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Newb needing sub help

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  • Newb needing sub help

    Hi All,


    Have been lurking here for a while and am really impressed with both the knowledge level and the willingness to help. I joined as I have a few questions that I could not get answered through searching here or on the web.


    I am adding a pair of Peavey SP118BX subs and have been reading a lot here on the necessity of a high pass filter to prevent excursion. I am not sure if it is just terminology, but I can't find any high pass filters as a stand alone unit; am I right in assuming when people here talk about a HPF they are refering to running a crossover with the response set to match the specs of the driver? Or are you suggesting you run both sides of a stereo crossover for the subs, raw signal into channel 1 and cut the top off at frequency "x" and then run that into channel 2 for the low roll-off at frequency "y" and out to the power amp?


    If this has already been explained somewhere please point me to the thread, I did look for it but could only find a lot of references to HPF without a good explanation of the how.


    Also, any good recommendations on amps that work well with these from people who are using them? My intended purpose for now is just addition to my bass rig, eventual use will be for PA as I continue to build a system and stop renting.






    Did I mention the new forum sucks?

  • #2

    A "crossover" in it's most simple terms is a pair of filters ... one high pass (that sends signal to the tops) and one low pass that sends signal to the bottoms).


    What we are talking about wrt a sub cabinet is also addind an additional high pass filter (HPF) that serves to limit how low  a signal can enter the box.  Finding a stand alone HPF is probably difficult these days.  They are usually included with a crossover, EQ, DSP and a number of power amps.  They are usually only adjustable in DSP units (driverack, etc)


    You should set a HPF at 49 Hz for the Peavey sub you mention if you intend running it at moderate levels. A little higher if you plan to drive the snot out of it and a little lower if you are not going to drive it much at all (like with a hi-fi system)


    You also have to remember that setting the HPF to the proper frequency will be nullified if you then add much bass boost at the channel level or with a system EQ.

    Don Boomer


    • RoadRanger
      RoadRanger commented
      Editing a comment

      Many power amps have a switchable HPF built-in. The QSC RMX family has a 30 and 50Hz choice for instance. Also some crossovers have one - the much loved (by me anyways ) DBX 223 has a switchable 40Hz HPF. 

    • Rob_H
      Rob_H commented
      Editing a comment

      Thanks for the quick response,


      How did you come up with 49 Hz? Is that a general setting or based on experience with the Peaveys? The reason I ask is the data sheet recommends 35 to 40 Hz @ 12 to 24 db/octave, just want to understand the difference.


      Also, I don't understand your comment on adding bass at the board end impacting what the low pass filters out. I am not questioning your knowledge, I just don't understand how what happens before the filter impacts what happens after it? If I understand what you are saying, the HPF happens in the xover (or possibly in an amp as well); if I have the HPF set at say 40 Hz and I add additional trim at 35 Hz upstream of the filter, wouldn't the HPF block it from getting in the signal path out to the amp anyway?


      Appreciate the help!



  • #3
    The hpf is based on the particular speaker and how hard it may be driven as well as the filters slope. For a 24 dB/oct slope and Butterworyh alignment, driven at no more than 1.5x the rms rating of the driver, I would use 40hz but as you deviate from these specs the hpf freq. should increase.


    • #4
      Good engineering does not always make for good marketing


      • #5
        Rms on those cabinets is along the same lines as continuous. Those have the newer BW drivers right?


        • Rob_H
          Rob_H commented
          Editing a comment

          118BX data sheet


          Correct, they are new style BW....link is above


          EDIT: added new style