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Old 11-20-2017, 08:05 PM   #1
Spork Schivago
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Default How do I test a speaker?

Hello,

My daughter has a toy portable phone that was given to us. There's no sound. We tore it apart and the circuit board where the wires are soldered was broken off the speaker. There weren't any markings on the speaker at all, but I found a set that look identical, except they have the wattage and resistance on them. They're the same physical size as the original and are 0.25 watt, 8 ohm.

I soldered the new ones in and there's still no sound. I first want to test the speakers to see if they're good. I'm going to test the continuity between the two pads and make sure there's no short. If there isn't, I was going to apply some voltage to the two pads to see if I heard anything. But what's the right amount of voltage? I don't want to damage them.

I figure if I put the right amount on, I should hear something. If the speakers are good, I'll check the transistor that's right by the wires on the circuit board. I think that transistor is being used as an amplifier.

Thanks.
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Old 11-20-2017, 09:00 PM   #2
stj
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Default Re: How do I test a speaker?

test it by hooking it to a headphone socket with a jack cable.
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Old 11-20-2017, 09:34 PM   #3
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Default Re: How do I test a speaker?

I took a multimeter, put it on continuity mode, checked that way, infinite resistance. Put the other speaker in, worked like a charm.

There's gotta be a way to calculate the safe voltage range for a speaker based on wattage and maybe resistance though. I had trouble googling it, but I'm having issues with my memory right now. Maybe tomorrow things will be better.
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Old 11-20-2017, 09:45 PM   #4
redwire
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Default Re: How do I test a speaker?

You can use a 1.5V battery and the cone should move up/down, depending on polarity. About 0.25W and is good for finding intermittents, where the speaker checks good on ohms but cuts out once you pump some bass into it. You leave DC power applied and poke around to hear any bad connection.

For some reason, these small speakers open-circuit. I think the fine magnet wire breaks somewhere. If the break is on the leads to terminal block, or at the cone, sometimes you can repair that.

Philmore, Mode Electronics, Parts Express sell them.
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Old 11-20-2017, 10:00 PM   #5
eccerr0r
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Default Re: How do I test a speaker?

Usually resistance for a PM speaker is sufficient as a test. The piezo element speakers and such can't be tested with resistance. It's tough to use a voltage source because you don't know the actual DC resistance of the speaker. If you have a current limited power supply, have at it, you can do some basic tests with that. Or you can use Rx1 on an old multimeter, usually that's safe unlike using that Rx1 for a semiconductor...

Or just get another known working amplifier and sound source, which has the added benefit of showing a bit of how well the speaker actually can reproduce sound.

Yes speaker magnet wire tends to break near the stress points: cone and terminals, regardless how big the speaker is. However I've yet to find a small paper cone (0.25W to 2W) PM speaker break the speaker magnet wire unless it was overdriven. It's those small transparent plastic cone speakers/dynamic microphones that die on me as well as those big subwoofers...
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Old 11-23-2017, 05:58 PM   #6
Spork Schivago
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Default Re: How do I test a speaker?

Quote:
Originally Posted by redwire View Post
You can use a 1.5V battery and the cone should move up/down, depending on polarity. About 0.25W and is good for finding intermittents, where the speaker checks good on ohms but cuts out once you pump some bass into it. You leave DC power applied and poke around to hear any bad connection.

For some reason, these small speakers open-circuit. I think the fine magnet wire breaks somewhere. If the break is on the leads to terminal block, or at the cone, sometimes you can repair that.

Philmore, Mode Electronics, Parts Express sell them.
That's what happened to this one. The fine magnet wire broke, but it's too short in length to resolder on. Like a piece broke off or something.

I had paid 4$ for two, so I just used the 2nd one.

The 1.5VDC thing, is that always safe though? Will that work no matter what wattage speaker? Or is there some formula to calculate a safe voltage that won't damage the speaker?

Now, the toy sounds too quiet. I think this is how it originally sounded, I never heard it working. But I'd like to make it a little louder. On the PCB, there's two yellow wires that go to the speaker.

Right in that area is what appears to be a transistor and a resistor. I believe the transistor is used to amplify the signal going to the speaker. I haven't studied the PCB since I got the speaker working, but I'm wondering if that resistor is to limit voltage going to the transistor or if it limits voltage going to the speaker.

I'm wondering if I could perhaps lower the value of the resistor to get a bit louder sound coming out of the speakers. When I finish with my current project, I'll try to upload some pics of the PCB and maybe some experts could chime in and verify my hypothesis.
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Old 11-23-2017, 06:04 PM   #7
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Default Re: How do I test a speaker?

did you try fresh batteries yet ?
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Old 11-23-2017, 06:04 PM   #8
Spork Schivago
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Default Re: How do I test a speaker?

Quote:
Originally Posted by eccerr0r View Post
...
Yes speaker magnet wire tends to break near the stress points: cone and terminals, regardless how big the speaker is. However I've yet to find a small paper cone (0.25W to 2W) PM speaker break the speaker magnet wire unless it was overdriven. It's those small transparent plastic cone speakers/dynamic microphones that die on me as well as those big subwoofers...
This speaker wire was broke before it was ever put in I believe. I think it just came broke. It came all the way from China. The packaging wasn't very good at all. Small vanila envelope with the speakers wrapped in some sort of saran wrap.
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Old 11-23-2017, 06:05 PM   #9
Spork Schivago
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Default Re: How do I test a speaker?

Quote:
Originally Posted by petehall347 View Post
did you try fresh batteries yet ?
No. We put them in when we got it (it was a hand me down). That was a month or two. The lights lit up and the baby played with it. Many times, leaving it on. I'll try new batteries before I tear it apart again. Good call.
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