Is it possible to 'tune' a sealed sonosub?

Discussion in 'Archived Threads 2001-2004' started by Ron-P, Apr 17, 2002.

  1. Ron-P

    Ron-P Producer

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    I've had my Tempest sonosub up and running for a week now. It is a 177L sealed enclosure (20"x34.5" inside). My fears have been realize, it is too big, I think. My room size is 10x12x8. The bass is very nice at times, but not as tight as my Velodyne CT-120 was. I am also running into a bad peek at around 40-45Hz upwards of 10+dbs. Because of this, I need to keep the amp turned down. I've played with locations, volumes and X-over settings and have it set pretty decently, but I would think I can do better.
    What I wanted was tight, fast bass with a good solid punch. What I am getting, it seems, is slower boomy type bass. It does out preform my Velo, but not to the extent I was expecting.
    It has been suggested to try and shrink the inside volume of the tube by putting phone books and such inside to try and tune it. Also, it was said by doing this it might help with the peek at the 40Hz location. I have it wired to an MCM 250 plate amp.
    Any help on taming this beast would be helpful. Or, should I try and port it from the top, would this help?
    Peace Out~[​IMG]
     
  2. Patrick Sun

    Patrick Sun Moderator
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    You should try killing that bass boost on the amp.
     
  3. Ron-P

    Ron-P Producer

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    Before I attempt that, would it be possible to use an old 2-channel receiver and run the sub off that to see how it would preform? Good idea or not?
    Peace Out~[​IMG]
     
  4. Patrick Sun

    Patrick Sun Moderator
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    It can't hurt.
     
  5. ThomasW

    ThomasW Cinematographer

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    Ron

    Sealed subs are tuned to a specific frequency.

    There are major placement issues or air leaks, if the Tempest isn't blowing the old sub into the weeds.

    BTW, why are you using such a low XO point. Try 75-85Hz

    Don't make the box smaller.......
     
  6. Cam S

    Cam S Screenwriter

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    My guess is that the sub has an air leak somewhere, and the fact that the MCM amp has bass boost.

    I have my Shiva in a 1.5 cuft box outta my car untill I build my ported box, and I have the tightest most unbelievable bass I have ever heard. It's seriously better than my $400 Eclipse sub, and $700 Eclipse amp that I had in this box and in my car. God I love this stuff!
     
  7. jeff lam

    jeff lam Screenwriter

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    The larger sealed enclosure should provide the tightest sound (low Q of about .577) What was the internal volume again? Did you stuff it with polyfil? I agree that the tempest should best the velo probably 5-10 fold!

    Like Pat said, get rid of the boost. Play with the placement. Check for leaks.
     
  8. Ron-P

    Ron-P Producer

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    I am sure there are no air leaks. Everything is sealed very well with caulking.
    I'm willing to bet that my problem is going to come down to room acoustics. The sub does really well at certain frequencies. When I hit that 40Hz peek, that is where it turns into more noise than bass. Once below 40Hz it works great. But, because of that peek, I have the amp only turned up 1/4 of the way.
    It does beat the Velo, there is no question. It's that 40Hz secton that seems to be the problem and the reason I have the amp turned low.
    177L with about .50" of polyfill around the inside of the tube.
    Peace Out~[​IMG]
     
  9. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Ron,

    I had the same problem with the same sub. The solution is a BFD.
     
  10. ThomasW

    ThomasW Cinematographer

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    Ron

    Try adjusting the amount of poly. Add fill 1/2lb or so at a time until you hear the bass stop getting tighter, and only the efficiency drops. At that point back off to the previous amount of poly.

    Check for air leaks around the driver.

    EDIT: Ron you only lined the sub?. That's for a ported design, not a sealed one. No wonder it booms

    Fill the tube with poly at a rate of 0.5-1.5lb/cu ft
     
  11. jeff lam

    jeff lam Screenwriter

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    177L is a little over 6 ft^3. I would say you need roughly 6 lbs of polyfill (isn't that the standard for sealed boxes...1 lb for every ft^3?) The BFD should also help with taming any peeks in your room.

    Did you have these peeks with the velo also? You should have if it is room induced. If not, it's gotta be that bass boost.
     
  12. Ron-P

    Ron-P Producer

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  13. jeff lam

    jeff lam Screenwriter

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    I don't think the lining matters. My sonosub is ported and I just stuffed it per Dan's recommendation. I specifically asked him about this if I had to line the wall with batting since it was ported or glue the polyfill to the sides and he said "No, just stuff the polyfill in there", and it was OK if it sits right on the back of the driver.

    So, Lining... stuffing, I don't think it really matters.
     
  14. Ron-P

    Ron-P Producer

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    I figure I've only got about 1-2lbs in. So I'll add another 4 tonight and hear what happens.
    I just got off the phone with Brian at Adire on my sub. He suggested to;
    1) Remove the sub from the corner because it is already too big for the room. Corner loading it is one likely cause for the 40Hz peek. Moving it away from a corner is almost impossible because I do not have an open space against just one wall.
    2) Remove the bass boost. He said on their amps they do not remove the bass boost but rather piggy-back it with another resister...anyone know about doing it this way. Much easier it seems.
    Well, I'll take this one step at a time and hopefully I can get this thing fully operational. Hopefully the poly-fill will help.
    Peace Out~[​IMG]
     
  15. ThomasW

    ThomasW Cinematographer

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    jeff
    A picture's worth a thousand words
    This is a lined sub
    [​IMG]
    This is a stuffed sub
    [​IMG]
    And yes Virginia there is a difference in how they sound
     
  16. JonWB

    JonWB Agent

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    You might want to review the information on this link regarding the amount of fill to put in you box (tube). There appears to be a sweat spot that varies a bit depending on the physical volume of your box.
    I'm not positive, but I'd figure that Adire simply adds in parallel the correctly rated resistor for no boost. That way they don't have to deal with de-soldering and then "re-"soldering. Don't ask me what amount of resistance you'd want to add to the existing resistors to get you to that end. Maybe one of the guys here that are a bit more electrically inclined could help with that one.
    Good Luck,
    Jon
     
  17. jeff lam

    jeff lam Screenwriter

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    TW,
    I think you maybe missunderstood my post. What I was saying is:
    My design calls for 4lbs of polyfill. It doesn't matter if the 4 lbs is stuffed or lined, glued to the walls. Of course a 1" lined sub (2 lbs) will sound different than a 4 lb stuffed sub everything else being the same.
    I just stated that Dan Wiggins told me I didn't have to line the tube but to just stuff the polyfill in there.
    and needless to say... I'll take his word for it![​IMG]
     
  18. Richard Greene

    Richard Greene Stunt Coordinator

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    Polyfill and other "velocity absorbers" such as fiberglass and foam work best in high velocity zones such as the center of an enclosure or the center of a room.

    They are considerably less effective when attached to walls of enclosures or rooms.

    The main reson you line the walls of a ported enclosure rather than stuffing it with polyfill is that lining the walls will barely affect the port tuning frequency while stuffing the enclosure will change the port tuning frequency ... and a lot of stuffing will also reduce port efficiency.
     

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