Just installed shiva, but........

Discussion in 'Archived Threads 2001-2004' started by Tony Richardson, Mar 23, 2001.

  1. Tony Richardson

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    I just installed my shiva driver into a 142.5 L tube tuned to 18.1 with the adire 4" flared port but the thing is making a terrible noise at about 102 db. My room is 25' x 16' x 8'
    It is not the klanking sound people have described when a driver bottoms out but more of a very distorted sound when it plays low at about 102 db .
    The scene I used to test the new speaker was from ID-4 in the opening where the ships are passing the moon and the plack comes on screen. Very low rumble.
    The performance is not any better than the old speaker I had in the tube
    The amp is from a sound dynamics sub and is rated at 150 watts at 8 ohms 300 watts max.
    I wired the shiva voice coils in parallel I think? I wired the positive to positive and negative to negative on the speaker and then ran the amp wires to one of the coils. Is this correct?
    I think it is the amp clipping but I don't know for sure with the shiva driver. What do you think?
     
  2. Jon Hancock

    Jon Hancock Stunt Coordinator

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    Off hand, with that *little* power on a Shiva, I'd say there are two possiblities.
    1) Clipping, in the conventional sense, running out of voltage from your amp. DOes the sub amp have EQ? If so, it will require 2X power for every 3 dB of EQ at low frequencies versus the 50 - 100 Hz range.
    2) Another, somehwat less likely possiblity, is protection circuits (V/I limiters) cutting in due to the reactive loadline of the drivers, and the amplifier being perhaps marginal with a 4 ohm load with significant phase shift between current and voltage.
    The only straightforward way to determine this is to measure with a scope, take a look at the voltage coming out of the amp. Both clipping and V/I limiting will show some serious waveform distortion; clipping, obviously, will be flattening the peaks, but V/I limiting can manifest in several ways, depending on the design of the protection circuit, and may have some notching or gaps in the sine wave drive.
    To get the most from a Shiva, I'd recommend at least a clean 250 to 300 Watts at 8 ohms that doubles at four. Then, you won't be clipping the amp, and you'll get the full impact of transients. Technically, that's only 3 dB more powerful. Another factor to bass tonality and impact is the power supply regulation of the amplifier; an amp with a lot of reservoir capacitance (80,000uF to 100,000uF or more) will definitely sound better; that's a factor I always follow in building full range amps.
    Regards,
    Jon
     
  3. Tony Richardson

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    Thanks John for you reply but I don't think it is the sub amp as I thought.
    I found that my son had set the receiver to +10 on the LFE control. It is normally set at -10 with the amp at just below the half way point. This setting has been the only way to calibrate at 5 db above the mains.
    With the amp set at just below the half way point to match the other speakers at reference level, why would the sub amp be clipping, even at +10 on the receiver?
    One thing I did find out is that the sub amp has a 3 db boost a 40 htz and a cut of 3db at 22 htz so I am going to get a new amp to flatten out the response down low.
    I used my rat shack meter and at 30 htz and below the sub drops off and barely registers at all. Definetly need a new amp!
     

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