No matter what a cheap three inch driver's specifications say it does, it has no useful response below 120Hz, and probably bog-all below 200Hz. Yes, it will make a noise if fed a 50Hz tone. But it's so inefficient at that low frequency that it'll barely be audible, even at full power. Or just use bigger speakers. If your sound card has an amplifier, all you'll need is a cable to connect the sound card to the speakers.
Most speakers have terminals which accept bare wire.
If you've any talent for woodwork, you can easily make your own speakers, with cheap drivers, terminals and other accessories from an electronics store and a few dollars worth of wood. Headphones are another option. If you don't mind the inconvenience, money spent on headphones will give you much better sound than the same amount spent on speakers. This means you need no sound card at all as long as you only want audio output, not input, and it also makes possible fancy multispeaker setups, with complex positional audio handled by the CPU or a dedicated audio processor. So unless you're really scratching for slots and system resources, you might as well stick with your standard sound card.