.  :-)

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New Project: 2003 Pathfinder




Posted By: Chopndroptx
Date Posted: January 22, 2005 at 1:22 AM

This could help too!!

https://www.the12volt.com/caraudio/boxcalcs.asp



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Chris- Kenwood KDC-MP522,2pr-INI 6000CS's,Alpine MRPF240,Viper D1200.1,2-Soundstream VGW-12's
98 Nissan Frontier Minitruck
Houston,TX




Posted By: stevdart
Date Posted: January 22, 2005 at 11:13 AM

That's good, but assumptions have to be made (all subs identical).  And series/parallel wiring gets confusing with this.  Once the coils are wired then the sub should be treated as a single impedance load to keep calculations simpler.  Here is a formula DYohn posted several months ago that I have been using:

The equation for parallel wiring is 1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc ...  The equation for series wiring is Rtotal = R1 + R2 + R3 etc...

Good input, audeo.  Glad you decided to stick around.



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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.




Posted By: audeogod
Date Posted: January 22, 2005 at 2:11 PM
Yeah, me too.  I have used that formula as well, but I started noticing that any time I needed it, it was for wiring parallel subs and all the ohm loads of the subs were always the same so the other one became easier to use.  In school, we called it the "one over one over" formula.  It helps if you have a calculator with a reciprocal button also( mine looks like 1/x ), but if not, then you can just divide the number 1 by the resistances to do the math.




Posted By: pimpincavy
Date Posted: January 22, 2005 at 11:01 PM
Good post!!! I saved it to a Notepad for future reference.

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