OT? testing computer speakers with cell phone?

[Paul]

Electrolytic capacitors can be NP (Non-polarized) or they can be the polarized type. If working your magic with the battery, you want to charge the capacitor according to the polarity symbols. Plus on the battery goes to plus on the capacitor. If you reverse the power to a polarized capacitor, it can blow up on you. It will fill the room with black sooty deposits floating in the air, if that happens. (Someone in electronics lab did the usual trick, reversed insertion, as a joke. So we got a demo of what a mess it makes.)

There is a little info here on NP capacitors. And how to make one. It isn't mandatory to use an NP capacitor in this application. You might use an NP cap in an amplifier with symmetric powering (+/-15V rails maybe). Whereas a cheap computer speaker probably runs off one rail, and so a polarized cap would always be charged correctly to some sane voltage.

The home made amplified speakers on my new computer, are DC coupled. It's a bridged amp, using two amp chips, and that allows removing the cap entirely. As the circuit is so well balanced, less than 10mV DC appears across the speaker when idle. (I was really impressed it came that close to zero!)

This schematic shows a polarized capacitor in series with the speaker. Schematic is on page 3. This is a single rail amplifier (+13.2V nominal). The purpose of the capacitor, is to prevent DC from appearing across the speaker terminals. (So the cone doesn't have a decided mechanical bias while running, preventing full travel.)

On page 6 here, you can see the "bridged" configuration. One amp goes up in voltage, while the other one goes down. Giving more power. And, as a bonus, the DC output of the two amps is matched closely enough, when the amplifiers are idle, there is no net DC across the speaker terminals. The large electrolytic in series with the speaker can then be removed. So if the amp on page 6 was driving your speaker, the big capacitor would not be inside the cabinet.

My amp is actually a stereo kit, so there are a total of four amp chips to produce stereo. Yes, the circuit still has electrolytic caps, just not 2200uF ones. The volume controls, while pretty to look at, I set them once and never dialed them again. I use the volume control on the computer for that.

Paul

[Paul]

On amplified devices, I use the "hum" test.

Take the 1/8" plug, and don't connect it to the computer. Touch your finger to the end contact (Tip). The left speaker should have a slight bit of hum in it, from your finger.

Now, touch your finger to the middle contact (called Ring). The right speaker should hum.

You can use that to test amplified computer speakers at a flea market, as long as there is AC power to run the amp.

No need for a Walkman or other signal source to run a signal into the amp.

The hum test does not give any indication of balance across the audio spectrum, so the test is not conclusive in terms of "whether the thing is crap or not". The hum test is basically just a continuity test, proving the item is "an amp". Not a "good" amp.

A computer amplified speaker should have enough gain, and a high enough input impedance, that you should hear some hum, when you turn up the volume and start touching the

1/8" plug contacts.

Paul

[Micky]

I'm glad I thought of that, for me and my friend. I'll tell her.

[The Real Bev]

There's a difference between "can" and "want to". Lawn (area containing grass and weeds) and gardening is fine, fixing crap is not. I've solved enough problems over my lifetime, now somebody else can do it for me! Well, mostly, I guess. I need to fight my instincts...

[J. P. Gilliver (John)]

In message , Paul writes: []

[] And to prevent coil heating.

[Paul]

I suppose. There would be nothing to cool the coil at all.

Someone here lists some possible causes of the speaker coil burning out.

Paul

[J. P. Gilliver (John)]

True, but especially in the case of a DC bias.

Oh dear, I'm not too impressed with that article: between stating the obvious, and various woolinesses and untruths, I have the feeling the author only has a tenuous grasp on the subject - or, being at my most generous, has something in mind but very poor ability to communicate it, possibly through trying to simplify.

[Don Y]

What's wrong with opening the "sound panel" applet and setting the balance to the far left (or right) and noticing "where" the sound goes? I do this with headphones/earbuds, desktop speakers, etc. all the time (easier than trying to read the little L and R molded in or printed on the plastic).

[Actually, I have several cheap pairs of earbuds that came with optional "decorative" colored "rings" that you could clip on the individual ear buds. The thinking, apparently, was to make the boring white earbuds flashier -- put a bit or red, blue, yellow, etc. on them. But, they apparently thought you'd put the same color on EACH as they provided two if each color! I, instead, elected to put a green and red on so I could quickly/easily sort out which is which when putting them on!]

[tlvp]

And then there are the odd-ball connectors the headphones for older Nokias, and Erikssons, and Moto TimePorts, use: not tip/ring/barrel plugs at all.

Remember? Cheers, -- tlvp

[tlvp]

Probably: the cord to the earbuds/headphone serves as radio antenna.

HTH. Cheers, -- tlvp

[nospam]

there were a lot of proprietary connectors.

[nospam]

not probably. it *does*.

[DerbyDad03]

I wonder if that is still true. That would mean that the radio feature could be used with a Bluetooth headset. If that is true, then the workaround would be to use a streaming radio app, such as Tune-In, which doesn't need an antenna.

On the other hand, I don't recall that any of my "newer" smartphones even came with an over-the-air radio feature. Why include a over-the-air radio feature when just about every station streams their content now?

On the other, other hand, I have a Bluetooth headset that has it's own over-the-air radio feature. It sucks, but's it there. (There's no "direct tuning" available, you have to rotate up or down through the stations using the volume up and down buttons. Did I mention that it sucks?)

[John D]

Test? I have computer speakers in my basement with sub that I plug my phone into all the time. This is common. The input to the speakers is probably a basic 1/8" stereo connection. Works for phones, tablets, and I'm sure some refrigerators. Very common. The seller is correct. This is the way to test them.

[J. P. Gilliver (John)]

tlvp's "Probably" was answering the preceding question, not qualifying the following statement. So it's "probably" that the "newer phone" will _display a message_ insisting something be plugged in; it's "definite" that it won't work very well as a radio if nothing is.

[Micky]

Well, I have the newer phone now, and indeed it requires the earbuds, or at least something, to be plugged in. I plugged in a computer speaker that required AC, but didn't plug that in. Later i found a setting to turn the speaker on even if something is plugged in. Maybe because this is Android 5.0.2 after all. Android 2 didn't have this and I don't know about Android 4.

And probalby Bluetooth will work anyway also.