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Ditching the centre speaker in a huge room?

Discussion in 'Home Cinema Speakers' started by AndrewB, Oct 25, 2005.

  1. AndrewB

    AndrewB
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    My dad is getting a 50" plasma which will go over the fireplace (I know, too high) in a very large room - roughly 30 feet by 25 feet, with 15 feet ceiling. I've sold him my REL Strata III sub, so he has the .1 part of a 5.1 system. He also has some existing Tannoy Mercury floorstanders which he wants to recycle into the rear speakers. So that leaves the L,C,R speakers to deal with.

    He has been impressed by the Monitor Audio Radius 225 speakers, so he was planning to get 3 of those, attached to the wall around the plasma. The centre would probably have to go over the top to avoid raising the plasma even higher. Now I have a few concerns about the plan:

    1. Although the primary seating position for viewing will be just 12 feet from the screen, I am concerned that even at this distance a separation between L&R speakers of just 5 feet is too narrow for an optimal soundstage. I am therefore thinking that the L&R speakers should instead be mounted either side of the chimney breast, which would place them about 8 feet apart and slightly behind the screen. This would also have the advantage of making the installation look less intrusive.

    2. Related to the above, the system will also be used for listening to music from the other end of the room (say 25 feet away). I am pretty sure that at this distance the L&R speakers should be at least 8 feet apart if not further. I am also wondering whether the 225s are really going to be up to the job, even combined with the REL sub, or whether we should be going for something bigger. But what?

    3. Having the centre speaker up above the screen doesn't seem ideal either, and I was wondering whether we couldn't in fact ditch the centre speaker entirely. This seems completely reasonable if the L&R are really so close to the screen. Not sure how it would play out if they were 8 feet apart - although it works in my home cinema (projector) setup but I do have £7k worth of L&R speaker so perhaps its asking a lot of the £200 Radiuses.

    Anyone tried out these combinations?

    My Dad mainly watches Sky Sports (golf and football) but the rest of the family likes films.

    Many thanks

    Andrew
     
  2. AndrewB

    AndrewB
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    Looking at this site suggests that if you are about 12 feet away from the screen then the official Dolby Digital/ITU placement for L&R speakers is to form an angle of between 22 degrees and 30 degrees with the listener and the centre of the screen.

    http://forum.ecoustics.com/bbs/messages/34579/129023.html

    Taking my example of a 12 feet viewing distance, this means that the L&R speakers should EACH be between 4.8 feet and 6.9 feet from the centre of the screen. Now the screen is around 4 feet wide, including the bezel, so this means that each speaker should be AT LEAST 2.8 feet and at most 4.9 feet from the edge of the screen. Or put another way, the L&R speakers should be between about 10 feet and 14 feet apart from each other, when you are listening/watching from 12 feet away.

    Most home cinema setups I have seen with Plasma screens seem to fail this requirement by a large margin!

    In contrast, most stereo setups are roughly equilateral or a little narrower so the L&R there would be appropriate for a serious AV setup. One argument for going narrower than the ITU standard is that this would allow you to ditch the centre speaker while still maintaining a stable centre image.

    It seems to me that there are reasonably good arguments that the use of a centre speaker in a home context, when the range of viewing angles is more restricted than a proper cinema, is unnecessary. Especially when people have their L&R speakers too close together anyway. Better to spend 50% more on the L&R speakers and ditch the centre...

    Andrew
     
  3. Smurfin

    Smurfin
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    I'd never ditch the centre, heard it many times without and it's just not as convincing (imho). And imho...the centre is just as important as the front L & R (perhaps even more so if you consider the amount of material the centre channel conveys).
     
  4. alexs2

    alexs2
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    Having tried it myself,it's not something I'd recommend either,even given good quality source/amp/speakers.
     
  5. AndrewB

    AndrewB
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    I have to say that the phantom centre arrangement works very well in my setup with ATC SCM50ASLs as the L&R and a screen which extends as wide as the speakers. In the case of wide projection screens your main L&R can actually be within the width of the screen, as mine are. (My viewing angle is exactly the THX-recommended 37 degrees, so I am 11.5 feet away from a screen which is 7 feet wide.) The matching ATC active centre is about the size of a small sofa and costs £5k so it is a bit of a non-starter, although I was using a KEF Q9c and then a smaller active ATC as a centre for a while.

    But I am nervous about these small (!) 50 inch plasma screens which is why I asked the question. It does seem to me that all of these plasma setups in which the L&R speakers are pretty much hard against the sides of the panel are possibly misguided unless the viewing distance is about 4 feet. You need more separation than that to create the soundfield IMO.

    Do you think a Radius 225 as a centre above the plasma, tilted down a bit would be OK? The bottom of the plasma is already about a foot above seated eye height, although the viewing distance makes the angle OK.

    Thanks for all the responses

    Andrew
     
  6. binbag

    binbag
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    Ditching the speaker that does the majority of the work and then getting 2 other speakers to do its work as well as their own would only seems like a good idea to a government official.

    The bloke who mixed the soundtrack had a centre speaker; shouldn't everyone who listens to his work have one too?
     
  7. Bvan

    Bvan
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    i much prefere the phantom centre. for a couple of reasons(more $ towards the front two which helps for music; a phantom immage that sits in the middle of the tv screen rather than bellow or above it;) i also prefere to have music hanging magically in mid air rahter than watching it come out of a box in front of me. these are purely personal biases and should be taken at that and for what theyre worth.

    but i do think the argument that because it was mixed with a centre channel it should be replayed with one, doesnt admit that it was mixed first and foremost for replay in the cineplex where most viewers are far from the sweetspot.

    if i had any challangers for the sweetspot i might get a centre, or if i was inclined to spend my money for the benefit of my non audiophile mates who have to sit in the corner.

    jmho. cheers

    b
     

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