Bottoming out with 20-39, how can I get some more headroom?

Discussion in 'Archived Threads 2001-2004' started by Scott_E, Sep 23, 2001.

  1. Scott_E

    Scott_E Stunt Coordinator

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    Well, based on what Ive read about calibrating an SVS, I setup my system and now seem to bottom out on heavy bass scenes. The one scene I'm using is the helicopter crash scene in the Matrix. I have a Samson S700 and a 20-39cs. For my settings, I have the knob on the samson turned all the way up, and the subwoofer level set to +2. This matches my taste for bass in alot of parts of the movie. When turned up to around volume 55 on my onkyo 595, During the helicopter crash, the sub bottoms. So, I set it at like -1, and it no longer bottoms. But, during other parts of the movie, the impact is lessened and alot of waves no longer felt. My question is this, in everything Ive read, it says to turn the knob all the way up on the amp, and then set the level for the sub on your reciever. Could I get some more headroom by not turning the knob all the way up on the samson, and then adjusting the bass level accordingly? I like the bass to be more pronounced than most, and I listen to alot of movies kinda loud (well it seems loud to me). I usually listen to them at volume 55 on my onkyo 595. So for all other parts of the movie, I have the sub set at around +2 or +3, and it souds completely perfect, but it does bottom out in heavy bass scenes, such as the helicopter crash. I dont have the Shack SPL meter yet but looking to buy in the next week. Can you make any suggestions? Do most people run the gain all the way up on their samson?
     
  2. Patrick Sun

    Patrick Sun Studio Mogul

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    You really need to calibrate your LFE levels (with a SPL meter, and test tones - Avia or Video Essentials is a good way to get the test tones), else you'll continue to experience exaggerated bass, and bottoming out of your sub. I think my LFE output level is set to -4dB, and I don't have problems with my subs bottoming out.
     
  3. Ned

    Ned Supporting Actor

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    Order the ART351 EQ and filter below 20hz.
    Other idea, you could order a custom tuned port around 23-25hz rather than 20hz. More output at some expense to extension.
    ------------------
    My Home Theater Page
    [Edited last by Ned on September 23, 2001 at 03:59 AM]
     
  4. Rick Radford

    Rick Radford Supporting Actor

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    Scott,
    I'm relatively new at this HT stuff, but I found that moving my 20-39cs around made quite a difference. You might check my thread here on sub placement.
    Basically, I found that by moving the sub to the left front corner from the right front corner allowed me to back off the sub settings by -6 dB.
    The only difference I can see (as to why that happens) is the left front corner faces a large opening to another room whereas the right front corner faces a wall 12' away. My room is 11.5 x 12 x 8 with HW floors.
    Have you tried the ol' trick of putting your sub where you sit.. and then moving around your room to see where the bass is strongest? That's how I decided to change corners. [​IMG]
    There might have been better spots in my room... but the SVS is too big to just put anywhere, and the left front corner was my best sounding option. When I put the SPL meter to the test, I found out how much better.
    As a for instance, with the Samson cranked to max, I run the sub channel at -14dB on my Onkyo 989 in order to keep the meter readings about 1 to 2 dB over the other speakers.. which should make it around +5 dB actual (given the low freq error of the RS SPL meter).
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    --RR
    [Edited last by Rick Radford on September 23, 2001 at 05:49 AM]
     
  5. Scott_E

    Scott_E Stunt Coordinator

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    My 20-39 is in my front right corner. The only opening in my room is at the front left corner. My bed is at my the center of the rear wall and is where my primary listening position is. Room measures 12.8 (front to back) x 8 (floor to ceiling) x 16.8 (side to side) So I am about 11 feet from the sub and sitting on my bed. By doing a little testing when I first got it (havent had a whole lot of time), with the sub in the front right corner, there is more impact and bass at the rear left corner than where I am sitting. I'm not sure if I would be sitting in a null or not since I dont know exactly how this thing is supposed to sound in my room anyway. I'm going to get the shack SPL meter today, so I'll see what happens then, any ideas folks?
     
  6. SkiingNinja

    SkiingNinja Second Unit

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    I second Ned's suggestion of getting the ART351 EQ (get that SPL meter too!). Since your sub is tuned to 20Hz, the driver is going to have massive excursion below that frequency. With the 351, you can cut all frquencies below 20Hz. You'll still get room shaking bass with no bottoming.
    From your measurements, it looks like you have a ~1700cu' room. A single sub should do fine with the subsonic filter @ 20 in that size room. BUT if you are just an insane bass freak, get a second SVS (I did [​IMG] . You'll gain another 6dB of headroom.
    One more thing, the RS SPL meter is inaccurate at lower frequencies. Go to this page for corrections.
    Have fun.
    Sean
     
  7. Patrick Sun

    Patrick Sun Studio Mogul

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  8. Wayne A. Pflughaupt

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  9. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    I already answered Scott in our ongoing private exchanges about this...so I won't repeat the whole conversation we're having,
    I wouldn't assume this is all due to subsonics though. If memory serves...the chopper explosion scene in the MATRIX is mostly>20hz...with VERY high amptitude peaks in the 25-35hz range.
    Chances are Scott is calibrated very high...has the system at fairly high levels and is just running into the limits of a single sub.
    I could be wrong of course...we'll know more once he gets that SPL meter [​IMG]
    TV
     

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