by Eric the Viking » 17 Oct 2021, 10:15
PC loudspeakers have usually had amplifiers built in. They're low-power, typicaly anywhere between two and five watts/channel. The '5.1 surround sound' stuff may be a bit more, but because the speakers are usually used very close to both screen and listener, and because they are electrically efficient, they don't need much power. It's why you usually have a 'wall-wart' power supply to power them, and they have volume controls etc. on one of the speaker pair. That's why with HiFi loudspeakers instead you need a separate power amp, just like traditional HiFi.
What comes out of a PC motherboard (even if it says "Speaker connection" somewhere or has an icon for that) is usually 'line level'. This is roughly the same as the level of the interconnecting cables we use between HiFi units*. It's like that partly for cheapness and partly for safety - you can't damage anything (usually!) if you put a plug in the wrong hole on the back of a PC. If there is a separate "line out socket" it will be functionally the same as the speaker connection. The difference will be that it may show up separately in the controls on-screen.
Most motherboards just have the one stereo "line out" socket, or a set of sockets for 5.1 multi-channel stuff. If you want to use a pair of speakers, connect the amplifier either to the line out connection or to the front-left and front-right channels of the 5.1 group of sockets, and then make sure you set the PC to stereo ouput, and NOT 5.1.
The reason for this is that film dialogue is almost always routed to the centre channel in a 5.1 system - it is almost always not mixed into the front left-right stereo pair (there are good reasons for this practice). When films (e.g. on telly) are listened to in stereo, the centre channel is automatically added to the left and right channels by the TV so you can hear it - otherwise all you'll get are music and sound effects - actors will probably seem to be miming!. Your PC may not default to the same behaviour, so if you get everything except speech it's not a fault - you just need to alter the sound settings.
Hope that helps.
E.
*technically it's a compromise at -10dB below 'proper' line level (0dB), but the latter is only used in professional applications. Again it was in part a cost-saving by manufacturers: -10dB kit was much cheaper and easier to make, and less damage is caused if you send domestic line sources into microphone or phono inputs by mistake!