Cascading Crossovers - how much of an issue?

Discussion in 'Archived Threads 2001-2004' started by Gregory S, Sep 19, 2002.

  1. Gregory S

    Gregory S Stunt Coordinator

    Joined:
    Jan 3, 2001
    Messages:
    53
    Likes Received:
    0
    Hi,

    I just received my HK AVR-520 and I will be using it with ACI Sapphire III LE speakers and an M&K MX-80 subwoofer. Seeing that I can't defeat the crossover in the subwoofer, the sub's crossover will have to be set to the maximun (150 Hz) and the 8O HZ crossover from the HK 520 will be sent to the sub.
    The way the M&K'S crossover works is any crossover frequency below 120 Hz has a slope of -18 db/octave and from 120 Hz on up the slope changes to -36 db/octave. So, if you sent a full-range signal to the sub and set the crossover at 80 Hz, then when the signal was between 80 Hz and 120 Hz the slope would be -18 db/oct. and when the frequency was at 120 HZ or higher the slope would be -36 db/oct.

    Now with the AVR-520 I'll be sending the sub a signal already crossed-over at 80 Hz. So, my question is what will happen? I always heard cascading the crossovers is a bad thing, but it seems that many of us are in this boat. To me it seems that the AVR-520 will be sending out a crossed-over signal at 80 Hz at a slope of -18db/oct., then the sub will get it and maybe apply another -18 db to it, unless it's above 120 Hz, where it will get another -36 db. Is this an issue? - HELP!

    Anyone have experience with this issue?

    Thanks,
    Greg
     
  2. Jonathan M

    Jonathan M Second Unit

    Joined:
    Jul 23, 2002
    Messages:
    267
    Likes Received:
    0
    Hi Greg,

    As to whether or not this is a bad thing is dependent on:

    1. The Q of the xover's in both the receiver and the sub.
    2. The relative cut-off frequencies
    3. And most important, the room it's in.

    I would say that unless you cannot find a suitable setting on the sub to satisfy your needs, the only thing to do is to put an external xover in between the receivers preamp and poweramp. This would allow you to control the bass management entirely yourself. This can be done with passive xovers (Need to know info regarding the output impedance of the preamp and input inpedances of the sub and poweramp) or active xovers (Probably commercial unit, unless you're happy to DIY)

    My advice would be to try and get someone else to adjust both the phase switch and xover frequency on the sub while you are listening in your normal position.

    Cheers
    Jonathan
     
  3. Kevin C Brown

    Kevin C Brown Producer

    Joined:
    Aug 3, 2000
    Messages:
    5,712
    Likes Received:
    0
    Greg- At the level of the crossover slopes you're talking about, I *really* don't think the receiver's crossover at 80 Hz, and the sub's crossover at 150 Hz are going to interact much.
    160 Hz is one octave up from 80 Hz.
    Based on your explanation, you *only* have the slope of -36 dB/octave to worry about for the sub. I.e., if you set the sub's crossover at 150 Hz, the slope from 80 to 120 is never used. At 150 Hz, the signal would be -3 dB down. Anything below roughly 135 Hz would be full signal level. At say 300 Hz, the signal would be 39 dB down (3 + 36).
    Now, thinking about the receiver's imposed slope on the signal going to the sub. 80 Hz on the receiver is almost one full octave down from 150 Hz on the sub. So the receiver's signal to the sub at 150 Hz is about 3 + 18 = 21 dB down. Then above roughly 150 Hz you have the additive 18 + 36 => -54 dB.
    In real world listening? 21 dB is a lot.
    In a nutshell, with the -18 dB/octave slope of the receiver starting at 80 Hz (remember, already 3 dB down), the receiver drops the signal fast enough that I don't think you'd ever notice what's going on above the 150 Hz where the sub's crossover kicks in.
    I'm writing this late at night, and when I re-read it, it doesn't make a lot of sense to me, but maybe you get the gist... [​IMG]
    I even had to edit it once to make it more intelligible!
     
  4. Kevin C Brown

    Kevin C Brown Producer

    Joined:
    Aug 3, 2000
    Messages:
    5,712
    Likes Received:
    0
    Another way: use an SPL meter and a discrete test tone disc like Stryke. Then at least you could measure what's going on around 80 Hz and around 150 hz (and above) to see if there's any problem. Plus, IMO, it's a lot easier to get the phase correct with a test tone disc and an SPL meter than by ear. [​IMG]
     
  5. Lewis Besze

    Lewis Besze Producer

    Joined:
    Jul 28, 1999
    Messages:
    3,134
    Likes Received:
    0
    Kevin is right,this is hardly an issue worth worry about,at least in your case.
     

Share This Page