For the enjoyment of films and TV a truly immersive and detailed sound is just as important as having a good picture. Neither TVs or projectors are capable of producing decent sound on their own. A sound-bar can improve the sound of a TV, but to get true cinema sound, you really need to look at a home cinema amplifier or AV-Receiver which powers a set of speakers. I’ll do a whole section on AV-Receivers shortly as they do much more than simply power the speakers. To begin with we’ll look at types of surround sound.
When a film is reproduced digitally either on BluRay disk, for streaming or broadcast, it has it’s soundtrack stored within the data as a digital codec. These codecs are developed by companies such as DOLBY and DTS. The broadcaster/film companies use this technology under license to distribute the content and the AV manufacturers license the technology for use in their equipment so it may be reproduced at home.
This is not technically surround sound or a digital codec, but is worth mentioning. It is the same basic format which has been used in music production, TV and films for many years. It uses two channels with two speakers. When these two speakers are correctly positioned it will produce a stereo image or soundstage. When listening to a well produced stereo recording on a decent HiFi or home cinema system you should experience the impression of the instruments which are on the left of the stage, sounding as though they are on the left, and those on the right, sounding as though they are coming from the right of the stage. If there is a singer in the centre of the stage, you should hear the vocals coming from the centre. This is all with just two well positioned speakers.
Stereo is still the best option for music playback and can be very effective for TV and films too.
This is the most commonly referred to surround-sound format for home cinema. It corresponds to a system which uses five channels of sound over five speakers and a sub-woofer.
The most important speakers are the front left and front right speakers, which do much the same job as a pair of stereo speakers. In fact, when you are using the system for stereo playback, that is what they are. As for with a stereo system, these should be positioned either side of the screen, a few metres apart.
The second pair of speakers are the rear/surround speakers. These should be positioned slightly to the back and to either side of the seating position.
The fifth speaker is the centre speaker. This is positioned either directly above or below the screen and handles the movie dialogue.
The .1 of a 5.1 system is the subwoofer. This usually has it’s own amplification built in and produces the low frequency bass for all of the other channels. This underpins the sound. It’s what makes explosions sound powerful in action films or the sound of a door closing in a horror film feel like it’s happening in the same room as you.
Because the sound waves which are produced by the subwoofer are so broad, the sub can be positioned just about anywhere within the room. In fact, even if the subwoofer is located at the back right of the room, if an explosion happens on the film on the left hand side of the picture, the sounds produced by the left speakers, combined with the sub will make the sound come from the left of the room. Even when the sub is to the right. Most home cinema systems use only one sub but it is possible to use two, to create a 5.2 system.
A 5.1 surround sound system provides 360º audio. This provides a more immersive viewing experience for films than is possible with stereo. It takes the ‘sound stage’ effect of a stereo system a step further and mean that you should experience the full effect of hearing objects whizz around the room during action sequences.
This is a 5.1 channel system with an extra two channels. It usually means having a surround sound speaker directly to both the left and the right of the seating position as well as two rear-surround speakers behind.
7.1 is a good solution for larger rooms and to get the better 360º sound effect.
5.1.2 or 7.1.2 or 5.1.4 or 7.1.4
The latest DTS:X and Dolby Atmos surround sound formats add the addition of extra channels which produce the sensation of sound coming from above. To be able to experience this technology you need to add the minimum of an extra two speakers. These can either be in-ceiling speakers or specially designed upward-firing modules which bounce the sound off your ceiling. A 5.1.2 system would be a 5.1 system with an extra two speakers.
Although at the time of writing not many films have been released with the Dolby Atmos or DTS:X codecs, the results I’ve heard have been very impressive and we are likely to see these codecs added to to the latest film releases.