Is there a trick to speakers, or did I just get a dud?

Thread Starter

s_mack

Joined Dec 17, 2011
198
Sorry, I have near-zero experience with speakers other than listening to them.

I bought a "thingy". It came with a little 8ohm speaker. In fact, I found the exact same one here: http://www.electrodragon.com/product/0-5w-8-ohm-mini-speaker/#prettyPhoto

Here's a picture



Mine came with a twisted pair pre-soldered to the blobs of solder south of the green tape(?). One of the blobs was lifted so bare PCB was under. As far as I can tell, the entire slab of metal to the right/left of the green tape is physically the same entity as where the blobs were soldered to. Is that incorrect? My meter sure thinks it is! I removed the wires and soldered them solidly to those slabs but no sound comes out of my "thingy".

OK, so maybe "thingy" is busted, right? I took my PC speakers and grabbed some aligator clips and attached it to the the 3.5mm plug and hooked it up and it worked fine, ruling out bad "thingy". So I'm back to the speaker. Is the speaker junked or am I mistaking how to solder it somehow?

One thing... before doing my "fix" my meter indicated that there was an intermittent short between - and + due to the lifted blob flapping around. So it is more than possible that it shorted while it was in "use". Does shorting a speaker like that permanently break it?

I never heard even a slight pop out of it.
 

Dodgydave

Joined Jun 22, 2012
8,389
Put your meter on Ohms and measure the resistance of the speaker coil, it should be about 8 ohms, if its open circuit then its damaged.
 

Alec_t

Joined Sep 17, 2013
10,362
If the coil measures ok, then glue the flapping part to something non-conductive and solid.
 

MrSoftware

Joined Oct 29, 2013
1,564
A speaker is pretty simple, electrically it's just a coil. Those two solder balls represent the ends of the wire that the coil is wound with. If all is well, you should get in the ballpark of 8ohm resistance across those two solder balls. If you get an open circuit then the wire is broken somewhere. If you get a short then the wires might be touching the metal speaker frame, or each other, somewhere that they shouldn't be.

That speaker is so small that repairing anything beyond the pads where you connect the wires is probably not practical.
 

Thread Starter

s_mack

Joined Dec 17, 2011
198
Open circuit. OK, thanks!

I have 10 more on the way by slow boat from China. Hopefully one of them works.
 

GopherT

Joined Nov 23, 2012
7,983
Open circuit. OK, thanks!

I have 10 more on the way by slow boat from China. Hopefully one of them works.
you can also look for the thin wires coming from the back of the paper cone - these should have been soldered to the little section of the PCB. If it is broken off of the PCB, you can try to re-attach the broken wire to the PCB or to a thicker wire. It should work fine once repaired.
 

Thread Starter

s_mack

Joined Dec 17, 2011
198
It is mylar, rather than paper... only way I can see to check that is to cut the mylar. I'd assume that would destroy the speaker?
 

Dodgydave

Joined Jun 22, 2012
8,389
The speaker wires will be glued to the black paper diagram with flying leads from the blobs of solder, it is possible to repair these leads, but it needs a gentle hand and soldering iron, otherwise bin it!
 
Last edited:

joeyd999

Joined Jun 6, 2011
4,239
Open circuit. OK, thanks!

I have 10 more on the way by slow boat from China. Hopefully one of them works.
While you are waiting, keep in mind that you won't get much (quality or volume) sound out of it until it is installed in some kind of enclosure.
 

Thread Starter

s_mack

Joined Dec 17, 2011
198
At $0.44 each... I'm not too terribly concerned about it so I cut the mylar off just to see what you were talking about. But by the time I located the wires, I severed them lol. Now I know what to look for next time :)
 

ian field

Joined Oct 27, 2012
6,543
Put your meter on Ohms and measure the resistance of the speaker coil, it should be about 8 ohms, if its open circuit then its damaged.
8 Ohms is the AC impedance - the DC resistance will be somewhat lower.

But some cheap meters can't resolve the difference anyway - a *REALLY* cheap meter might not even notice any resistance.
 

Thread Starter

s_mack

Joined Dec 17, 2011
198
Mine isn't a Fluke, but it isn't a $5 special from the Dollar Store either.
 

ian field

Joined Oct 27, 2012
6,543
Mine isn't a Fluke, but it isn't a $5 special from the Dollar Store either.
In days of old - 3 Ohm speakers were common, 4 Ohm speakers aren't exactly rare - some of the "not too bad" meters have trouble with those.

Unless you're rich, a DMM probably doesn't have a zero Ohms adjust - then you can't null out the resistance of the test leads, that can amount to some fraction of an Ohm.

Unless you've spent laboratory instrument prices, speaker resistances are approaching the margin of diminishing accuracy.

Most people get by - but you have to bear these things in mind.
 

Cjuried

Joined Aug 31, 2015
2
8 Ohms is the AC impedance - the DC resistance will be somewhat lower.

But some cheap meters can't resolve the difference anyway - a *REALLY* cheap meter might not even notice any resistance.

Using a common DMM set to resistance will get you close. Use a LCR Bridge/Impedance meter, if you wish to document the "true" measurement of the speakers Impedance, to include inductive and capacitive reactance.
 

ian field

Joined Oct 27, 2012
6,543
Using a common DMM set to resistance will get you close. Use a LCR Bridge/Impedance meter, if you wish to document the "true" measurement of the speakers Impedance, to include inductive and capacitive reactance.
The traditional way to measure low resistances, is to pass a calibrated constant current through them and measure the volt drop.

With speakers, you need pretty low current to avoid slamming the cone, but with careful design you can get it in the same ball park as the test current from a DMM Ohms range.
 
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