Most PCs own two (or more) sound sources: A sound card and the built-in PC Honker. The second one can neither be controlled in its volume nor be heard out of the normal speakers. But one can change this.
For doing this one needs a sound card with an unused input (Line-In or, available on most original SoundBlaster-Cards, a special input for it). The only thing to do is making the cable for it, the sound card itself remains unchanged.
The mainboard speaker connector consists of 4 pins, however only the outer 2 are used. Cut a 4 pinned part off from the 2,54 mm pinout connector. The 2 outer pins of the so-created plug are connected by the resistor (it discharges the capacitor and simulates the speaker). One end of the resistor is also to be sold with the capacitor. The main reason for using the capacitor is to prevent hardware damage as a result of using the plug the wrong way.
In the simplest case the sound card offers an input created for just this use. It is often called PC-Speaker or similar and consists of 2 pins with 2.54mm distance (e.g. SB, SB 16, SB 32). In this case one cuts a two pin part of the connector array and attaches ONE pin of it to the cable. The second pin remains open!
If one wants to use the CD-ROM-input, one cuts a 4-pinned part of and connects BOTH outer ends of it with the cable. This applies to all CD-ROM inputs with Left-Ground-Ground-Right pinout. Other CD-Audio connectors may use another pinout (they should be documented in the manual).
The third possibility is to sold the cable to the middle contact of a 3.5mm audio plug and put it into the Line-In input of the sound card.
It is easy to do: The end with the resistor replaces the PC speaker plug, the other is attached to the sound card. Just turn the plugs 180 degrees if it doesnīt work. As Iīve explained before, nothing serious can happen. Exception: If you are using the version for the CD-ROM input, make sure that it really is the CD-ROM input and not an output connector However, even in this case hardware damage will only occur under very rare circumstances.