"This section will help show you how to balance all your speakers with regard to each other. You will find the abbreviation db, for Decibels, units used for measuring sound levels. Rear Speakers:
Very commonly, people make the mistake of wanting to use the full power of their rear speakers, to the point of turning them up to the maximum, at + 10 db compared to the main speakers. Firstly, not all films have rear effects even if they are encoded in Dolby Surround: if you take, for example, a film like "le père Noël est une ordure", your rear speakers will not be of any use. All the "action" of the film (dialogues) takes place in the foreground. It is thus absolutely normal that you hear nothing or very little from the Surround speakers. It should be said that one should NEVER be distracted by the sound of the Surround speakers, as your attention should always be centred on what’s going on in front of you - on the screen. Finally, in the case that the Surround speakers are small, the fact of being at +10 db will only produce a poor quality, saturated sound. In a cinema, it’s very rare, even in highly spectacular films, to have rear effects that distract the spectators. It’s sure that in a cinema, the rear speakers are more numerous, but just the same, they are much further away from your ears than those in your living room. The cinema also being a lot bigger, the sound coming from the rear speakers as a result has the time to "develop" before arriving at your ears.
It is with the purpose of remedying this proximity of rear speakers in home cinema installations that Bipolar and Dipolar speakers were invented. The principle is that no direct sound should disturb you, especially in the upper frequencies. Thus, in creating a "sonic magma" in the rear speakers, you have the advantage of Surround effects without being indisposed. These speakers, through the fact that they "disperse" the sound completely, generally need (with the same output and distance as classic rear speakers) a little more volume. If you have classic "direct" dispersion speakers, the level in the rear speakers should remain quite low. As we noted above, there’s no interest in being distracted by Surround effects, and that’s why Bipolar and Dipolar speakers were invented. It’s worth noting that it’s possible to simulate this effect by placing your speakers in such a way that the sound doesn’t come directly to you. If you have five identical or virtually identical hi-fi speakers, the fact of reflecting the sound from your Surround speakers off a wall, similar to the method used by BOSE with DIRECT REFLECTING, you’ll be able to take advantage of your rear speakers without being aggressed by their proximity. For this, the room must lend itself to the idea. You should undertake a few tests, reflecting your speakers in various corners of the room, until you find a position which is pleasant on the ears and compatible with your habitat. It could, for example, be judicious to turn your speakers towards the side walls, to be able to increase the Surround volume while still being less aggressed by the sound of the rear speakers. The Central Speaker:
Often, newcomers to the Home Cinema world confuse the "central speaker" with the "bass box", giving the term: "central box". It is important not to confuse these two objects, which are profoundly different.
It goes without saying that volume adjustment and placing of a central speaker is a little easier. In the case that you have three identical speakers placed at the same distance from you, their volume levels should be the same, although in Dolby Surround Prologic mode, you are authorised to increase the level of the central speaker by one or two db. In fact, in Prologic mode uniquely, everything that comes out of the central speaker was previously in the main speakers. You will thus still find some of the dialogue in the main speakers. This is what is called crosstalk. By slightly augmenting the central speaker volume, and thus giving the central speaker a little more emphasis, you erase this effect of crosstalk. In Dolby Digital and DTS, you should not have this problem, as all the channels are separate. One of the problems we most often come across with the central speaker comes from the fact that for aesthetic reasons, it is ten times smaller than the main speakers, thus creating enormous problems in the reproduction of the central channel. These problems are generally due to differences in output and of the simple physical presence of the speaker. In this case, the fact of possessing a good pair of main speakers will tempt you to push the system towards its limits, and in order for your small central speaker to be heard between the two main speakers, you will have to increase the central volume. Don’t expect too much from your central speaker. Preserve it intact by not pushing the system too hard. As for your Surround speakers, when you push the small speaker too far, it saturates and you’ll hear more "noise" than sound. You should keep in mind that with a speaker system, the maximum level should be based on the weakest element in the system. If your main speakers are too big and you can only use a small middle speaker, it’s sometimes preferable not to use it at all, which will help avoid situations as outlined above. The final adjustments:
After all this setting-up, if there’s still someone awake in the house, let’s go on to what happens with your amplifier. Your amp. is endowed with a "Test Tone" function. This function will serve to determine an equal sound level between all of your speakers. Once you activate this function, a rather disagreeable sound, known as "pink" noise will come from your speakers, one by one. It will be possible, with corresponding buttons, to change the levels of your central and Surround speakers. Some amplifiers also permit you to adjust the main speakers, but this often gives rise to confusion, especially with the balance. In fact, it is important not to touch the volume of the main speakers, and to leave them set at "0", except in the case that they are not each the same distance from you. In this case, the right and left values will not be the same. If, during your final adjustments, you find yourself with a level of +5 for the two main speakers, +7 for the central and +6 for the Surround, you’d be better off taking away 5 db all around and having, as a result, 0 db in the main speakers, +2 for the central speaker and +1 for the Surround in comparison to the main speakers. Important:
if you adjust your amplifier by ear, a small central or Surround speaker will tend to lead you to believe that it is more powerful than the large main speakers. In fact it works harder on the high frequencies. The best way of adjusting the sound of the amplifier is to set everything at 0 and to listen. It’s in fact you who will decide the level you like in the centre and rear speakers, within the limits of the absurd situations that we have previously outlined.
If you possess a sonometer, the procedure is different. Everyone will tell you that to balance your five speakers, you should have a sonometer, an apparatus that allows you to analyse sound levels in decibels, and which will sense a real difference between a small speaker that "screams" to be heard and a big speaker that "talks". You will thus be able to adjust your speaker levels exactly. It is quite probable that after tuning the system according to your sonometer, you may not be happy with the result, because the sonometer will have indicated the ideal values which probably don’t correspond with your personal taste. The sonometer thus allows you to give a basis to your speaker level adjustment… a basis from which it’s best not to stray too far to adapt to your tastes. In fact, the sonometer’s real role is to prevent you from going too far astray. "