November 28, 2010

My Centre Channel Conundrum

A Sonus Faber center chamel shown here.
If you are a home theatre purist, please don't read this post. You would probably find what I did as 'sacrilegious' to Home Theatre.

When I was planning the home theatre package for my new home, the location of the centre channel came as a headache.

The problem was two-fold. One was the location of the centre speaker itself; The other was the distance relationship between the centre and the left-right (L-R) pair.

The central position where the centre channel speaker was to be located was occupied by my hifi rack. A possible solution was to get a tall stand, so that the centre speaker could be positioned behind the rack and be higher than the rack, so that its line of sight to the audience was not obstructed.

However, this meant that the projector screen got to be located higher off the ground. I calculated that for the bottom part of the screen to clear the centre speaker, it would have to be more that 36" from the floor. That was a position too high for my taste. I personally prefer the picture to be at eye-level. In fact, AV Designs' advice was for the bottom of the screen about 24"-30" from the floor.

Even if I decided to position the centre speaker thus, ignoring the fact that a screen positioned too high would mean I had to 'look up' at the screen like sitting in the cinema front row, the speaker's position close to the front wall would be 60"-70" from the plane of the left-right speakers (the left-right speakers are positioned about 90" from the front wall, a position I optimised for stereo/hifi). AV Designs' James Tan advised that this would likely cause a disjointed sound from the left-centre-right array, even after compensating for their distance difference in the AVR setting. His experience was that the distance differential between the centre speaker plane and the L-R speaker plane should not be more than 40".

Another possible solution I thought would be for the centre speaker to go in front of the hifi rack. That would look weird, I rejected that idea instantly.

So I toyed with the idea of not installing a centre speaker at all. Some people I spoke with thought that you would lose a lot of information on the movie soundtrack omitting a channel. The dialogue would be gone, as dialogue is usually encoded in the centre channel.

Well, not really. If you switch off the centre channel in the AVR, it will automatically route the centre channel sound to the left and right channels equally. This is called a 'phantom centre'. I remembered seeing this done in a Holfi surround sound demo in an early hifi show in KL, though it was meant for music. The argument was that the centre channel speaker would adversely affect the imaging as integrating and matching the centre speaker to the L-R was not easy.

The same was advocated by Jim Smith in his book 'Get Better Sound' too (tip #24). He put forth the same argument that the centre channel muddy up the sound. However, there is a price to be paid. The duty of the centre channel is to anchor the soundstage at centre for viewers who are seated off-centre. Not having a dedicated centre channel would mean that there would be no soundstaging for viewers who are seated away from the sweet spot, just like in a stereo set-up.

I briefly tested the 2 settings in AV Designs' showroom, one with centre on, one with centre off. Yes, with the centre channel off and listening from an off-centre position, the sound was not so dimensional. At the same time, vocal also sounded slightly recessed and thinner. I did feel that the vocal was smoother and the diction clearer though.

Anyway, I decided to ditch the centre channel in my own set-up.

Well, this was sure like listening to stereo. In the sweet spot, you'd get a nice soundstage, with depth and width. Off centre, the soundstage diminished. The vocal also sounded a little recessed. Though I feel these did not affect the enjoyment of the movie much, after watching close to 15 movies this way.

The disadvantage of not having a dedicated centre channel was that I could not adjust the gain of the centre channel independently, say, to make vocal more prominent by boosting it 1/2-1db higher. Anyway, the diction still came off very clear, so catching the vocal on screen was not a problem. This goes to show that a setup good for hifi should be able to tackle movie soundtrack well too.

If you also try this in your home theatre, I'd like to hear about your result.


Seta said...

I did just the same thing. Can't get the center speaker to integrate with the main speakers as I couldn't afford (and wouldn't) the wilson audio watch center - so tried other brands. In the end, without the center actually sounded much, much better. Cheers!

OdioSleuth said...


Wilson for HT, wow!
Glad to hear you have also achieved good result without a dedicated centre.
You are right, matching of the centre with the fronts is the crucial point.