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Is this cab not ported? How does that affect sound?

Discussion in 'Amps and Cabs [BG]' started by jock, Jun 30, 2001.


  1. jock

    jock

    Jun 7, 2000
    Stockholm, Sweden
    It´s supposed to be Ashdowns answer to bag end´s s-15d but this one hasn´t got the port on the back (like bag end)and not one on the front as far as I can tell.
    How does that affect the sound and efficiency?

    /Jocke
     
  2. Just get the bag end , never been a big fan of any manufacturer's answer to someone else's winning design.
     
  3. rickbass

    rickbass Supporting Member

    As far as affecting the sound, the ones I tried were way too "thuddy" and old school-sounding for all the slapping, popping, and jazz music I have to do.

    I'm not saying they're bad by any means. They'll give an infinite baffle Fender or Ampeg a run for the money.
     
  4. There's no way to stuff a 15 inch speaker into a 2 cu.ft. box, not port it and sound good. Ashdown or not. IMHO.
     
  5. rickbass

    rickbass Supporting Member

    I definitely believe that, Joris. I'd hate to think what my little Carvin Cyclops would sound like with a 15", 2-8's and a tweeter all crammed into it's 31 1/2"H x 15"D x 22"W enclosure would sound like if it wasn't double ported.

    Pretty dead and dull, I guess.
     
  6. Every design requires a specific minimum port area to avoid whistling and other port noises. Multiple porting per se adds nothing special to the sound because the cabinet is tuned to a specific frequency no matter how many ports are used.

    The reason for multiple ports is it is easier and cheaper to locate two smaller ports than a single large one. 3" PVC is far less expensive per unit of square area than is the larger diameter PVC.
     
  7. rickbass

    rickbass Supporting Member

    Okay, to make bgavin happy, I'll say, "I'm glad it's ported." ;)
     
  8. Naa.... you don't have to worry about that.

    If you want to make me REALLY happy, give me a winning lottery ticket..

    :D
     
  9. rickbass

    rickbass Supporting Member

    Thing is, you have people who are experts that can't agree on number of ports/port placementand whether it affects sound, like Andy Lewis of Acme.

    I started a thread some time ago titled "Port Wars" that threw this out for discussion.
     
  10. Pretty much all the Ashdown stuff is like that and its voiced, as someone said for old school thump. Ashdown's biggest users right now are John Entwistle and Adam Clayton. Personally, I like the sound...but no, its not good for slapping or popping.
     
  11. This if from the Acme web site:

    Only after a port’s output leaves the cabinet, and enters the environment, does it assume the characteristics of a wave, one of which is direction of propagation. Direction does assume importance when speaking of waves. Only, however, at frequencies where the size of the source is large compared to the wavelength under consideration. The highest frequencies at which the port in our Low-B systems contribute to system output have wavelengths of 14 feet or so. The speakers are obviously quite small compared to these wavelengths, and the port output is omnidirectional. Again, port placement is irrelevant to system performance.

    Why does the B-2 have ports in the back? Because that’s where they fit. Why does the B-4 have its third port in the front? Same reason.

    ----

    The statement above about locating the port on the rear of the box because that is where it fits, is the important point made here. He is very honest about that.

    Yes, bass is spherical in nature, more so the lower the frequency. However, if your rear facing port is close to a wall such as the stage in a bar, that sound wave is going to hit the wall and deflect or get absorbed. If this unimportant, perhaps you should turn your amp around and let it face the wall. After all, bass is spherical, and the location is unimportant... :D Of course this is an over simplification, because the highs would be completely lost. A side mounted port would make a lot more sense, but would look really dorky from a marketing perspective.

    A ported box is a Helmholtz resonator. It is nothing more than a Coke bottle where you blow across the top of the mouth and get a sound. In a cabinet, you tune it with a volume of air in a port(s) that is relative to the volume of the cabinet. It makes no difference if multiple ports do the tuning.

    Ports negatively contribute to the sound when they are too small for the installed driver. The velocity of air in the port goes above 0.1 Mach and you hear whistling noises. This is avoided by using a larger port area, and a duct to correct the tuning back to the correct frequency.

    The point of all this is that double porting does not improve the sound of a cabinet.
     
  12. rickbass

    rickbass Supporting Member

    Sincerely, I'm glad there are people with the smarts and education to worry about all that, bgavin.

    I just plug in and if it sounds exquisite, it goes on my list, no matter whether is has half a dozen ports or none.
     
  13. LOL :D

    Some time ago I designed a very large subwoofer (one 18" in 8.5 cu.ft) which theoretically required a single 10" port 3 feet long or something to that magnitude. I looked at it closely and decided on a real world porting with 4 4" ports, 16" long. It really makes no difference at all, and who in the world could care, besides me and the guy building the cabinet?