The International Telecommunication Union’s radio communications division recommended ITU-R BS.775-3 for a multi-channel stereo audio system with or without video. Which was updated in 2012. And will be discussed in excerpts, the main points of which we mentioned in the previous post.
Figure 1. depicts the ITU recommendations for a 3/2 loudspeaker arrangement with three front and two surround channels for home theaters with an HDTV screen. The recommended front loudspeaker height is recommended for listeners seated at floor level.
A general rule can be given that states that front loudspeakers should not be placed higher than about 60% of screen height with respect to the “ventriloquism effect” which is the impression of sound emerging from a sound source somewhere on the screen instead of a loudspeaker.
The recommendation for placing the surround speakers possibly higher than front speakers can be explained by the sound being therefore able to radiate freely above the listeners to cause similar envelopment at the audience area.
Figure 2. shows the recommended arrangement for a 3/4 loudspeaker arrangement with three front and four surround channels.
Figure 3. shows another loudspeaker arrangement recommended by Dolby. One significant difference in this arrangement is the possibly decreased separation between the front left/right speakers that can be favourable in sound reproduction for movies due to viewing-angle considerations.
In this post, we went to the recommendations of surround sound by ITU-R BS.775-3 and examined its considerations. Items needed to improve sound and increase learning will be published in future posts. These will pave the way for creating a home theater of the highest quality.
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