Near-field subwoofer placement

Discussion in 'Archived Threads 2001-2004' started by Norman Short, Mar 9, 2002.

  1. Norman Short

    Norman Short Stunt Coordinator

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    I read somewhere an article talking about putting the subwoofer very close to or directly behind the listening position as an alternative to conventional corner placement. The writer argued that you don't need nearly as much power to get the same SPL output at the listening position, and your bass would be made up much more of direct rather than reflected waves. It also enabled bass to be better performing for you while saving some calls from irate neighbors. This sounds logical, but corner loading seems to be the prevalent point of view here on the forum. Of course I can try out both for myself, but I was just wondering what if any downsides to such an approach there are, and perhaps there is some flaw the article's author hadn't considered. I realize you would lose the corner loading, but wouldn't proximity make up for that?

    Norman Short
     
  2. JohnDG

    JohnDG Stunt Coordinator

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    Make sure that your receiver has a time delay option for your sub.

    In my initial setup (sub closer than the mains, older receiver with delay settings only for the surrounds), the sub was distracting and not at all integrated with the other speakers. Once I upgraded the receiver, the problem went away.

    IMHO corner loading is preferred as you can get the most output from the sub this way. However, you are going to want to get an equailizer for the sub to flatten out the frequency response in your room. IIUC, with a sub placed away from the walls, you normally only have to deal with the null/peak caused by the ceiling.

    jdg
     
  3. Wayne A. Pflughaupt

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    Norman,

    John has pointed you in the right direction, so I won’t reiterate his good advice.

    There are a lot of flaky theories out there when it comes to sub placement, most without rigorous substantiation. For instance, I’m betting the author of this article did not show any measurements to back up his claims, right?

    The fact is, near-field placement does not eliminate the effects of the room; you will still get reflected waves. It would seem that adding multiple time-delayed reflected waves to direct waves would muddy things up, not make them better.

    But if you have neighbor issues, Norman, that is another matter not related to acoustics. If this is what is driving your placement decisions, you have little choice but to live with whatever you get from less than optimal placement. But I expect this would be better than no bass at all.

    Regards,

    Wayne A. Pflughaupt
     
  4. Norman Short

    Norman Short Stunt Coordinator

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    Thanks for bringing up some good points. Neighbor issues aren't a problem for me at all; I live on a farm with the nearest neighbor hundreds of yards away [​IMG].
    Thinking about it now, it would be obvious that you'd have to be able to delay the sub, and that you'd still get most of the reflected waves you would otherwise along with a higher percentage of direct sound.
    I've always known corner placement is recommended but I wasn't sure why it was superior to near field placement. The only reason it made sense to me is that I spend most of the time as the only one watching or listening. Everything else is set up for hitting a one seat sweet spot. Considering there is an 18db output difference between having a sub 1m away vs the 3m distance I currently use with a sub in the corner, it also made some sense of getting bass to the seating postition vs. trying to fill the room. In the end it sounds like corner placement will continue to be the best course.
    Norman Short
     
  5. Richard Greene

    Richard Greene Stunt Coordinator

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    Assuming you are sitting well away from walls near the middle of the room and the subwoofer is within a few feet of your seat:

    Any subwoofer on the floor will be in the high pressure zone and fully excite the floor-to-ceiling standing wave.

    In a typical room with an 8 foot ceiling that standing wave peak will be at 71Hz. -- that will be the maximum output

    of a near-field middle-of-the-room subwoofer.

    Since the middle of the room is a low pressure zone for both wall-to-wall standing waves, they won't be excited very much. The result is a subwoofer peaking at 71Hz. with falling response at lower frequencies, especially below 50Hz. Lot's of equalization (boost) and extra amplifier power can restore a reasonably flat frequency response at ONE seating position if the driver doesn't run out of XMAX first -- but having both the listener and subwoofer located in a low pressure zone makes it tough to generate loud bass at low frequencies.

    But near-field (with equalization) can be a good subwoofer position if you have a square room because a corner subwoofer excites all room modes to the maximum ... and that's not a good thing in a square room with stacked room modes.
     

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