Sub crossover ?

Discussion in 'Speakers' started by Robt_P, Feb 16, 2004.

  1. Robt_P

    Robt_P Auditioning

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    I just received my Hsu SFT-3 (Max extension) the other day and have a question. When I run Avia's low frequency sweeps from 200hz-20hz, it seems as though my sub starts outputting at around 130hz or so. The sub crossover is is set to "out" (disabled) and the speaker settings on my H/K AVR320 is set to "small" with the crossover point at 100hz.

    Is this normal?
     
  2. Lew Crippen

    Lew Crippen Executive Producer

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    I’m not sure about ‘normal’, but it is not surprising.

    Crossovers are not discrete, but gradual, so that at 100 Hz your mains and sub should each reproduce 50% of the sound. And as the frequencies go up, the mains produce more and the sub less. Conversely, as the sound being reproduced goes below 100 Hz the sub produces more and the mains less.

    One quick rule of thumb is that the curve is about one octave, meaning that the mains will still be reproducing sound at one half the crossover point and the sub at twice the crossover point. However most crossovers have a steeper curve going up, so that the sub does not reproduce at twice the frequency. So one might think that the sub would go to maybe about 150 Hz, instead of 200 Hz.

    To that consideration, you must consider that crossovers are designed differently. Apparently the one in your H/K is a bit steeper, with a result that 130 Hz is the point where your sub no longer is called on to produce sound.

    I would be interesting to know how far down your mains go when set to small.
     
  3. JakubH

    JakubH Stunt Coordinator

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    Lew is correct, and yes its normal. Most AV recievers use 1st or 2nd order filters on the sub/mains. This means that the mains are either 6db or 12db down an octave below the crossover point (1st order & 2nd order respectively), while the sub is 6 or 12 db down an octave above the crossover frequency.

    This is why some people use an outboard crossover with steeper slopes (4rd - 6th order), set the mains to large, and run the preamps out to the external crossover.
     

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