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Ceiling Bass Traps

Discussion in 'Acoustics' started by Zing, Sep 29, 2010.

  1. Zing

    Zing Retired Admin Famous

    I've had surplus acoustic panels from my old theater since moving into this new house. They consist of four 2" thick absorbers made with Roxul and four 6" bass traps made with Rockboard 60.

    Not all that long ago, I decided to use two of my four bass traps as first-relection-point panels mostly because they can stand on their own on the floor as I can't mount them on my side walls due to windows and sliding doors. It's not ideal but it gets the job done with noticeable benefits and I can live with it until the room gets remodeled. More recently, I mounted two of the 2" panels on the ceiling's first-reflection-point, again, providing noticeable improvement. So that leaves me with two more 6" traps that I could really stand to use.

    Since moving the sub up front, I began to think that I should mount those two traps on the ceiling but I'm running into difficulties mounting them. I could perservere through these challenges or I could buy something else that won't present these mounting issues. So before I do either, I thought I'd check with you to make sure my efforts (or dollars) will be worthwhile.

    In the crude drawing below, the brown grid represents the beamed ceiling, the red box is the sub, green boxes are the mains and the faint gray rectangles up front represent where and how I'd like to mount these traps.

    My question is whether putting these 6" panels up on the ceiling (with a 3" gap between them and the surface of the ceiling) will offer enough trapping to warrant the troubles. If mounting my particular traps becomes impossible, then I could buy a pair of open-back 4" panels that I know won't present any mounting difficulties.

    Can any of you speculate that I should proceed one way or the other?

  2. jamhead

    jamhead Well-Known Member

    I would mount them at the ceiling/wall corners rather than just the ceiling.

    Are there frames around these panels? Could you use eye hooks?
  3. Zing

    Zing Retired Admin Famous

    I only have about 8-9 inches of depth to play with so I can't corner-mount them. They'll interfere with shelves otherwise. It's got to be parallel with the ceiling or nothing at all.

    No frames, though there could be, which is one of many options I've considered. These traps are made of 3 pieces of 2'x4'x2" Rockboard 60 inside a Ready Acoustics Super Sub bag.
  4. Flint

    Flint "Do you know who I am?" Superstar

    I'd put them as close to a corner as possible and out in the middle of the ceiling.
  5. Zing

    Zing Retired Admin Famous

    Do you mean like this? (I only edited the right side)

  6. Flint

    Flint "Do you know who I am?" Superstar

    Sure --- just butt them up as close to the corner as you can. That's all.
  7. Zing

    Zing Retired Admin Famous

    That's easy enough to do (butting the edges) but I'd still like to know how to categorize this project. Is it merely better than nothing or will it actually do something?
  8. Flint

    Flint "Do you know who I am?" Superstar

    Depending on the surface area of the panels in relation to the surface area of the room's reflective surfaces, it could make a significant difference.

    Any amount of bass trapping will tighten up the sound at least a tad, if not a bunch. The only way to really know is to install them.
  9. Zing

    Zing Retired Admin Famous

    After recently speaking with JWL from Real Traps, I'm posting this chart for reference. Thanks again for your time and input Jim.

    The green trace is the raw response and the yellow is my best attempt to smooth the response using my processor's EQ.

    Attached Files:

  10. JWL

    JWL Member

    With bass trapping in general, there are 2 main parameters to consider: first, is the effectiveness of each individual trap; second, is total coverage area in the room. The more high-quality traps you get into the room, the better the overall sound will be. This is of course an oversimplification to some degree, but it really is true.

    Just getting the traps into the room is probably more than half the battle, however you can definitely optimize performance with good placement. Generally, you want to put the traps in the spots of the room where the biggest bass buildups occur. This is typically in corners, but can also be other places (front and rear walls are very common). I recommend a listening test to find "where the bass lives" in your room to determine best overall placement. Find the places with the biggest bass buildups, and put the traps there where possible.

    Regarding your response curve, that's actually pretty respectable, especially for a room with only 2 bass traps in it. The more traps you can add, the flatter things will get. Make sure you re-calibrate your EQ after you install each round of traps.
  11. Zing

    Zing Retired Admin Famous

    The internal test tones of a processor are pink noise, no? Could I accomplish the same thing by running the sub output's test tone and measuring it at various locations? Or is there something different with and/or better about the test file you linked to?
  12. JWL

    JWL Member

    The test tone that you can download there is pink noise, filtered at 400Hz (ie, everything above 400Hz is filtered out). This allows you to hear the low end buildup more clearly. You can certainly use pink noise, but the high frequencies tend to dominate what you hear, the test tone above sounds more "rumble" than "hiss."
  13. Zing

    Zing Retired Admin Famous

    I have to believe the sub's test tone is filtered, and likely even lower than 400. Maybe it's not pink noise after all but some specific single frequency. I guess I should download that tone just in case.
  14. Zing

    Zing Retired Admin Famous

    So would you characterize that as a null ranging from 35Hz to 95Hz or would you say those are individual peaks at those frequencies?
  15. Rope

    Rope Well-Known Member Famous

    AVIA disc has a subwoofer phase test tone, which I have used to set phase and also find where the bass "lives" in my listening area.

    OC705 work well for trapping low frequencies, especially "super chunking" vertical corners, and horizontal if need be.

  16. JWL

    JWL Member

    Looks to me like nulls centered at 45Hz, 75Hz, 175Hz, and 300Hz, with a peak at 95Hz. However I wouldn't worry too much about attacking each individual problematic frequency; all of these will be improved as you add bass traps (the entire frequency response of the room is flattened as you add traps).
  17. JWL

    JWL Member

    Test tones can be useful (ie, individual frequencies), but sometimes nulls and peaks can be very close together. For instance, you could have a +12dB peak at, say, 58Hz, and a -12dB null at, say, 62Hz. If you have a 60Hz test tone, it will be somewhat difficult to hear what's going on. This is why I prefer to use filtered pink noise, which excites all frequencies (below 400Hz) equally.

    Of course, even better is to measure the room with software, that will give you by far the most information.
  18. JWL

    JWL Member

    There is no question 705 works well for bass trapping in general, though other materials are generally more cost-effective. For instance, 703 performs similarly and is often about half the cost of 705. In some regions, rockwool is significantly cheaper and performs reasonably well.

    The main benefit of 705 relative to these other materials is that it is stiffer and holds up better over time (rockwool tends to flake and/or sag over time).

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