Has anyone ever used any formula to build HT Room?

Discussion in 'Archived Threads 2001-2004' started by Ricardo E Garcia, Mar 26, 2001.

  1. Ricardo E Garcia

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    I'm in the planning stages right now and I've found a spreadsheet that Stereophile Guide to Home Theater had on their web site that is supposed to help you in selecting room dimensions that are sonically correct. Here's the location of the sheet
    http://www.guidetohometheater.com/shownews.cgi?388
    I punched in the numbers of my proposed room.
    27L x 14W x 9H
    and the sheet showed several flaws in this room size. 12 problem frequencies to be exact. And 6 of them are below 180Hz.
    I played with the numbers some and found the best I can do is 4 problem requencies and the lowest one is at 221Hz.
    But now I have a room size of 24L x 12.73W x 7.55H I'm losing quite a bit of space.
    Does anyone have any suggestions on maybe some other proposed dimensions that would allow me to keep more of my room and still be sonically correct?
    Thanks!
    ------------------
    Rick
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    You can follow the "Golden Cube" rules to try and avoid standing waves. But a simpler solution would be a $200 device called the "Behring Feedback Destroyer".
    It is a programmable filter that will take those particular frequencies and reduce them so your walls dont over-emphasize these sounds.
    Search the Advanced Topics section of this site for "BFD" and you will find lots of discussion of this device.
    You should also note that the formula's used to tell you about problem frequencies make gross assumptions that all your walls, floor and ceilings are smooth, un-broken planes. A heavy bookcase, windows, doors will break up the walls and also break up the frequency response and avoid the standing wave problems. (This is why most combo living/HT rooms dont have standing wave problems. It tends to be an issue only for dedicated theater rooms.)
    I have even seen small, fake columns along walls used in some demo rooms/dedicated media rooms to break up a otherwise "problem-looking" room into smaller sections which eliminate standing waves very nicely.
    What I'm trying to say is that you should not mess up your room size over this. Change a foot or two according to the spreadsheet to minimize problems, but plan to solve the remaining problems with room-treatments or equalizations.
    Good Luck.
     
  3. Terrence B

    Terrence B Agent

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    Ricardo,
    These kind of acoustical modeling software is not very reliable. Its calculations are built upon a perfectly rectanglar room, with smooth side walls and ceiling. If you have any unique features such as rounded corners and irregular shapes in your room, then this software can't help you. It also doesn't take into consideration the flexibility of your walls, the air's effect on high frequencies or the material your walls are made of. All of these things can effect the sonic signature of a room. I would suggest hiring a acoustic consultant. Acoustic's are something that cannot just be read about, and applied. You need a high degree of interpretive skill to understand computer assisted acoustic modeling. This particular software cannot give you a complete snapshot of what is happening in your room. Just an estimate, a very rough one at that.
    Terrence
     
  4. Ricardo E Garcia

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    Bob: I have not heard of this device before, I will look into it for possible future use.
    Terrence: I understand that I can't possible gleen all that there is to know about sound from what I read, but I can at the very least learn as much as I can a try to apply that knowledge to minimize (although very slightly, but possibly majorly) problem areas in an HT room that hasn't been built yet.
    Even if there are more factors than I can possibly consider in designing an HT, if I start with a flawed room, then it just gets worse from there. I'm just trying to find dimensions that will minimize problem areas in a room. From what I understand, low frequency waves are more difficult to deal with than higher frequency waves. And also from what I've read, it takes alot more to combat problem areas (nulls and convergance of waves) with lower frequency waves. Where it might take only a few inches of acoustical treatment to deal with higher frequency problems, it could take a few feet of the same treatment to deal with the lower frequency problems.
    Acoustic Engineer in training [​IMG]
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    Rick
     
  5. Richard Greene

    Richard Greene Stunt Coordinator

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    Sorry, but I have to annoy another poster -- many of his statements in this post were wrong ... so I will correct them. Let's get ready ro rumble:
    Bob wrote:
    "You can follow the "Golden Cube" rules to try and avoid standing waves."
    RG responds:
    I don't know what the "Golden Cube" is ... but I do know
    a cubical room is the worst shape for standing waves
    (a spherical room would actually be worse than a cube,
    but who has a spherical room?).
    You must mean the "golden ratio", not "Golden Cube".
    You are also wrong in thinking the golden ratio avoids standing waves.
    It does not avoid or eliminate any standing waves.
    It merely distributes the standing wave frequencies more evenly than many other room dimensions would.
    Bob wrote:
    "But a simpler solution would be a $200 device called the "Behring Feedback Destroyer". It is a programmable filter that will take those particular frequencies and reduce them
    so your walls dont over-emphasize these sounds."
    RG responds:
    The BFD does not eliminate standing waves.
    No equalizer does.
    Standing waves are a time-based acoustic effect caused by listening room reflections.
    At best, an equalizer can reduce output of certain frequencies from your speakers (NOW) that cause standing waves in your room (LATER).
    But there will still be standing waves
    Bob wrote:
    " A heavy bookcase, windows, doors will break up the walls and also break up the frequency response and avoid the standing wave problems. (This is why most combo living/HT rooms dont have standing wave problems. It tends to be an issue only for dedicated theater rooms.)"
    RG responds:
    This statement could not be more wrong.
    Am I sure Bob is wrong?
    I'm so sure I'd bet my entire bonus on it!
    (a $25 gift certificate and a frozen turkey!)
    I have never measured a listening room that had no standing waves. Sometimes only one serious standing wave peak is found -- never zero. There is no location within a home listening room where speakers could be placed that do not excite at least one room mode.
    Bob wrote:
    "I have even seen small, fake columns along walls used in some demo rooms/dedicated media rooms to break up a otherwise "problem-looking" room into smaller sections which eliminate standing waves very nicely."
    RG replies:
    Only in-room sound absorption can eliminate standing waves. Equalizers absorb no sound energy.
    Fake columns absorb no sound energy.
    I'm not sure if it would be possible to break up standing waves by placing many large objects in the listening room
    but I do know that extra diffusion added to a typical home listening room mainly ruins the stereo image (especially if diffussors are placed anywhere near your listening position) because they add more room reflections rather than absorbing sound energy.
    Open doors and windows do allow more sound energy to leave the listening room - so that's an indirect way to reduce bass output. But there will still be reflections and standing waves as long as there are still walls, floors
    and ceilings. If an open door or window happens to be
    near a subwoofer, it acts somewhat like a speaker enclosure tuning port (helmholtz resonator) and severely roughens
    in-room bass frequency response.
    Bob wrote:
    "What I'm trying to say is that you should not mess up your room size over this. Change a foot or two according to the spreadsheet to minimize problems ..."
    RG replies:
    Room dimensions are most important.
    Room size is important too.
    Larger rooms have more even bass energy distribution
    than small rooms.
    The "golden ratio" spread out standing wave frequencies so there are no overlapping modes or adjacent modes
    The classic golden ratio dimensions are:
    1.0x by 1.62x by 2.62x ...
    Other ratios that work include:
    1.0x by 1.6x x 2.33x. and
    1.0x by 1.4x by 1.9x.
    Most important is to have a tall ceiling and a large room -- any room dimension under 15ft. places the associated axial room mode, assuming the mode is 5Hz. wide, right in four-string bass guitar territory (above 40Hz.) where the standing wave will be more often excited by music content than if it was at a frequency well below 40Hz.
    The lower in frequency the axial (usually the most audible room modes) modes are, the less often they
    will be excited by music content.
     
  6. Ricardo E Garcia

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    Richard, thanks for the enlightening and frustrating post.
    Frustrating because my planned area for the HT has 2 dimensions below 15'
    Here's a link to a basic plan for the basement, do you have any suggestions? Click on the picture for an image that looks little better.
    http://members.home.net/rickgarcia/Basement.htm
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    Rick
     

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