What is the point of a centre speaker?

Surtsey

Member
2019-09-21 4:51 pm
I've thought about it carefully: I can see no point in a centre speaker. The more I consider the concept, the more nonsensical it seems.

Ignoring the 0.1, the subwoofer, because its primary function is not audio, stereo is adequate for music reproduction (on account of us having two ears). I can understand the how quadrophonic sound can enhance the audio visual speaker. But a centre speaker is a total fraud. It doesn't perform any function that is not covered by front-left and front-right.

Simplified: Band is on stage; vocalist is dead centre. This means 50% of the vocal is sent to left and right. Close your eyes: the voice comes from dead centre. Lead guitar is to the left of the vocalist: 55% of signal is sent to the left channel, 45% to the right. Close your eyes and you hear the guitar to the left of the vocalist.

What can a centre speaker do to improve this?
 

Brinkman

Member
Paid Member
2007-08-17 5:48 pm
Oakland, CA
What Pano said. Those 5.1, 7.2 etc encoded mixes have A LOT going through the center channel. Keep in mind also, Alan Blumlein originally proposed a three channel paradigm for “stereo” but that seemed outrageous for the standards of the era and two-channel stereo was the compromise.

Subsequent albums have been mixed and mastered in the three channel format over the years; John Williams mixed the original SW score in three channel stereo and a number of classical albums have been reissued on compact disc in their three-channel stereo mixes.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
I thought I read Earl Geddes say once that the centre channel is near to unnecessary, but I wanted to be sure and I couldn't find that quote. I found these..
gedlee said:
I don't use the center for stereo, don't need it, the imaging is perfect without it.
link
a center channel does improve things, but its a marginal improvement, not a massive one.
link
And why not just feed the center with L+R? Because this leaves the common signal at the L & R. It should be removed
link
the idea of a center channel is almost as old as stereo. Its a shame that it was never adapted, but there are good ways to derive an uncorrelated center channel from LR.
link
 

Surtsey

Member
2019-09-21 4:51 pm
All the comments about dialogue through the centre speaker are proving my point. It is not supposed to! If a character is speaking on the R/H side of the screen their position is represented by the bias to the R/H speaker.

The fact remains: you only have two ears!
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
No, the comments are not making your point. Rather to opposite. The phantom center is a great illusion, done better in some systems than others, but a center speaker really anchors it.

Films used to be mixed with almost all dialogue in the center, no matter what. That has changed somewhat. You can get away without the center for stereo music, so many people do. Doesn't means it's ideal.
 
All the comments about dialogue through the centre speaker are proving my point. It is not supposed to! If a character is speaking on the R/H side of the screen their position is represented by the bias to the R/H speaker.

The fact remains: you only have two ears!
Without stereo sound you cannot produce left and right, but without a centre you cannot reliably produce a centred sound if the listener is seated heavily off-centre.

With a phantom centre speaker, sounds which should be centred are perceived to be coming from outside the screen for listeners sitting on the far left and right of the theater, because their perception of direction is strongly influenced by the sound arriving significantly sooner and louder from the closer stereo speaker.

With a real centre speaker, the sound always appears to be coming from the centre/screen, no matter where the listener is seated.

It's the same reason why there is 7.1 surround (and more) instead of just 5.1 - having front/rear pairs of left/right speakers only accurately places sounds for a single listening position which is equidistant between the 4 speakers. For a listening position which is closer to a certain speaker, the direction of all sounds becomes biased in the direction of the closer speaker.

Having a dedicated centre audio track which is predominantly dialogue is also handy (regardless of physical speaker configuration) because you can turn it up to be able to watch a movie at a low volume without disturbing others with the sounds of loud explosions, LFE rumbles etc. The dialogue can still be biased to one side by simultaneously playing the voice through the centre and left/right, while still allowing the movie to be watchable with every channel except the centre significantly turned down in volume.
 
Last edited:
The fact that we have two ears has nothing to do with the fact that most audio reproduction is done with two speakers.

Dolby has a fair amount of writing on why a center speaker is better, even for listeners seated in the center. If you are seated off center, the Hass effect guarantees that the image will pull to the closer speaker. Having a center channel fixes that.

When trying to reproduce sound, the goal is to reproduce the entire sound field, so that no matter where you sit, the sound reaching you ears is correct. This requires an infinite number of channels of reproduction. The more audio channels there are in the recording and playback system, the closer it will be able to recreate the entire soundfield.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Dolby has a fair amount of writing on why a center speaker is better, even for listeners seated in the center. If you are seated off center, the Hass effect guarantees that the image will pull to the closer speaker. Having a center channel fixes that.
If you're not in the middle and it's a problem, then stereo is broken and that case is only of limited interest. What do they say the reasons are?
 

eriksquires

Member
2013-05-10 4:11 pm
Hi Surtsey,

I have a little experience about this in both motion pictures and home.

With a 10 meter screen, and even wider seating positions, a center is essential. In the home many argue, as I did, that the center was rubbish, until I tried it and read up on it.

Properly integrated (i.e. equalized) it really brings out the center area and makes it palpable and makes the front just as immersive as the surrounds. It also does make dialogues sound a lot better than with a phantom. But this is with caveats. Just using my own gauge, I wouldn't say it's a must have, but that it adds about 20% to the experience. The other is that the speaker must be equalized to match the other speakers. Sticking a center on a counter or in a box in an entertainment center is not better than no center. I can 100% see how anyone who hears this might think it's in fact no better.



Best,


E
 
Pano mentioned combing.

I tried an ambiophonics barrier(6' high x 6' long) between speakers (moved side by side).

The voice was a point source, like a person talking to you.

When wall knocked down and speakers moved apart, the voice became a 3' wide x 3' tall blob that seemed 3-6db lower in volume.

I realize the barrier also knocked down wall reflections, so your right ear would not hear the sound from the left speaker bouncing off the right wall then hitting your right ear.


For movies, a center is essential for more than 1 listener.
 
...
With a phantom centre speaker, sounds which should be centred are perceived to be coming from outside the screen for listeners sitting on the far left and right of the theater, because their perception of direction is strongly influenced by the sound arriving significantly sooner and louder from the closer stereo speaker.
...

Constant directivity speakers with toe in can handle the loudness issue. There still is the delay though. Just reading about Precedence effect Precedence effect - Wikipedia
which seems to state that few milliseconds path delay won't move the phantom center, and up to maybe 5 milliseconds delay the phantom center moves slightly. So, your message is a bit too generalized ;) The two millisecond window might cater a three seat sofa or wider in a home theater to perceive solid phantom center. Not the case in a big theater though (very large screen). But still, shouldn't drag the center to the nearest speaker until about 50ms difference, that is more than 15 meters path difference. Of course acoustics matter and all, just wanted to check out this one aspect about stereo phantom center.
Carry on :)
 
Last edited:
What Pano said. Those 5.1, 7.2 etc encoded mixes have A LOT going through the center channel. Keep in mind also, Alan Blumlein originally proposed a three channel paradigm for “stereo” but that seemed outrageous for the standards of the era and two-channel stereo was the compromise.

Subsequent albums have been mixed and mastered in the three channel format over the years; John Williams mixed the original SW score in three channel stereo and a number of classical albums have been reissued on compact disc in their three-channel stereo mixes.

What would you do with three channels when it comes to headphones?
You place it to your forehead?
 
Last edited:
Why would someone speaking on the right of my screen come from a speaker several feet to the right of that? That's just wrong.

Besides, most films are so full of sound it's advantageous to be able to turn up the centre speaker a little so speech is louder than explosions etc.

Music is stereo and should be kept as such.
 
I stopped going to cinemas because i do not like the sound. What is the point for sound comming from behind me, when the screen is infront of me. The helicopter image infront, yet the helicopter sound in the back, makes no sense. Often so much phasing, it hurts to listen to. I see no point in 5 channel, 7 channel or even 3 channel sound.
Properly set up two channels perfectly recreate center channel. If screen is too big, fine, but for home, definitely not needed.