Optimizing Center Channel Performance - Dispersion, Placement & Image

[leveler]

One of the known disadvantages of a television compared to an acoustically transparent screen is that the center channel speaker must be mounted above or below the TV, causing the center channel image to shift below the left and right speakers. This image shift could be eliminated by using a phantom center image, however, this badly harms listeners outside the sweet spot. I assume the system will perform better by optimizing the performance of a center channel below the TV, rather than removing it entirely.

I have a few questions about how to optimize the performance of the center channel speaker, given the constraint that it be placed below a television, rather than behind an acoustically transparent screen.

1) I intend to use 3 matching bookshelf speakers as the left, center, and right channel speakers. The speakers will then be timbre matched and avoid the design issues inherent in horizontal center channels. Are there any issues I should consider when using a bookshelf speaker as a center channel speaker below a TV?
2) I intend to angle the center channel speaker up towards the listening position. What is the best solution for angling a center channel bookshelf speaker up towards the listening position? Are there any mounts that will fit below the television and allow for stable articulation/angling up towards the listening position?
3) What impact (if any) does wide vs narrow dispersion characteristics of a bookshelf speaker have on the localization of the center channel below the television? Is it possible that a wide dispersion speaker, angled up, will be perceived as 'more centered' in the screen than a narrow dispersion speaker? Would this effect be more pronounced in a horizontal center channel speaker, considering the inherently wide vertical dispersion characteristics.

Are there any other center channel optimizations I should consider when placing the center channel below the television?

 

[Pogre]

I raised my tv so my center's tweeter can be level with the main speakers. There are several mounting options out there for tvs.

 

[ryanosaur]

I appreciate the thought you've put into this, but there's a bit of overthinking here, too.

First, a good quality 3-way W-TM-W design is much less problematic than a more common 2-way MTM in horizontal alignment.
That said, I use an upright standmount as my center, between 2 Towers. 3 matching towers would arguably be the best option.

If you want best performance overall, put the Center channel on its own stand, not on top of other equipment. You can use a monitor isolation pad to angle the speaker. I use them and they work well for this.
You want the screen to be about 1' away from the front Baffle of the speaker. (Make certain you can also easily hit the IR sensor with your remote while seated.)
If you have no choice but to put the Center on top of some equipment/entertainment hutch... make certain the front Baffle overhangs by about 1".

I use wide dispersion speakers in my room, all 7 channels. I think it sound great in HT. I am much more into music though.

 

[shadyJ]

1) I intend to use 3 matching bookshelf speakers as the left, center, and right channel speakers. The speakers will then be timbre matched and avoid the design issues inherent in horizontal center channels. Are there any issues I should consider when using a bookshelf speaker as a center channel speaker below a TV?

So long as you angle the speaker to face the listening position, as you indicate your intentions to do so below, you are all set here.

2) I intend to angle the center channel speaker up towards the listening position. What is the best solution for angling a center channel bookshelf speaker up towards the listening position? Are there any mounts that will fit below the television and allow for stable articulation/angling up towards the listening position?

There are desktop speaker stands that can angle your speaker. Go a good search for desktop speaker stands that have adjustable angling.

3) What impact (if any) does wide vs narrow dispersion characteristics of a bookshelf speaker have on the localization of the center channel below the television? Is it possible that a wide dispersion speaker, angled up, will be perceived as 'more centered' in the screen than a narrow dispersion speaker? Would this effect be more pronounced in a horizontal center channel speaker, considering the inherently wide vertical dispersion characteristics.

A narrow dispersion speaker might possibly have more precise imaging here since it won't produce as many acoustic reflections. The less lateral reflections you have, the lower the apparent source width.

Are there any other center channel optimizations I should consider when placing the center channel below the television?

ryanosaur has good placement suggestions. Do not hem the speaker in a cloistered area. The more "out in the open" it is, the fewer acoustic problems it will incur.

 

[leveler]

Thanks for the replies everyone. It sounds like there are no special considerations I need to make when using a bookshelf as a center channel. I'll go ahead with that plan to ensure timbre matching and avoid lobing.

Desktop speaker stands are a great suggestion. These will have the articulation I need and the low profile required to keep the center bookshelf speaker below the television.

A narrow dispersion speaker might possibly have more precise imaging here since it won't produce as many acoustic reflections. The less lateral reflections you have, the lower the apparent source width.

I agree the narrow dispersion speakers will have more precise imaging due to the reduction in reflections. In your opinion, considering the non-optimal placement of the center channel below the screen, is it possible that the increased reflections caused by a wide dispersion speaker are extremely desirable? Here is my (potentially faulty) rationale.

A center channel speaker placed below a television suffers acoustically because the center image moves below the screen. If that is the case, then a narrow dispersion speaker with accurate imaging would exaggerate this negative effect. The speaker is more localizable because more of the direct sound reaches the listener.

A wide dispersion speaker would help mask this deficiency. Wide dispersion speakers will increase the apparent source width/height. This results in the speaker being less localizable, therefore it is less noticeable that it is in a suboptimal position.

I haven't had the opportunity to listen to many properly configured systems, so I can't speculate how exaggerated this effect would be, if it would be noticeable at all. Thoughts?

Shout out to Matthew Poes, who's really made me think hard about dispersion.

 

[shadyJ]

I agree the narrow dispersion speakers will have more precise imaging due to the reduction in reflections. In your opinion, considering the non-optimal placement of the center channel below the screen, is it possible that the increased reflections caused by a wide dispersion speaker are extremely desirable? Here is my (potentially faulty) rationale.

A center channel speaker placed below a television suffers acoustically because the center image moves below the screen. If that is the case, then a narrow dispersion speaker with accurate imaging would exaggerate this negative effect. The speaker is more localizable because more of the direct sound reaches the listener.

A wide dispersion speaker would help mask this deficiency. Wide dispersion speakers will increase the apparent source width/height. This results in the speaker being less localizable, therefore it is less noticeable that it is in a suboptimal position.

I haven't had the opportunity to listen to many properly configured systems, so I can't speculate how exaggerated this effect would be, if it would be noticeable at all. Thoughts?

It looks to me like you are overthinking things. If your screen is so huge that it forces the center speaker to be on the floor then you might have something to be concerned about. But if you aren't faced with that circumstance, the speaker should be close enough to the screen that the imaging will be good enough. I doubt you would notice that the sound isn't coming directly from the characters on the screen. You would have to be listening for that specifically to notice it. If the movie or TV show is any good, you will be far more engaged by the drama than if the sound is being emitted 10 inches lower than the characters' mouths.

 

[j_garcia]

I will put it a little different: You are WAY overthinking something you haven't even heard. Most calibration systems these days will help out with slightly imperfect positioning so while placement is still very important, if you can get it pretty good before calibration, the calibration can help even out any anomalies. Ultimately, until you've actually heard the gear in your room, you can't entirely say one way or another what is going to be the final state.

 

[ryanosaur]

It looks to me like you are overthinking things.

This.


Even Poes has said, when it comes to some of the distortions that we are loosely discussing (diffraction from screen or other boundaries, that on paper they are there... but are they even audible?

For me, its a game of best practices, without doing silly-expensive specialized purchases.

Find Speaker you like, and that you WANT to LISTEN TO!
Set them up to the best of your ability in your room.
Run room correction, perhaps measure.
Make any adjustments necessary to satisfy.
Enjoy!

 

[leveler]

Thanks everyone! I appreciate being able to draw on your collective experience. I'll just trust my ears on this last point.

 

[lovinthehd]

There are also center speaker stands with some angling built into both the platform itself and use of different height feet to an extent too. I use one like this just below the level of the tv screen as seen from my seat but out in front of the tv by a coupla feet along with my towers; in this case I do supplement the height of the stand itself with a small riser I built to get it right up under the level of the tv angled towards my seat a bit. I use the Infinity RC263 and no problem with the sound/screen combo.

 

[Pandaman617]

So I use 3 identical Mirage HDT-F bookshelf speakers (two 6.5” woofers, two 2” midranges and one 1” tweeter) and have found better performance with the center HDT in the vertical position but in terms of placement options in my room using a tv mount that works with a horizontal center exponentially easier to deal with. That being said I run all 3 vertical, because you know, sound quality.

 

[cheyne barnhouse]

Friendly thread bump here...lol.

I posted this over on AVS in one of their threads as well, but I also wanted to post it here for discussion. One of the new specs being touted about the channel layout for the DTS-X Pro and IMAX Enhanced soundtracks is the 'Center Front Height' channel, and this has piqued my interest..

Many, if not most, home theater enthusiasts suffer from some sort of compromise when it comes to locating their center channel either below or above their screen, so this new spec surprised me and I'm wondering about it's potential implications.

From the small amount of info I've been able to find online about the purpose and function of the Front Center Height channel, it sounds like they decided to implement a sort of 'dual center channel' approach. There are a couple of YouTube videos where the Sound United guys talk about the speaker layouts for IMAX Enhanced and DTS-X Pro (and Auro), and the IMAX theater screens were mentioned as the original motivation for their need to implement 2 center channels, because the IMAX screens were so large. That concept then got adapted for the home environment and they mentioned using this new Front Center Height channel as simply another discreet speaker in the setup, and that it used phantom imaging between it and the other speakers nearby (L / C / R / and Wide spkrs) to better lock the sound to the screen.

Historically, the dual center channel approach has been frowned upon because of the potential for comb filtering, lobing and other negative side effects. The forums and threads covering this topic mention one reason for why doing dual center channels was a bad idea, and that was 'if it was so easily done and such a reasonable approach then one of the big companies would have done this and just added a 2nd discreet center channel above the screen'. It seems to me like this may be what has happened here with the CFH channel approach by IMAX and DTS.

I may very well be wrong in my interpretation of this channel's use, but I'm curious what everyone's thoughts are about it and it's potential, considering that it would solve the center channel localization problem that so many people have.