Damping a cab...

Discussion in 'Amps and Cabs' started by KBN, Feb 29, 2008.

  1. KBN

    KBN Member

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    I just picked up a Mojo marshall style over sized 2x12 with a closed back and it is a little too resonant for me. It is a good sounding cab, but I am playing hard rock so I am looking at adding some damping to the cab. What is the best thing to use and how much should I do? All sides? A couple? I don't know a whole lot about cabs so any help you could give me would be really appreciated.
     
  2. bosstone

    bosstone Member

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    You can cut a 2 X 4" to fit between the speakers on the front baffle and rear baffle and put screws in from both baffles. This is done all the time on many cabinets, especially 4 X 12" cabs.
     
  3. cram

    cram Member

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    I think the drill is to fill two sides of it like an L with a fluffy substance. I picked up cotton fabric for a 2x12 and started off by lining a thin layer of it all the way around, but it didn't do much. I posted the process here and then someone mentioned the L shape.

    I then rolled up a bunch of it and secured it down with staple and wire on two sides (bottom and right). Much better.

    As I apply this to all I am learning about room acoustics, this is similar to a bass trap where you'd stack rigid fiber board triangles in a corner from floor to ceiling with a fabric facing to keep them in one place - the low frequencies will build up in corners of a room and make it sound boomy.

    I'm sure there's some sort of parallel there.
     
  4. danel59

    danel59 Member

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    Andy Fuchs uses the material for carpet backing, or used to, and applies it to all of the sides. Not sure about now though
     
  5. rockon1

    rockon1 Member

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    I recently stuffed my oversized Lopo 2x12. Love it! The bass is tighter. The mids are more accurate and the highs are slighly dampened-in a good way. Went to a local upholstery place anf bought a big sheet of 3 in thick poly batting.(looks like fiberglass batting but obviously non irritating !) I puffed it up a bit and filled the entire box with it but not too tightly. Supposedly this gives the drivers the illusion of a larger box but with more dampening. I can crank the bass with zero flubbing too. Im using a G12H-30 and G12-65 in the cab. Again Im really digging the results. Bob
     
  6. doc

    doc Member

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    You might try some Acoustistuff from Parts Express.
     
  7. Fuchsaudio

    Fuchsaudio Member

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    Adding carpet backing or cotton sheets to a box controls resonance and fools the drivers into thinking they have more virtual cabinet volume (particularly in a closed box). Cheap, easy to install (just takes a staple gun), and you can tune to taste. One side, two sides, etc, add until you are happy.
     
  8. rockon1

    rockon1 Member

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    Much cheaper at an uphoslstery store. Was going to get if from PE but the price was too much. The place I went to had both but I opted for the batting so I didnt stuff the back of my speakers! Of coarse if a upholstery store isnt available PE is definately a good choice.


    http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-330

    ..
     
  9. KBN

    KBN Member

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    How about the suggestion of adding the post like most 4x12 cabinets have? What exactly is the purpose and how would that change the tone? Thanks for all the help so far and thank you for bearing with my questions. Only recently have I discovered how much tone comes from the cabinet itself (as opposed to just being there to hold the speakers and having something to set the amp head on... :) ) and I don't know much about cabinet design and how design aspects change tone.
     
  10. rockon1

    rockon1 Member

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    Might help a tiny bit. Try stuffing the cab. Its easy,'tuneable" and easily reversed if you dont like it! Bob
     
  11. bosstone

    bosstone Member

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    The cab works somewhat like a drum, with the front and back panels flexing slightly in and out. If you brace them together you will dampen much of the cab's resonance. The side are comparatively more subject to tension than beam forces and not as susceptible to flexing. Adding a baffle to baffle brace in my large, detuned single 12", cab, made of 3/4" voidless Balti ply made significant difference.
     
  12. KBN

    KBN Member

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    Very cool. I think I will try that along with a little bit of foam. What did you use to brace it? 2x2? 2x4?
     
  13. bosstone

    bosstone Member

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    I used a common old 2 X 4". It took several skim cuts on the end of the 2 X 4" to get the length exactly right. I would suggest using only method at a time to see dial in the effect you want. Either method can be removed.
     
  14. rockon1

    rockon1 Member

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    Theres a big difference between acoustic dampening material, foam and even lining the cab with dampening material. Ive tried all of them. Lining the cab deadened it but thats all it seems.I didnt like it that much. Ripped it out almost immediately.By far (so far) the best (for my ears) is acoustic stuffing. I literally filled the cab with it. Like Fuchsaudio mentioned it "virtually" increases the internal volume while also deadening it. I'd recommend trying both and seeing. I gave up on acoustic lining and such until I recntly tried the stuffing method instead.
    :BEERBob
     
  15. ancient

    ancient Member

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    Does dampening a cab's resonance create more or less bass?

    I recently purchased an oversized 2x12 closed back and even at low volume levels (with the bass rolled all the way off) it still seems to carry through out the building :confused:

    Is the solution to stuff, add lining and a brace btw the baffels?
     
  16. rockon1

    rockon1 Member

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    Stuff it. It reduces bass a bit but also makes it more accurate-less boomy and flubby. If you dont like it experiment with just lining it . Bob
     
  17. cram

    cram Member

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    loaded question - think of the linear wave example of a frequency. Highs have a short wavelength while low end has a long one. When these waves reflect back upon each other they can create a NULL all the way to nearly creating a doubling effect. It's more prevalent in low frequencies for our ears because the wavelength is longer.

    So the reflective sound is cancelled out and we're left with a tighter sounding cab.

    This thread's got me thinking about trying a cab completely stuffed with material... Hadn't done this yet. I guess I thought it best to have two sides reflective.
     
  18. Tone_Terrific

    Tone_Terrific Member

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    The classic formula for cab damping is adding the damping material to the back and 1 of each parallel sides. I agree that it does make a difference but you may not like it. Try any and all methods if you want.
    Reinforcing the back or sides is a diffeent issue, but worth doing if the cab has floppy panels.
     
  19. KBN

    KBN Member

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    So I took the cab apart this afternoon and added a brace from the middle of front baffle to the back panel. I used a 2x2. I also added 2 inches of polyester batting to the back panel. Made a significant difference and much more to my liking. I have the cab wired for 16 ohms and the only amp I have at the house right now that has 16 ohm output is my modded Valve Jr, but tomorrow I will take the cab with me to rehearsal and will hook it up to my Reeves 50 and really give it a go. Thanks for all the help guys.

    Keith
     

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