Subwoofer placement in WIDE room... I swear I can hear where the bass is coming from!

Discussion in 'Archived Threads 2001-2004' started by Jeff Meininger, Aug 9, 2002.

  1. Jeff Meininger

    Jeff Meininger Second Unit

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    Conventional wisdom on subwoofer placement indicates that humans have a hard time locating bass frequencies, so you can put your sub just about anywhere you like.

    Not in my case! I swear that I can (easily) hear where the bass is coming from. Maybe it's all in my mind, but I really think I can tell.

    I have 2 possible explanations for this...

    1. My subwoofer is way too cheap/small for my large, high-ceiling living room. I know this, and I need to upgrade one day. The sound from my sub is hollow and boomy, and I often hear a "blowing over the top of an empty coke bottle" sound coming from it. Perhaps it is THIS noise that my ears are locating, and not the actual bass frequencies recorded on the audio track?

    2. Perhaps the dimensions of the room and placement of the sub are sub-optimal? The room has dimensions of roughly 2.35:1 (I'm not kidding!!). If you divided the room in half, the HT is in the left half of this big open room. The right half is mostly empty space. With the sub located at the far left front corner (under the left front speaker), I can hear the sound coming from there. I'd even go so far as to say that my left ear starts hurting before my right ear does if I listen to very loud stuff.

    I've solved the problem by putting the subwoofer pretty much front-and-center. There is precious little real-estate there, though, and when I upgrade to a larger sub, It's going to have to go back in the corner.

    So, is it more likely that my sub is just producing audio artifacts of high enough frequency that I'm able to hear where they come from (and a better sub will fix the problem) or is the layout of my WIDE room such that I'm going to notice the problem if I put the sub in the corner no matter how high-quality that sub is? The HT is also the living room, and placement of a large sub anywhere but in the far corner is a problem. The only other possible place would be under the RIGHT front speaker, which is just about in the front-center of the room (but to the far right of th e HT area).

    I ask because I don't want to invest time in a DIY or money on a better sub if I'm going to have the "all the bass is coming from the left" or "all the bass is coming from the right" problem.
     
  2. Brian Corr

    Brian Corr Supporting Actor

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    What freq. are you crossing over at?
    Are your mains large or small sats?
    You may pick up an SPL meter and a disc with test tones and measure your rooms freq. response to see if you have dips and peaks.
     
  3. John Kotches

    John Kotches Cinematographer

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    There are a number of possibilities.
    1) Your sub is producing substantial distortion. Since the distortion products start at 2x the fundamental frequency the distortion products are far easier to localize.
    2) Something near the subwoofer is rattling giving you a sonic clue as to the subwoofers location.
    3) You are feeling the pressure from the subwoofer on some transients.
    4) You know where the subwoofer is, and your brain is messing with you [​IMG]
    Regards,
     
  4. Jeff Meininger

    Jeff Meininger Second Unit

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    I've set my crossover at 100Hz and 120Hz, and can't really tell a difference. I can locate the sub with either setting. The mains are small.

    As far as feeling pressure from the sub on some transients... what are "transients"? (I'm a newb.)

    I don't think something is rattling near the subwoofer. If anything rattles, it's usually the glass curio cabinet (displaying glass glasses) at the opposite end of the room. I could be wrong, though.

    So is it UNlikely that the WIDE shape of the room and the sub's position close to the wall closest to the listener is the problem? If the shape of the room isn't a concern, that would make me happy as I could solve my problem with a better sub.
     
  5. Neil Joseph

    Neil Joseph Lead Actor

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    I agree that the combination of placement and crossover are the most likely culprits, assuming everything is at calibrated levels of course.
     
  6. ColinM

    ColinM Cinematographer

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    I have a 23x13 room set up like yours, and once had to put the sub in the farthest-to-the-right corner on the front wall, 15 feet to the right of the right main. Response was much stronger and peaky, eq'd no problem, but it was much easier to tell where it was. When it was within 5 feet of the mains, it sounded like it was dead center between them.

    It became less of an issue if I dialed the xover down to 60/70, but the right side of my head felt it more than the left...drove me nuts.
     
  7. AntonS

    AntonS Stunt Coordinator

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    Are you actually hearing the sub on the side or more like feeling it? It can be possible to feel the sub on the side if it's pointing directly at you. It's not really the sound but rather air pressure of the moving air hitting one airdrum more that the other. Our ears are quite sensitive to that. The result is that you kind of feel more energy (not really sound volume) coming frome one side. That's why I actually like down-firing subs. Anyway, try pointing the sub driver away from you.

    If you actually hear the sub, it's most probably distortions.
     
  8. Wayne A. Pflughaupt

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    Jeff,
    Here’s your problem:
     
  9. Bob McElfresh

    Bob McElfresh Producer

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    Lets take a step back to examine the concepts...

    Human hearing is most sensitive in the upper mid range, about 12khz. As the frequency reduces, your sensitivity reduces as well. While you can still perceive 80 hz sounds, you are just less-sensitive to it and less able to tell the direction. This does not mean you cannot tell the direction, just you are less sensitive to it.

    You get a lot of subwoofer frequencies reflected by the walls in most rooms. This helps disguse the location of the source.

    Both of these contribute to the myth: "you should not be able to tell the sub location".

    So dont think something is wrong if you can tell roughly where the sound-source is.

    PS: to really test this, disconnect all other speakers and play sound through the sub only. Your speakers may be drawing your attention.
     
  10. Wayne A. Pflughaupt

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    Bob,

     
  11. Henry_W

    Henry_W Stunt Coordinator

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    I have a very subjective experience - an older, boomy (Infinity BU-2) sub in the exact location as new sub (SVS 20-39pci)with both SPL'd to same levels with crossover at 80hz managed by the reciever.

    You could 'hear' the old sub and find it with your eyes closed. Cannot do the same with the newer sub. That makes me think that the higher frequencies at the sub were creating distortion - however, I let my ears decide and did not delve into the engineering.
     
  12. Neil Joseph

    Neil Joseph Lead Actor

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    Read this thread also because this member has the same issues you point out.
     
  13. Abdul Jalib

    Abdul Jalib Stunt Coordinator

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    There are a ton of possibilities. Probably it's a combination of a cheap sub that's putting out higher frequency noise and your high crossover that's already directional at its start point.

    Another possibility is related to room size. The frequency range where bass becomes directional is a function of room size. When you hear the reflection of a wave before the end of the same wave reaches your ear, this makes it pretty much impossible to locate the bass. 80 Hz is the frequency commonly given where bass becomes nondirectional in a typical sized home theater room, but in a very large room even 60 Hz may give your brain directional cues.
     
  14. Neil Joseph

    Neil Joseph Lead Actor

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    Ditto to above statement regarding room size, cranking up the sub volume, and the sub "giving" itself away.
     
  15. Bob McElfresh

    Bob McElfresh Producer

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  16. Ken Garrison

    Ken Garrison Supporting Actor

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    I don't like placing my sub WAY over to the left or WAY over to the right. I like my sub as close as to the front center as I can. My bass reflector is to the left of my right speaker. That's as close as center as I can get it. And it works well that way. Yeah, I can sense where the bass is coming from. I hate listening to those "so-called" stereo enhanced LPs with headphones. The extra pressure coming from one headphone starts to hurt after a while. So, I like my bass balanced. Older music used to put the bass on to one side and drums to one side. I guess the Beatles invented the way of putting the drums and bass in the middle. Stereo drums are also kinda cool instead of putting the set over to the right or left. PUt it in the middle as well as the bass. Sounds good that way.
     
  17. Larry B

    Larry B Screenwriter

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    Anton:
     
  18. Larry B

    Larry B Screenwriter

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    Jeff:

    The abililty to localize lower frequencies is enhanced by moving one's head.

    Larry
     
  19. AntonS

    AntonS Stunt Coordinator

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  20. Richard Greene

    Richard Greene Stunt Coordinator

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    This rule of thumb works well to produce sonically invisible subs:

    Bass output at 160Hz. should be down 24dB or more relative to bass output at 50Hz.

    therefore:

    12dB/octave filter = crossover frequency (CF) no higher than 40Hz.

    18dB/octave filter = CF no higher than 60Hz.

    24dB/octave filter = CF no higher than 80Hz.

    If you use a small subwoofer in a large room, causing the sub to produce a lot of harmonic distortion above 80Hz., or the wall near the sub rattles, the above rules may not work.

    For program material that has lots of output below 25hz. you will often feel pressurization on one side of your body if you use one sub in the front left corner (or front right corner). Using two corner subs will prevent this (although that doesn't seem important for music where there is little output below 25Hz. and virtually no stereo bass on CDs ... but it can be important for action movies with lots of sub-25Hz. output).

    Subwoofers are sonically invisible below 40Hz. except for the pressuization effect below 25Hz.
    Bass is usually sonically invisible below 80Hz. if there is bass above 80Hz. coming from satellite speakers (that helps mask the subwoofer location)
    Bass above 80Hz. can be sonically visible if loud enough relative to bass below 80Hz. ... so bass above 80Hz. should be sharply restricted by using 24db/octave filters at 80Hz. or lower. Some people would be happy with a 100Hz. 24dB/octave filter too.

    Rectangular or L-shaped listening rooms can only be fully energized by a subwoofer located in a room corner -- that doesn't mean a corner sub will sound good but it will have more output than a non-corner sub. Two mono subs in the same room corner will have 1 to 3db more maximum output than two stereo subs in the left and right corners on the same side of the room due to destructive interference (cancellations at a specific bass frequency related to the distance between the subs). Corner subs on opposite sides of the room will have phase (cancellation) problems toward the center of the room and could sound better when hooked up out of phase. Subs behind the listener are easier to locate with your ears than sub near the front speakers.

    Subwoofers integrate best with the main speakers when they are located half way between them ... but that location is one of the worst possible for bass frequency response and maximum bass output (corners are better).

    Almost any subwoofer position will benefit from parametric EQ ... so if you have a parametric EQ, you might as well put your sub in the front corner and get maximum output too.
     

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