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  • Limit to the number of ports

    I know that this is an odd question, but I am curious. I have seen speakers with at least 2 ports. Is that an actual limit? Or, can you do more? The reason I ask is that I was looking at the little 8 inch subwoofer that came out on sale today. For the port, it is suggested to use a rectangle that is 1x10x30. When I plugged the numbers into bass box pro, I thought, for laughs and giggles, why not see if I could do more than a couple of round ports. 3 or 4 round ports actually makes it feasible with size limitations, etc.

  • #2
    If the ports are too small in diameter, there will be port noise, aka "chuffing." Theoretically, you could have as many ports as you please, there's no real limit, except cost and aesthetics.

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    • #3
      Shove some straws in your round ports!
      Later,
      Wolf
      "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
      "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
      "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
      "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

      *InDIYana event website*

      Photobucket pages:
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      My blog/writeups/thoughts here at PE:
      http://techtalk.parts-express.com/blog.php?u=4102

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      • #4
        As the number of ports increase (and their IDs get smaller) you really don't gain anything - since they have to maintain the same length VS total X-Sectional area.
        I'm curious as to how/why your design gets more feasible w/more ports?

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        • #5
          There is no limit to the number of ports you can have, but know this: All things being equal, every time you add an additional port, performance will degrade.

          Here's what happens when you increase the number of ports:

          If you keep the port area the same, then your port length to diameter ratio will increase dramatically. This will lower the port resonance frequency into the midrange where it is not nice. This will make the port resonance issue worse since you have multiple ports resonating.

          Also, even if you keep the port area the same, the single large port will experience less port turbulence than multiple ports. This is sort of easy to see since it is obvious that the single large port has much less surface area inside the port that creates friction with the air. With multiple ports, there's way more surface area for friction and a lot more losses compared to a single port.

          2 or even 3 ports are generally fine, but don't go crazy on the number of ports.

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          • #6
            Grandpa's Ports
            Click image for larger version

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            "Not a Speaker Designer - Not even on the Internet"
            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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            • #7
              It always amazes me how pissy people get when they feel like a question is posted that isn't worth their time. Hey, you know what? IF YOU FEEL THAT WAY, DON'T RESPOND TO THE DAMN POST. Enjoy your effing lives. Parts Express just lost a customer.

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              • #8
                Wtf?
                Francis

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                • #9
                  Yeah... seems like something has been misinterpreted here. All I see is good advice on ports, and a very interesting patent drawing! Also... as much as we like Parts Express, we're not their salespeople.
                  Voxel Down Firing with Dayton SA70
                  Translam Subwoofers - The Jedi Mind Tricks

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                  • #10
                    It's all Ben's fault for telling him to "shove some straws into his ports". Too bad he didn't understand what Ben was saying.

                    If you are out there billiam and you don't mind some humble pie, come on back and let these guys further explain. None of the responses were pissy, but you certainly got that way when you didn't understand them.
                    My "No-Name" CC Speaker
                    Kerry's "Silverbacks"
                    Ben's Synchaeta's for Mom
                    The Archers
                    Rick's "db" Desktop CBT Arrays
                    The Gandalf's

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                    • #11
                      I am even more upset than the OP. I thought it said "Limit to the number of posts." This seemed like a great topic and I was looking forward to it. Straws in the port is actually aperiodic damping I believe.

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                      • #12
                        Originally posted by fpitas View Post
                        Wtf?
                        +1. I would say he is the pissy one for misunderstanding a post and overreacting to it. I believe an apology is in order!
                        Don't worry, if your parachute fails, you have the rest of your life to fix it.

                        If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

                        Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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                        • #13
                          Originally posted by fdieck View Post
                          I am even more upset than the OP. I thought it said "Limit to the number of posts." This seemed like a great topic and I was looking forward to it. Straws in the port is actually aperiodic damping I believe.
                          ​No, it's improved Laminar Air Flow. Helps reduce turbulence inside the port.

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                          • #14
                            Originally posted by Sydney View Post
                            Grandpa's Ports
                            Hey, I want one of those.

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                            • #15
                              Originally posted by View Post

                              ​No, it's improved Laminar Air Flow. Helps reduce turbulence inside the port.
                              Bingo! Man- I really wasn't being snarky....

                              There is no limit to the number of ports you can have, but know this: All things being equal, every time you add an additional port, performance will degrade.
                              bcodemz- What you said there is not exactly true. 2 ports will have less friction than a single if the combined end-area is larger. Normally the reason to add a second is to reduce turbulence. In fact, maybe I'm misinterpreting you here, but:

                              Here's what happens when you increase the number of ports:

                              If you keep the port area the same, then your port length to diameter ratio will increase dramatically. This will lower the port resonance frequency into the midrange where it is not nice. This will make the port resonance issue worse since you have multiple ports resonating.
                              I'm not sure what you mean by this. If you decrease the diameter of the ports, the port resonance (not the tuning, this is not the Fb we are discussing) will increase in frequency, and- it's usually already in the midrange passband before the change you are suggesting. The larger the diameter, the larger, lower, and deeper the dip in response will be due to the pipe resonance.

                              The longer port (higher ratio as you stated) will induce higher group delay, but enlarging the enclosure will reduce their length for the same Fb.

                              There was a design I did that I went with 4x 1" diameter ports. This is because the larger 2" would not be beneficial in the resonance range, and was very detrimental in the simulation. It pushed the resonance higher to where it was in the stopband for the woofer, and resulted in very minimal ripple of FR. Being a 5.25" woofer, I was not able to make them chuff up to the limits of the woofer's mechanical operation. This is because there were 4 of them present. While I'm sure there are some cases where the ports of this style may whistle, it was not apparent in this case. For additional info, the port exits were heavily rounded with a 0.75" RO bit.

                              Later,
                              Wolf
                              "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                              "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                              "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                              "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                              *InDIYana event website*

                              Photobucket pages:
                              http://photobucket.com/Wolf-Speakers_and_more

                              My blog/writeups/thoughts here at PE:
                              http://techtalk.parts-express.com/blog.php?u=4102

                              Comment

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