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How do you make a High Pass Filter @ 40 Hz?

Discussion in 'Amps [BG]' started by GlennW, Jan 7, 2008.


  1. GlennW

    GlennW

    Sep 6, 2006
    All I found searching was stuff I don't understand.

    I'm building a medium size full range cabinet for an Eminence KappaLite 3015 following their specs. The cab will be used alone. It says to use a High Pass Filter @ 40 Hz. What's an easy way to do this?
     
  2. joegeezer

    joegeezer

    Mar 9, 2005
    Northern Wisconsin
    Disclosures:
    Avatar Club#12 Eden Club Lucky# 13--USA Peavey Club#37 Carvin Club#5
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  4. billfitzmaurice

    billfitzmaurice

    Sep 15, 2004
    New Hampshire
    Disclosures:
    Owner, Bill Fitzmaurice Loudspeaker Design
    These filters are usually built into the LMS (Loudspeaker Management System) of PA systems. Building one using passive crossover components would be prohibitively expensive, well over $100.
     
  5. GlennW

    GlennW

    Sep 6, 2006
    Thanks, I think I'll skip that step and see how it goes.
     
  6. Johnny Crab

    Johnny Crab ACME,QSC,Fame/Hondo/Greco user & BOSE Abuser Gold Supporting Member

    Feb 11, 2004
    South Texas
  7. GlennW

    GlennW

    Sep 6, 2006
    Thanks, they have a 30 Hz and and a 50 Hz. I'll keep the link handy in case.
     
  8. Passinwind

    Passinwind Charlie Escher Supporting Member

    I generally use the built-in ones in my power amps, although most tend to be a little above or below 40Hz IME. My Ashly parametric EQs have an adjustable one, as do quite a few other pro audio EQs.
     
  9. coyoteboy

    coyoteboy easy there, Ned Supporting Member

    Mar 29, 2000
    Sactomato, CA
    Is there such a thing as a passive variable frequency high or low pass filter?
     
  10. *smb

    *smb

    Nov 26, 2006
    Yes. It's a capacitor in series with a variable resistor.
     
  11. GlennW

    GlennW

    Sep 6, 2006
    I got a speaker from ebay with something like that. It was '59 blue Jensen 15" and it had a big (40 uF?) cap and what was left of what I think was a rheostat. Would something like that work?
     
  12. *smb

    *smb

    Nov 26, 2006
    Chances are it was made by someone like me with a head full of maths and graphs and little real-world knowledge. I'd test the values of everything with a multimeter, find the current ratings of each component, calculate where the cut-off point should be and then give it a low-volume trial run.
     
  13. GlennW

    GlennW

    Sep 6, 2006
    Thanks for the idea, I might look into that. That's kind of the answer I was expecting...I'm 99% sure I threw that stuff away after "saving it" for a few months.
     
  14. The filters frequency is determined by the fixed value of the capacitor... no? :confused:
     
  15. Edword

    Edword

    Jun 23, 2005
    Detroitish
    FWIW, I wrote to Eminence last week, asking about the availability of a 40Hz high-pass filter, after seeing it in one of their cab design specs.

    This was their reply:

    We do not offer the high pass filter. Ideally, it is done actively. Parts Express might be a good place to find a schematic to build a passive filter. Although, this may not be necessary for bass applications, as there's not much information below 40Hz. It's recommended to protect the driver from overexcursion problems. Pro audio is where it's absolutely necessary.
     
  16. A9X

    A9X

    Dec 27, 2003
    Sinny, Oztraya
    This is how I'd do it, but there is a lot of redundancy in the boards for what you want.
    http://sound.westhost.com/project09.htm

    The Ashly EQ is probably the best idea.

    That will do wonders for the efficiency of the system.
     
  17. GlennW

    GlennW

    Sep 6, 2006
    Thanks everybody for the input.

    My only concern was the bass drum from a drum machine. I don't know what Hz that is. I'll just forget about the HPF for now and play with the EQ on the amp.
     
  18. billfitzmaurice

    billfitzmaurice

    Sep 15, 2004
    New Hampshire
    Disclosures:
    Owner, Bill Fitzmaurice Loudspeaker Design
    A capacitor alone is a 1st order filter, and offers virtually no protection. BTW, at 40 Hz you'd need a 350uF capacitor.
     
  19. asad137

    asad137

    Jan 18, 2007
    Minneapolis
    Disclosures:
    Physicist
    No, the time constant is given by R*C.

    Asad
     



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