Bass Traps again

Discussion in 'Home Theater Projects' started by Jack*Mains, Aug 1, 2005.

  1. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Hey everyone,
    Im having some time off work and I would like to acousticly treat my room while I have some spare time.

    I've been looking around but failed to find any definitive guides on how to build a good bass trap.
    What I find sometimes is that my sub is working like mad, and the whole house is shaking, but you hear surprisingly little at listening position.

    I found the best position for a sub, but it stil seems not enough.

    I was looking to build a bunch of bass traps and throw them in every corner of the room to experiment, but so far did not find any guides on how to do so.

    Could someone please point me in the right direction?
     
  2. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
  3. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Aren't nulls caused by destructive interference with the reflecting waves? The bass trap should eliminate the reflected waves and eliminate the nulls.

    From my understanding at least.
     
  4. Mattak

    Mattak Stunt Coordinator

    Joined:
    Dec 15, 2003
    Messages:
    247
    Likes Received:
    0
    May I ask how you found the best position for the sub? One method I've heard of is to place the sub at listening position and then go around the room to find out where it's loudest, then put the sub there...
     
  5. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Thats exactly what I attempted to do [​IMG]
    The only problem is the sub is a 142L Shiva and the thing weights about 100pounds, and measured 25" on each side of the cube box.

    This makes placement options rather limited.
    I found the best places out of the possible locations and left it there. It happens to be the corner behind the front left speaker.
     
  6. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Any thoughts on whether this will actually help out my problem?
     
  7. MikeGee

    MikeGee Second Unit

    Joined:
    Dec 11, 2004
    Messages:
    291
    Likes Received:
    1
    I'm curious to know if that will help you out as well. I am going to be helping my brother design his basement next month and if these DIY bass traps are that effective i'll make sure we build several of them.
     
  8. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    I guess Im just going to have to build a few.

    Question:
    Will the panels be effective for lower frequencies, or do I have to build those huge round traps and put them into the corners of the room if I want to have any effect on the lower end?
     
  9. glenn.k

    glenn.k Auditioning

    Joined:
    Jun 29, 2005
    Messages:
    4
    Likes Received:
    0
    Hey guys,

    Jack your on the right track. If building you want to use 4" rigid fiberglass. Start with straddling them in corners the work around the room. I have found that most rooms need between 8 to 10. But if your low on money 6 is not bad either. Every room needs bass traps to really get a clear bass sound.


    Glenn
    GIK Acoustics
     
  10. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Interesting...
    I just finished reading everything on Jon's website about bass traps, but I still have a few questions.

    #1, Due to my room shape and placement, I would not be able to put bass traps in the front corners of the room. Maybe I can manage to fit a panel into the corners, but not a 16" cylinder. I can still, however, put traps into the back corners. Would this still be effective, or a waste of time?

    #2, If I do make traps for the back two corners, I can make them the full height of the room, 8' Would this be better then the 4' versions described, or would it have negative effects on performance?

    Please take a look at pictures of my room here, so you will understand what I am talking about

    http://crazydemon.no-ip.com/photo/th...ls.php?album=8
    EDIT: I just took this picture to give you a better idea of the shape of the room. It is taken from the front left corner (where the sub is) looking back at the room.
    http://crazydemon.no-ip.com/back3.jpg
    Thanks again.
     
  11. David_Rivshin

    David_Rivshin Second Unit

    Joined:
    Dec 13, 2001
    Messages:
    352
    Likes Received:
    0
    I'm about to build myself a low frequency resonant absorber. I figure it's an easier build than a hemholtz resonator, and pretty inexpensive, so I can experiment around without worry. So here is the basic plan:

    1) a 2'x4' box made out of cheap 1x4 pine boards
    2) 2'x4' sheet of 3/4" MDF, attached in the obvious way to the box
    3) lay the finished 5 sided box on the floor, open side down (to create the last side) and some R13 fiberglass stuffed under it, tweaked to get the right effect

    Since I can easily get 2'x4' MDF sheets, and 1x4x4' pine boards easily, the only cuts I need to make are to turn a 4' 1x4 into a pair of 22.5" boards. Then it's just a matter of screwing it all together. Wood cost is about $12 (with tax) for me, plus some fiberglass and screws.

    The theory goes as such (straight from Master Handbook of Acoustics): The resonant frequency of such a box will be about 170/sqrt(surface_density(lb/ft^2) * airspace(inches))
    Since the surface density of 3/4" MDF is about 2.75 lb/ft^2, and the airspace will be about 3.5", the result is a resonant frequency of about 55Hz. It's actually good that it's abit high, because when I add the fiberglass the resonant frequency should drop abit, hopefully landing around the 36Hz I need, and the absorbtion should be amplified. Or so the theory goes. Hopefully I'll see some fruits from this in the next few days to see how well theory matches reality.

    (Note, that an alternative form would be 1x6 boards, and 1/2" MDF, which gives a theoretical resonant frequency of about 53.5Hz, and more room for fiberglass).

    -- Dave
     
  12. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Cool, let me know how those work out for you.

    Right now I am thinking of putting 2 bass traps behind the listening position. and a whole bunch of panels in front.
     
  13. glenn.k

    glenn.k Auditioning

    Joined:
    Jun 29, 2005
    Messages:
    4
    Likes Received:
    0
    #1, Due to my room shape and placement, I would not be able to put bass traps in the front corners of the room. Maybe I can manage to fit a panel into the corners, but not a 16" cylinder. I can still, however, put traps into the back corners. Would this still be effective, or a waste of time?

    yes putting them in the back corner is fine. Actually I like them on the back wall if you have the room also. If not in corners just make sure you space them off the wall.

    #2, If I do make traps for the back two corners, I can make them the full height of the room, 8' Would this be better then the 4' versions described, or would it have negative effects on performance?

    If you can put a space between them. The sides/tops of the panel (if like ours) is absorbing sound also.

    Glenn
    GIK Acoustics.com
     
  14. Jack*Mains

    Jack*Mains Stunt Coordinator

    Joined:
    Sep 25, 2002
    Messages:
    156
    Likes Received:
    0
    Thanks a lot glenn, thats pretty much what I needed to hear
     
  15. Kevin Deacon

    Kevin Deacon Second Unit

    Joined:
    Dec 18, 2001
    Messages:
    324
    Likes Received:
    0
    Before building something that is questionable, try just buying the packages of fiberglass that are about 3 feet high when stood on end in white plastic. Stack 3 of these in the corners and listen. You will be amazed at the difference in focused bass concerning the soundstage. Jon Risch calls this the quick and dirty bass trap. Mine are in the front corners. If you can't put them in the front then your bass will still echo from the front.

    http://www.geocities.com/jonrisch/a.htm

    Sounds like you definately have some null issues. You may want to pick up the Behringer Feedback Destroyer so you can equalize all the bass freqs. My subwoofer sounded real bad before I BFD'd it.

    good luck.
     
  16. glenn.k

    glenn.k Auditioning

    Joined:
    Jun 29, 2005
    Messages:
    4
    Likes Received:
    0
    Kevin is right that works darn well also. I tell people all the time if they have closet off to the side to put rolls of fiberglass.

    Glenn
    GIK Acoustics
     
  17. Tony Loewen

    Tony Loewen Stunt Coordinator

    Joined:
    Nov 21, 2003
    Messages:
    134
    Likes Received:
    0
  18. Tony Loewen

    Tony Loewen Stunt Coordinator

    Joined:
    Nov 21, 2003
    Messages:
    134
    Likes Received:
    0
    Oh, and decent bass trapping will help smooth out a null, maybe not eliminate it completely, but it will go a long way.
     
  19. glenn.k

    glenn.k Auditioning

    Joined:
    Jun 29, 2005
    Messages:
    4
    Likes Received:
    0
    Tony,
    I tell people all the time "Before you go buy that dream ______________
     

Share This Page