speaker ohm testing
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=76236
Printed Date: June 18, 2025 at 10:55 PM
Topic: speaker ohm testing
Posted By: racefan15
Subject: speaker ohm testing
Date Posted: April 14, 2006 at 2:17 PM
OK, I have 2 12"DVC 4 ohm subs (the new Orion HP series). I have them in the back of my 00' mustang gt and had to build the box insode the trunk, so checking my wiring is not that easy. I want to know if I go the store and get an ohm meter, is all I have to do is touch the leads of the meter to the positive and negative speaker connection on my amp to see what the load on the amp is? Im pretty sure i wired everything correctly to give me a 1 ohm load, but i want to make sure that the amp is really getting the minimum of 1 ohm and that i wired it correctly... Thanks again guys.
Replies:
Posted By: boulderguy
Date Posted: April 14, 2006 at 2:29 PM
Yes.
Posted By: Steven Kephart
Date Posted: April 14, 2006 at 2:30 PM
Sort of. What you will be metering is the DC resistance of the subs. Impedance is the total resistive load from resistance, inductance, and capacitance in an AC circuit. Generally a 4 ohm nominal impedance will have a DCR of 3.2 ohms. A 1 ohm nominal impedance will have a DCR of around .8 ohms. However I have found many manufacturers DCR's vary quite a bit from this and therefore their impedance ratings on the subs be off as well. For instance an Infinity Kappa component set was rated at 2 ohms, and it's DCR was up at 2.8 ohms.
Posted By: boulderguy
Date Posted: April 14, 2006 at 2:37 PM
(I think he'll like my answer better...) 
Posted By: racefan15
Date Posted: April 14, 2006 at 2:42 PM
LOL, yes boulder. But that is only because I dont understand what Steven is talking about. Im not that great at all this stuff. Just trying to do things myself so if anything ever goes wrong I can fix it myself. Is there an easy test with the same volt meter than can tell me how many amps my system is drawing from my stock alternator? Thanks to both of you for your answers.
Posted By: Steven Kephart
Date Posted: April 14, 2006 at 2:47 PM
boulderguy wrote:
(I think he'll like my answer better...)
True, but when he produces the test and his meter shows a number other than 1 ohms, this will create even more confusion. Hopefully my answer explains the difference he will more than likely find. Let's just say I'm trying to answer a future questions ahead of time.
Posted By: boulderguy
Date Posted: April 14, 2006 at 2:49 PM
What's he's saying is that your reading won't be precise - a 1 ohm setup may read as .8 or 1.3 ohms. For the alt test, hold the hood latch in one hand & alternator contact in the other while your friend revs the engine. If you can make it more than 20 secs, you need a HO alternator. Really, I don't know how to test that.
Posted By: boulderguy
Date Posted: April 14, 2006 at 2:51 PM
Steven Kephart wrote:
Let's just say I'm trying to answer a future questions ahead of time.
Good plan. Now if we could just get them to search...
Posted By: geepherder
Date Posted: April 14, 2006 at 2:51 PM
You generally just go by the fuse ratings of the amp. If you plan for that much draw, you'll be good. However, if you want to test, use a clamp on meter that goes over the power wire. Current usage will constantly change with the music/volume level since it is dynamic.
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My ex once told me I have a perfect face for radio.
Posted By: boulderguy
Date Posted: April 14, 2006 at 3:00 PM
racefan15 wrote:
Im not that great at all this stuff. Just trying to do things myself so if anything ever goes wrong I can fix it myself.
While I'm all about DIY & learning, this scenario pretty much guarantees you'll be doing repairs. Unless you enjoy the work consider using a good local shop, you can buy 1000's of hours of experience for a couple hundred bucks.
Posted By: racefan15
Date Posted: April 14, 2006 at 3:09 PM
Good advice boulder. Now back to Stevens advice... how would you suggest doing it the accurate way then? Thanks guys.
Posted By: haemphyst
Date Posted: April 14, 2006 at 4:24 PM
Without an impedance meter, you can't. Your DCR (what your meter will measure) will generally be lower than your actual impedance. Your best bet is to pay careful attention to HOW you are wiring your woofers (parallel, series-parallel, series), and then do the math, based on the manufacturers specification for YOUR woofer set.
If you INSIST on using the meter method, you might be even further confused by the numbers you receive. Steven was correct in giving you a heads-up, letting you know that you are going to see odd numbers, and not even close to what you think you are expecting.
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: stevdart
Date Posted: April 14, 2006 at 4:41 PM
Steven's points are good and you'll be glad to hear them now before you start testing. If you were testing using my digital multimeter and read 1.9 ohms, you'd probably think you had a 2 ohm impedance. My meter reads .7 to .8 ohms when I touch the probes together...this is "internal resistance". So everytime I use it to get a DCR or resistance measurement I have to subtract that .8 ohm internal resistance from the reading. In the case of getting 1.9 ohms, the real reading would be 1.1 ohms DCR and that figures to be an impedance value of about 1.4 ohms. Close enough to 1 ohm, better than being under. When your target value is a very low number, like in your case with wanting to find 1 ohms, the difficulty in getting an accurate measurement is increased because of the factors 1) internal meter resistance, and 2) conversion of DCR reading to nominal impedance (which should be something like DCR X 1.25 = impedance). ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
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