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Is there ever too small a port length?

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  • Is there ever too small a port length?

    Hey everyone, while I've used winisd in the past for sealed boxes, but I decided to design two ported enclosures for my car as part of a quarantine project. And after messing around with winisd these are the results I've come up with.

    Yes I'm using two different subwoofers, no they wont be playing the same frequencies. I'm having the max-x handle 45hz-85hz, and having the ultimax handle 22hz-45hz.

    I would just like to know if the length of the port is required to be longer. Rear port air velocity is fine on both of them, both subs are under 6 m/s at peak, and the only complication is the ultimax reaches danger excursion at 20hz. Which it wont be going down too anyways.

    If you're curious about the setup, I drive a 1990 MA70 Supra, I'm going to be using the slanted rear of the car to direct the waves coming out of the ultimax. The ultimax will be firing upwards at the rear window, while the max-x for right now will be in front of it(closer towards the rear seats) firing forwards(on a slight angle for clearance reasons). In the future, when the ultimax 10 gets restocked I will be replacing the max-x, but this is a temporary setup to show off to the kids who buy facebook marketplace subwoofers that have their gain cranked. OR worse, the ones who use line output converters, just thinking about that makes me shiver. The max-x will also be dsp corrected using the dayton LFE dsp.

    If any of you require anymore info let me know


  • #2
    I'm on my phone so can't see the graphs very well. Just wondering if you've included cabin gain in you results? My sealed car sub rolls off quite early, (I'd need to look on my pc to see exactly how early) but due to cabin gain I get good bass, flat down to about 25hz. I can only imagine a port being needed if you were into very high SPLs and weren't worried about sound quality.

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    • #3
      Originally posted by fatmarley View Post
      I'm on my phone so can't see the graphs very well. Just wondering if you've included cabin gain in you results? My sealed car sub rolls off quite early, (I'd need to look on my pc to see exactly how early) but due to cabin gain I get good bass, flat down to about 25hz. I can only imagine a port being needed if you were into very high SPLs and weren't worried about sound quality.
      I haven't included cabin gain, because this is just going to be an spl build with good quality components, my daily car which is a 13' gti I have built for sound quality, very flat sound just how I like it. But I figured since this car is slow, she's an old horse I bought for 700$, I thought I would design it around bass alone.

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      • #4
        Two subwoofer designs playing two different frequency ranges?

        I'd export those two curves and import them into REW to see how they sum.
        Brian Steele
        www.diysubwoofers.org

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        • #5
          On many economy 3 ways in the 70s the port was just a circular hole in the front baffle. The length was only the thickness of the
          front baffle. They helped reinforce the upper bass frequencies around 80-100 hz. So I would say no minimum length.

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          • #6
            Once upon a time most bass reflex were just a hole in the baffle, even very expensive speakers. Using a duct got popular around the 60s, when cabinets were shrinking.
            Francis

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            • #7
              It was once thought by some that if the hole was smaller than the cone that would cause a loss of port output. Apparently those early bass reflex designers didn't know about Bernoulli's Principle. Not all designers were mistaken on that point. Harry Olson in his 1940 'Elements of Acoustical Engineering' still referred to bass reflex as phase inverter enclosures, but he did use ducts, and provided the math on how to calculate them.
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

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              • #8
                Originally posted by Brian Steele View Post
                Two subwoofer designs playing two different frequency ranges?

                I'd export those two curves and import them into REW to see how they sum.
                thank you for the tip, I'll be sure to do that since Im eager to start on this project

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                • #9
                  Originally posted by Regore View Post
                  On many economy 3 ways in the 70s the port was just a circular hole in the front baffle. The length was only the thickness of the
                  front baffle. They helped reinforce the upper bass frequencies around 80-100 hz. So I would say no minimum length.
                  Here I am thinking ports were this very complicated matter when realistically it was a controlled hole. As you can tell, I'm new to ported enclosures but I'm always eager to learn, and still have much to learn in fact. Thank you guys for the input! This helps re leave me of some stress

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                  • #10
                    Post deleted.

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