It does not have other names, it is known as a center channel or central speaker. Until not long ago, it has not been given the importance it deserved. Through this channel occupies a very important percentage of the entire soundtrack of the film, including almost all the dialogue, many effects, and part of the music. It usually has an elongated shape (low height and very wide), and is always mounted (or should be) above or below the display device, although it is also seen in other more peculiar positions and not always acoustically recommendable, as integrated into the wall or , in a video projection system, placed behind an “acoustically transparent” screen.
Basically it comes to say that (although in a Home Theater we have a front left and right channel) if we do not have a central channel, only the person who is sitting exactly the same distance from the two (in the center) will be able to hear the sounds really coming from between the two speakers, which is where the visualization device is placed (remember that this was a way of calling the TV or the projection screen) and, in this way, associating the dialogues with the faces that we see and give it more credibility by making us believe that they come out of them. In the same way, only the one who is sitting in the center could correctly hear the motion, for example, the noise of the engine of a car going from the left to the right passing in front of us.
Take the opportunity to remember that a simple two channels in a stereo configuration are able to do so, without any problem as long as we are sitting in the center of them, a sound image from a point source located between them. Just as having two eyes helps us better calculate the distance to different objects, having two ears allows us to place in the space with closed eyes where a sound source is located. This what the brain does by interpreting the difference of time it takes to get the sound to one and the other ear. A sound in the real world that is occurring in front of us will simultaneously reach both ears. In the same way, two speakers that reproduce the same sound will send the same signals to both ears, making us believe that the sound is right in front of us. A problem that can be associated with this is that the brain has to be constantly rebuilding that central image sensation. Therefore, some say that the central channel speaker also serves to avoid what is called auditory fatigue, as well as possible distractions on our part.
To avoid all the problems discussed in the two previous paragraphs, the so-called central channel speaker was added. This way, whoever is sitting to the left or right can also hear everything that has been commented, even those that are located on the edge of the sofa. Also, although for example we are located relatively close to the front left speaker, the presence of a central channel will prevent all the sound from collapsing towards that same side. And finally, specifically in low-quality speakers, a central channel speaker would help to reduce the load on the left and right channels, dividing the sound of two into three speakers, thus offering a clearer sound.
What are the Phantom, Wide and Normal center channel modes?
It is possible to dispense of the central channel speaker in a Home Theater equipment, but it is an unwise option given the large “hole” of sound that would occur in the sound scene in case of not sitting perfectly centered between the two main channels. For this, you have to put the center channel in “Phantom” or “None” mode, in which case its sound is redistributed between the two front speakers.
In addition, the A / V receivers offer two other settings related to the central channel speakers: “Wide” and “Normal”. Both affect the range of audio frequencies that are sent to the center speaker. When it is changed to “Wide” or “Large”, the receiver sends the entire channel to the central channel speaker. However, in “Normal” or “Small”, the lowest frequencies are filtered, that is, they are suppressed, in order to avoid overloading it, since at low frequencies it is when the cones reach their maximum travel.
Most central channels speakers are made of a relatively small size compared to the main channels, either for aesthetic and practical reasons to be able to place them under or on top of a screen, or for technical reasons, since the ability of the central speaker to offer a large extension in low frequencies in order to get more clarity in mid frequencies by avoiding their masking by the bass. Therefore, the “Wide” mode should only be used if the central unit is very large, equivalent to the main channels, which must also be large and of the “full-range” type, I.e, provided with good-quality, high-quality bass transducers.
What Is Inside Of a Center Channel Speaker?
In modern, mid-range and high-end receivers, you can directly select the cutoff frequency, below which we want to suppress the lower frequencies to prevent them from reaching the central channel speaker and thus protect it. The THX standard dictates 80 Hz, which is a very reasonable figure that can be taken as reference. In case of being a very small center, with 3 “or 4” mid-woofers, it is advisable to raise it up to 100 or 120 Hz. If it is a central one with 6 “mid-woofers and, even, 8” woofers, we can lower it to the minimum, normally 40 Hz. Even if you have a central unit with these large woofers, it may not be advisable to send frequencies below that frequency (that is, put them in “Wide” mode).
Materialization Of The Center Channel Speaker
Carrying out the materialization of an independent central channel speaker is usually a challenge. First, a speaker is needed near the screen where the image is played. This means that if you are using a direct view television or a rear screen projector, the speaker must be magnetically neutralized so that it does not interfere with the images. It also needs a monophonic amplifier, and it is not easy to find it.
If the equipment of certain commercial rooms has only four amplification channels, remember that the two channels of after effects have the same signal. If you have a center speaker but do not have a monophonic amplifier, a two-channel amplifier will be used. We will connect only one of the rear outputs of the Pro Logic decoder to one of the channels of the amplifier and send a signal to both surround speakers (later in this case) with that channel. The other amplifier channel is used for the center channel. Most Pro Logic decoders have individual balance controls for the channels, but if we use an amplifier or a power stage with independent level controls it is much better for channel balance.
TOP CENTER CHANNEL SPEAKER
What type of PBX to choose for the speaker system
There are clearly two simple options although not recommended. One of them is to put the “Phantom” mode of the previous section, that is, to dispense directly from the central channel, and the other is to use the speakers of the television itself. Normally, these have some type of input (by RCA connectors or, directly, with an adapter and the scart) that allow using the internal speakers of the same as if they were the center channel of the surround sound system. However, it is not recommended for three reasons. If the TV has two speakers, these will be located on both sides of the screen and, therefore, very close to the left and right speakers. Another, that its quality will almost certainly be inferior to that of the rest of our speakers. And finally, and most importantly, the part that will be of lower quality, it will sound different, and you can distinguish perfectly if the sound comes from the center or the left or the right, as we will discuss in a moment. Therefore, we will reject the idea from now on of using TV speakers as the central channel.
Although in principle we can mount a central speaker of any brand along with the left and right speakers, it would be better to put one as close as possible to those channels. All speakers sound slightly different from each other. It does not matter how high your quality is or how flat your frequency response is. They always introduce a slight coloration, that is, variations of precision in their sound. If the center channel has a different type of sound than the left and right channels, we will never get a smooth and continuous sound field on the front speakers. That is, when a sound goes from left to right, it would lose its character and change abruptly.
The simplest example to understand this is a car passing from the left channel to the right channel, which, if the mixture is correct, would also pass through the center. If this channel has a different sound than the other two, the car would sound with a certain character when it starts to move, it would change when crossing the central one, and it would return to the original hue when it reaches the right. This would destroy the ideal uniformity of the sound scene that we intend to recreate.
The solution is to acquire three front channels designed to work together, “matched”. If so, their similar and almost identical tonal characteristics will not only offer a transition (or panning in the world of mixes) between the three channels but will produce a more stable and coherent sound field at the front of the room. If the left and right channels that already exist are to be conserved due to their high quality, the most sensible solution is to add a central speaker made by the same manufacturer and, if possible, from the same series, in such a way that it sounds like we have already said, as similar as possible to the other two channels. These exchanges normally use transducers from the same supplier and frequency divisor filters with similar topologies.
For a theoretically perfect home theater, the three center channels speakers should be totally identical. However, this option in most cases is not possible, since in the center we will also have the TV screen or the projector screen, and in these cases, logically you cannot put both in the same space unless our room is big and of a great height, reason why from the beginning it was decided to make the plants very little high and in horizontal disposition, to make them more compatible with the space available.
In commercial movie theaters, this option is chosen, that is, the central channel equal to the two front ones. All of them are placed behind the screen, which is always perforated in such a way that it is, in a certain way, acoustically transparent to the sound.