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Denon amp and useless crossover frequency

Discussion in 'AV Receivers & Amplifiers' started by Jules, Aug 21, 2004.

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  1. Jules

    Jules
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    During a subwoofer calibration run with an SPL metre, I noticed something I should have noticed years ago... and I'm baffled.

    My Denon A1SE has speaker set up options for small/large, and crossover frequency options of 40/60/80/100 or 120 Hz.

    BUT... I set the speakers to small and crossover frequency to 120Hz (just to see), and unplugged the subwoofer while leaving the amp to beleive that the subwoofer was still connected.
    Then I measured the SPL with a 50Hz signal from the speakers.
    To my bewilderment, the SPL metre measured the same 50Hz reading with the crossover frequency set to 40Hz and 120Hz.

    I've tried every possibilty to rule out my conclusion, but I can't conclude anything other than the crossover frequency options in the amp do absolutely nothing!
    It explains why I can't remove a peak in the crossover frequency with the subwoofer as the amp is still kicking out the same level of bass signals to speakers regardless of the crossover settings.

    Is this a trate of Denon Amps? Anyone else noticed it?
    If not, could I ask anyone with a series of test tones, an SPL metre and a Denon amp to try it out and see if you conclude the same thing.

    Thanks
     
  2. karkus30

    karkus30
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    I sort of suspected something like that, although I never tested for it. I think when you set the speakers to small, then you get an output to the sub and a rolled off frequency cut off. Brick wall cut offs would make for a very difficult set up, I reckon they just start to roll back the output as the frequency dips below the xover point. Its probably only a fraction of a db down at the threshold value and will dip lower as the frequency decends, probably cutting back at around 30Hz.

    There must be someone who knows the answer. It took a BFD to set my system up and its still not perfect.
     
  3. Arcangel

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    It's perfectly normal as every amp does it. There are no brick wall filters and the crossover will follow a certain slope, whether that be 6db/12db/24db etc etc per octave.

    Stick with the Fixed THX on the Denon as that works very well indeed. :)

    Some info here on crossover slopes.

    http://www.bcae1.com/xovrslop.htm
     
  4. Jules

    Jules
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    I hear what you're saying, and I was aware it's not a brick wall filter.
    But what I'm saying is that at 50Hz, there is absolutely no difference whatsoever in SPL readings using the various crossover frequencies.

    However, I've managed to confuse myself still further....

    My speakers are KEF THX TDM23's, and each of these has a reversable slug that is supposed to adjust frequency response for 'wall' or 'free-space' positioning. But this makes no difference either!!
    What's going on?
     
  5. Arcangel

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    Presumably your room and/or sub is boosting certain frequencies at the listening position. Set all your speakers to small, all bass to the sub, set the Denon's crossover to Fixed THX, bypass the sub's crossover, set Phase to 0. Also set the Boundary Gain switch on the Kef THX's to the correct position (this affects response at around 80hz to 100hz). Then switch on the Denon's THX Ultra2 Boundary Gain Compensation and see what effect that has.:) This trims the response out from about 55hz downwards. It can help so it's worth trying out.

    By the sounds of it though, you may have to reposition your sub in another place. Anyway, give the above a go and see what happens.
     
  6. bigmacx

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    Were you running in 'pure direct' mode? I can't remember if this bypasses the bass management settings or not, might be worth checking. Have you tried the reverse, i.e. unplugging the speakers and seeing at which point the sub is kicking in at different cross over settings.

    Mac.
     
  7. Arcangel

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    Just another thing worth doing. Make sure all your delay times are accurately set. On the Denon you can adjust them in 1cm increments. The default is usually 10cm increments. Just go to the Delay Times/Speaker Distances in the setup menu, select Meters as your setting and when it goes to the next menu you'll see STEP at the top of the screen, change this to 0.01 from 0.1. You'll need to re-measure all your speakers distances and after you change them you'll have to rebalance the channel levels. It's worth doing as this can affect the sound by quite a bit. :)
     
  8. Jules

    Jules
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    Thanks for the replies, but everything you've suggested I've already ruled out as being the problem.

    I have made a huge improvement to my system by doing exactly the opposite of what I've always done and what everyone recommends.
    Despite owing THX speakers (that are supposed to tail off at 80Hz, but don't), I've set my front 3 speakers to 'large'. All the phase related problems between each individual speaker and the sub have disappeared. Much better!

    But I still think the crossover in the amp is useless.
    Which leads to another point..... If the amps crossover is very gradual, then the issue of conserving amplifier power by setting all speakers to small is greatly over-stated in my opion.
     
  9. Arcangel

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    Don't think the crossover is there to necessary relieve strain on the amplifier (although it helps). What the all small setting does is stop low bass frequencies coming from up to eight different speakers (7.1). Instead, you have only one bass source to contend with i.e the sub.

    In the end it's your system so if setting them to Large works for you, who am I to suggest otherwise! :)

    Still reckon you should move the sub and stick with all speakers small, all bass to sub though. Especially as you have THX speakers. Have a read of this:-

    http://www.avsforum.com/avs-vb/showthread.php?threadid=376142&perpage=20&pagenumber=3
     

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