subwoofer built in wall question

Discussion in 'Archived Threads 2001-2004' started by Keith M., Mar 18, 2003.

  1. Keith M.

    Keith M. Second Unit

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    I am currently building my dedicated HT and have a Definitive Tech PF-18TL subwoofer. This thing rocks but it is huge!! Probably the reason they dont make them anymore... [​IMG]

    I was thinking of putting it in the adjacent equipment room and cut out a space in the wall for the front of it...Would this ruin the bass response?

    Comments/Suggestions welcomed...
     
  2. Bob McElfresh

    Bob McElfresh Producer

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    That would be horrible.

    You get a LOT of sound by wall-reflections from a external sub. This is why corner-loading is so popular - it gives long lengths of walls the ability to reflect sound. You could almost call a subwoofer a "Indirect" speaker because of this.

    You would loose all of this shoving the woofer into another room with a pass-through hole. You would still get direct sound, and the opposite wall would reflect some, but you would loose all the near-wall reflections you get by having the sub in the same room with you.

    Try this: do you have a narrow doorway out of the room? Put the sub in the doorframe pushed so the face is flush with the door (so the sub is not sticking into the HT room). Connect it up and level-adjust (as best you can) with a SPL meter. Then sit down and listen to a favorite movie. How much quality in sound did you loose?

    Note: you can make a long, cheap subwoofer cable with RG6 CATV coax and 2 "F-to-RCA-Male" adaptors from Radio Shack. $12 last time I looked. A lot cheaper than cutting a hole, trying the new placement, then needing to patch/paint the hole back up.
     
  3. Brian Bunge

    Brian Bunge Producer

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    Bob,

    How would what he's considering differ from an infinite baffle install (other than the obvious)? As long as careful consideration to placement is taken into account there's no reason why this can't work very well. He'd also need to make sure that the driver is radiating strictly into the HT room so he'd need to seal it around the hole in the wall.

    Also, max output (corner placement) and smoothest response are mutually exclusive. Having one does not automatically give you the other.
     
  4. Moving from a 3 boundary corner away a bit doesn't also mean you loose a full 3db by moving to a 2 boundary space. Depending how the room and listener setup is, you can actually get a better responce as brian eluded to. I have both modeled this on the RRC and measured this on TrueRTA. I have owned numerous subs of very different size and possition, and corner loading wasn't the best most of the time.

    I actually have my subs about 3ft from the side and 2ft from the side wall and get a much smoother responce than when corner loaded.

    if you go to pics of IB setups you will notice that MANY of them are NOT corner loaded. I know that Keiths isn't a true IB since he is not at 10x the Vas, but he does actually eliminate some of the upper bass frequency cancelations from primary reflection cancelations (assuming that the driver is "quasi-flush" to the wall.
     
  5. Keith M.

    Keith M. Second Unit

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    Couple questions:

    1) Should I build a full enclosure around the back of the sub?
    2) Should I insulate it in any way?

    3) How much of the lfe will bleed into the adjoining room?

    4) Since this is a basement, the floors are cement, does this make this any less doable?


    5) What is "quasi-flush" to the wall mean?


    here is an ascii diagram of what im thinking of:
    Code:
     +-----------+------------------------------------+
     | +---+ L C R |
     | |Eq. |
     | +---+ |
     |MEDIA | |
     | +----+ |
     | | SUB |
     | +----+ |
     +-- ------| |
     DOOR | |
     |
     DOOR |
     | |
     |LS SEATING AREA RS|
     | |
     | LR RR |
     +------------------------------------+
     


    Hope this help everyone better visualize it. The room where the sub is, will have the back ass of the equipment rack and media shelves. It will have a door and the longest wall is a concrete foundation wall...
     
  6. 1) isn;t the sub already in an enclosure?
    2)not sure what you mean
    3) bleed into what room? The driver is going to effectively be in the listening room
    4)the floor is cement in the equipment room and listening room. I don't see you point
    5) are you going to cut a hole in the wall such that it framing is flush to the sub enclosure?
     
  7. Bob McElfresh

    Bob McElfresh Producer

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    Oh I agree that LOUD and SMOOTH are not the same and that audiophiles prefer a smoother sound while moviephiles prefer a more intense sound.

    But a lot of this is adjustable by simply moving the sub from a corner to somewhere like a 3/5 position or 1/3 position along a wall. Even an inch or two can make a big difference at the listening position.

    How many of you want to tell Keith where along his wall to cut and perminent-install the sub? Even if you picked a place along that wall, shoving the 18" sub into the wall will change things.

    Even with a nice RTA - this would be challenging.

    Keith: My 'conservitive' advice would be that you put the sub in the upper-right corner and play with moving it along that long, un-broken wall to get pleasing sound. This is cheap, easy, non-perminent and acoustically the best choice.

    If you REALLY want to embedd the sub into the other room, at least do this:

    - Make a long subwoofer cable out of some RG6 coax and some "F-to-RCA-Male" adaptors from Radio Shack.

    - Disable all other speakers.

    - Place the sub in the primary listening position (yes, shove the couch/chair out of the way).

    - Play a bass-heavy scene from a favorite movie in a A-B repeat loop and crawl along the wall where you might install the sub. Listen for differences in sound (smooth/boomy) and mark the locations with the best sound on the floor with masking tape. Hopefully you will have several points marked when you are done.

    (Note: This same technique works if you decide to keep the sub in the room along that long right wall.)

    - Find the mark that best fits where you want to cut into the next room and use this as the center position for the hole.

     
  8. Keith M.

    Keith M. Second Unit

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    Anthony:
    1) isn;t the sub already in an enclosure?

    Yes, but should I build a 2x4 frame around the sub or just cut a hole in the drywall for the front of it and let it stand free in the other room


    2)not sure what you mean

    If I frame around the sub, should I fill it with batting/insulation or just have the sub by itself?

    Im thinking of this almost like a built in box that the sub can fit into with the front of the sub flush to the finished wall...
     

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