Muddy EBS Shiva sub

Discussion in 'Archived Threads 2001-2004' started by Jack*Mains, Dec 3, 2002.

  1. Jack*Mains

    Jack*Mains Stunt Coordinator

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    Hey everyone. I've just finished building an EBS allignment shiva and while im generally pleased with the results, there are a few things I would like to ask.

    It seems that the bass is a little muddy, or boomy. Im using an AVA250 plate amp with the crossover set to just over 60H. The signal im feeding it is not coming from a sub out on the receiver, but instead from the pre outs on 2 channel stereo as im using this sub purely for music. Im wondering if this could be the main cause?

    The box turned out extremely sturdy as ive made it out of MDF and glued/screwed together the final product. The thing im worried about, is I lined the walls with polyfill sheets and wondering if that could the degrade the quality of the sound.


    On a related topic, I tried wiring the sub voice coils in parallel for a net result of 4Ohms, but found that simply hooking up one voice coil for 8 Ohms seems to yield better results. Not in terms of loudness, but in quality. Again, is it just me, or could there be a reason for this?


    Any thoughts are welcome.
     
  2. for a well built sub...
    mud and boom
    is usually the room
    [​IMG]
     
  3. Jack*Mains

    Jack*Mains Stunt Coordinator

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    Heh, may be true.
    I tried many places though, and I get 'generally' the same results. Some spots are definitely better then other, but even the best spots aren't too stunning.
    I popped open the top and got rid of the polyfill lining, and that seemed to make it less muddy and more tight. I think its well withing the acceptable range, but is there anything else I should consider.
    Here is an image of the lower floor plan of my house. THe green area is the home theater room, the red is an open wet bar area, and yellow are the sub placements i've tried. I think the rest is pretty self explanatory. All dimensions are in millimeters.
    The floor plan is to scale, but the 'equipment' is probably not, as I've just added it.Placement
    http://www.vi2.com/uploader.php?n=39814
    For some reason simply clicking the link doesnt work for me. If it doesnt for you, just copy and paste the URL into the browser, might have to refresh too.
    Cheers.
     
  4. Isaac C

    Isaac C Stunt Coordinator

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    Also, it could just be psychoacoustics at play. Try to apply a 30Hz subsonic filter and see if it still sounds boomy. The presence of really low bass frequencies is often mistaken for 'muddyness.' [​IMG]
     
  5. Stephen Dodds

    Stephen Dodds Second Unit

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    I'd try the room. Do a test sweep or test tones and check the results. I suspect a Behringer Feedback might be in your future.

    Steve
     
  6. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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    If you room is anything like mine then try NOT corner loading the sub. I have a 122L sealed tempest used 80% to 90% for music. I have to place the sub along a long wall to keep it from being boomy. Here are some pictures of my room.
    [​IMG]
    The sub is between me and the white directors chair.
    If I corner load the sub like below, the boomy pressure is out of control.
    [​IMG]
    From this picture, the sub is now directly right of the right speaker. I am standing behind the couch you see in the first picture.
    I also built 2 ASC clone tube traps. You can see one almost completed in the first picture. They did not correct any of my peaks or valleys but they sure did wonders on cleaning up the mud. [​IMG]
    Ronnie
     
  7. Brian D B

    Brian D B Auditioning

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    Muddy bass can be caused by an enclosure that is too big. Try putting something in the enclosre to take up some air space and see it that makes any difference.
     
  8. Lewis Besze

    Lewis Besze Producer

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    Well I have both, 2 big subs in the same corner,and with the aid of BFD it's anything but boomy.It' is true though that I had to attenuate @46hz by 10db,so without the BFD it could be boomy.
    Any DIY'er should have a BFD IMO.
     
  9. Jack*Mains

    Jack*Mains Stunt Coordinator

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    I've built the box to Adire's EBS specs and used plywood for the baffle instead of MDF for extra strength. THe whole box is glued / screwed down, except for the top which is just help on my many screws in case I need to make any modifications. Im fairly sure there are no air leaks and the top does not vibrate against the rest of the cabinet.

    Another thing is that at relitively high volumes, the sub seems to distort. It doesnt sound like bottoming, but rather like overloading or something. I do not have an SPL meter at the moment, so I cant say exacly what volumes this happens at, but it doesnt seem to be teribly high.

    Going from single voice coil, to dual in parallel did not seem to make a difference.

    Also, there doesnt seem to be a whole lot of air moving through the port. Im wondering if this could be due to the fact that the port is too close to the back wall. It's the way is was in the blue prints, but it just doest seem right, its almost touching it.

    Thats about it for now, thanks for all the thoughts.


    Almost forgot.. what exacly is a BFD?
     
  10. Ronnie Ferrell

    Ronnie Ferrell Second Unit

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  11. Rory Buszka

    Rory Buszka Supporting Actor

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    EBS alignments use a larger box and trade that extra volume for some tightness. If the suspension of the driver is more optimized for a mid-size sealed or ported box, then putting it in a larger ported box will make it a bit more flabby.

    correct me if I'm wrong, I'm not completely sure about this.
     
  12. Michael R Price

    Michael R Price Screenwriter

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    I don't think the EBS alignment compromises group delay except at the very lowest frequencies where they probably don't matter. Sure, the extra low bass will probably hang around in your room which is part of the reason why "fast" bass tends to be rolled off early. If you have a correctly built/tuned box, and your amp has no EQ getting in the way, the sub should not sound boomy by itself. I would try running a nearfield sweep and seeing if the response shows any anomalies. Do you have a guess as to what frequencies the boominess occurs at?

    Your distortion may be in the form of a hidden air leak... it may be the amp clipping... or, it is something in your room rattling. (This "distortion" happens to me and I don't even have a subwoofer.)
     
  13. Jack*Mains

    Jack*Mains Stunt Coordinator

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    I was just wondering, how critical are small air leaks in regards to performance and quality?

    I will glue the top on if theyre quite critical to make sure i've eliminated everything. Otherwise, its quite convenient to have a removable top while it's still in the testing stages.

    Do you think building an SBB4 allignment might improve the boominess?

    THanks again.
     
  14. Mark_E_Smith

    Mark_E_Smith Second Unit

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    What kind of plywood did you use? It might be resonating or moving. Also the port must have at least 3 inches (or more if dia of port is larger) spacing from the back wall other wise the port wont work and you will have a very leaky sealed sub.
     
  15. Jack*Mains

    Jack*Mains Stunt Coordinator

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    Mark, this might be the problem, the port is only about 1/2" from the back wall. Actually, the port itself is about 3" away, but the flared part is a lot closer.

    Thats the way it was in Adire's plans, so I assumed that would work..
     
  16. Mark_E_Smith

    Mark_E_Smith Second Unit

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    Jack I looked at the Adire site and I think I misunderstood you. If your tube is 12" long, the side of the port is close to the back of the baffle and you will have 8" of clearance for the port to work. Should be OK. What kind of plywood did you use? Most standard plywood is unacceptable for subwoofer apps or speakers for that matter. If you knock on the case with your knuckes does it sound like a drum (hollow)or like a solid piece of wood?
     
  17. Jack Gilvey

    Jack Gilvey Producer

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    I don't think the boominess you're experiencing is a property of the sub itself. I built the same Shiva alignment (not as in the plans, though, my own dimensions) and am using the same amp. It's anything but boomy, going exceptionally deep while maintaining great composure.
     
  18. Jack*Mains

    Jack*Mains Stunt Coordinator

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    Mark,

    it sound somewhat hollow if I knock knock on it. A lot like my mains sound if I knock on them, which are built by JBL.

    If I know on the bottom baffle it sounds a bit more like a solid piece of wood. If would be rather hard to replace the bottom baffle at this point as it is already glued. THe ply wood I used is your regular 3/4" thick birch layered stuff. I was told that plywood would work better for the baffle because of the extra strength.

    Would it help to get another piece of MDF and glue it to the bottom of the current plywood baffle?

    Also, I didnt use spikes, just pieces of 2x2" that I cut to 3 1/2"

    Thanks again.
     
  19. Mark_E_Smith

    Mark_E_Smith Second Unit

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    You could try gluing the MDF to the Birch. You want it to sound like a piece of wood, hollow means it is resonating. Was the plywood Baltic Birch? Did it have 13 laminations? BB is OK for speaker building, but IMHO and I will yield to anyone like Jack Gilvey on anything about subwoofers, you want a HEAVY enclosure. All things have a resonate frequency, the heavier the lower, it might be that with the birch plywood you are lighter than the MDF design and it might have a resonant frequency in the listening range.
     
  20. Jack*Mains

    Jack*Mains Stunt Coordinator

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    That may be true, but only the bottom baffle is plywood. Im pretty sure its BB, but only 7 laminations. It weight just as much as MDF though.

    Heavy? If the quality of the sub was based solely on the weight, I would have the best sounding sub on the planet. This thing is at least 150 pounds.
     

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