What cross over to use, 80hz or 120Hz?

Discussion in 'Live Sound [BG]' started by Dp1363, Jun 25, 2020.

  1. Dp1363

    Dp1363 Supporting Member

    Jan 8, 2011
    South Jersey US
    I have a X32 Rack digital mixer. I needed to reconfigure my setup due to making some changes to my overall mix. Before I reconfigured my mixer I had a crossover setup on the X32 between the main L & R out, and the MRC for subs. The crossover point was at 98Hz.

    Now I need to run the whole mix through the main L & R out, route it to my subs and plan to use the sub's built in crossover. However, the only options available on the subs crossover are 80Hz or 120Hz. The subs are model 15" RCF 705 AS.

    Which crossover would be the better choice? Since the subs are 15's I was thinking of using the crossover set at 120Hz, since the 15's should be able to handle some higher frequencies with less mud than 18's would. Or does it make sense to limit them to the 80Hz and keep the frequencies above 80Hz out of the subs?
  2. Stumbo

    Stumbo Guest

    Feb 11, 2008
    What's the frequency range of the subs?

    Do you have a graph?
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  3. Dp1363

    Dp1363 Supporting Member

    Jan 8, 2011
    South Jersey US
    40 Hz ÷ 120 Hz

  4. thumbknuckle

    thumbknuckle In Memoriam

    May 23, 2012
    Westfield, MA
    What are the tops and what are you crossing them over at?
  5. Dp1363

    Dp1363 Supporting Member

    Jan 8, 2011
    South Jersey US
    Tops are RCF HD 32-A MK4 they cross over at 700 Hz.
  6. Wasnex


    Dec 25, 2011
    It look looks like these cabs can run down to 80hz. IMHO the best course of action would be to try both 80 and 120hz and choose whichever sounds best. Given the frequency response graphs, I think 80hz will probably provide the flattest frequency response and best fidelity, but it may depend upon how loud you plan to push the system and how much bass you plan to run.
  7. bbh

    bbh Supporting Member

    Sep 27, 2011
    I believe in whatever sounds best. I’m guessing the higher xover will make the system sound seamless. However, crossing over lower could clean up the sound. A lot depends on who is mixing. Didn’t RCF help you out?when I did sound, I’d carry a noise generator to give me a great starting point just about every time.
  8. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    That's the way I'd go. This dovetails the high-pass filters on your vocal channels. You don't want anything intelligible (vocals) coming from the subs.

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  9. And I

    And I

    Feb 19, 2009
    Witchtown, MA
    I'd always start lower and only go up if you hear it's needed. Your full range speakers will be just fine down to 80hz. Your sub is already down 10db at 120hz. My guess is you'll hear something missing when you try 120hz.
  10. 40Hz

    40Hz Supporting Member

    May 24, 2006
    My guess based on my own experience and the information you provided is that it probably would be 80Hz. But you’ll need to check it by ear. So I’d pipe some full range source into it and do multiple A/B comparisons. And do it over a few days since you might change your mind a few times before you settle on what settings you really prefer hearing.

    You may also need to adjust things from your preferred settings depending on the room anyway. So trust your ears. And if the place fills up recheck multiple times in the course of the show. Having someone out on the floor whose ears you trust to provide feedback is helpful since an empty house soundcheck sometimes only puts you in the ballpark.

    Luck! :)
  11. iiipopes

    iiipopes Supporting Member

    May 4, 2009
    I have usually preferred a 120 Hz crossover, because the natural dip at that point where the woofer ends and the midrange takes over is about where many smaller venues have a room resonance, so it cuts down on standing waves.
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  12. Dirk Diggler

    Dirk Diggler Supporting Member

    Mar 3, 2004
    Anytown USA
    1st there are no rules, that's why most crossovers are variable.
    It all depends on the speakers, amplifiers, and even the room.

    If your speakers only go down to 80hz, what are you crossing over?
    Answer: Nothing if you're set at 80hz.

    Good luck,
  13. thumbknuckle

    thumbknuckle In Memoriam

    May 23, 2012
    Westfield, MA
    You are crossing over your tops at 700 Hz? Did you mean 70? Even if you set the subs to 120 you are leaving a 3 octave hole in the middle of your system.
  14. darwin-bass


    Mar 29, 2013
    Salem OR
    Are you planning to mix the subs at the same volume level as the mains or are you going to crank the subs to get that chest thump effect?

    Based on the graph, if you want the sub to be a smooth extension of the mains, I'd try 80Hz first. If you want the subs 10+ dB louder than the mains, I'd go with 120 Hz. Then I'd listen and pick what sounded best.
  15. sawzalot

    sawzalot Supporting Member

    Oct 18, 2007
    The charts for the sub don't quite make sense... The top chart says "Low pass 80 hz" so we can't see what they can do above that to determine if they have enough sensitivity in the 80-120hz region. But it may not matter:

    According to the specs, the RCF's have an internal crossover between the low frequency driver and the high frequency driver at 700Hz--that's what the "700Hz" number means.

    Their frequency response is listed as down to 45 Hz but the frequency charts in the downloads section of the RCF website shows they start dropping off rapidly below 80 Hz. If it were me I think I'd cross these over at 80 and see how it sounds. If you cross over at 120 I'm betting you'll get a bit of mud as you'll have both the subs and the tops reproducing the 80-120 hz range, but it might sound ok so I'd try it.


    MYLOWFREQ Supporting Member

    May 13, 2011
    I'd keep it at 80Hz. Seems like the sub peaks at around 65Hz, and the tops can go down to 45Hz. Cut everything below 80Hz on the tops, and you'll still have most of your bass on tops.

    You can always try both and see which you like the best.
  17. vvvmmm


    Dec 6, 2016
    Mmmmmm, there's this thing called 'slope" ...

    I never had an issue with PA, but it's a welcome concept, the basis of love even, for things like the Pulteq EQ ...
  18. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Can you +/- 15Hz at 90 for the center and navigate for the room? How precise is the published data?
  19. Bassndrums73


    Mar 13, 2018
    Let your ears be the judge and may the bass be with you.
    iiipopes likes this.
  20. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    all the online stuff i'm seeing is for the 705 AS MK2. that one shows as having 80 and 110Hz crossover settings.

    with 12" tops i vote for the higher setting either way, and those tops will probably still far outstrip the subs if you let them (unless you've got like four subs to two tops)