Sound question

Discussion in 'Archived Threads 2001-2004' started by Joe McCabe, Nov 13, 2001.

  1. Joe McCabe

    Joe McCabe Second Unit

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    I am in the process of having a dedicated room built, and have some questions about whether my plans will effect the sound from the speakers.
    I am having my speakers built into the wall, and the wall will then be covered in black fabric. Is there a certain amount of space that will be needed around the speakers? (i.e. drywall opening)
    How, will this effect my sound??
    Thanks in advance for any advice!
     
  2. Mike LS

    Mike LS Supporting Actor

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    I guess the answer here depends on what type of speakers you're using for this.
    Are you using in-wall speakers? Or are you just having regular speakers recessed into the wall?
    If you're using regular speakers, you may well have problems with them being cased into the wall.
    Speakers need open space on all sides in order to function properly. That's why most would suggest that you have your speakers at least a foot or so from any walls.
    Another thing with having them in the walls is that it can (and probably will) affect the imaging in the room. You speakers need to be even, or more preferrably several inches in front of your display screen. Having them behind the screen may affect that.
     
  3. Neil Joseph

    Neil Joseph Lead Actor

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    I imagine that if you create a space bigger than the speaker is so that there is a foot space in the back as well as both sides, that you may see some bass boost as well. Let us know what kind of speakers they are and how low they go.
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  4. Mac F

    Mac F Agent

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    This brings up two different questions. Any speaker set close to the wall will excite more room nodes than the same speaker pulled a little into the room. This will emphasize some frequencies more than others, and give an uneven frequency response to the whole room. How bad this might be will be determined by the dimensions of the room.
    The other problem is diffraction of sound waves. As sound spreads out from the speaker cone, it will diffract around any edges, toward the sides of the speaker. Sound will then strike the room wall and bounce back to the listening area. Because this is a slightly longer path, it will arrive a little later than the original wave front, but not so late as to appear as a second sound. The result is that the sound is smeared slightly, which will affect the imaging properties of the system. If we weren't concerned about imaging from speakers, we would be better off with a mono system.
    If you look at older speakers, from the 1960 & 70's, the large full range speakers, they almost always had a broad front surface and were shallow front to back. This made them look better in the average home. If you look at many of the recently designed high end speakers, they will be narrow from side to side and much deeper front to back. This will minimize the diffraction as much as possible. The ultimate in a broad surface is the in wall speaker, where the entire wall acts as the baffle. A number of audiophiles even remove the speaker grill to minimize diffraction. I haven't gotten this fanatic yet, but I'm working on it.
     
  5. Joe McCabe

    Joe McCabe Second Unit

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    My speakers are all (Center, Fronts, Rears and Sub) Mirage FRX if that helps.
    Maybe I should go into a little more detail.
    When I say built into the wall, I don't mean it in the way that immediately comes to mind.
    With the speakers, I am also having my TW65H80 recessed into the wall so only the screen will be visible.
    Now, the otherside of the wall will be opened so I can get behind the TV if I need to change any cables or anything.
    So, the speakers will also be opened up on the otherside too.
    The contractor and I were thinking that if we left enough space around the speakers, that it wouldn't cause the sound to be comprimised, and that maybe the "space" behind the drywall and the actual outer wall would possibly help the sound.
    Is that wrong??
     
  6. Mac F

    Mac F Agent

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    first of all, I like your idea of access through the wall. I had a friend who did that for his stereo years ago, and I have been jealous ever since. This became much worse after I graduated to bifocals, and find it difficult to read labels on component backs.
    Will it affect the sound? yes. Will it matter? don't know.
    Unless your contractor has special knowledge about audio, I wouldn't put much faith in his opinions. For example, an amateur photographer will immediately notice problems with lighting, poses, etc. while normal people will be quite content with their kids snapshots.
    The real question is if it will detract from your enjoyment. The problem with room nodes is with base frequencies, and will be determined by the front to back length of the theater. The problem with diffraction will be higher frequencies. This can have some effect on the sound imaging. If your primary interest is in movies, this won't be quite as critical because the screen gives you visual clues to localize the sound sources. It becomes more important if you are interested in music. Much popular music is recorded on multi-channel recorders and mixed down to make the commercial CD. Most of the stereo imaging is fake, but we still like it because we enjoy the music itself. If your primary enjoyment is to sit back, close your eyes and point to places on the sound stage and say the violin is here, the flute is there, stereo imaging is extremely important. There are more audiophiles who do this than most people would guess. Where the line is between acceptable and unacceptable is determined by the final user.
    As an experiment to do now: set up your system as a two channel stereo in a comparable sized room and put on some of your favorite music. Walk around the room and listen for differences due to your location. Move the speakers against the wall and repeat. Move them about two feet into the room and repeat. Put them in the corners. Did you notice any difference. If you can't hear the difference, them put them where they look best. If you do hear a difference, will it annoy you forever if it is not fixed?
    Some experts minimize reflections from behind the speakers with sound absorbing material across the entire front wall. This approach is called Live End Dead End. I've read that many recording studios are set up this way. The only one I've ever been inside was not. As a compromise, you might put fiberglass around the speakers mounted into the wall.
    I hope this helps some, there is no exact answer here. No matter what you do, there is some compromise involved.
     

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