A question of vented enclosure design

Discussion in 'Archived Threads 2001-2004' started by Jerry Parker, Jul 14, 2002.

  1. Jerry Parker

    Jerry Parker Stunt Coordinator

    Joined:
    Jan 15, 2001
    Messages:
    174
    Likes Received:
    0
    Trophy Points:
    0
    On another messageboard I was having an arugement with another member. He said: "and it isnt a sealed box. its ported its 3.5 cubic feet. the port is 12inchs high,4 inchs wide and very long" He was refering to a custom enclosure he designed for a lightning audio subwoofer. Now he said the design was flat from 15hz to 50hz. This is a 12" driver with 10mm xmax btw. I told him for a tune of 15hz he would need a 13 foot long vent. He then responded by saying he had the port snaked around the enclosure, but didnt respond to my question of vent length.

    My question is, why would someone want to do something like that? The vent being 13 feet long MUST cause pipe resonances. Second, the enclosure must be HUGE, the port would be many times larger than the actual internal airspace. What other disadvantages are there to having such a long vent? Thanks!
     
  2. Chris Carswell

    Chris Carswell Supporting Actor

    Joined:
    Mar 5, 2002
    Messages:
    598
    Likes Received:
    0
    Trophy Points:
    0
    I believe the proper term the corresponds with this fellow is bull shit!!!
    There are reasons why he didn't answer your questions......
     
  3. Brian Bunge

    Brian Bunge Producer

    Joined:
    Sep 11, 2000
    Messages:
    3,716
    Likes Received:
    0
    Trophy Points:
    0
    I'm assuming it's being used in a car and is probably tuned around 30Hz. While I didn't figure out what a 3.5ft^3 enclosure with a 4" port 12" long is tuned to, I just figured that 30Hz was about right from my experiences with car audio subs. I know most seem to tune around 30-40Hz.

    Cabin gain would still give him pretty good output down low, although I don't know about being flat to 15Hz.

    Brian
     
  4. Jerry Parker

    Jerry Parker Stunt Coordinator

    Joined:
    Jan 15, 2001
    Messages:
    174
    Likes Received:
    0
    Trophy Points:
    0
    Thats just the thing - he CLAIMED that it was for home use. He commented that it was flat from 15hz to 50hz [​IMG] He said he used bassbox to design the enclosure.
    Then, he said that Lightning audio was a really good company because they rate their drivers on mechanical power handling, not thermal!!! That too makes no sense, as mechanical power handling is frequency and enclosure dependent!
    The real fact of the matter is, he was probably trying to sound cool or something, yet had no idea what he was talking about. [​IMG]
     
  5. Jerry Parker

    Jerry Parker Stunt Coordinator

    Joined:
    Jan 15, 2001
    Messages:
    174
    Likes Received:
    0
    Trophy Points:
    0
    Oh, another point. The fs on the driver he claimed to use was 30hz. His f3 point is ONE OCTAVE below the fs. That too sounds redicoulous.
     
  6. Jeff Rosz

    Jeff Rosz Second Unit

    Joined:
    Sep 24, 2000
    Messages:
    335
    Likes Received:
    0
    Trophy Points:
    0
    brian,
    i think he's talking about a rectangular vent here...
     
  7. Brian Bunge

    Brian Bunge Producer

    Joined:
    Sep 11, 2000
    Messages:
    3,716
    Likes Received:
    0
    Trophy Points:
    0
    Jeff,

    Ah...I see that now. I guess the jet lag was starting to get to me last night. Thanks!

    Brian
     
  8. Greg Monfort

    Greg Monfort Supporting Actor

    Joined:
    May 30, 2000
    Messages:
    884
    Likes Received:
    0
    Trophy Points:
    0
    Couldn't find any specs, but a low Q driver in a bandpass could in theory do this, though with a ~22.5ft vent. Since the first vent pipe mode would be a null at ~50Hz and the BP would have a rising response in this BW, his claim of a ~flat response could 'in theory' be valid. Since it's mechanically limited down low it's not going to play all that loud, maybe 100dB peaks, but then you didn't say he claimed it could.
    Having built a similar concept with an el cheapo RS 8" driver some years ago for a small HT (tiny BP cab with 12" dia x 8ft Quikcrete tube vent, making it more a TL than a BP, and dubbed the 'Sonic Cannon' [​IMG]), I'll accept his claims at face value until I see the driver's specs.
    GM
     
  9. Jerry Parker

    Jerry Parker Stunt Coordinator

    Joined:
    Jan 15, 2001
    Messages:
    174
    Likes Received:
    0
    Trophy Points:
    0
    Thanks for the responses guys. He never did tell me a vent length, but 13 feet is what it would have to be for a 15hz tune, I used winisd for the calculations, you guys could try other software.
    http://www.lightningaudio.com/products/ the driver is the lightning audio x1.12.vc2 and is the storm vc2 subwoofer.
    The spec of 30hz fs makes me very skeptical that the driver is really truly flat inroom to 15hz. My 1803 has an fs of 25hz, and HAS to be equilized to be flat to 20hz, 15hz would be much harder. Not to mention the blueprint probably has more displacement than 4 or 5 of those lightning audio speakers.
    In any case, I do not believe him.
     

Share This Page