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Your centre speaker

Discussion in 'Home Cinema Speakers' started by EvilMudge, Feb 4, 2003.

  1. EvilMudge

    EvilMudge
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    Warning, Technical Post :smoke:
    :lesson:
    Many people will argue that a dedicated centre speaker is a waste of time, since it will not tonally match with the L&R speakers, causing panned sounds to change as they go across the front soundstage. This is all acceptable where the centre uses different drivers and has a radically different enclosure to the L&R pair. However where the centre speaker uses identical dirvers and has a similar internal volume WRT to a pair of small floorstanders/large bookshelf speakers, there are good reasons for using a dedicated centre.

    For example, most centres are designed with a Mid-Tweeter-Mid configuration. In a vertical axis this design is used to control interactions with the floor and ceiling, and to give a wide horizontal dispersion. So, rotating this arrangement controls horizontal dispersion and gives a wide vertical dispersion. A lot of advocates of the identical LCR designs claim this is simply because manufacturers attempt to get as much sound out of their centres as possible in order to make them match the LRs in efficiency.
    However, there are some extremely good reasons for having good vertical dispersion and weak horizontal dispersion.
    Many Centres are placed out of axis with the left and right speakers. Often this disparity can be enough to radically affect the sound of the centre compared to stereo pair - because your head is out of the normal dispersion pattern for the centre. This can be even more important where a large front projection system is used, because the centre speaker is often sited several feet above or below the axis of the other speakers.
    Secondly, where the stereo pair are close together, the centre's bass output will interact with the stereo pair unless the output is controlled somehow. With a wide enough front soundstage this is less of an issue, but without this the imaging across the front can be greatly compromised if all 3 speakers are too close together.

    Any opinions?
     
  2. Apocalypse

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    Dom H will latch onto this post like Bill Clinton onto an intern :)

    I troubles me that I physically cannot have the centre on the same level as the fronts, I feel like I am missing out on some quality especially when sounds pan across the screen.

    Interesting thread, be good to hear what the experts say about this.
     
  3. alexs2

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    Interesting one,Mudge.....I've changed my system from a stereo only with an entry level AV system in the same room,to a slightly more proper AV system as listed below.

    Whilst everything was being changed around,I was using the B&Ws with a Mission centre for a while.....the mismatch tonally( as well as financially) was obvious,with the centre being very different and leading to odd effects with sounds crossing the centre stage.

    I now use a B&W CDM1 CNT in it's place and with very similar drive units,the integration is much better.....I've found no significant interactions with the bass from the different speakers,but the centre speaker is placed exactly centrally,and all the speakers are set to small,and with a crossover frequency of 50Hz.

    Also,using power amps with not only a good amount of reserve,but also superb bass control does help in terms of attack and definition.
     
  4. deckard

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    Good post, the point about about vertical axis dispersion is a particular bugbear of mine...

    Despite my centre being well matched to my mains (Linn Trikan/Keilidhs) I'm restricted to putting it either above or below my telly. Either of which throws the tonal balance out of sync - aaargh!!:mad:

    I suppose I'll have to make a custom TV stand to get the correct height placing.

    It's not quite as simple as having near identical speakers.
     
  5. Lowrider

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    Well said, I agree with you... :smashin:

    As for center height, I much prefer it under the TV, otherwise the sound seems to come from the ceiling, instead of from the sreen, it is also weird with music, using DPLII...
     
  6. wilber

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    Used to have a similar issue as Deckard - matched Tannoys but on top of TV looked pants but below TV was off axis. Kefs Q range is much better thank you very much. I'm not into their techno babble, but the Q9C does not suffer from this problem - tried the speaker on the rack & on the TV & I can't hear the difference. Not only that but they are wonderful speakers (compared to what I used to have anyway & in the price bracket I could afford)
     
  7. catrevilla

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    Cat here,

    Everything you said is spot on. Just to let you know though, the sound that you're going to perceive in the center speaker doing what you said is your basic type of "Surround sound." This means that obviously you'll have your LR chanels mixed and that you'll perceive a depth effect, like something of a echo. That's surround effect. Precisely when it was being experimented with a center speaker connected to the LR channels, Surround effect was discovered, which nowadays it has been made more sophisticated, employing matrix methods, time delay, and channel blending.

    Cheers,

    Cat.
     
  8. Matt F

    Matt F
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    Having had both, I'd always recommend 3 identical fronts if you can get away with it - not necessarily 3 LCR type speakers, just 3 normal small 2-way standmounts. I use the M&K MPS1510 which are just small 2-way monitors. Presently the centre is used on its side and it sounds fine like this however, the intention is to eventually use all 3 in a vertical orientation, preferably just below a nice large plasma screen :rolleyes:

    The mid-tweeter-mid design is, IMO flawed and that is why you see the likes of B&W (with their LCR speakers) using 2.5 way designs rather than 2 way - with a 2 way (i.e. both mid units playing the same frequencies) anyone sitting off centre will hear the effects of what's known as comb-filtering - the same sounds coming from identical speakers but at different distances from you - it can create a ragged response and smear the sound from the tweeter that sits inbetween them - the 2.5 way design gets around this by letting the two identical mid drivers handle different frequencies.

    If you look at the M&K dedicated centres you will see that, where two mid drivers are used, they are always arranged in a tweeter-mid-mid arrangement. They do this for a very good reason.

    Alternatives are Dynaudio's Audience 42C which makes do with one mid unit and one tweeter.

    KEF's Uniq drivers are another good way around the problem.

    One thing I find really annoying about a lot of centre speakers is that quite a few of them use rear ports which, when you think about where most centre speakers end up being put (under the TV) is hardly a good idea.

    I'm sure Uncle E will have some comments on this subject too.

    Matt.
     
  9. EvilMudge

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    Matt,
    2.5 ways suffer just as much from Comb filtering of this variety as ordinary 2 ways, since most (the B&W you mention for instance) only crossover the 2 way at 400Hz. Anything above 400Hz get's output by both drivers. Correct seating design (oh boy theres a new one, forget acoustics, let's take floor plan as the starting point of the audio chain :D) should result in everyone sitting in their local hotspot.
    Also the comb-filtering effect varies depending on how far off axis you sit and how much space there is between the mids.
    Putting the tweeter at one end compromises the point source behaviour of the centre, so that anything sitting on the wrong side of the room hears a group delay between mid and upper audio frequencies.
    Have to agree with you about rear porting, but if you put your centre behind your projection screen you really wouldn't want a front port.


    I have to add that most centres really are quite dire, sometimes you're lucky to get even the same tweeter as the rest of the range.
     
  10. Lowrider

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    Some centers, the Proac CC2 included, offset the tweeter to avoid some of those problems, regarding the rear port wich mine has too, I just covered it with a thick layer of foam, so I don´t get any boom anymore, of course if you do that to a small speaker you may loose some bass, but as they are normally set to small, it won´t matter much...
     
  11. Dom H

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    I'm waiting for eric to appear otherwise what ever I write will be cremated :D

    ah sod it <puts on fake bears/glasses>


    People always moan about the problems with dedicated centres but are so adament they won't turn the damn things off because that would be a waste of money.

    They sound crap to me to so I have always turned them off (reluctently) or not bothered with them all together. Problems solved.
     
  12. EvilMudge

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    Dom,

    I seem to remember you posting some photos of your set up - there didn't seem to be any room for a decent centre, if you could even find one that matched (grrr - most manufacturers really will sell you utter cack if you let them:mad: ). Not surprised you don't have/want one. If you did try to squeeze in a centre it would have to have the horizontal dispersion of a gnat fart to work right.:D

    Spare a thought for those of us with a twelve foot gap between the stereo pair (which images just fine with music, but with centre mixed dialogue sounds less effective).
     
  13. bob007

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    This will be as soon as he pops on his bears costume. :D
    This was one of my concerns when I decided to change from CRT TV to RP, the front three speakers were more a less on the same plain with the Sony 36" but now with the Tosh 56" the centre is now sitting a good 18"- 20" above the main pair. Not a concern or worry anymore, the dialogue is firmly locked to the screen and when sounds pan across the screen there is no noticable change in the sound, by that I mean the sound does not rise and dip.

    I can only put this down to the good qualities of the speaker.

    Just a thought, if the speakers are at different heights (taking mine as an example), with the dialogue locked to the screen doesn't this also include the other effects will be too? Then if the main pair are either side of the screen there shouldn't be a major problem with the panning of sounds. Down to the quality of speaker as well I suppose.

    I do agree that having identical speakers across the front and on the same plain is the best option.
     
  14. Dom H

    Dom H
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    heres a pic

    I expect the majority of people have a similar distance between their fronts, they are exactly 6ft apart.
     
  15. Jase

    Jase
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    Yep!:smashin:
     
  16. Lowrider

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    I dont know about the majority of people, but mine are 8´apart...

    I did try to use 3 identical speakers in the front, but didn´t like when my TV turned blue... :rolleyes:
     
  17. Apocalypse

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    I'm about to switch from floorstanders to stand mounted fronts so any tips on which stands perform well, yours look like the Nexus range from Atacama. I have access to tons and tons of kiln dried sand so that's no problem but do other fillers like Atabites do a better job, also how full is the stand, 3/4 of maxed?

    And there is no way a TV pic can be so clear from a digi cam shot, cheater :laugh:

    Phil
     
  18. Dom H

    Dom H
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    I dont have mine filled I'd like to hear from people that do, did it make a difference? Any ideas for a cheap filler thats easy to get hold of and also how to fill them.


    I don't know what your talking about :laugh:

    pics of progressive sets come out as clear as that tho
     
  19. Lowrider

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    Mine are filled with sand from a pet store... Did it make any difference, I didn´t do a blind test, add sand, remove sand... :suicide:

    I was advised not to fill them to the rim, so I didn´t, they don´t wooble as much now...
     
  20. deckard

    deckard
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    Used to have Atacama SE20's under my old JPW P1 speakers.

    Fillling them 3/4 full with sand tightened the sound up quite noticeably. Like Lowrider said you certainly wouldn't want to tip the sand out to compare but I filled one stand and listened to a mono source to compare.

    Definitely better filled; sand or expensive lead bits - that's up to you!
     
  21. Geoffrey Shrek

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    Er, try to make sure you use shielded speakers :zonked:
     
  22. NicolasB

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    Stand-wise I quite like the look of Atacama's new SE series - the SE6 for fronts and SE10 for surrounds. Bit pricier than the Nexus ones, but not too bad. See here - bear in mind that the prices on that page are ex. VAT and ex. Delivery.

    One test of a speaker stand is to hit it with something metal. If it rings, that's bad. If it sounds completely dead, that's good. Heavier is often better than lighter too.

    One thing about centre speaker discussions that puzzles me: while it is obviously true that the shape of the cabinet can have a huge influence on the sound of the speaker, is it not also true that one of the biggest differences between a good speaker and a bad one is precisely the fact that the good speaker's sound is much less influenced by the cabinet? A lot of speaker technology seems to dedicated to reducing the influence of the cabinet as much as possible - that's why Gallo use spherical cases, and why B&W have that curious elongated tear-drop shape for the tweeter (and the midrange driver on their higher-end speakers) - this is all designed to eliminate internal standing waves. If this is true, then doesn't it follow that the higher quality and more neutral-sounding a set of speakers is, the less likely it is to matter that the cabinet of the centre speaker is a different shape from the side speaker cabinets?
     
  23. uncle eric

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    More to do with size Nicolas.
    More often than not, dedicated centres are a fair bit smaller than their L/R counterparts hence will produce and entirely alien sound when compared to these two, even with the same drivers.
    :Edit: I have extensively experimented with this over the years and swear by it.

    Crossing over at 80Hz rather than say 50Hz makes the difference slightly less in your face but it's still painfully obvious.
     
  24. EvilMudge

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    Nic,
    one of the big arguments against dedicated centres is the lack of internal volume compared to a floor standing speaker. This affects the acoustic loading of the bass and midrange frequencies. My centre is fairly large, has twice as many identical bass/midrange drivers as the stereo pair, yet has a lower rated sensitivity than the floorstanders. However when calibrated to 75dB, sounds pan perfectly across the front soundstage (which as I've mentioned is rather wide.)
     
  25. Dom H

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    All the dedicated centres I have tried have had lots of colouration in the upper bass region, male vocals suffered considerabley.

    This may be as someone mentioned my mains interfering, either way removing the centre sounded much, much better, particularly with diologue.
     
  26. EvilMudge

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    Dom,
    Are those B&W DM602s you have?

    I'm not suprised you get 'colouration' of the upper bass - as that's mainly all centre's are good for (have to go very up market to get one that genuinely dips below 70Hz) and in such a congested soundstage the superposition of the output from the front three is bound to selectively enhance certain frequencies.

    As an aside - does anyone remember the early pro-logic decoders (I've still got a Marantz one lying around). They had crude bass management for the centre - normal and wide mode. Normal was supposedly for use with smaller centres and wide for larger ones, but the wide setting only seemed to work properly if the front soundstage was fairly wide ;)
     
  27. Dom H

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    Yeah they are 602's.

    The 2 things that cured the problems with deep vocals in my setup was to remove the centre and also put up some thick padding behind the sofa against the wall (the sofa backs on to the wall)

    Surely alot of people use dedicated centres with a similar separation and I also expect they are designed to be used in such a situation, why then the problems?
     
  28. Steve.EX

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    I would certainly agree with Eric on the grounds that i use Kef 203's at present which share exactly the same drivers/ratio as my 202 center which while very large for a center is still approx 1/3 less in internal enclosure volume and there is a very small change in perhaps perceived "weight" (rather than tonality i feel) of course setting an 80hz x-crossover makes this almost imperceptable (certainly not painful).

    Steve.
     
  29. dunkyboy

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    I use three [identical] ATC Active 10s across the front. These are designed specifically with wide horizontal dispersion and tight vertical dispersion in mind and so sound absolutely scrumptious. :)

    Speaking of stands, I've been using £75 Atacama SE24's, filled with sand, for a year and a half now with no complaints, but just last month I decided I'd experiment with something more substantial (and expensive!)

    A local hifi shop let me take home an old pair of £275 25kg beasts from standmaker-no-more Target for the weekend to see if I could hear a difference. I really didn't expect much of anything, maybe slightly tighter bass (hard to imagine with ATCs) but I was blown away by how much more stable and holographic the soundstage was - the imaging (which had always been razor-sharp with the ATCs) was even sharper, and it no longer took any effort to pick out individual instruments from a complicated mix. Suddenly my speakers sounded infinitely more natural and easier to listen to.

    Needless to say I rang the shop the following Tuesday and bought them. They're second hand so I didn't have to shell out anything near the full £275, but even if I had to it would have been worth it, for the improvement they brought.

    Of course, now I've got the stereo pair on the big ugly Targets and the centre speaker on an Atacama SE24! It doesn't look particularly good (the three identical speakers on identical stands had looked particularly impressive...) but I haven't noticed any glaring disparity in the sound whilst watching movies. Perhaps with home cinema the difference the stands make is less apparent, or perhaps my humble Yamaha DSP-800 processor is insufficiently gifted to show up any differences...

    Cheers,

    Dunc

    P.S. - Can anyone tell me if that's really how you spell 'scrumptious'?? :)
     
  30. Lowrider

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    Shrek,

    Most front speakers are not shielded, at least mine aren´t, so if you have a TV, like me... :thumbsdow

    Eric,

    If one has floorstanders, it is difficult to find a center as big, but not with monitors, my center has twice the size of my fronts...
     

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