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A revisit of a much discussed topic - front vs rear port

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  • A revisit of a much discussed topic - front vs rear port

    In doing some googling, I see that this is a topic that has been discussed in great detail, however I couldn't really get a clear answer from what I found.

    What is the general consensus on front versus rear port?

    In what I found from tests done, it appears there can be significant mid range leakage particularly around 1500 Hz that can escape from the port. That being said however I realize that it can be somewhat minimized with proper internal damping, but does it have really a more negative affect escaping from the front or rear of the enclosure?

    The reason I ask is in some of the charts that I saw in other threads, unless I am interpreting them wrong which is certainly possible, it appeared that although you will have the mid range leakage to deal with in a straightforward fashion coming from the front port which certainly can be an audible issue, it appeared the mid range leaking from the rear can be more detrimental causing dips in response depending on the surface and distance behind the speaker, making it less predictable to deal with then if it was just on the front and more consistent.

    Any thoughts on this? I should also note that I am not for the purposes of this question concerned about chuffing or port resonance, so assume that has been dealt with for this question such as large flares and a deadened port wall. I also realize that downfiring and passive radiators are alternate and potentially better options as well.

    It should also be noted that I don't mind and actually sometimes prefer the look of a front port.

  • #2
    Midrange tends not to escape front ports, unless you neglect to damp the inside of the cabinet back. They tend not to escape rear ports either, so long as you can't look through them and see the driver cone.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      This is an interesting question, is the port excited by the air vibration in the cabinet or by the vibration of cabinet walls? If it's the air vibration I imagine that would be suppressed by the damping (polyfill, etc.) in the cabinet. Regardless, the difference between front and rear mounting might have more to do with changes in room gain at low frequencies than its contribution to the midrange.

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      • #4
        Compromise, mount the port on the side! LOL
        ​Actually I prefer my ports on the rear, then I don't have to worry about it or have to look at it either.

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        • #5
          I prefer the rear, but mostly for aesthetic reasons. If I do place a port on the front, I usually will go for a slot port, as I find them a lot more attractive that a plastic tube shoved in a hole.

          I would think that a rear port would have benefits for any mid-range leakage, or even wind noise, since any higher frequency content exiting the port would be directed away from the listener, and further attenuated.
          I'm not deaf, I'm just not listening!

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          • #6
            I've been doing some reading up myself about this topic, in preparation for my next build.

            I found no definitive answer, like you. Interestingly enough though, both Earl Geddes, and Jeff Bagby said they subjectively prefer the port to be front mounted, and placed near the woofer driver. But had no real data or reason to back it up. There was a vague reference that Geddes had dome some experiments about port placement, but I don't believe that he published any data. Some elusive white paper may exist, but I could not find it.

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            • #7
              Compromise, mount the port on the side! LOL
              ​.
              Yep, Google Royd Minstrel.

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              • #8
                Thanks guys, and joking aside I actually never considered a side port. Like I said, I don't mind the looks of a front port when it is an aero port with the big flare, and I subjectively tend to prefer front ported speakers as well, so in full disclosure I am likely to lean towards a front port..maybe. I just don't want to muck up the mid or muddy things with mid leakage.

                So this got me to researching it as one would think, as suggested here as well, that the rear would eliminate the issue but it seems to complicate it in post 4 of this thread:
                http://techtalk.parts-express.com/fo...t-or-rear-port

                Am I interpreting the measurements wrong that things get complicated and have weird phase interactions when a rear port interacts with a wall boundary and recombines?

                That thread is an excellent discussion on the topic but I feel lacks a solid answer of which is measurably truly better.

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                • #9
                  Originally posted by Michael P View Post
                  is the port excited by the air vibration in the cabinet or by the vibration of cabinet walls?
                  If the cabinet walls are vibrating you have a defective cabinet.The mass of air in the port vibrates at and near the box resonant frequency, Fb, excited by frequencies in that range produced by the driver.
                  If it's the air vibration I imagine that would be suppressed by the damping (polyfill, etc.) in the cabinet.
                  Damping has no effect at the frequencies where the port functions. It is possible to over-damp a ported cab by stuffing it. With sufficient stuffing the port will cease to function and it will act as a sealed cab.
                  www.billfitzmaurice.com
                  www.billfitzmaurice.info/forum

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                  • #10
                    On the subject, down-firing ports are used on some tower speakers. That requires some sort of stand on the bottom of the speaker.
                    Francis

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                    • #11
                      That's where proper dampening comes into play. If you have a front port, FG or Roxul is king in keeping mid frequencies from exiting the port. I prefer those materials over any foam/poly fill available. The best is a wall of Roxul in the middle of the cab with acoustistuff behind it.
                      A mains
                      The Ventures
                      Open Invit8tions
                      RSR
                      Sound Troopers
                      Acorns
                      442
                      DGBG's
                      The Monuments

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                      • #12
                        I will perhaps grab some roxul, never used it before but I see it is stocked at lowes

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                        • #13
                          Originally posted by dynamo View Post
                          I will perhaps grab some roxul, never used it before but I see it is stocked at lowes
                          ​Placement is more important than the make or brand of the absorptive material.
                          Further, acoustical tiles and acoustical foam are used on the ceiling and walls of sound studios, not rolls of fiberglas or other fluffy materials.

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                          • #14
                            +1 to what AE said, get the board stuff, the fluffy FG ( like R19) can be used behind it in place of acoustistuff for max suppression.
                            A mains
                            The Ventures
                            Open Invit8tions
                            RSR
                            Sound Troopers
                            Acorns
                            442
                            DGBG's
                            The Monuments

                            Comment


                            • #15
                              By midrange leakage, are we referring to actual backwave escaping or the pipe resonance? One of them is decidedly trickier to deal with.
                              Don't listen to me - I have not sold any $150,000 speakers.

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