Too Much port Area, how do I know?

Discussion in 'Amps and Cabs [BG]' started by rufus.K, Oct 22, 2015.


  1. rufus.K

    rufus.K

    Oct 18, 2015
    SoCal
    So Ive got this speaker cabinet. Its made by a well known brand, which I wont mention cos I dont want to hear why I shouldnt do this based on the brand... But it was/is a combo, one of their popular models with a 2ru airhead and one of their amps on top. Ive removed the head, and want to cut the air head off of it., make a standalone cabinet. No big deal there except hiding the surgery. While Im at it, Im thinking of adding another port/tube to it, to match the port area of another of their models with almost identical box volume. So how do I know, by listening to it, if Ive got tooo much free area in port volume. What are the basic characteristics of too much porting in reference to the sound I hear? I can and am willing to re-fill the hole if its just terrible in the end, as Im cutting the airhead off anyway. I like the cabinet well enough, but I really want to to do this for science's sake, and would like a little idea of what affect it will have, in general terms.
    I realize I could model the cab with software, or be actually scientific about this, but then we wouldn't have the opportunity to have this little chat, would we...
     
  2. seamonkey

    seamonkey

    Aug 6, 2004
    There's actually a lot of support for some WAC designs around here.

    Many of the real successful ones just turn out to match the science in the end.

    Some give a big hump in the middle bass which fool a lot of people into thinking it has real bass.
    It's absolutely true that you can just ad hoc drill holes, and ad ports and you may find a sound you like better than stock. In your case since you can return to stock, I say give it a try.
    Follow some science guidelines like don't make the port to small that it chuffs. If you burn out a speaker or two by underloading it, well then you can buy a new and possibly better driver. Worst you'd be is out some bucks, and you'll have a learning experience. In the end you can return to stop design.
     
  3. rufus.K

    rufus.K

    Oct 18, 2015
    SoCal
    Does WAC stand for Without A Care?
    Its is ported to begin with, just not as large as another later model, so hopefully it wont chuff. So more port area will raise the tuning from lower to mid bass, if I understand correctly? Im hoping for more articulation, rather than depth, when Im done, and its paired with another box Ive got.
     
  4. Well... porting a cab is supposed to enhance bass response. Changing the porting changes the bass response. At some set of frequencies, the port resonance enhances the base response. Change the porting and you change the set of frequencies that get enhanced. You should be able to hear the enhancement change. Before, it was somewhat louder in one frequency range. After, it is somewhat louder in a different frequency range. Like seamonkey put it, there's a hump in the sound somewhere. Change the porting, and you change where the hump is. Adjust to taste.
     
  5. rufus.K

    rufus.K

    Oct 18, 2015
    SoCal
    Now with port shelves, I understand that that the airflow over the back of the shelf (like blowing accross a bottle) is where the interaction starts... Is that so with port tubes?
    if I go creating a multiple of tubes, each with their own "mouth", this cant be better than if I were to enlarge one of the existing ones, yes?
    Harder to return it to stock then, though.
     
  6. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    \
    Can't have it both ways...[​IMG]

    Port area trades against port depth if you want to maintain the same box tuning. If you aren't exactly duplicating the cab volume of your target cab and using an identical driver, you're essentially just throwing darts without doing modeling and/or actually measuring.

    That depends on what tradeoff set you are going for. There's never a free lunch, ever.

    If you would tell us what the cab in question is someone might do your homework for you BTW.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Guys, I suggest that you review the science behind ported speakers before making suggestions that do not match the science. Kinda scary.
     
    JackANSI, hover, dheafey and 4 others like this.
  8. Bassmec

    Bassmec

    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    image.jpeg
    Self noise from any kind of ports is a very serious problem in recording studio monitors, my son Henry goes that extra mile in his range of custom sub bass designs to avoid edges that can induce chuff and hooting.:)
    You will need to model the enclosure with software to see how port changes will change the frequency response, assuming you have the TS parameters for the driver.
     
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    You also need to TEST the design to be sure it performs as you think the software predicts. I can't tell you the number of mistakes I have seen that get caught in the testing process.
     
    JackANSI likes this.
  10. rufus.K

    rufus.K

    Oct 18, 2015
    SoCal
    Yeah, guess I cant have it both ways... was trying to fish out some rules of thumb. Youre right about off of this. So to divulge, it'd be butchering an Aguilar GS112, and getting closer to the diameter of an Aguilar SL112 port wise. I didnt know port area trades against port depth.
     
  11. rufus.K

    rufus.K

    Oct 18, 2015
    SoCal
    Damn... great looking tube indeed
     
  12. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    Aguilar made a GS112 with an airhead?
     
  13. Arjank

    Arjank

    Oct 9, 2007
    Above Amsterdam
    A lot of the times the problem lies in the port length that has been predicted by the software. I use two software tools, one (AJhorn) to calculate the exact tuning frequency and Boxsim to calculate the length. Boxsim is one of the only tools that takes the position of the port (distance port to bottom, top, left, right and back side) into account which has a major influence on the port lenght. This is where it goes wrong most of the time.
     
  14. Arjank

    Arjank

    Oct 9, 2007
    Above Amsterdam
    It depends.
    Really, if the ratio of port area, length and enclosure volume reach a certain point then the whole system will morph into a transmissionline system. You can already see this happening with designs that have a rather long shelf port, a standing wave will occur inside the port. If this standing wave is situated somewhere between 150-300hz then it's rather tough to get rid of it with lining/damping the enclosure. This standing wave will color the sound, making it "hollow" sounding in some case.
     
  15. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    It is often done purposely, even with cylindrical ports. Compare all the similar sized 2x10s, and you'll see all kinds of tuned-in lower mid bumps. Warwick's, Avatar's, G-K, GB, etc.
     
  16. Arjank

    Arjank

    Oct 9, 2007
    Above Amsterdam
    That lower mid bump isn't caused by a standing wave inside the port but due to the fact that they've used drivers with relative high Qts(Qes) and a to small cabinet for that driver where they didn't lower the tuning of the port to get a flatter response.
     
  17. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    The surprising thing is, they don't all have the mid bump. There is at least one pretty flat one that I know of.
     
  18. Arjank

    Arjank

    Oct 9, 2007
    Above Amsterdam
    Then they've used the right combination of driver, cabsize and port tuning.
     
  19. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    Sorry, more to your point, the bump can be flattened out with cabinet tuning to some extent. Moving the cab tuning frequency changes both the amplitude & frequency of the center of the bump.
     
  20. Arjank

    Arjank

    Oct 9, 2007
    Above Amsterdam
    Correct
     
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