Yes, that is correct. The R1280T 2.0 features an active speaker (right) with a built-in amplifier and power supply, while the left speaker is passive and receives the amplified signal through a connecting cable from the active speaker.
These speakers are not passive, but active, so they have a built-in amplifier and do not require an external amplifier to operate. They have volume, bass and treble control directly on the active speaker and connect via RCA inputs to audio sources such as turntables with built-in amplifiers. They are designed to offer 42 W total power (21 W per channel) with internal amplification.
That is difficult to answer. I use the speakers on the PC in the office and find it's quite enough. The office is about 25 square metres and 3 metres high. I've never had to turn up the volume and if I did, I'm sure the neighbours would get a kick out of it too ;) I also find the bass quite decent for the small things. Loud is relative. They wouldn't be enough for a disco or a concert. Hope this helps....