{"id":1224,"date":"2014-02-22T21:13:23","date_gmt":"2014-02-22T19:13:23","guid":{"rendered":"http:\/\/www.tonmeister.ca\/wordpress\/?p=1224"},"modified":"2020-01-21T17:16:16","modified_gmt":"2020-01-21T15:16:16","slug":"bo-tech-multichannel-setup-tips-and-tricks","status":"publish","type":"post","link":"https:\/\/www.tonmeister.ca\/wordpress\/2014\/02\/22\/bo-tech-multichannel-setup-tips-and-tricks\/","title":{"rendered":"B&O Tech: Multichannel setup tips and tricks"},"content":{"rendered":"

#14 in\u00a0a series of articles<\/a>\u00a0about the technology behind\u00a0Bang & Olufsen<\/a>\u00a0loudspeakers<\/strong><\/p>\n

\u00a0<\/span><\/p>\n

Rather than talk about technologies inside B&O equipment, this week I’ll try to go through a couple of strategies on how to properly calibrate the main channels in a surround system – and how to do it improperly, but make it sound better for your friends. I’ll use the example of a BeoPlay V1<\/a>, a\u00a0BeoVision 11<\/a>\u00a0or a\u00a0BeoSystem 4<\/a>\u00a0as the heart of the system – but the basic concepts are the same for any other surround processor.<\/p>\n

 <\/p>\n

Location, location, location<\/h2>\n

The first step in setting up any surround sound system is the correct placement of your loudspeakers. There are two standard configuration recommendations. The first is from the International Telecommunications Union<\/a>, in a document called \u00a0Recommendation ITU-R BS.775-2 –\u00a0Multichannel stereophonic sound system with and without accompanying picture<\/strong> (available as a PDF file from the ITU here<\/a>). The second is called Recommendations for Surround Sound Production<\/strong> from the Producers and Engineers Wing of the Recording Academy of the National Academy of Recording Arts and Sciences<\/a> (or NARAS – better known as the people that bring you the Grammys). Tha recommendation can be downloaded as a PDF file from here<\/a>).<\/p>\n

The short versions of these two recommendations are as follows:<\/p>\n

ITU-775<\/h3>\n

The ITU standard configuration is the one people who do research into multichannel audio use for their experiments. It’s also the one we use at Bang & Olufsen<\/a> when we’re testing our loudspeakers in the Acoustics Department or tuning the parameters in the TrueImage<\/a> upmixing algorithm. \u00a0The nice thing about this configuration is that it matches a surround sound system for someone who sits on a sofa placed against a wall, and has their surround loudspeakers adjacent to the same wall.<\/p>\n

In a perfect loudspeaker configuration, all of your loudspeakers are the same distance from the listening position. They have all been calibrated to have the same loudness at the listening position. Also, they are all large, full-range loudspeakers (and therefore, you do not need a subwoofer).<\/p>\n

The Centre Front loudspeaker should be in the centre, at the front (we’ll call that 0\u00b0). The Left Front and Right Front loudspeakers should be at \u00b130\u00b0 relative to that angle. The Left and Right Surround loudspeakers should be located symmetrically at an angle of between \u00b1100\u00b0 and \u00b1120\u00b0.<\/p>\n

 <\/p>\n

\"ITU<\/a>
Fig 1. ITU 775 recommendation for 5-channel loudspeaker configuration<\/figcaption><\/figure>\n

 <\/p>\n

The ITU-775 document doesn’t specifically state the standard configuration for a 7-channel system, but it does provide a recommendation for a 5-channel system that uses 7 loudspeakers (in cases where you have a larger system and you use two loudspeakers per surround channel). However, the recommendation is still a pretty good recommendation for a 7-channel setup. (This also makes sense, since, if you have 7 loudspeakers, you may occasionally like to use them as a 5-channel system without having to place extra loudspeakers in your room.) If you dig around, you’ll see that this also fits the typical setups used in re-recording studios for doing 7-channel mixes and mastering for Blu-ray releases of films. A good example of this is Tron Legacy<\/a>, which was produced using a system very much like the one shown below – with matching loudspeakers at 0\u00b0, \u00b130\u00b0, \u00b190\u00b0 and \u00b1150\u00b0. (this also makes sense from a radially symmetry perspective, since, ignoring the centre channel, you have equal loudspeaker spacings of 60\u00b0.<\/p>\n

 <\/p>\n

\"ITU<\/a>
Fig 2. ITU 775 recommendation for 7-loudspeaker configuration<\/figcaption><\/figure>\n

 <\/p>\n

 <\/p>\n

NARAS<\/h3>\n

 <\/p>\n

The NARAS recommendation is a little different, although the people that wrote it were aware of the ITU recommendation (which came first…), so they made sure that their version didn’t contradict the existing standard. Their version uses the same layout for the front three loudspeakers, but suggests that the surround loudspeakers be a little further back – within the \u00b1110\u00b0 to \u00b1150\u00b0 angle, with an “optimal range” of \u00b1135\u00b0 to \u00b1150\u00b0.<\/p>\n

Like the ITU standard, the NARAS document also recommends that all loudspeakers be the same type of full-range loudspeakers, all the same distance from the listening position, all level-adjusted to be the same at the listening position.<\/p>\n

 <\/p>\n

\"NARAS<\/a>
Fig 3. NARAS recommendation for 5-channel loudspeaker configuration<\/figcaption><\/figure>\n

 <\/p>\n

The Real World<\/h2>\n

Both the ITU and the NARAS standards are really designed by and for people who work and live in recording studios<\/a> or run perceptual experiments<\/a> involving multichannel audio. This means that they have one chair and no friends – at least when they watch movies and listen to music… However, if you have a sofa and<\/em> friends, then you will start having some questions – or at least some doubts.<\/p>\n

For example, if \u00a0you are “normal” (whatever that might mean) but a little careful about your surround sound setup, you probably have something that looks like the drawing below.<\/p>\n

\"A<\/a>
Fig 4. A reasonably good multichannel setup in the real world with a “correct” calibration scheme.<\/figcaption><\/figure>\n

What happens if we were to calibrate this system “perfectly” using the centre of the sofa as our reference “sweet spot” as shown in Figure 4? We’d apply a delay to the Centre Front loudspeaker to make the time of arrival of its signals match the Left Front and Right Front loudspeakers (usually done by setting the Speaker Distance). We’d also apply a delay to the surround loudspeakers to do the same. We’d also probably drop the levels of the centre and surround loudspeakers to match the Left Front and Right Front signals (because they’re closer, and therefore louder).<\/p>\n

However, let’s think about what happens if you sit on the left side of that sofa? Now, the Left Surround loudspeaker is very close to your left ear – and that has some serious implications on your experience. Firstly, since sound pressure doubles with every halving of distance, (assuming that this diagram is to scale) then sitting on the left side of the sofa means that you’ll get roughly a 6 dB boost (possibly more, if you’re leaning…) in the signal from that one loudspeaker. In addition, since that loudspeaker is so close and arriving at your listening position early, your brain will be able to figure out that the loudspeaker is<\/em> close because you’re pretty good at localising sources when they’re near your head. The same problem, albeit on a much smaller scale, happens with the centre loudspeaker. If its time-alignment delay is calibrated using the centre position, then, if you’re sitting on the left side of the sofa, then the Left Front loudspeaker’s signal will arrive before the Centre Front. The end result of this is that, if you’re sitting on the side of the sofa, you’ll have too much from one of the surround loudspeakers and the intelligibility of the dialogue will be reduced a little.<\/p>\n

So, how should<\/em> we calibrate the system to make things a little better for your friends? Take a look at Figure 5, below.<\/p>\n

\"A<\/a>
Fig 5. A reasonably good multichannel setup in the real world with an alternative calibration scheme.<\/figcaption><\/figure>\n

What I’m trying to show with this diagram is that both the distance and the level for each loudspeaker should be measured to the closest person in your listening area. So, in this case, the Left Front and Left Surround loudspeakers are calibrated to the left position on the sofa. However, the Centre Front loudspeaker is calibrated at the centre of the sofa. The result of this is that the centre speaker will be delayed – but less than it would have been if you had calibrated it as in Figure 4, because the Left Front loudspeaker is closer to the person on the left side of the sofa than to the person in the centre of the sofa. Also, the Surround loudspeakers will be delayed much more than they would have been using the scheme in Figure 4. However, they’ll still be symmetrical (so the person in the “sweet spot” won’t feel like the surround channels are lopsided, and the friends on the sides of the sofa won’t notice that they’re sitting on top of a loudspeaker… Also, this will result in the centre channel being a bit louder and the surround channels being a little lower in level – both of which are technically incorrect for the person in the sweet spot, but at least it’s a mistake in the right direction – so you’re improving intelligibility of the dialogue<\/p>\n

If you do calibrate the system this way, you’ll technically be incorrectly calibrated at the sweet spot, but your friends on the sides of the sofa will be much happier – and you won’t notice too<\/em> much. Of course, if you have a BeoPlay V1<\/a>, a BeoVision 11<\/a> or a BeoSystem 4<\/a>, you can make this configuration just one of your nine available Speaker Groups – you can always use another one for a “perfect” calibration for the sweet spot when you’re home alone.<\/p>\n

If, after aligning your system using this method, you still find that the dialogue is a little hard to understand, and the surrounds are a little hot (this is often the case when your sofa and the surround loudspeakers are all situated against the same wall, you should not be afraid to do the following:<\/p>\n