Question Crossover confusion

Discussion in 'AV Pre-Amp/Processors & Power Amps' started by jorjov, May 22, 2019.

  1. jorjov

    jorjov
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    Hi all!

    I have a Marantz SR8012 that I struggle a bit with.
    I have ran Audyssey.
    All speakers set to small. Also in 2 Channel Playback
    Crossover set to 100Hz on all speakers. Also in 2 Channel Playback.
    SW Mode is set to LFE.
    2 subwoofers (B&W ASW610XP)
    Sound mode is Music/Stereo (no direct or pure direct)
    Audyssey is set to reference.

    When I play test tones from 40Hz to 150Hz both the subwoofers and main (front) speakers are outputting sound. I can feel the woofers moving on my front speakers all the way from 40-50Hz and up. I also get sound out of the sub from 100Hz and up. What is causing this behaviour? I have played test tones from multiple sources with the same result. It's like the crossover is not in play at all.

    Best regards
    Jorn
     
  2. jamieu

    jamieu
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    Maybe I am misreading the question, but a crossover doesn't just cut off below & above a given frequency, it's more of a slope. So you'd expect to hear some >100Hz content from your sub and some <100Hz content from your mains.
     
  3. jorjov

    jorjov
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    Thanks for the reply jamieu :)
    I know there can occur some bleeding. But I didn't expect the main speakers to play fairly load at 40-50 Hz. I would expect a roll-off at around maybe 80-90 Hz.
    Having said that I tried turning off the subs, and only played using the 2 front speakers (B&W CM10 S2). The sound was quite a lot fuller at Direct/Pure Direct than ordinary stereo. So I guess there is a cutoff, but I expected it to be more pronounced.
     
  4. Mark.Yudkin

    Mark.Yudkin
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    The THX crossover definition is:
    The reason for the differentiation between the LCR and the subwoofer is the THX rolloff specification for the LCR speakers of -12dB/octave, summing to -24dB/octave effective. For this to work at the 80 crossover frequency, signals must be -3dB for both LCR and subwoofer at crossover (sum is then 0dB = flat).

    Most AVR's follow the THX definitions, but rather than fixing the filters, adjust the LPF / HPF during the setup to obtain a -24dB/octave total.

    We can now plug in the above numbers in your case of a 100Hz crossover: At 100Hz you need -3dB in both LCR and subwoofer. At 50Hz (one octave) you therefore have -27dB effective on the LCR, the same as the subwoofer at 200Hz (one octave). At 25Hz (LCR) you have -51dB, same as subwoofer at 400Hz. This is not very loud, but if you're looking for it, you'll find it.
     
  5. jorjov

    jorjov
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    Well, I definitely found it. By chance really, when I was EQ'ing the subs. Anyway, thanks a lot for the clarification Mark. Much appreciated :)
     

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