Does the Shiva is so strong, or am I ruining it ?

Discussion in 'Archived Threads 2001-2004' started by Jones_Rush, Jul 6, 2001.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

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    I checked my 3c/f sealed Shiva today with some movies.
    Overall I thought it gave very clean bass, but the bass wasn't really "bone crashing". I never thought it will be "bone crashing" since it is in a closed box (even though I once heard a Servo-15 sub, which is also closed, and the bass was "bone crashing", but it is a 15" driver)
    I was ready to draw my conclusions about this sub,
    but thought I would try to drive it harder before I come to any conclusion.
    I played the Dolby Digital trailers, and turned the volume control to 1/3 way up (the amp is rated at 272w @ 4ohm).
    When I played the "Dolby Digital Rain" demo, I couldn't believe my ears, there was a strong bass effect which lasted 2 seconds and it almost tore my room apart. I took my RS SPL meter, played it again, and measured close to 110db SPL at the listening spot, uncorrected!!!. I think
    that this bass effect (the splash of the water) is centered at about 20-25hz (can anyone verify?), which mean I should add about 5-7db SPL to my readings. I never read that the Shiva in a small closed box can give ~115db at 20hz.
    My question is : am I ruining the Shiva ?, I mean, when this bass effect was playing, I noticed that the driver was going back and forth like crazy. The bass was clean, but when I turned all the speakers off except for the sub and played it again, I heard some noise from the driver when it was playing this bass effect (If I was bottoming it, why haven't I heard noises when the other speakers were on ? usually when people report that they bottomed their sub they say that the bottoming noise was masking the sound of all the other speakers).
    The pressures on the Shiva seemed huge, can the Shiva withstand such pressures without damage ?. You have to remember that I was using only 33% of the amp's power (unless the volume control is not linear), which
    mean ~ 90watts.
    If I'm not ruining anything and these are the true capabilities of the Shiva, then I have underestimated it by far.
    when I think of it again, my question is even simpler that I thought:
    Can the Shiva driver in a sealed 3c/f box withstand 100 watts of power all centered at ~ 20hz ? (If the limit of power in this situation is lower or higher than 100w, what is it ?)
    P.S
    My room measures are 13x9x8 feet and the room was closed during listening.
     
  2. Julian Data

    Julian Data Second Unit

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    Sounds like you were clipping your amp for the sub.
    What was the measuring distance?
    ------------------
     
  3. Jack Gilvey

    Jack Gilvey Producer

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    quote: You have to remember that I was using only 33% of the amp's power (unless the volume control is not linear), which mean ~ 90watts.
    [/quote]
    Volume controls don't tell you how much wattage is being used. It depends on the strength of the input signal. You could have been delivering all of the amp's power at that control setting. It's really tough to get an accurate number like 115db @ 20 from an SPL meter measuring that sequence, because it's probably many unknown frequencies, and there's no accounting for doubling or other distortions.
    While bottoming certainly doesn't mask the sound of the other speakers, it's usually quite audible, at least moreso than your description. It sounds like you were just reaching the limits of the amp and driver.
    Sounds like you've got yourself a great sub there, though.
     
  4. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Julian, the measuring distance was 7 feet.
    Jack, you are right, I have no certainty that what I've measured was exactly 115db at 20hz. To tell the truth, It doesn't matter, what matter is that the bass I heard was way way above my expectations.
    But again, isn't it harmful for the driver to move so fast back and forth to the point it makes some noise ?
    Is there a way I could find out if I'm doing damage ? (should I smell something ? should something overheat ?...)
     
  5. Geoff L

    Geoff L Screenwriter

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    Hi Rush,
    Sounds as though you have a good understanding now why we all love the DIY thing!
    Driver going in and out big time, you gota love x-max. [​IMG]
    Like others have noted, your more than likely running out of clean amp power. Driveing the Shiva with a clipping signal continualy will shorten it's life dramaticly. Just back off the sub level or vol pot a little to keep the amp out of the clip zone and the Shiva will be very thankful.
    As far as the big cone travel, nothing to worry about as long as the amp dosnt clip and the driver isnt bottoming out. Dosnt matter how loud it is, or whats falling off the walls, if the above are in the safe zones all will be ok with the sub.
    ------
    You might try running the vol pot on the amp about 2/3rds up and adjust the sub level down on your reciever or pre-pro.
    ------
    There is less chance of distortion to the amp inputs this way and allow for adjustments up or down in vol. This may allow a you to get a touch more clean volume if your signal was a little dirty due to a exsesively high sub out signal to the amp. (Only guessing, as your vol pot is only at 1/3 on the amp)... This certainly dose not mean that you will, but in theory a posibility you may want to give try.
    Sounds as though your pretty pleased with your first sub???
    Congratulations....
     
  6. Jones_Rush

    Jones_Rush Stunt Coordinator

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  7. Jack Gilvey

    Jack Gilvey Producer

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    quote: Even though I have almost no experience in electronics, I still find it a bit hard to believe that an amp that its volume control is positioned 1/3 way up, can send a clipping signal no matter what, I just can't see the logic (maybe due to my lack of knowledge). [/quote]
    If the input signal is strong enough, enough voltage is sent "through" the volume control to allow the amp to develop it's full output. All the amp's volume control does (most of the time, and volume controls do differ in their characteristics) is attenuate the input signal, you're not controlling the amp's wattage with it directly.
    quote: To me, the most logical thing to assume would be that the Shiva just reached its excursion limits at this enclosure and did some flapping noise (is it possible ?). [/quote]
    Of course it's possible, even probable given the SPL you've reported. It sounds like you might be travelling somewhere beyond Xmax, but have not quite reached the excursion/bottoming limits of your Shiva. Also possible is the presence of subsonics below 20Hz, which can cause premature amp clipping and driver overexcursion. For Adire's Rava, which is close to your design I think, the "rumble" filter is customized. While the standard AVA250's subsonic filter has a corner frequency of 18Hz (not rolling off yet), and only rolls off truly subsonic signals, the filter in the Rava is considerably more aggressive, being already down 3db @ 18Hz(if I recall correctly). This will obviously be more effective at protecting the driver, possibly at the expense of some of the deepest bass.
    Let me say that I'm very happy that you like the sub,I know how much time and effort you've put into it. You can see how nicely a 12" not only provides very deep bass, but can still blend beautifully up high.
     

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