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Old 06-17-2012, 01:45 PM   #1
sd_dracula

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How to check speaker impedance with multimeter

Hi guys,

Whats the easiest way to test how many ohms I'm getting per channel in my current installed, factory system with one of those cheapo multimeters of this type:



If I put the dial to 2000 (200 doesn't work for some reason) in the ohm range (lower left in the pic) and test a spare speaker that is not connected to the car I get 004 which is 4 ohms which is correct for that speaker.

Now because I have a few speakers wired in parallel in the car I want to get the ohms per channel (expecting 2 ohm for 2 x 4 ohm speakers in parallel).

Have tried it at the - + poles of a car speaker (with radio on and off) and I'm getting some crazy values like 030-040 which cant be right as that's 40 ohms.
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Old 06-17-2012, 01:53 PM   #2
basicxj

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Quote:
Originally Posted by sd_dracula View Post
Hi guys,

Whats the easiest way to test how many ohms I'm getting per channel in my current installed, factory system with one of those cheapo multimeters of this type:

If I put the dial to 2000 (200 doesn't work for some reason) in the ohm range (lower left in the pic) and test a spare speaker that is not connected to the car I get 004 which is 4 ohms which is correct for that speaker.

Now because I have a few speakers wired in parallel in the car I want to get the ohms per channel (expecting 2 ohm for 2 x 4 ohm speakers in parallel).

Have tried it at the - + poles of a car speaker (with radio on and off) and I'm getting some crazy values like 030-040 which cant be right as that's 40 ohms.
Measure across the speaker terminals with the speaker disconnected from everything.
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Old 06-17-2012, 02:02 PM   #3
sandt38

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If you are reading it hooked to an amp you are also reading the amplifier. If you are reading them hooked to the HU, you are reading the HUs internals as well. Disconnect the speakers from the power source, and check it that way. Be aware that you will be reading resistance across all terminations, and across the wire in the system.

Just wondering, why are you checking the full system's impedance?

Oh yeah, FWIW you have the meter set correctly. Expect to see ~003 for a 4 ohm speaker (typically 3.6ohms).
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Old 06-17-2012, 02:10 PM   #4
sd_dracula

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Quote:
Originally Posted by basicxj View Post
Measure across the speaker terminals with the speaker disconnected from everything.
Thanks that was it.
I've disconnected the wire coming from the HU and now for the mid-range and tweeter I get 002-003 which is fine.

Quote:
Originally Posted by sandt38 View Post
If you are reading it hooked to an amp you are also reading the amplifier. If you are reading them hooked to the HU, you are reading the HUs internals as well. Disconnect the speakers from the power source, and check it that way. Be aware that you will be reading resistance across all terminations, and across the wire in the system.

Just wondering, why are you checking the full system's impedance?
I need to double check one thing, the car comes factory wired with 2 front mids + 2 front underseat subs wired in parallel to the mids and 2 rear shelf mids.
I am just after adding a factory tweeter to each mid effectively lowering the resistance at the front from 2 ohms to 1.33 (3 speakers now in parallel) and from 4 ohms to 2 ohms at the rear.

I want to buy an amp to drive the all the speakers and subs since the bass is pretty much gone now (I do have treble though) probably due to the lack of power of the HU.

So my question is if I leave the front channels as they are at 1.33 and run that on an amp which takes a minimum of 2 ohms, it will blow it right?
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Old 06-17-2012, 02:21 PM   #5
basicxj

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Quote:
Originally Posted by sd_dracula View Post
Thanks that was it.
I've disconnected the wire coming from the HU and now for the mid-range and tweeter I get 002-003 which is fine.



I need to double check one thing, the car comes factory wired with 2 front mids + 2 front underseat subs wired in parallel to the mids and 2 rear shelf mids.
I am just after adding a factory tweeter to each mid effectively lowering the resistance at the front from 2 ohms to 1.33 (3 speakers now in parallel) and from 4 ohms to 2 ohms at the rear.

I want to buy an amp to drive the all the speakers and subs since the bass is pretty much gone now (I do have treble though) probably due to the lack of power of the HU.

So my question is if I leave the front channels as they are at 1.33 and run that on an amp which takes a minimum of 2 ohms, it will blow it right?
Most full range amplifiers have power ratings for both 4 and 2 ohms, usually with a minimum stable operating impedance of 2 ohms. Because impedance is nominal (it changes as the frequency being reproduced makes the speaker's excursion and temperature vary), you will see impedances both above and below that 1.33 ohms which may trigger a protection circuit in the amp and will likely cause damage over time.

In spite of the fact car manufacturers (and some vehicle owners) like to cram way more in terms of speakers in a vehicle than are necessary or optimum, I'm a big fan of the K.I.S.S principal when it comes to car audio...that means one pair of tweeters up front, one pair of mids up front, and subwoofer(s). Adding more speakers and speaker locations to this basic recipe causes degradation of sound quality, stereo image and sense of stage (that would take a ton of costly signal processing to "fix")- each speaker and each speaker location playing into an enclosed listening space like a vehicle interior comes with both direct and reflected energy when listened to from the driver's seat, and the more sources you use, the more confused that 2 channel stereo signal becomes and the harder it is to get sound similar to what was recorded in your source music. With car audio, less is usually more.
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Old 06-17-2012, 03:50 PM   #6
sd_dracula

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Well I haven't added anything that isnt also done at the factory (Even the tweeters added are OEM ones).
The car can come with 3 options:
- 6 speakers (2 subs 4 mids) - no amp/no tweeters (standard STEREO)
- 10 speakers (2 subs 4 mids 4 tweeters) - amp for subs only (HIFI)
- 13 speakers (2 subs 7 mids 4 tweeters) amp for subs + mids + tweeters (Logic 7)

All I've is done is move from 6 to 10 speakers in terms of extra speakers, and have not touched the OEM wiring so far it was a simple PnP. The tweeters actually plug into the mids, my car was just missing them) which have made a world of difference in quality of the sound but the subs have been drowned a bit due to lack of power I presume.

Last edited by sd_dracula; 06-17-2012 at 03:57 PM.
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