Netflix is now streaming Dolby Atmos sound with Atmos-recorded movies. The good news is that this makes streamed Atmos movies every bit as exciting as they are on Blu-ray. The bad news is that, as well as stumping up for an Atmos sound system you'll also have to pay extra for a premium Netflix package.

You may be wondering just what Dolby Atmos is. It has the movie and sound purists very excited because it introduces another level of surround to surround-sound. Until Atmos, surrounding yourself with sound meant having three speakers in front of you at right, left and centre, two behind at right and left, and a subwoofer. This is a traditional 5.1 system, the five referring to the five speakers and the remainder to the sub. There are also 7.1 systems, while 5.2 and 7.2 systems have two subs.

Atmos adds overhead speakers, so that passing helicopters sound like they're overhead. But the system is only partly about effects; it's mostly about atmosphere.

The best Atmos set-up I've heard was a Steinway Lyngdorf Model S 7.2.2 system: seven surround speakers, two subs and two overhead speakers recessed into the ceiling. The movie was Everest and, OK, there was a helicopter but the system was at its most impressive generating the atmosphere of the Mount Everest base camp. There were breezes, birds and the buzz of the tent city with lots of people doing stuff while the two central characters walked through it all in conversation. I didn't need to imagine, I was there immersed in the entire fabric of the place.

The only problem is that the whole package  costs $135,000, and that's before installation.

You can do it a lot cheaper, and now that Netflix is bringing Atmos to the masses lots of people will be wondering just how cheap. Lesson the first: don't go too cheap.

Just as there are lots of soundbars consisting of a single speaker attempting to mimic surround sound by bouncing frequencies off side and rear walls, so there are Atmos systems that mimic overhead sound by bouncing off the ceiling. These usually have surround speakers with an extra driver mounted at the top and angled skyward, ideally with a bit of adjustment to allow for ceiling height and the length to the listeners.

But just as with simulated surround sound, simulated Atmos works better with some systems than others, and better again in some rooms than others. A cube is good. But no simulations work as well as the real thing. You need to audition any simulated system thoroughly.

I wouldn't invest in Atmos without a genuine Atmos amplifier, a sub, five surround and two overhead speakers. There are amplifiers out there that promise Atmos but really just deliver a simulation, so you should be looking for one that is at least 5.1.2.

There are some that are designated 7.2 but can deliver genuine sound using five channels for surround, two for overhead and two for subs – Onkyo's NR676 and NR575 ($1399 and $1199 respectively) are examples. For overhead speakers you'll need flush mount in-ceiling jobs that are the best acoustical match for your five surround ones. Take advice on this from a specialist hi-fi supplier. Such people can also arrange installation and will know a lot more about the whole business than you. Listen carefully.

I guess the next step is in-floor speakers. What would happen to these when someone spills a drink doesn't bear thinking about.