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Port Placement Inside Cabinet Walls - Box-Building Gurus

Discussion in 'Amps and Cabs [BG]' started by PJaye, Jun 11, 2018.


  1. PJaye

    PJaye

    Feb 2, 2004
    Boston/Worcester
    Hi All,
    I looked for answers here, but only found the standard "rear port/cab distance from wall" subjects. My mechanical CAD drawing of a cab build looks good except maybe port placement. Is it crucial that ports get placed 1-port diameter away from any adjacent cab wall? The ports are in (4) front CORNERS facing forward on the front baffle, as the two drivers are. The clincher is that they're only .625" (5/8") away from two intersecting panels. Should I move all ports to the back to prevent problems? Thanks for your help!
    Paul
     
  2. Should be fine. The other threads you read were talking about setting the cab too close to a building wall.
     
  3. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    Actually, if you have a single driver cab, having the ports placed equidistant and symmetrically around the driver can have benefits if you're using a large driver like a 15 or 18.
     
    BadExample likes this.
  4. But as far as being too close to the corner of the cab, not an issue. Many successful cabs have had either triangular ports where two sides of the port are two of the cab walls, or one large rectangular port where 2 or 3 sides of the rectangle are the cab walls.
     
    basscooker likes this.
  5. PJaye

    PJaye

    Feb 2, 2004
    Boston/Worcester
    Thanks for your responses, guys. This is for a 2x8 or 4x8; drivers stacked vertically. Port-Edge-2x8-4x8.
     
  6. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    Are you set on the joints? The surface area is nice, but if you're using 1/2" ply that might be a bit too little thickness of wood for the corners. If your handle is top-mounted, that is a lot of stress for 1/4" of wood. My $0.02.
     
    BadExample likes this.
  7. PJaye

    PJaye

    Feb 2, 2004
    Boston/Worcester
    Maybe 5/8 (15mm) might be better. For handles, I could go with 90-degree/corner types.
     
    BadExample and basscooker like this.
  8. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    Just a thought I had. I would hate to hear later on that an accidental drop cracked an edge and irreparably damaged your hard work. Corner bar handles will definitely help with strength, but wouldn't prevent damage from direct impact. I'm a fan of butt joints for this reason. Sorry for derail. Enjoy the build!

    What speakers have you chosen? I love 8's for some unknown reason. Please post up a build thread once you start making sawdust! :)
     
  9. PJaye

    PJaye

    Feb 2, 2004
    Boston/Worcester
    Well, trying to keep the box weight and cost down! The drivers I had in mind are 8" Paper Cone Woofer (P/Express 290-4007). But, checked the max power curve in WinISD, and two of them would be power limited to 110 watts.:rollno: In 1.8FT3 tuned to 50Hz looked OK otherwise. F3=50 and F6=44. Forget the Faital 8PR200. $150 a pop?
     
  10. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky
    Owner, Chopshopamps.com
    "Non build thread" build thread, what? 4x8

    I like these. Inexpensive and sturdy. Pretty good numbers and they are cast frame not stamped. The 1x boxes I built sound awesome for bass or prerecorded music as long as you respect their limits. I can put everything my Genz Benz Shuttle 3 has to give at 8 ohms into that cab with no worries.
     
    BadExample likes this.
  11. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    My understanding is that the reason for having the ports well clear of the walls is that a wall adjacent to a port has an effect on the port resonant frequency and thus changes the tuning.
     
  12. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    The ports being close to the enclosure walls on two sides like that will increase the effective port length a little bit. So the actual tuning frequency will be a little bit lower than a modelling program would predict. Imo this is unlikely to be a problem. If I had to take a guess, in this case I'd assume an effective port length increase of about 1/4 of a diameter. So if those are 4" diameter ports, I'd ballpark guess that the effective increase in port length is about one inch.
     
    wave rider, BadExample and Stumbo like this.
  13. HaphAsSard

    HaphAsSard

    Dec 1, 2013
    Italia
    I thought the one-diameter warning was about a front port preferably needing to have its inner opening at that minimum distance from the back wall to prevent chuffin' and a-puffin'.
     
    BadExample likes this.
  14. But joints with PL glue is about as strong as it gets. I'd go with 1/2" ply and butt joints. Makes life in the shop easier too.
     
    basscooker likes this.
  15. PJaye

    PJaye

    Feb 2, 2004
    Boston/Worcester
    In the newest WinISD (v.0.7.0.850), I can no longer tweak the port length directly to show any subtle changes; it's grayed-out. Is there a way to unlock that feature?
     
    Last edited: Jun 12, 2018
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I agree with this, though I find that with larger ports it's closer to 1/8 of the diameter.
     
    DukeLeJeune likes this.
  17. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    This is also generally true, but for larger diameter ports it may be closer without issues.
     
    HaphAsSard likes this.
  18. StatesideRambler

    StatesideRambler

    Jul 1, 2015
    This may be obsolete information since I gave up building cabs some years ago. I toss it in for your consideration. In the past JBL guidelines (other loudspeaker people agreed) advised that a single port performed best and two ports of equal size were generally acceptable as well. More than two meant the openings were getting small, therefore they often caused peculiarities in the frequency response of the cab.
     
  19. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Things have changed as driver performance has improved. As ports get small, non-linearities get introduced that we can for the most part ignore these days.
     
    Stumbo likes this.
  20. leftyjohn

    leftyjohn

    Mar 20, 2018
    NW US
    I did this on a Fender Dualshowman cabinet. The tuning/porting was for Altec 421A's and it worked very well.
     
    basscooker likes this.