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DIY Subwoofer, Is stuffing needed?

Discussion in 'DIY Speaker & Subwoofer Building' started by Kornmong, Jul 13, 2005.

  1. Kornmong

    Kornmong
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    Im doing a DIY subwoofer and have nearly completed it, just doing touch ups.

    Today I bought some spikey foam that looks like egg holders, Im going to put this on all the walls of the sub (inside)

    will this improve low frequency extension, quality of sound, stop tinny noises and just be better with it in?

    Is it proven that stuffing will help?

    Thanks
     
  2. Nimby

    Nimby
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    You usually only stuff a closed box (so called infinite baffle) with loose fill fibre. This may be in addition to wall-fixed fibre or foam.

    A reflex box will be better for a 1" lining on the inside walls only.

    I tended to concentrate on the wall behind the driver in my DIY subs and speakers using thick car sound absorption felt to soak up any direct reflections. On the rest of the walls I just used 1" polyester fibre.

    I really haven't a clue how well your foam will work unless it is designed for the purpose. It will aborb high frequencies. But subs aren't usually fed high frequencies unless they are passive and fed a full-range signal.

    Bandpass subs tend to be used this way because they roll-off acoustically either side of the power band reducing the need for crossovers. But they still benefit from sound absorbent felt/fibre inside to kill unwanted mid range output from the port(s).

    Nimby
     
  3. Barend

    Barend
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    My REL Q150E has no stuffing at all and still sounds good...
     
  4. Nimby

    Nimby
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    Stuffing a closed box loudspeaker lightly with sound absorbent material fools the box into thinking it is slightly larger. This means lower compression on the back of the cone. Theoretically providing marginally improved bass.

    Something to do with heat generated by friction within the fibrous materials most often used (?) I've forgotten the exact details as it was years ago when I last read anything on the subject in a hifi mag. Someone here is bound to know more given a good nudge.

    In fact some sound absorbent foams are now claimed to be "adiabatic". It used to be long fibre wool in the last century.

    Nimby
     
  5. Barend

    Barend
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    Nimby,
    I think I'll have a go at trying this on my REL, maybe it helps a bit on my nightmarish room mode too...
    Darned 70Hz (and 35Hz, bit less) makes me crazy, even tried a DSP based equalizer, problem is the frequency and notch shifts a bit when I move to and fro, even when I nudge my head...
    Room is 4x4x4 metres, normal coach etc. and cork floor.
    Sub is fron firing.
    Would bottom firing fare better?
    It's irritating on bass lines, and the 35Hz makes LFE effects sound all the same...
    Any ideas?
     
  6. Nimby

    Nimby
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    Sorry, but I think you're wasting your time messing with subwoofer stuffing when your room is the real problem. You'll invalidate the warranty by opening it up! Let's assume that REL know just enough about making subs to decide whether saving a few pence on stuffing is important to them (and you the user).

    What would I do? :rolleyes: Easy! :) Move! :smashin:

    Or, you can draw the square that forms your room's floor plan on a big bit of paper. Then try all possible rotations of your listening triangle (main speakers to listening position) on your plan. Keep the main speakers the same distance from you but assymetric to the room. So both speakers aren't sitting in the nearest corners just because that's easiest. Listening across the diagonal of the room may be the best option to get away from the constant reinforcing of particular frquencies that you presently experience. But be warned, it may not help at all!

    Once you've eliminated your speakers from the room resonances you can try the subwoofer somewhere else. Like next door! :devil:

    Or try raising the sub on various surfaces at different heights to get it away from the floor where you get maximum boundary gain effects. Try it on top of cupboards, on coffee tables or anything else you have handy. But obviously it must be somewhere safe from the sub walking off the edge of a cliff from the vibration. Even bring the sub out into the room where you won't fall over it. You can always park it out of the way when not in use.

    You could even try this with your speakers in their present position. Try any safe positioning idea with your sub so you don't to excite the room's natural resonances. I'm assuming you don't have your sub gain set too high.

    Downfiring probably won't produce any noticable effect over front firing and may be slightly worse.

    Try Room Arranger if you want to play with your room layout on your monitor. It's much more fun than bits of paper even if it takes much longer. :)

    http://www.roomarranger.com/

    The following software suggest you should be swamped at 43 and 86Hz. Which suggests your room is slightly larger than you think it is at around 4.6metres cubed. A 4 metre high room is rather odd too! Are you sure you can't move? :D

    http://www.mcsquared.com/modecalc.htm

    Regards
    Nimby
     
  7. Barend

    Barend
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    Hey Nimby,
    Thanks a lot for your thinking!
    Due to WAF problems :D I will try raising the sub a bit, cannot move or raise the stereo speakers, they're KEF Ref 203 floorstanders, both the KEFs and the sub produce the same resonances @ 35 and 70 Hz.
    Cannot move myself, my sweet spot nor any other furniture or my W won't allow me to buy and play with all this kit all of the time :D .
     
  8. Nimby

    Nimby
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    Have you tried bribery? :cool:

    Nimby
     
  9. Kornmong

    Kornmong
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    This is what my sub box looks like with port flanges just glued on, oh and the stuffing should i leave it or rip it out or wait and test first,

    or will no matter what will it sound crapper with it in?

    <a href="http://www.imageshack.us"><img src="http://img328.imageshack.us/img328/75/subwooferbox4tq.jpg" border="0" width="452" alt="Image Hosted by ImageShack.us" /></a>
     
  10. Kornmong

    Kornmong
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  11. Nimby

    Nimby
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    You certainly have a problem with those ports blocked by the foam.
    Just remove the foam in that area to let the ports breath properly.


    Nimby
     
  12. Kornmong

    Kornmong
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    There not blocked im not that stupid theres holes for the pipes through, the foam is only on the walls of the sub box, the sub isnt full of it, geez
     
  13. Kornmong

    Kornmong
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    How did you think the ports were blocked?
     
  14. Ian J

    Ian J
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    Have you been reading "How to Win Friends and Influence People" again as you won't get much help with an attitude like yours.
     
  15. Nimby

    Nimby
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    At a glance I thought the ports were pressing against the foam rather than passing right through it to the front of the baffle. Silly me! :oops:

    He's not likely to get much response to any further questions Ian. :rolleyes:

    Perhaps he should apply for a change of user name? Suggestions on a postcard please: :devil:

    Nimby
     
  16. Kornmong

    Kornmong
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    :lease: dont ignore me

    but come on I showed the tinest amount of attitude

    I read the rules and my post dosent insult anyone or disrespect anyone

    Its not like I called him all the names in the book, I just thought you were saying that im stupid and blocked the holes,even I a begginer DIYer know how to make ports

    Im sorry for the attitude :( It wont happen again unless...... :devil: lol)
     
  17. IronGiant

    IronGiant
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    I'm sure they'll forgive you :thumbsup: Guys... ?
     

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