Testing blown open circuit speakers with multimeter

Thread Starter

john2k

Joined Nov 14, 2019
146
I need to test the speaks on my car from the connector just behind the radio. I would like to test if any of them are blown. If speakers were blown then would I get a certain ohm reading between the two wires?
 

AlbertHall

Joined Jun 4, 2014
11,524
They should read very low resistance, <10Ω. If they read high or open circuit then the speaker may be blown or the wires connecting it are broken. In this case you need to test directly at the speaker terminals.
 

Thread Starter

john2k

Joined Nov 14, 2019
146
They should read very low resistance, <10Ω. If they read high or open circuit then the speaker may be blown or the wires connecting it are broken. In this case you need to test directly at the speaker terminals.
Thanks. If I disconnect the radio/stereo completely where the speaker outputs go from and if I measured resistance between two pins for a particular speaker should it not read any resistance at all?
 

Thread Starter

john2k

Joined Nov 14, 2019
146
I have 4 speakers two fronts and two rears the 2 rears are measuring at 3.7ohms and one of the fronts is also 3.7ohms but one of the other front one is measuring at 27ohms. Could that speaker be damaged? If there was a short on the wire going to the speaker then will it not read lower resistance?
 

AlbertHall

Joined Jun 4, 2014
11,524
What readings do you get across each speaker? (now seen your reply)

One speaker reading high is clearly faulty. I would expect that to be a bad connection between the connector behind the radio and the speaker terminals and is unlikely, but not impossible, to be a speaker fault. Measure the resistance across the actual speaker terminals for this speaker.
 

Thread Starter

john2k

Joined Nov 14, 2019
146
That same speaker is now reading even higher at 50ohms lol. That speaker is in the door card so I'll have to remove the door card. Should I disconnect the speaker completely and measure the impedance of the speaker directly at the pins? If it still reads high then speaker is blown? So a blown speaker does it read higher impedance? I was thinking a blown speaker night actually short and read close to 0 ohms
 

Dodgydave

Joined Jun 22, 2012
10,060
Measure the speaker directly on it's terminals, if it reads ok then check the cables to the radio .

It sounds like you have bad connections ..
 

Tonyr1084

Joined Sep 24, 2015
6,344
A speaker is just a coil of wire wrapped around a magnet. Changes in the current and voltage levels cause the speaker to vibrate back and forth, thus reproducing sound. If the coil is shorted then you will read zero ohms across its terminals. If you're reading high resistance then there's something going on. Perhaps the speaker has a filter cap to block low frequencies. A bad cap can cause strange readings. If the speaker shows open (for resistance) then the speaker itself is blown and will need to be replaced.

If the speaker measures out properly then measure the wires going back to the radio WITHOUT PLUGGING THE SPEAKER INTO THE RADIO. Sorry, I'm not yelling, just trying to make a strong point that if you plug into the radio and try to test the wires you'll not get the proper readings as the amplifier circuitry may add or change the readings in an untold way.

@Dodgydave said, and I agree, that you probably have a poor connection. It could be a bad crimp or bad solder joint anywhere from the speaker itself to the plug that plugs into the radio. When checking the wire for a good connection it should read zero ohms. HOWEVER: Let's be clear, wire has resistance. The longer the wire the more the resistance. The smaller the wire the more the resistance. IF you take the leads of your test meter and short them together you'll rarely see zero ohms. I typically see about 0.6 ohms when I do that with my meter and its leads. When checking a wire who's length is a hundred feet or more you'll see significant increases in resistance. However, for reading the wire from the door to the radio I would expect, with accounting for the test leads, possibly one ohm, maybe slightly more, but not more than 1.5 ohms. Still, even 2 ohms, I'd call that good. Since you're seeing 27 to 50 ohms, I must agree with Dave and suspect a bad connection somewhere.

Was this radio installed after market? Or is it factory original? If after market, I've seen guys twist wires together and tape them, and expect that to work well. It usually doesn't. When I install an after market radio I use crimps and the proper crimping tool to make the connections. Even those can tarnish and develop high resistance.

To recap:
You could have a bad solder connection at the speaker.
You could have a bad crimp at the speaker.
You could have a bad crimp at the plug.
If it's after market, whomever installed it may have done a less than good job and may have twisted wires together.
OR everything is fine but the wires have been flexed at the door so much that they're beginning to break down. That happens too. You could have broken strands inside the insulation (good luck finding that). Or you could have a pinched wire somewhere, and the insulation is breaking down causing an intermittent short circuit to ground.

To be sure, you must fully diagnose the problem before you start fixing or buying parts.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
9,468
While checking the resistance across the speaker terminals it makes sense to also check for any ground connection of the wires, since many amplifiers in auto sound systems do not use the body for either side of the connection. Sharp edges rubbing against wires can damage the insulation and cause a shorted circuit to the body metal.
If an external audio amplifier is available yiou can also check each speaker for performance and distortion, since it is possible for a speaker to be rubbing but still pass the resistance check.
 

Thread Starter

john2k

Joined Nov 14, 2019
146
Ok just to clarify it's an original radio with no wiring modifications at all. The resistance measurements I did across the two terminals were on the connector that plugs straight into the radio which has a built in amp. I measured the resistance with the radio completely removed just with a empty connector. The crimps and everything look like new still. The strange thing is if I plug the radio in and play audio I get perfectly fine sound coming out of the speaker that was reading high impedance values. All speakers sound good. So not sure why I'm getting a high ohm reading on just that one speaker
 

Audioguru again

Joined Oct 21, 2019
3,634
Car door speakers and their push-on connectors get wet when it rains and you moved the window up and down. The speaker is probably made to be waterproof but the connectors corrode and cause a higher than normal resistance poor connection like you have. You might not hear that the level is reduced a little. Unplug then plug over and over so that the connector works properly again.
 

Thread Starter

john2k

Joined Nov 14, 2019
146
Thank you all.

When weather permits next I will take that particular door card off and disconnect the speaker connector and measure the resistance between the two terminals. It should read the low 4ohms or so like the rest. If so I can then measure the resistance of each cable from both ends to see if there is any high readings. If not then I'm assuming it would mean just poor contact on either end of the connection points right?

So just to clarify, it definitely is not a short circuit because that would give a close to 0 ohm reading right? So a high reading would point towards a poor connection where the contacts are not fully connected
 

LesJones

Joined Jan 8, 2017
3,506
One thing you could try is no if the resistance (at the radio end of the wires.) reading changes when the door is opened and closed. It is just possible the wire as partly fractured where it flexes near the door hinge.

Les.
 

MisterBill2

Joined Jan 23, 2018
9,468
One thing you could try is no if the resistance (at the radio end of the wires.) reading changes when the door is opened and closed. It is just possible the wire as partly fractured where it flexes near the door hinge.

Les.
That is what I was suggesting. It certainly happened that way on my Dodge van.
 
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