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Is a centre speaker really necessary?

Discussion in 'Home Cinema Speakers' started by Oxfordman, May 10, 2004.

  1. Oxfordman

    Oxfordman
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    A lot of people visiting this forum have quite decent ‘hi-fi’ systems but also want a good home cinema set-up, although not many can have separate rooms for each. This question is primarily addressed to them. By definition a good stereo set-up produces a sharp and accurate central image for the vocals. As the tweeters of the main speakers are/should be at ear-level, in the absence of a centre speaker, the vocals/dialogue appear to come from an ideally located point as it coincides in most set-ups with the centre of TV screen. Since the centre speaker has to be located about 2 feet below or above the centre of the screen, there is an inevitable trade-off. Everybody recognises the importance of a good tonal matching between the centre and the main speakers, a task not always easy if you want to keep your ‘cherished’ main speakers, often not longer in production! So there is a second trade-off. I understand the argument that a centre speaker enlarges the optimum listening area, but only up to a point, as seating too far away from the ‘sweet spot’ might not affect adversely the dialogue sound but puts ‘out of balance’ the sound from all the other 4-6 speakers, so carefully adjusted for the correct delay/distance and sound pressure! (be it by ear or SPL meter).

    I have tried a centre speaker for a while to disprove my own arguments but with no much success! I have now removed it but since so many of you cannot be all wrong (let alone the recommendations of Dolby Labs, DTS and speaker manufacturers!) I can’t help feeling I am missing something!

    Could any of you ‘proud’ of your home cinema system try the ‘phantom’ centre mode and describe the disadvantages you perceive?. It would be most helpful. It might even convince the ‘other-half’ that all TVs (even her ‘lovely’ Loewe Aconda) are meant to have a speaker sitting on top!

    Many thanks
     
  2. Ian J

    Ian J
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    In a room where everything is optimumly placed you could get away without a centre speaker without too much trouble.

    Unfortunately most rooms aren't like that. My own left speaker is two feet to the left of the TV and the right speaker is seven or eight feet to the right of the TV. Not ideal but needs must and without a centre speaker to lock the dialogue to the screen, surround sound just wouldn't be workable in my room.
     
  3. eviljohn2

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    It also depends on the quality of you amplifier. I've spent the last month or so managing without a centre speaker (repaired it now) and my Denon 1802 doesn't do a great job of downmixing the discrete centre channel from DVDs into the main speakers.

    Similarly, DPL2 and other DSPs don't work correctly without a centre speaker due to the nature of the algorithms used. It made the sound dull.

    It's certainly possible to manage without and my setup is far from ideal anyway! :)
     
  4. Oxfordman

    Oxfordman
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    Thank you Ian and eviljohn2 for your replies.
    I can see that in your case Ian the centre speaker is essential. Fortunately, my main speakers are at equal distance from the TV and the surrounds and back speakers are also placed symmetrically.

    I agree with you eviljohn2 that any discrete channel output from DVDs should sound better than a downmixed/matrixed one. I am now intrigued by your comment about the nature of the PL2 algorithms (I don’t use DSPs). Perhaps it is time to reinstate the centre speaker and look out for the dullness in the sound!

    Thank you both again
     
  5. eviljohn2

    eviljohn2
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    You certainly shouldn't write DSP's off entirely. The vast majority make most things sound terrible but my experience of DPL2 is that it makes a big improvement to most "televisual" stereo sources, such as VHS and normal telly not only for films but loads of things. "Modern" cartoons such as the Futurama or X-Men: Evolution are encoded with a Pro Logic signal and sound excellent (better than many 5.1 mixes IMO).

    I do stick with stereo for music though. Try them out yourself for various sources and see what you think :)
     
  6. Oxfordman

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    eviljohn2, I do use DPL2 a lot as well as DTS neo6 for TV vewing and I agree they improve the sound considelably. I should have expressed it more clearly. With 'other DSPs' I meant sound field processing like 'concert', 'hall' 'jazz' etc and the various forms of 'digital cinema sound' and the like. Thanks again.
     
  7. Dfour

    Dfour
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    I am waiting for my new front 3 AE evo's to turn up and am running without a centre in phantomn mode and can tell I dont have ti as the dialogue isnt as focused as it could be. I also cant have the speakers at the same distance apart because of my room so a centre is esential to me.
    Yamaha's are the king of DSP modes and i do use them with the presence speakers fitted.
     
  8. Oxfordman

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    Thanks Dfour for your contribution. I have just completed some ‘very subjective’ tests with and without the centre speaker and I am afraid I still cannot perceive any advantage in my system, although appreciate that in many/most cases, the room geometry, the dispersion characteristics and the placement of the main speakers, make a centre speaker essential. Perhaps in my case the symmetrical speaker arrangement is the ‘culprit’ but most probably I am biased!

    eviljohn2, I could not detect the sound ‘dullness’ in DPL2 in the absence of a centre you mentioned. BTW, shouldn’t you also have a dull sound when you listen to music in 2ch stereo where, for all intends and purposes, the front soundstage should produce the same sound as DPL2 without the centre? The way I understand it is: sounds that are common to left and right channels and in phase go to the centre speaker while sounds out of phase are sent to the surrounds. So no ‘new’ sounds are produced by the centre that are not already in the central image of a 2ch stereo (nor are removed when there is no centre!). Is this a misleading over-simplification of the DLP2 algorithm? Of course you can adjust/increase the level of the centre to personal preferences while without it you are ‘stuck’ with what the recording engineer liked best! Mind you can easily go too far and the front soundstage collapses to a ‘glorious mono’

    So in the absence of anyone with a ‘symmetrical set-up’ agreeing with my ‘very subjective’ findings I have to accept the centre speaker does not only lock the dialogue to the screen but also enhances the whole audio-visual experience, even if I don’t understand how!
     
  9. alfalfa

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  10. Keiron

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    This is an interesting debate, I have a Dynaudio set up, and I'm not convinved that an actual centre is better than a phantom centre. To my ears, with a centre, it's always obvious that the sound is coming from somewhere other than the screen. Curiously, when I use just the L & R speakers with no centre, this effect isn't obvious. What's more, without an actual centre, the sound is much fuller and richer, not surprising really since I guess two speakers give a lot more clout than a single, smallish centre. I'm yet to be convinced either way.
     
  11. avanzato

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    Ignoring any issues of personal preference movie sound is conceived and mixed for a centre channel, if you aren't using one then your system could be considered as 'wrong'. So in a movie system that sounds better without the centre speaker, it's the centre that's the problem (mismatched or too small etc.).

    For music? Are there any rules yet?

    Have you all played around with the DPL2 settings? I found the controls quite dramatically changed the sound, from flat to overblown. Stereo used to be my preferred way of listening to music but I do find DPL2 adds a nice dimension to a fair number of CD's.

    BTW 'The Audio Perfectionist' clearly has an agenda against THX which is fair enough. OTOH like the artical says I have used my own ears and judgement, however I came to the conclusion that I prefer THX speakers for movies not 'HiFi' ones. YMMV
     
  12. Oxfordman

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    Alfalfa, thank you for the link to this most interesting article. What a gem! It totally confirms my experience and I am ‘thrilled to bits’ that I have decided to trust my ears for several years now, and not to use a centre despite the ‘common wisdom’. You made my day! Is this the kind of article the AV magazines and the speaker manufacturers don’t want us to read? I saw in a recent magazine a centre speaker costing nearly 2 grand. It will be very difficult to convince anyone who spends even a fraction of this sort of money that they might be better off without it!

    Keiron, I am delighted you joined the debate and your experience with your set up is most valuable in helping to throw some light on the subject.

    Avanzato, I too find some music sounds better using DPL2, but is this due to the centre speaker or to the out of phase sounds sent to the surrounds? It might be worth trying it with a ‘phantom’ centre.
     
  13. Keiron

    Keiron
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    Yes, I love listening to music using DLP2 since I got my new Rotel processor recently, and I've always considered myself something of a purist (Stax phones no less!) However, I find with DPL2 that I tend to increase the "width" of the centre speaker to the point that it almost becomes redundant. Unless I'm missing something with my Rotel, it's a shame that there aren't similar "centre width" settings with DD and DTS.
     
  14. tmcevoy

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  15. avanzato

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    I've experimented before but I tried turning off my centre again last night and using DPL2. TBH it sounded awful the soundstage of the front was hollow and 'cuppy', even changing the centre width and dimension settings didn't help. IMO if you want to use phantom centre I'd avoid DPL2 and use standard Prologic on stereo CD's. It adds some ambience to the surrounds but without messing around with the front channels, basically a refined version of the age old Hafler technique.

    edit: Ah Ha!

    I had an obvious :rolleyes: thought and tried again.

    Seems that DPL2 (on my amp at least) is only phantom when the width setting is on +7. Any other setting with the centre turned off just loses the info that would be sent to the centre channel. I still prefer it with the centre on and width +5/+6 as it gives some centre fill, that IMO is 'better'.
     
  16. Oxfordman

    Oxfordman
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    Tmcevoy, thanks for the links to the two very interesting articles. Quite reassuring!

    Mat, it was very good of you to experiment with your set up. I was a bit puzzled about your first test. I actually thought there was something strange with your amp (it seemed unlikely that anyone familiar with the Hafler technique would put up with hollow soundstage in 2ch stereo!) Glad you found the explanation.

    Having read the three articles above and the opinions of the participants in this debate, I hope we can agree that in some systems a centre speaker is essential, in others it enhances the sound quality, while there are some systems, which not only don’t need one but might actually be better off without it!

    Now is bass directional? Don’t worry, just kidding!
     
  17. eviljohn2

    eviljohn2
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    That one's easy :D

    Low frequency sound waves (bass) are as directional as any other sound waves. The difference is that the human ear isn't capable of pinpointing their direction as easily as it can with higher frequencies. The way that the human ear can locate sound is absolutely marvellous and still baffles me, so if anyone can help with that one... ;)
     
  18. Nimby

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    It helps to have two ears eviljohn2. There is a delay in the time of arrival of sounds from one side of the head to the other except when the sound is straight ahead.

    The head acts as a shield further increasing the delay and increasing the intensity variation between the two ears.

    The Pinnae (sticky out bits) help to direct sound into the lugholes (technical term).

    Over millions of years of development the brain became expert at sorting the directional signals as an aid to survival. Such as finding a mate, hearing calls from the pack or sensing danger.

    Low frequencies were probably absent from the early forests that were the natural home of early man. So low frequency sounds are difficult to pinpoint in comparison with higher frequncies. The frequency fresponse of the ear is also markedly poor at low frequencies.

    Interestingly low frequncies carry enormous distances and if you go low enough the sound will actually circle the earth!

    Hope this helps? :)

    Nimby
     
  19. eviljohn2

    eviljohn2
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    Thanks Nimby, that makes sense as it's the same triangulation method as the eyes use for depth perception.

    Using that method entirely though it's not possible to distinguish whether an equidistant sound is emanating from behing or in front of the listener as the lugholes are effectively point sinks.

    Sound travels at ~330 m/s in air if anybody's interested, so the brain is doing some quite fast calculations there :)
     
  20. chrisgeary

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    Im also fascinated by the way our ears work.. I understand about delays so we can pinpoint direction, but how on earth do we know whether its in front or behind us? Especially when its directly in front or directly behind. That has always amazed me.

    Low frequencies direction are probably hard to detect because the wavelength is very long, therefore delay between the two is virtually negligable (is that the right spelling?) - whereas at higher frequencies, a small delay will results in several phase shifts before it hits the other ear. Well thats my complete and uneducated guess anyway =)
     
  21. eviljohn2

    eviljohn2
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    Here we go:
    http://www.school-for-champions.com/senses/heardirection.htm

    Chris, you're right about the wavelengths.

    For interested people here's some wave theory:

    Velocity of wave = Frequency * Wavelength

    We know that V = 330m/s so freq and wavelength are inversely proportional with this relationship.

    Here's some examples around the audible range:

    Frequency(Hz) | Wavelength(m)
    10 | 33
    25 | 13.2
    50 | 6.6
    100 | 3.3
    250 | 1.32
    500 | 0.66
    1000 | 0.33
    2500 | 0.132
    5000 | 0.066
    10000 | 0.033
    25000 | 0.0132

    You can see that sound waves are only on a scale similar to the human ear when the frequency is greater than about 5000Hz!

    :) :lesson:
     
  22. chrisgeary

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    out of interest, do you what the frequency is below which we start to question direction, and the frequency below which we definitely cannot tell anymore?
     
  23. Nimby

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    Regarding whether we can discern sounds from for or aft:
    I believe the shape of the Pinnae are important here. These aren't symmetrical and have a definite forward tendency on most people. As mentioned in the link.

    As regards frequency when directionality is lost I haven't a clue without looking it up. It can't be that high a frequency as sensitivity to the higher frequencies drops rapidly with age. The elderly can still obtain directional information from speech, busses arriving etc.

    Nimby
     
  24. eviljohn2

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    Bear in mind that the human hearing is most sensitive in this midrange where voices are. In the same way as eyes are most sensitive to EM waves in the middle of the visual range. That is, we can see green (ie. resolve differenct shades) much better than any other colour, presumably because of the greenery we evolved in. :)
     
  25. smithers

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    With my setup I find little use for a center channel. The main speaker are equidistance from the TV and toed-in just slightly. I checked the L-C-R SPL using avia and the phantom center channel's SPL was virtually the same as the right/left speakers (maybe 1 dB under as it kept fluctuating).

    I have a big couch centered in front of the TV and there's never more than 3 people watching a movie at the same time. In my situation a center isn't necessary.
     
  26. Barend

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    With movies the dialogue is much clearer through the center speaker than through a virtual center.
    With music, much depends on the speaker tonal uniformity and angle, my Reference 203's picture the lead singer right in the middle all the same, but I don't like music coming out just from the center box (Ref 202c), that's why I prefer GOOD sacd discs spreading it out off the center towards L + R.
    That said, all my old cds sound really a lot better thru my new speakers.
    Barend
     

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