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Old 01-14-2013, 01:08 PM   #1
stf92
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Desktop beeper (aka internal speaker) with polarity?


Hi: Desktop computers have two pins on the motherboard (mb) which go through a cable to a speaker (drive in audio terms). Mine is a miserable transducer which has the polarity marked on it. So I take it this mb output is not, as it was in the old days, for connecting a moving coil speaker, i.e., the kind of speaker there used to be on old mb. Because the latter has no polarity. You can reverse the polarity and it will work.

Are all modern desktops like this one, that is, the speaker output has a polarity which you must respect? The question is rather vague, because maybe high-end desktops have speakers in the old fashion (no polarity). So this datum: the mb is the Gigabyte H61M-S1. May be I am wrong and the transducer has no polarity? My opinion: the plus sing marked on it is a mere decoration.

Last edited by stf92; 01-14-2013 at 01:57 PM.
 
Old 01-14-2013, 02:15 PM   #2
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Modern speaker are not moving couil speakers, they are Piezo speakers: http://en.wikipedia.org/wiki/Loudspe...ctric_speakers
Therefore your assumption that the polarity is mere decoration is wrong, if you connect it wrong you will not get any sound from the speaker (but nothing will get destroyed or something like that, just reverse the connection and it works).
 
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Old 01-14-2013, 02:17 PM   #3
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I just took a look at my motherboard manual (mine is a Gigabyte too, a GA-990XA-UD3) and the polarity of the speaker connection is shown in the manual. That said I think my case just has a moving-coil speaker and I don't recall whether I paid any attention when wiring up the speaker.
 
Old 01-14-2013, 02:30 PM   #4
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Piezo speaker are by far cheaper than moving coil speakers, I haven't seen a motherboard or case coming with moving coil for years. May be you were just lucky (the chance is simply put 50% to do it right).
 
Old 01-14-2013, 02:39 PM   #5
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I thought I'd read somewhere in the manual that many of the motherboard connections could be plugged in either way, but re-reading it all the polarities are marked and there's a note to observe polarity. I knew the LEDs, by their nature, had to go the right way so perhaps I did pay attention to the speaker terminals too.
I've an ultra cheapo case so it must be a piezo as it's just too tacky for anything more expensive, come to think of it.
 
Old 01-14-2013, 04:17 PM   #6
stf92
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Quote:
Originally Posted by TobiSGD View Post
Modern speaker are not moving couil speakers, they are Piezo speakers: http://en.wikipedia.org/wiki/Loudspe...ctric_speakers
Therefore your assumption that the polarity is mere decoration is wrong, if you connect it wrong you will not get any sound from the speaker (but nothing will get destroyed or something like that, just reverse the connection and it works).
I aimed at having an audible bell character (0x07). Also having a means of debugging some programs in which the CRT cant be used for that. As the frequency response curve of these moving coil speakers was very uneven, by varying the frequency one could find the point at which the loudness was a maximum.

My piezo-electric, a thing I did not know it was, is only audible at night. So, I though I could just unplug it and plug in a speaker with a powerful magnet I have from a very old PC. I now see I can't, given what you've said. And even if the output signal could drive a moving coil, i.e. if it were an audio signal with no DC component, the mb amplifier would have to be able to deliver good power. In the last mb's with moving coil I've seen, entry level it's true, the amplifier delivered the 8-ohm load a power in the order of nanowatts. And the magnet was a joke compared to that in the first PCs.

I could insert a capacitor in series with the speaker, but again, the output power over 8-ohms would be too low. You can't know how disappointed I am! Thanks for your very useful post.
 
Old 01-14-2013, 06:24 PM   #7
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So put a capacitor in series and connect it to an el-cheapo amplified speaker system. You know the type with a 3.5 mm plug.

jlinkels
 
Old 01-14-2013, 06:30 PM   #8
stf92
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But it's the bell character I want to hear. You are speaking about the sound card!?

Last edited by stf92; 01-14-2013 at 06:37 PM.
 
Old 01-14-2013, 06:34 PM   #9
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I thin jlinkels meant that you should connect that to the onboard pc-speaker output.
 
Old 01-14-2013, 07:05 PM   #10
stf92
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Originally Posted by TobiSGD View Post
I thin jlinkels meant that you should connect that to the onboard pc-speaker output.
And what is the role of the 3.5mm plug? Although perhaps I should first know what the blody el-chipo is that I can't find in any dictionary.
 
Old 01-14-2013, 07:32 PM   #11
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El-cheapo is a slang form of cheap device. What he means is a simple active speaker, sets of these can be bought here sometimes in supermarkets for about 10€, with a bad sound quality, but for the purpose of just hearing the bell more than sufficient. The 3.5mm plug was just an indicator for what he meant, it will be cut of anyways.

Side-note: sometimes a look at the Urban Dictionary is worth a lot: http://www.urbandictionary.com/defin...rm=el%20cheapo
 
Old 01-14-2013, 08:00 PM   #12
stf92
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I see. The terminology used today it confuses me. Speaker is an enclosure containing the driver. I was usin "speaker" in the sense of "driver". I mean, a speaker is the set with two elements: enclosure and driver. I do not know what loudspeaker means today. Using the proper (up to day) terminology then, some speakers include an amplifier. The amplifier is within the enclosure. I myself am sitting in front of two of this type right now (the PC desktop little speakers, but the amplifiers, right and left channel, are built in only one of them).

It seems a good solution. The only problem left unsolved is where to get the connector that would plug into the motherboard socket (a simple pair of pins). I have some, but used. I.e., a cable comes out of the conector. To disassemble it and reassemble it I think would be an impossible mission. And if I find a place where I can buy one of those connectors, then again to assemble it together with the cable would be very difficult without a special tool and the result, poor.
 
Old 01-15-2013, 05:44 AM   #13
stf92
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After some time googling, I got
:
Quote:
a [piezo] buzzer typically has it's own internal oscillator and drive, thus you only need to apply power to make it work. What you have sounds like a piezo speaker, thus you have to provide it with an AC waveform with your audio signal. The easiest way to do this is to use the AVR's PWM functionality [AVR is an Atmel line of microcontrollers], with complimentary outputs. Attach each of the complimentary outputs to the terminals of the piezo, this will in effect present it with a +/-5V [10Vp-p] signal. Then simply drive the PWM with your audio data for the tone/signal you'd like to generate. (you can use a simple square wave of the frequency you want, but you may find that it sounds a bit staticy, feeding the PWM with a series of sinewave samples will likely produce a cleaner sounding result.)
(from http://www.avrfreaks.net/index.php?n...topic&p=812568).

And
Quote:
The [computer] case speaker is a peizo buzzer normally, ...
(from http://www.tomshardware.com/forum/29...phones-speaker). That computer is an e6700/asus p5b. I do not know if the asserrtion in the post ("the case speaker is normally a piezo buzzer") can be generalized to all modern home desktop computers.

So, neither moving coil speaker, nor "el-cheapo amplified speaker system", nor even a piezo speaker will do. A solution to this problem (making the beep louder) would be too complicated, as I see it. Of course, the writer in the second post used the word 'normally'. Perhaps some high-end home desktop computer uses another approach for the internal speaker.
 
Old 01-15-2013, 06:37 AM   #14
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Quote:
Originally Posted by stf92 View Post
Perhaps some high-end home desktop computer uses another approach for the internal speaker.
I can assure you they don't. In times of 7.1 surround sound systems and sound themes for system sounds generated by the audio subsystem no one really cares about the PC speaker, it mostly nowadays has the only function to act as error signal if the system doesn't boot due to hardware error.
 
Old 01-15-2013, 06:51 AM   #15
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Quote:
Originally Posted by stf92 View Post
Quote: a [piezo] buzzer typically has it's own internal oscillator and drive, thus you only need to apply power to make it work. What you have sounds like a piezo speaker, thus you have to provide it with an AC waveform with your audio signal. The easiest way to do this is to use the AVR's PWM functionality [AVR is an Atmel line of microcontrollers], with complimentary outputs. Attach each of the complimentary outputs to the terminals of the piezo, this will in effect present it with a +/-5V [10Vp-p] signal. Then simply drive the PWM with your audio data for the tone/signal you'd like to generate. (you can use a simple square wave of the frequency you want, but you may find that it sounds a bit staticy, feeding the PWM with a series of sinewave samples will likely produce a cleaner sounding result.)
This is nonsense. Either you have a piezo speaker with an internal oscillator, which you drive with DC. Or you have something which needs a 10Vp-p signal which is AC. Which will drive a normal speaker. Having a piezo speaker and drive it with AC is nonsense.

Legacy connections stay legacy unless it is very clearly indicated that they have changed. Asus does not say in the manual it has changed. The speaker signal is still +5V-speaker, as it has been for decades. Not speaker-GND as would have been likely for a DC output. The 5V-speaker is constructed as such so an open-collector output can be used to drive the speaker.

Besides, if you have an ATX case in which you can mount this MB which still happens to have a conventional AC-drive speaker a modern ATX mainboard would not be able to drive the speaker? Can't believe that.

jlinkels
 
  


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