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Crossover Frequency - Denon / SVS / Mission

Discussion in 'Archived Threads 2001-2004' started by Gary Thomas, Dec 17, 2001.

  1. Gary Thomas

    Gary Thomas Second Unit

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    Here's the set-up:

    Denon 3802

    Mission Mains: 45hz

    Center: 75hz

    Side Surround: 100hz

    Rear Surround: 75hz

    SVS CS-Ultra

    ART 351 EQ

    The mains, SVS & ART are new. In the past I had the Denon crossed over at 80hz, realizing there was a gap in the side surrounds.

    Would you recommend using a 100hz crossover?

    The Denon can send the signal to the bass at 80hz, 100hz or 120hz.
     
  2. Steve_Ma

    Steve_Ma Second Unit

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    I would reccomend the 100Hz x-over. In your case, I think it would makse sense.

    --S
     
  3. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    I cannot agree. Take a cold hard look at the tradeoff. At 100 Hz, the sub will get some voice and lots of localizing mid bass from all 5 channels (remember, 100Hz is where the cross STARTS to roll off- plenty of energy at 110,120,130 Hz sent to sub). This is a big price to pay to fill a little 1/4 octave "gap" (not a true gap anyway but a dip as the surrounds do not roll off hard either) in the rear surrounds, which in 99% of source material there will be little down there to lose. In fact, I think 60 would be better than 80.
     
  4. Gary Thomas

    Gary Thomas Second Unit

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    One vote for each...any other thoughts?

    It looks like the Outlaw bass management component in only designed for use w/ a dvd-a player. Any ideas to get the benefit of this type of bass management (customized for each speaker) that can be used with all sources: CD, Sat. TV, VCR? It would have to go between the sources & receiver, as I don't have external amps.
     
  5. BruceD

    BruceD Screenwriter

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    Gary,

    here is what I said in another thread:

    quote:

    -----------------------------------------------------------

    I route all my bass (LFE and re-directed bass from center and surrounds) to my front L&R speakers (and sub), which allows me to use the sub in 2-channel stereo mode as well as HT!!

    Because (IMHO) you can never get both optimum imaging and bass output with a single main speaker placement, even for floorstanders like I have that go down to 32Hz.

    Let me explain.

    First I don't use any of what I consider the flawed xovers provided on most receivers or pre-pros (IMHO), like the THX -12dB high pass (with phase anomolies), -24dB low pass. They are not optimized for music, but instead for effects, again IMHO.

    So, here is what I do;

    1) Set my DD/DTS processor to NO sub, Mains to LARGE, center and surrounds to small (sends all redirected bass
     
  6. Lee-c

    Lee-c Second Unit

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    But even if the receiver is trying to send some frequencies above 100Hz to the sub, if you

    have the SVS set to a 100Hz xover, then it wouldn't play anything above 100Hz, right?

    This would leave the mains to handle everything over 100Hz exclusively.
     
  7. BruceD

    BruceD Screenwriter

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    Lee,

    The thing to remember is; a crossover is not like a brick wall, but more like a ski slope.

    i.e. it is a gradual reduction in output.

    How gradual the reduction is controlled by how steep the slope is. Examples are: 6dB/octave (gentle slope), 12dB/octave slope, 24dB/octave (steep slope), etc.

    As you can see from the examples above, output levels at 40Hz for an 80Hz crossover depend on the slope. A crossover with a 6dB slope will have much more output at 40Hz than one with a 24dB slope, a difference you could definately hear.

    BruceD
     
  8. Lee-c

    Lee-c Second Unit

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    Bruce,

    I understand that the crossover on the receiver is not a brick wall, but I was under the impression

    that the crossover on the sub itself was. So, if you have a 100Hz crossover on your receiver,

    the mains will still play sounds below that freq. (though the drop-off has begun); and apparently

    the sub will also get sent some notes above 100Hz (wasn't aware of that part until it got

    mentioned in this thread). But if a sub's built-in crossover is set to 100Hz, wouldn't that

    prevent the sub from reproducing anything above 100Hz, regardless of what the receiver

    might send it?

    I certainly hope that is the case, as I wouldn't want my SVS sub (plan to get one soon)

    to play anything at all above 100Hz that might cause localization issues of any kind.
     
  9. BruceD

    BruceD Screenwriter

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    Typically the receiver implements both halves of the crossover and if your sub is connected to the receiver's SUB-out, the crossover inh the sub itself should be disabled or turned all the way up.

    The receivers two halves are:

    1) high-pass to the mains (typically -12dB slope xover)

    this means everything below the xover is attenuated by -12dB/octave. If xover = 80Hz, then the signal would be down -12dB by 40Hz (but down less at 60Hz or 70Hz).

    2) low-pass to the sub (typically -24dB slope xover)

    this means everything above the xover is attenuated by -24dB/octave. If the xover = 80Hz, then the signal would be down -24dB at 160Hz (but down less at 90Hz or 100Hz).

    This allows the mains to produce more bass output across the crossover (depending on the low frequency rolloff of the mains of course) and actually duplicate what the sub is also producing. This can cause peaks or muddy the sound.

    I found it particularly difficult to get a smooth integration of mains and sub with a receiver's internal crossover.

    The receiver's designers intended the internal -12dB high-pass slope to work with a speaker's natural -12dB low frequency rolloff to create a combined -24dB high pass slope.

    The problem with this (IMHO) is that the speaker's -12dB natural rolloff is based on a sealed or acoustic suspension speaker only, not the ported speaker that everybody uses today.

    I think this could be one of the causes of people reporting problems with sub integration.

    It is also one of the reasons why I went to my own electronic xover method.

    By the way the LFE channel is spec'd by Dolby to deliever 20Hz to 120Hz of frequency content.

    BruceD
     
  10. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    Bruce,

    That Marchand/BFD combo sounds KILLER. Best of all worlds (except simplicity !) Have you ever tried setting the Marchand a little lower, maybe 50 ? Seems the Danes could handle that and the sub would get nothing localizable for sure. Guess you would have to redo the BFD program.

    Thanks for the great posts in this thread and eleswhere.
     
  11. Lee-c

    Lee-c Second Unit

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    Bruce,
    Thanks for the info. [​IMG] But why would one want to set the sub's built-in crossover all the way up
    so that it reproduces all those notes above 100Hz (assuming that's the receiver's crossover point)
    that the receiver might send it?
    The main speakers will be getting full strength signals all the way down to 100Hz, so I see
    no need to have the sub duplicate any sounds above 100Hz at all. That's the mains' job, let
    them do it on their own. Why not just set the sub's internal crossover to 100Hz (which I assume
    is a brick wall?) and let the mains start to hand over the workload to the sub at that point?
    By keeping the sub's output strictly to 100Hz and below, any concerns over localization can
    be done away with. And the mains should have no trouble with their end of the workload at 100Hz and up.
    Any thoughts and suggestions welcome. [​IMG]
     
  12. BruceD

    BruceD Screenwriter

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    Lee,

    No crossover is a brickwall, although some subs implement something like a -48dB/octave filter above 150Hz or so. They all let frequencies get through to some degree.

    The point about the receiver's and sub's crossovers is that you don't want cascading crossovers - two different crossovers trying to work togehter.

    Cascading example:

    1) receiver xover set at 100Hz

    2) sub xover set at 100Hz

    This will not work like a simple 100Hz crossover, in fact the result is very unpredictable.

    The normally correct setup is:

    1) receiver xover set at 100Hz

    2) the sub xover turned OFF

    If you can't turn the sub xover OFF, then you want to set the sub's xover as high as it will go, like 150Hz or 200Hz.

    You ask why? So that any signal sent to the sub from the receiver doesn't have much strength left by the time it gets to the sub's higher crossover. Remember, the receiver is already cutting the signal by -24dB above 100Hz, so that any signal getting to the sub's 150Hz or 200Hz xover will already be attenuated (smaller in strength).

    BruceD
     
  13. BruceD

    BruceD Screenwriter

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    Gary,

    I would probably vote for the 80Hz xover also, as I don't think you will notice the small gap in the side surrounds.

    Just my opinion, but if the sides are on a side wall their bass response is probably lower and stronger than the 100Hz anyway, so you are probably missing even less here than you might think.

    BruceD
     
  14. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    Hi Gary, you pretty much got all sides of the issue already. All good advice...mostly geared toward personal preference issues to a large degree.
    If you want to see what the sides are capable of in your room...you could run some full bandwidth pink noise thru them and using something like
    www.spectraplus.com
    you'll get a good idea of the actual in room performance of the sides.(it's possible they are fine to 80hz).
    If you can spend some time with spectra(this assumes you have a notebook PC or a desktop near the HT room)...you'll be able to try out all your bass management options and watch the real time analyzing screen on spectra to determine which is giving you more accurate response curves at your key listening seats.
    If you get the feeling the sides are definitely rolling off around 100hz...I wouldn't hesitate to set the HP to 100hz(could you do it just for the sides?). Try the 100hz setting out for a weekend and see what you think. Chances are the differences will be extremely subtle...and probably only present on a small % of source material regardless.
    In other words, have fun tweaking as time allows...but don't let this kind of stuff keep you awake at night..[​IMG]
    TV
     

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