Different port lengths with lspcad and Unibox

Discussion in 'Archived Threads 2001-2004' started by Kyle Richardson, Feb 14, 2002.

  1. Kyle Richardson

    Kyle Richardson Screenwriter

    Joined:
    Jan 1, 1998
    Messages:
    1,073
    Likes Received:
    0
    I'm just a touch confused. I'm entering in the same numbers in both programs but they are giving me different port lengths!

    283 liters

    22Hz tuning

    3ea 4" ports

    Ql=15

    Qa=100

    Unibox says 47.91cm and lspcad says 33.7cm for each port length. Why such the large difference?? I tend to believe Lspcad more but I was wondering what you guys are coming up with.

    Thanks

    Kyle Richardson

    Acoustic Visions
     
  2. Patrick Sun

    Patrick Sun Moderator
    Moderator

    Joined:
    Jun 30, 1999
    Messages:
    38,717
    Likes Received:
    463
    One of them is doing the multiple ports calc wrongly. [​IMG]
     
  3. Pete Mazz

    Pete Mazz Supporting Actor

    Joined:
    May 17, 2000
    Messages:
    761
    Likes Received:
    0
    With WinSpeakerz, I get 40.6....go figure!

    Pete
     
  4. Kyle Richardson

    Kyle Richardson Screenwriter

    Joined:
    Jan 1, 1998
    Messages:
    1,073
    Likes Received:
    0
    Well, its good to see I'm not crazy. Now I just need to find out which one is correct.

    Kyle Richardson

    Acoustic Visions
     
  5. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    Don't know about UniBox I'm too cheap to upgrade my Excel-97 to a newer version.... [​IMG]
    But the most recent subs I've built using LspCAD have been dead on. The single 1503 modeled to a tuning of 18Hz, when we actually measured the sub the tuning was 18.4Hz
     
  6. Achim Eilers

    Achim Eilers Auditioning

    Joined:
    Jan 19, 2002
    Messages:
    7
    Likes Received:
    0
    Just ran your numbers in BassBox:

    41.54cm 1 flush end

    44.08cm 2 flared ends

    hope that helps

    Achim.
     
  7. Pete Mazz

    Pete Mazz Supporting Actor

    Joined:
    May 17, 2000
    Messages:
    761
    Likes Received:
    0
    Maybe all the sims are based on the "magic 8 ball" port length calculator! [​IMG]
    Pete
     
  8. Greg Monfort

    Greg Monfort Supporting Actor

    Joined:
    May 30, 2000
    Messages:
    884
    Likes Received:
    0
    Assuming the vents aren't flared and using an early formula that's worked well for me over the decades, I get a vent length of 40.386cm, very close to Winspeakerz's 40.6cm.

    Anyway, there's always some variance in the system and why you should always cut them a bit long and fine tune them if hitting a particular frequency spot on is desired. Even if not, tuning a bit low (longer vent) is a good idea for high power apps as the system Q goes up with VC heating and the lower tuning offsets it some if it wasn't factored into the design.

    GM
     

Share This Page