Ideal port tuning

Discussion in 'Amps and Cabs [BG]' started by Sundogue, Nov 16, 2004.

  1. Sundogue


    Apr 26, 2001
    Wausau, WI
    I'm getting a lot of mixed information regarding this...

    When tuning a ported cab, is it best to get the Fb to match the Fs?

    Or is it better to tune the cab's frequency so it goes lower than the speaker's ideal frequency?

    What are the advantages/disadvantages of tuning the cab so it's higher/lower/matched relative to the speakers being used?

    What are the possible dangers to the speakers, if any, of tuning it too low, or too high?

    Like a badly designed cab, this information seems as clear as mud. :)
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    If the tuning frequency is above the lowest frequency that you'll put through the box, the theory is that the drivers are unloaded below the tuning frequency and the box won't act as an acoustic spring to protect the cones from overexcursion.

    I'm not sure how that all works out in practice as there are plenty of commercially available cabinets that are tuned above the low 30s...

    When I measured the tuning frequency on the Goliath IIs that I had, I came up with a freq in the low 30s.

    Did you measure the tuning frequency on the 410 TVX to find out what it is?

    Tuning too low will cause steeper roll-off above the tuning frequency. Plugging numbers into WinISD will show you what happens on paper (or virtual paper).
  3. Sundogue


    Apr 26, 2001
    Wausau, WI
    Well, that's part of what is confusing.

    On one hand, I keep hearing that if a cab is tuned to let's say 40Hz, anything played below that risks damaging the driver.

    But I play a 5 string (although I seldom go below D on the B string, and even that is rare...I use the B string more for positioning of certain lines) through my 410TVX (which is tuned to 40Hz) and the low B sounds clear and certainly hasn't blown my speakers. And I've even hammered on the low B at quite loud volumes and it's never done any damage.

    In fact, I've played my low B on a variety of cabs/speakers, at some pretty significant volumes (though I don't play very loud anymore). I've played it pretty heavy through 210's, specifically the BAM210 and Carvin RC210 combos and they came through just fine.

    So it's a bit confusing.

    Additionally, does EQ'ing and using a compressor come into play here? I typically use a compressor when I play and perhaps that helps defeat some excursion on the low end. Any thoughts are greatly appreciated.

    Also, I keep reading conflicting info on port location. Some say it doesn't matter where the port is located, and yet others say the port should be at least a diameter away from any walls. If that is the case, why would a vent located at the bottom work then?

    Picky, picky, picky I know. But it's an interesting subject that seems to raise four new questions for every answer! :)
  4. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    Most of what you are hearing when you play your B string is not the fundamental, but the upper harmonic content.

    I pound my low B at some high volume levels, and it sounds great, but I have my high-pass filter on my QSC power amp set at 50hz, so the cab is seeing nothing below that. To me, that really tightens up my sound, and I still hear the low B fine. Certainly, no fundamental, but plenty of harmonic content.
  5. Sundogue


    Apr 26, 2001
    Wausau, WI
    I can live with not actually hearing the fundamental. I'm not making a true, stand alone sub. I'm more concerned about blowing my speakers if the cab is tuned to say 40Hz and I play a low B at loud volume.

    But I haven't blown any 10" speakers yet and they've all been loaded in cabs rated at 40Hz (and let's face it, that's probably a generous rating at that for most commercially available cabs).