Questions about parametric eq boost.

Discussion in 'Archived Threads 2001-2004' started by Jones_Rush, Apr 4, 2001.

  1. Jones_Rush

    Jones_Rush Stunt Coordinator

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    Let's say I'm using a parametric eq like the BFD to boost 53hz by 4db and use a very small bandwidth for the boost.
    By doing this I actually reduced the dynamic range of my system: BFD/AMP/SUB by 4db, the first one to "suffer" from this is usually the amp, if the amp is stronger than the sub then the sub will be the first to clip, and if both the amp/sub are stronger than the BFD, then the BFD will be the first to clip. My question is, after the first boost of +4db at 53hz, If I choose to boost any OTHER frequency at +4db (and make sure the bandwidth is small enough to not affect 53hz), will it further decrease the dynamic range of my system ?, according to common sense, any other boosting by 4db (at OTHER feq's than 53hz) shouldn't reduce the dynamic range any further than the first boost has already reduced it, am I right ?.
    Another question, If I use a 250W amp and boost a frequency at 4db, does it mean that I'll now have the headroom of an approx 100W amp ?. If my calculations are correct, it means that those who use a 250W plate amp with the notorious +6db at 30hz boost, actually get headroom of a 65W amp. How can you watch a movie with a headroom of 65W sub amp ??? at enjoyable listening SPL's any "boom" will end with a clip...
     
  2. Greg Monfort

    Greg Monfort Supporting Actor

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    Dynamic range is frequency dependent, so you haven't limited it over a wide BW. What you have limited is max wide BW continuous SPL assuming a ~flat FR.
    250W = 10*log(250) = ~24dB. 4dB boost = 2^[(dB2-dB1)/3.01] = 2^(24-4/3.01) = ~100W (~20dB). 6dB boost = ~63W (~18dB) headroom at the EQ'd frequencies. The rest of the BW has ~24dB.
    Whether this is sufficient is dependent on how efficient the speakers are, how far away you sit, program material, etc..
    GM
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    Loud is beautiful, if it's clean
     
  3. Timmy

    Timmy Stunt Coordinator

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    If you boost all frequencies, then the amp is taxed greatly; but to add 3 or 4 db of boost at a very narrow band of frequencies will have a much smaller effect on the amp.
    Now, if you are using your BFD to extend a subs low end roll off; then as stated above the lower the frequencies
    the more amplifier power is required.
    Active EQ is used on many commercial subs; the Sunfire line is a prime example. The box is very small; but with a hefty amplifier and active EQ; it can be made to perform almost perfectly......AKA: the brute force method.
    If all one wants is to extend the low end rolloff of their existing powered sub; I would think it better to replace the unit with a better one; then to try and buy a BFD and juggle settings so that the existing amp and driver is not overtaxed.
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