Sub placement - What constitutes a corner?

Discussion in 'Speakers' started by Steve Kuester, Apr 7, 2003.

  1. Steve Kuester

    Steve Kuester Second Unit

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    I know there a ton of sub placement threads, but I searched and didn't see this addressed specifically.

    I've got my SVS 20-39cs in the right front corner of my room. It's about 6 ft to the right of my right main, 11 ft from the center and 16 ft from the left main. It's a big room (L shaped 30 ft wide by 23 ft deep)

    Now that I've started listening to DVD-A, quite often I can easily tell where the sub is. I know corner loading a sub is supposed to give you some added volume, and I need it with this size room.

    Here's my question, how big/thick does a wall need to be to give a sub an added boost? If I moved my sub towards the middle of my front soundstage (still along that front wall) and set it next to say, a large bookshelf, will the side of that bookshelf act as another wall and the sub would still be considered corner loaded?

    Does this make any sense? If not, let me know and I will try to re-word.
     
  2. Wayne A. Pflughaupt

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    Wayne
    Basically, you have to keep in pretty close to the corner –less than a foot away – to be considered corner loading. The further away from either corner wall you move it, the lower output will be, and response will worsen.

    Depending on your crossover frequency, a factor can be program material. For instance, if you have a typical crossover frequency in the 80-100Hz range – if the program content happens to have exaggerated response in the range of an octave above or below the crossover frequency, that could indeed cause localization.

    But in your situation, since you are localizing most of the time, I’d suggest either lowering the crossover frequency, or getting a crossover with steeper slopes. In my installation with steep 24dB/octave slopes, location is minimal with a 90Hz crossover point.

    Regards,
    Wayne A. Pflughaupt
     
  3. Tekara

    Tekara Supporting Actor

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    alright, so my living room sucks for subs it's big, is combined into a single room with the dining area has an opening into my kitchen which while not big is still space, and manages to round out with a 10' cieling. so now then the home theater lines up on one wall, I have dual SVS ultra's one is in a corner consiting of two outside walls, the other is in the opsited corner with one wall being an outside wall and one being an inside wall.

    the difference in volume between the two subs is very noticeable. the one in the two ouside walls corner will easily put out 2 to 3 more dB of SPL then the other sub in the inside/outside wall corner. The only reason I don't group them both into the same better corner is purely aesthetic.

    if your wondering how I found out about this, I used to have my living room at a angle the home theater in the "good" corner and the one sub was still in the inside/outside wall corner and the other was along the wall next to the one of the two couches. then one day, I decided to change (I hated how there wasn't a seat in the Ht that you didn't have to turn your head to see the TV) and after I did I found that moving the one sub from along the wall the corner made a MASSIVE difference in the amount of bass I was getting, where I once had to run my bass a bit "hot" I now found that I needed to run it a bit low. so I decided to take use of my rat shack SPL meater and found out that the outside/outside corner was the best corner in my house for bass.

    anyway, shouldn't have made that so long, but it should help you out a bit.
     
  4. Steve Kuester

    Steve Kuester Second Unit

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    Wayne,
    For movies, (DD, DTS) I never really could localize all that often as I use the 80Hz crossover point on my Denon 3802. Where I am hearing the problem is on DVD-A. One example - the Metallica "Black" album. On the song "sad but true" the bottom half of the snare drum is definitely coming from the sub. (I don't know why it was mixed there, but it is)

    My understanding of hi-rez audio tells me that a crossover won't do me any good, as I can't send the higher frequencies from the sub channel to the mains. That's where my question came in about "making" my own corner in the middle of the front soundstage.
     
  5. Tekara

    Tekara Supporting Actor

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    that would be odd. . . you should have the ability to adjust the LFE crossover frequencies and there should be options for adjusting the frequency where the low end signal of the speakers (when set to "small") are sent to the LFE channel.

    if you are looking to make your own "wall" I found that hard materials like the concrete my walls are made of seem to do great for reflecting bass back out into the listening area. I have no science behind that just pure speculation, so please do take with a grain of salt.
     
  6. Steve Kuester

    Steve Kuester Second Unit

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    I don't have a problem with low frequencies being redirected to the sub. I'm talking about frequencies that seem higher than 80hz being sent to the sub during DVD-A playback. That's why I'm going to try to move the sub to the center. I just wanted to see if there was any way I can keep the "corner volume" from my sub in the middle of a wall.
    thanks
     
  7. Tekara

    Tekara Supporting Actor

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    yes that is what I am refering to, there is a high pass crossover for the LFE channel that you can set. This will cause only frequencies lower than the set value to be sent to the sub, nothing higher. so you can set this to 80hz and the sub won't recieve frequencies higher than 80hz.

    there is usually two places that this is set at, one is when the reciever is putting out non-encoded audio and the other is when the reciever is putting out encoded audio. so you need to make sure you are setting the right one. The encoded audio is the LFE crossover and the non-encoded audio should just be a normal subwoofer crossover.
     
  8. Richard Greene

    Richard Greene Stunt Coordinator

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    Tom Nousaine usually defines a corner as having at least six feet of solid walls on both sides (no open doorways or open windows ... and even closed doors and closed windows are not so great -- potential rattle problems).

    I've done hundreds of measurements since I started to use corners for subwoofers back in 1994 after hearing a Tom Nousaine presentation at a local audio club meeting.

    The "tricorner" is the intersection of two walls and the floor. In general, the effect of the corner on bass output under 80Hz. does not significantly change until the subwoofer driver is 1/4 of the distance between walls.

    If your room was 16' wide, for example, the sub driver could be located up to 4 feet from the tricorner before the influence of the corner begins to sharply decrease.

    The high pressure zone next to walls is quite wide but does drop rapidly past 1/4 of the distance between opposing surfaces. In my own room, which is 16' feet wide, the BFD settings do not even have to change if the subwoofer driver is one or two or three feet from the tricorner (I could change themn slightly but would not hear a difference).
    At four feet from the tricorner the settings do have to be changed but not by a lot -- beyond four feet from the tricorner the bass frequency response changes rapidly in my 16' wide listening room. With a room 24 feet long, for another example, the subwoofer could be up to six feet from the front wall (wall behind the main speakers) before rapid changes to bass frequency response began.

    I would recommend that bass drivers be kept at least one foot from any plasterboard wall to avoid rattling walls.

    Most audiophiles are surprised about how far a subwoofer driver can be located from a corner while still getting most of the benefits of the corner. That means the subwoofer could possibly be located closer to the right or left speaker than you may have assumed, with little change to its frequency response ... but most likely with BETTER integration with those speakers simply by being located physically closer to them.

    As always, experiemnt and measure -- bass theories only
    apply to well-sealed rectangular rooms with very stiff solid steel or cement walls -- your room with flexible plasterboard walls may differ even if it is rectangular.

    Bass graduate school -- Floyd Toole white paper:
    http://www.harman.com/wp/pdf/Loudspeakers&RoomsPt3.pdf
     
  9. Kevin C Brown

    Kevin C Brown Producer

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    Hmmm. I can only relate what I've heard over the years:

    a) a corner is best for raw output
    b) 1/3 or 2/5 along the longest wall is best for the best compromise between output and flattest freq response

    c) stay away from 1/2, 1/4, 1/8 divisions between walls. That's where freq response dips into a null spot.

    Here's a measurement I always keep in the back of my head: wavelength at 80 Hz is 13.75 ft. Somehow this also goes into all the above. SGHT and some other mags have covered room nodes, speaker wavelengths, and such. My impression is too, that you have to be pretty close to the walls in the corner to get the best benefit of corner loading. I don't have the knowledge power at hand to disagree with what Richard says [​IMG], but my gut (and experimenting with sub placement of my own over the years) says to be within a ft of the corner as well.
     
  10. Steve Kuester

    Steve Kuester Second Unit

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    Thanks,
    Thats what I was looking for. (Richard, very interesting link) I can olny move the sub a couple feet from the corner before it drastically drops off, and 2 feet does not make a difference as far as integrating with the front soundstage. Unfortunately, it also looks much better directly in the corner as opposed to 2 feet from it.

    "6 feet of solid walls on both sides.." Hmmm, I guess I can't make one of those.:b

    And again, listening to DVD-A is when I can localize. I know I want an ICBM, but unless I'm misunderstanding the manual, it doesn't filter the highs from the sub. I might just be stuck.
    thanks again.
     
  11. JohnDG

    JohnDG Stunt Coordinator

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    Per the localization, I've also found that the sub distance delay is a factor. Try to push the sub back another foot and see if this helps integrate the sound.

    jdg
     
  12. RichardHOS

    RichardHOS Second Unit

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    Kevin Brown:

    b) 1/3 or 2/5 along the longest wall is best for the best compromise between output and flattest freq response

    c) stay away from 1/2, 1/4, 1/8 divisions between walls. That's where freq response dips into a null spot.


    I've read whitepapers stating that placing a sub in a null might be exactly what you want to do. It essentially eliminates that room mode from being activated with any appreciable amplitude. One rigorous examination of the problem indicated that a sub in the middle (1/2 point) of each of the four walls in a typical room gave the best (smoothest) response vs. frequency and position without using massive numbers of subs.

    Placing the sub at 1/3 or 2/5 points might place the sub in a peak, which means greater output, and also means greater variability of response from position to position whith the room.

    Pick your poison I guess.
     
  13. Michael Giusto

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    You know I never really paid much attention to how my subwoofer is setup and after reading this thread I think it's about time I get this setup the right way once and for all.

    I've got a Velodyne Sub (not sure which model number, but will post back with it later tonight when I get home) and the Denon AVR-3802.

    What settings should I have the Denon on as well as where should I have the dial on my Velodyne set to?

    I'll post back if I need to provide more detailed info about the controls on the back of my velodyne (I know there are at least two toggle switches and two dials, one of the dials for volume. I have a y-cable running from my Denon Sub out to the back of the velodyne. One connection comes out of the Dennon but Two connections connect into the Velodyne red and white inputs.

    Thanks for any assistance!

    Michael
     
  14. Kevin C Brown

    Kevin C Brown Producer

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    Richard- It's just like making sure your sub is in phase with the mains. You want the overlap in freq to be such that you have the highest output. Similarly, if you put your sub (or speakers even) in a 1/2, 1/4, etc, spot, you're robbing your sub (or speakers) of output. That's actually in the manual that came with my speakers too. But everyone has to experiment for themselves as well. [​IMG]
     

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