No ohm reading at speaker terminals

[bluesguitar]

I recently purchased a pair of 1961 Jensen speakers. Have been testing them and noticed that one wasn't making any sound. Took it out of the cabinet and tried to test the leads. I can get no movement of the cone when applying a charge from a battery. Also, my multimeter indicates no ohm reading at all. Everything was fine when I first got them. I applied a battery charge to each speaker to make sure I had them wired in phase. I know the battery and multimeter are working fine. Anyone have an idea what the problem may be? Wouldn't you be able to get some kind of ohm reading even on a blown speaker? Near as I can tell the wire from the terminals to the cone seem to be good.

[ampdoc1]

You will not get any reading on your DVM if the speaker is blown.

You didn't mention how much battery voltage you put on the speaker, but you probably burned up the voice coil at some time. While I've done it, testing a speaker with a battery, rather than a DVM, is not a good idea.

[bluesguitar]

@ampdoc1- You may be right about the ohm reading of a blown speaker, however I doubt your concern about the use of a battery is valid. I have seen many amp and speaker techs on youtube recommend the use of a battery to test speaker phase. This includes Gerald Webber. I have never heard of a warning concerning this procedure. They use 9v batteries and I only use a D size which only produces 1.5 volts.

[xtian]

This is an interesting theory question. If you put nine volts square wave, that's 10 watts into 8 ohms or 20 watts into 4 ohms. So does the possibility exist that you could burn up a 15 watt voice coil? The signal isn't oscillating... Surely you could shock a fragile coil to death?

[sluckey]

A typical 9V battery cannot produce enough current to destroy a typical guitar amp speaker. When you connect the battery, the voltage drops very low.

[ampdoc1]

It seemed obvious that the sender is fairly inexperienced, and I just put the note on batteries as a "flag" for him.

We all used to be NUBIES,..Information and learning are why we're here.

[bluesguitar]

@ampdoc1- I appreciate this website, because it is a valuable source of information when I come across a problem that I'm not familiar with. I've never experienced a blown speaker before, although I've changed out and checked the phase on many. I appreciate your input concerning the ohm reading. However, my experience and knowledge of using a battery to check speaker phase qualifies me as more than inexperienced, or nubie. It would appear that your "flag" exposes your inexperience concerning this procedure. Again, I respect and value this site. We all need to be open to correction from time to time.

[JazzGuitarGimp]

When applying a DC voltage to a soeaker, we need to consider the DC resistance of the voice coil, not its AC impedance. A 4R speaker will have a DC resistance of about 3R. Apply a fresh 9V battery, and you've got 3A of current, which equates to 27 watts. I am pretty sure a fresh 9V battery can produce 3A for a short amount of time. This will likely fry a 15 watt speaker.

[Jana]

Whether or not the battery toasted the speaker, it seems the speaker is blown. If you aren't getting any ohm reading, that indicates the coil has an open in it. FWIW, I would never use a 9 volt battery to check the speaker cone movement.

[cbass]

I use dead 9v batteries to test speaker phase . well not totally dead. I wouldn't recommend for normal people to do what I do

[bluesguitar]

Lots of theory in the comments. I wouldn't argue with safety first. However, for the more practical minded do this experiment. Google this topic and let me know if you find a single instance of a person stating that they actually fried a voice coil using a 9v battery. Not hearsay, but actual first hand experience. Also, make note of how many speaker repair shops have no problem recommending this test. It would be safe to assume they have done it hundreds, if not thousands of times in their work, and have not stated one instance of frying a voice coil. Just sayin.

[ampdoc1]

Sorry, just trying to help. But you did not say what size battery you used, and that is why I noted a warning.

I am certainly not the most experienced or best source on this site. But as for my knowledge, I've repaired over 1000 amps in my years, and I understood how to test and determine problems with speakers when I was 18.

Evidently you didn't !!!

[epis]

There is nothing wrong with battery speaker test. Person just need to pay attention not to leave battery hooked up.
Just a touch is enough to check the speaker, what bluesguitar probably did.
Bluesguitar, did you try to check resistance of the speaker coil at tinsel wires ?
I would assume (because of speaker age) connection is lost (broken) at the spot where wires are soldered to the posts (terminals).
Wires might look OK visually but not electrically.Good luck

[Stevem]

Your speaker has just shown its age, not blown!
You may be able to fix it as I have many times.
Use a single edge new razor to cut the voice coil cover off, be it paper of felt.
Next look for where the voice coil wires come up and out and pass over the upper lip of the voice coil before they get glued onto to the cone and pass onto the tinsel wire.
Many times that unsupported section of voice coil wire breaks just do to age and vibration, and many times I have soldered in new wire from the tinsel portion to the broken area and got the driver back up and running.

Note that you will need to use your iron to heat off the enamel coating from the voice coil lead to get it to tin up some first.

Once you fix it use gel type super glue to hold down both the repair point and the other voice coil lead that is likely unsupported also.

Work cafeful and do not let any crap get down into the voice coil gap around the magnet pole, a good blow out with keyboard dust removing spray works great, after that just glue the voice coil cover that you cut off back on!

[JMFahey]

A fresh AA battery can give between 1 and 2A into a dead short (the multimeter set on the 10A scale) which means its internal resistance is around 1 ohm .
This is a measured by me, not guessed or read somewhere value.
Even if you put 6 x AA batteries in series to get 9V you still have same current, because voltages add up, but also do internal resistances.

Too lazy now on this holiday to go measure a 9V battery, but it having 6 1.5V batteries in series inside which are individually much smaller than AA, logic is that internal resistance is even higher.
How much?
Only (later) measuring will confirm but I would be surprised if they could offer more than 0.5A ... and that into a dead short, because series resistance would be at least 6 ohms, and probably twice as much.

So a 9V source, with internal resistance 6 ohms, in series with an 8 ohms speaker , which woukld actually have around 6 ohms resistance, would drop half voltage, for effective 4.5V DC .

Which amounts to 4.5*4.5/6= 3.3W .

And that with 6 fresh AA in series; with a typical 9V battery it would be hard to get more than 1W into that speaker.

In either case, piece of cake, not power enough to blow any guitar speaker.

Might be dangerous for an earphone, cellphone 3/8"speaker or similar tiny one.