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Speakers and room acoustics advice

Discussion in 'Home Cinema Speakers' started by Audionyx, Dec 28, 2002.

  1. Audionyx

    Audionyx
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    Hi all,

    Wishing seasons greatings to everyone and for the coming year.

    I am needing a bit of advice with regards to speakers as I am seriously considering a major overhaul of my system.

    Currently for hifi I use Arcam FMJCD23, Musical Fidelity A3.2 pre/power amps and B&W CDM1NT stand mounters on sand filled stands. AV is Arcam FMJDV27, Denon 3802, Kef KHT2005 system. These systems run concurrently in a room measuring 4.5m x 4m. My TV and front speakers are at one end in the middle of the wall so placement is not an issue.

    I am generally delighted with both systems, however I feel that a change in speakers may be on the cards. For music, the 1NTs give amazing detail and an incredible stereo image, however can sizzle a bit in the treble and often lack that extra something in the bottom end. The multi channel system is also spot on, however I want to combine the two systems.

    I want to keep the 'eggs' as rears as they are unobtrusive and work very well in my room. It is the front and centre speakers I am considering changing.

    Speakers auditioned: Quad 21L, Kef Q5, Monitor Audio S8, Wharfedale Pacific, B&W C4.

    None of the above speakers match the 1NTs for imagery and detail and all 'boom' a bit in my room. The Kef's and Quad's were the closest to my sonic preference though. I would really like to audition the Q7's so if anyone can offer views on these I would be grateful.

    HiFi news and HiFi choice both rate these speakers yet how would I avoid emphasis in the bass? I find my B&W's too analytical and although magic sounding with good recordings, they have me reaching for the 'eject' button on bad ones!

    Any ideas would be welcomed guys - thank you
     
  2. steve1056

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    Don't B&W make floor standing versions of the CDM1NT's? 7NT and 9NT? Have you tried these?

    Have you tried Dynaudios? Either the Audience or Contour range might suit you. My room is similar in size to yours and I have Dynaudio Contours which sound amazinginly natural. Give them a try.

    Cheers

    Steve
     
  3. Audionyx

    Audionyx
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    Steve,

    thanks for advice - I am trying to make the change for free so unable to consider b&w's 7nt! I may look at dynaudio but like the look of Kef's - need to know if anyone uses Foam bungs in the rear ports and how this affects sound quality

    Regards


    Darren
     
  4. uncle eric

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    Darren,
    Don't be in a rush to bin your speakers.
    You have an almost square room which is the worst possible acoustic shape for a room. Also, from your comments, I assume you are placing your speaker system centrally along the rooms axis.
    The above are the two main reasons you are experiencing "boom" in your room.

    Again, assuming that your front L/C/R or L/R is slap bang in the middle of the 4 meter wall, I'd say you are getting poor axial (width) resonances at certain part(s) of the frequency spectrum hence the boom. This is not difficult to calculate.
    Taking the 4 meter measurement as your rooms width, this is 13.13 feet in old money. So we take the speed of sound, 1129fs / (2 x 13.13 ft) = 43Hz. This means that whenever your speakers produce 43Hz (or multiples of 43Hz) the air in your room vibrates, or "resonates" along the width axis in your room.
    Although the 1NT's are rated down to 60Hz at -/+ 3 dB's, this is not a brick wall figure (obviously) and your room helps to "boost" this low right down to the problem area which is 43Hz (albeit at much lower dB's). You will also have a second axial width resonance at 86Hz, a third at 129Hz etc.

    A brief note here. The lower down the frequency spectrum you go, the more obvious the problem becomes.

    Try to move the front soundstage over to the left or right either way. Even a small movement of 6 to 12 inches will reep big rewards and should improve things no end.

    People often ask me what to do with the surround channels in this slightly off centre configuration. There are a few choices. Firstly, and perhaps most obviously, adjusting the delay settings of the surrounds (via your amp/processor) will help restablish correct settings. The solution I used in the Batcave, was to actually place the entire system in a central position (thus everything looks symmetrical hence normal) and place bookcases that are almost floor to ceiling and wall to wall down one complete side of the room. This breaks down the axial width resonances and at the same time, offers good diffusion for secondary reflections.

    While I'm on this subject. I made the point earlier suggesting that the lower down the frequency scale one goes, the more obvious acoustic problems become. This is yet another reason why sats are often prefered in many environments. Imagine how difficult it is to place (or move) full range speakers into ideal positions.
    The 80Hz sat floor is much more forgiving and using sats will mean the use of a sub (and you should be using one regardless) which means you would only have to worry about positioning of your subwoofer and not your entire front soundstage.
     
  5. Phil Hinton

    Phil Hinton
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    Eric,
    I learn something new everyday, good post.
     
  6. Audionyx

    Audionyx
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    Superb response Eric!

    I am fascinated by your knowledge and description of axial resonance. You are correct in that my front speakers (both 1nts and kef eggs) are placed either side of my tv which in turn is placed in front of a chimney breast on the narrow wall. The fronts of the speakers are 70cm from the wall. I have experimented with the speakers' distance from the wall.

    Closer to the wall emphasises the bass but sacrifices imagery - I tow the 1NT's in so that the cones point at my prefered seating position - this makes my music almost perfect! Is it just that my music system is that good that poor recordings sound this way? With over 400cd's I reckon only 30 sound "hi-fi"! Are the 1Nt's just too analytical??

    I am reluctant to change as I feel what I have is the best for my room but always feel something better is a credit card away! Also, the true love of my love has said she is not overly keen on all those speakers!

    Thanks again for your qualified advice Eric - have a good one mate!

    Regards


    Darren
     
  7. Apone

    Apone
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    Excellent response Eric!!

    It's always a good idea to try different speaker positions. I remember I spent a whole weekend trying the sub in different positions and listening to get an 'acceptable compromise' between good sound and positioning.

    Regards

    Mahmood
     
  8. magking

    magking
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  9. Audionyx

    Audionyx
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    I always knew of the importance of speaker matching to room acoustics and by experimentation have discovered what the subtle gains and improvements that can lead to a closer audio zen!

    The science of axial resonance detailed by the knowledgable uncle eric has set me off on further experimentation!

    The B&W CDM1NT are amazing speakers and do benefit from good toe-in and experimentation with placement in relation to the rear wall.

    I realise that my understanding of music reproduction (clean, detailed, perfect timing and no emphasis at any frequency point) may be impossible to achieve in my room but I remain undeterred!

    Thanks for all of your input - any more ideas and experiences are welcomed with fascination.

    Regards


    Darren
     
  10. bowenjones

    bowenjones
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    What would you say is the perfect acoustic shape for a room
    as, when I renovate my home, I will be using a room solely
    for a home cinema set-up.
    As I am currently designing the lay-out, your input would be
    most welcome.
    Apart from watching movies I also listen to a lot of music,
    especially surround sound music so please consider that in
    your reply.
    I haven't decided on a system yet as the renovation will
    take some time and who knows what will be on the market
    come completion.
    I am looking at a room size of approx. 25 ft. x 20 ft. but I
    can alter that by a few feet either way.
    Regards,
    Stu.
     
  11. The Nightfly

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    I'm currently experimenting with some DIY helmholtz resonators in my HiFi room to try and selectively filter out room resonances. They are made to specific lengths in order to be tuned to an exact frequency in order to be effective. A resonator in a sound field *eats* energy. These pipes will effectively act as notch filters at the resonant frequency.

    The theory is as follows: When you put this device in a sound field at the resonance frequency it will expose a low acoustic impedance at the hole and the sound level will drop in the vicinity, sound pressure is 'shorted out'. But inside the pipe, where you don't hear it, sound level goes up and the energy is dissipated into heat. Helmholtz resonators are a means for selective sound absorption in architectural acoustics (eg the Sydney Operahouse)

    I've carefully measured the frequency response of my room below 100Hz and found I have three significant peaks. I'm going to tackle the two highest peaks at 78 and 88Hz first. Because they are close together they are more easilly noticed and generally there is more musical content at this frequency than the other peak I have at 48Hz. Once the tubes are constructed and working they can be hiden behind/under sofas or curtains or covered in fabric and placed in corners.

    If there is any interest in the results I'll post back.

    Allan
     
  12. Audionyx

    Audionyx
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    The plot thickens! Ignorance to these devices has provoked interest! Let me know how these fair...

    Darren
     
  13. sinister_stu

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    I think that a double cube (width = height and length = 2*width) is the perfect room shape for acoustics, as far as I can remember.

    I'm currently studying electronic engineering and have done some work on Helmholtz resonators. I might have to try to remember some of the stuff we supposedly learnt.
     
  14. uncle eric

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    Stu,
    How high is your ceiling?
     
  15. bowenjones

    bowenjones
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    Well at the moment I'm toying with the idea of having
    my third beroom located in the loft therefore giving me
    about 16 feet headroom in my h/c.
    I'd rather it not be that high though (unless it makes a
    considerable differance acoustically) as I would like the third bedroom to be split-level.
     
  16. uncle eric

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    I always advocate the 2/3/5 ratio.

    x2 being the ceiling height x3 being the room width, x5 being the room length.

    In other words, if you take a ceiling hight of say 9ft. Using this as a x2 ratio, you will end up with a room as follows.
    Height 9ft (2x4.5)
    Width 13.5 feet (3x4.5)
    Length 22.5 feet (5x4.5)
     
  17. uncle eric

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    As this is a dedicated room, I would also be thinking about wiring in height channels which are not as far away as many think.
    There are a few DVD's already encoded with this info.
     
  18. bowenjones

    bowenjones
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    Thanks Eric,
    So going on your calculations I can design a room thats
    12 feet high
    18 feet wide and
    30 feet long.
    What do you think of the 2 cubes example that has been
    put forward in this thread? Can you see any problems in
    a room thats 12x12x24?
     
  19. bowenjones

    bowenjones
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    I agree and, by the time it's completed, they might even be
    commonplace!!!
     
  20. Lowrider

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    Equal dimensions will reinforce ressonances...

    The formula I´ve heard as ideal is:

    height = width x .6
    lenght = width x 1.6

    So if height = 12´, width = 20´ and length = 32´
     
  21. uncle eric

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    I will do a more comprehensive post in a new thread on this subject later today.
    Needless to say there are many schools of thought on room size/shape, my preference is 2/3/5.
     
  22. NicolasB

    NicolasB
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    Don't you have to damp Helmholtz resonators in order for them to absorb sound? :confused:
     
  23. Audionyx

    Audionyx
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    Superb responses to this thread - there are some very knowledgeable people out there!

    For those of us with acoustically imperfect rooms - what is the solution?

    Helmholtz resonators are out of the question. If any man is brave enough to convince my missus on this then go for it!

    I have heard that soft furnishings (tappestries etc) can help as does furniture placement (obviously).

    The more that is spent on electronics, the more I have become aware of recording productions and now room factors!

    Regards

    Darren
     
  24. alexs2

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  25. The Nightfly

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    Nicolas,

    The principle is simply to get a resonance going inside the tube, that in itself will absorb energy from the air outside the tube. Harking back to speaker design principles, damping has the effect of lowering the 'Q' of a resonance and also, in this case, I suspect it will also lower the resonant frequency (one of the effects of damping material inside a 'speaker is to make the enclosure appear acoustically larger to the speaker cone).

    I think damping material could be used here and the effect would be to lower the resonant frequency (or allow a shorter tube to acheive a particular frequency) and broaden the frequency over which the device is effective but at the expense of having a smaller effect.

    At the moment, this is all theory, and the practice is coming along slowly. Initial experiments are not 100% encouraging and I think I may need to set up some carefully controlled experiments before continuing. This may take longer than I thought !

    Allan
     
  26. Lowrider

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    The most important is to avoid dimensions equal or multiples, be it 2x3x5 or whatever...

    You can do a pretty good job with soft furniture, rugs and drapes, professional room treatment is for studios and other dedicated rooms...

    My rules of thumb are:

    dead end behind the speakers, a window with heavy drapes is very good, because the glass will not reflect bass, and the courtains absorb treble,

    live end behind listening position, and as far away as possible,

    minimize first reflections, heavy rug in front of speakers, and something soft on the side walls closest to speakers, use a mirror to determine where they came from,

    irregular furniture, soft opposite to hard...

    This works more than well enough, without upseting the wife... ;)
     
  27. Geoffrey Shrek

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    I just use my wife as for sound absorbtion :D
     
  28. bowenjones

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    And I absorb my wifes sound!
     
  29. Lowrider

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    Its a shame we can only have one wife at a time, the best sound I got in my house was the other day, when I had 20 guests absorbing the sound... ;)
     
  30. Guest

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    There is another way of creating the "perfect"room, one of which many appear to be blissfully ignorant;)

    My room is an acoustic nightmare, effectively 2x1x1 with partition walls. But I get soundstaging that has hardened audiophiles weeping! Depth is amazing, everything is precisely focused and the true meaning of a 3d soundstage is revealed:D

    Without going to the expense of compromising the design of your living enviroment, just buy some true digital room correction, courtesy of our friends from TACT. You can then forget about room dimensions and flawed treatments and get the real deal!

    I understand that the new TCS processor is due to be unveiled early next year, and will do room correction in 7.3 channels:D

    Trust me here, this stuff really works, even in my HC setup of Tact front soundstage and Rotel processing, the room is no longer a problem. Early and late reflections are removed and I can put the speakers anywhere I want and still get excellent results.

    The Tact RCS2.2X controls the two main channels and 2 subs. No more peaks or nulls, create the tone that I want, and bass resolution to die for. All for around 3.5K, alot less than new rooms;)

    Best Regards

    Michael
     

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