Announcement

Collapse
No announcement yet.

Vent velocity

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Vent velocity

    What do you guys target as an acceptable vent velocity? I'm working on a small ported design that will use a 5" driver with a 1.5" port. The velocity is showing a max of 45m/s at about 38Hz. The design is 9.4L with an Fb of 45.9Hz. The 38hz is also where the driver will start to exceed xmax.

    I've done plenty of sub designs, but this is my first attempt at a wide-range driver. The MarkAudio Alpair10. I need to start breaking these things in for another build later.
    https://www.facebook.com/Mosaic-Audi...7373763888294/

  • #2
    Re: Vent velocity

    When I design ML-TLs I check the predicted port air velocity when the driver is being pushed to Xmax+15%. I don't like to ever exceed a port velocity of 5% of the speed of sound which is 17 m/s, about 1/3 of what you say is predicted for your vented design. It's not quite cut and dry, however, as the frequency at which the velocity peaks is also important. In your case with it peaking at 38 Hz, I would try to limit the velocity to 3% of the speed of sound, or ~10 m/s especially because 38 Hz is likely to be excited by most music. If it were peaking at 20 Hz, or lower, it wouldn't matter quite as much.
    Paul

    Originally posted by isaeagle4031 View Post
    What do you guys target as an acceptable vent velocity? I'm working on a small ported design that will use a 5" driver with a 1.5" port. The velocity is showing a max of 45m/s at about 38Hz. The design is 9.4L with an Fb of 45.9Hz. The 38hz is also where the driver will start to exceed xmax.

    I've done plenty of sub designs, but this is my first attempt at a wide-range driver. The MarkAudio Alpair10. I need to start breaking these things in for another build later.

    Comment


    • #3
      Re: Vent velocity

      Thanks Paul. I'm playing around with it. There are some MLTL designs for this driver, but I really don't want to build something quite that extensive for it for now. In order to get the VV down to the levels you mentioned I would need to go jump up to about a 3"port which seemed rather large for such a small driver. I've upped the enclosure volume to 15L as well just playing around.

      The final enclosure will be smaller than this as I am planning on using this as a dedicated midrange/bass unit.
      https://www.facebook.com/Mosaic-Audi...7373763888294/

      Comment


      • #4
        Re: Vent velocity

        Originally posted by isaeagle4031 View Post
        What do you guys target as an acceptable vent velocity?
        I agree with Paul K. 5% the speed of sound max, but try to shoot for 3%.

        I will add another "rule of thumb" that helps figure out port dimensions...at least it works for larger drivers. Try to shoot for a minimum of 12 sqin of port area, with 14-16 being ideal per square foot of enclosure space. So, your 15l enclosure should have a port area of about 7-8 inches, 6 being the minimum. A 3" cylinder has an area of 7.06". Seems excessive, I know, especially for such a small driver and cabinet. But that's what it is. You can fudge those numbers a bit by using flared ends, but it still requires a rather large area to eliminate chuffing.

        Comment


        • #5
          Re: Vent velocity

          Originally posted by isaeagle4031 View Post
          Thanks Paul. I'm playing around with it. There are some MLTL designs for this driver, but I really don't want to build something quite that extensive for it for now. In order to get the VV down to the levels you mentioned I would need to go jump up to about a 3"port which seemed rather large for such a small driver. I've upped the enclosure volume to 15L as well just playing around.

          The final enclosure will be smaller than this as I am planning on using this as a dedicated midrange/bass unit.
          If it will be the mid for your monkey coffins, then I would seal and liberally stuff them.

          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


          • #6
            Re: Vent velocity

            They will be the mid, but seeing as how they are a "full-range" driver, I wanted to give them a try as such. I've never owned a pair, so there ya go!:D

            The boxes are done, just need a baffle and holes cut. I might post pics on them later. (Boxes are only done, because I used the ones I got from Mark & Joel last weekend;))
            https://www.facebook.com/Mosaic-Audi...7373763888294/

            Comment


            • #7
              Re: Vent velocity

              I wasn't suggesting you use an ML-TL, just relating my experience with them because they also use a port whose air velocity needs to be considered.
              Paul

              Originally posted by isaeagle4031 View Post
              Thanks Paul. I'm playing around with it. There are some MLTL designs for this driver, but I really don't want to build something quite that extensive for it for now. In order to get the VV down to the levels you mentioned I would need to go jump up to about a 3"port which seemed rather large for such a small driver. I've upped the enclosure volume to 15L as well just playing around.

              The final enclosure will be smaller than this as I am planning on using this as a dedicated midrange/bass unit.

              Comment


              • #8
                Re: Vent velocity

                I know Paul. I only said that because the MLTL seems to be very popular for this driver. I'm going to use a baffle that will allow me to swap port diameters and play around with it. I've got plenty of port tube (thanks Dan N) so that won't be an issue.
                https://www.facebook.com/Mosaic-Audi...7373763888294/

                Comment


                • #9
                  Re: Vent velocity

                  Originally posted by isaeagle4031 View Post
                  They will be the mid, but seeing as how they are a "full-range" driver, I wanted to give them a try as such. I've never owned a pair, so there ya go!:D

                  The boxes are done, just need a baffle and holes cut. I might post pics on them later. (Boxes are only done, because I used the ones I got from Mark & Joel last weekend;))
                  How about a 2"id? Would it fit (probably 50% again as long)?

                  Comment


                  • #10
                    Re: Vent velocity

                    I've found that there are some pretty significant discrepancies in vent air velocity calculations from one simulation program to the next. I'd be curious what driver specifically, and what program is being used to come up with the simulated results.

                    45m/s is way higher than I would want in any design, regardless of the program used to simulate it. With low Vas drivers and small boxes, it's not uncommon to have unusually large port dimensions to achieve the desired tuning with low velocity. My suggestion is to use hornresp to simulate these more "radical" enclosure characteristics. The nice thing about using hornresp, is that, it will simulate a velocity higher than real world in most cases because it assumes perfectly rigid panels and tubular/conical enclosure shapes. If you design the enclosure with hornresp to have a nice low peak air velocity, then it's a safe bet than in the real world, the results will be even "better."
                    Pro/Fi Cinema Speaker project: "From the Ashes"

                    Comment


                    • #11
                      Re: Vent velocity

                      The driver is the MarkAudio Alpair 10 and the program is Jeff Bs WooferBox and Circuit Designer.
                      https://www.facebook.com/Mosaic-Audi...7373763888294/

                      Comment


                      • #12
                        Re: My modeling results...

                        Just out of curiosity I modeled a vented box with one of Martin's worksheets (he does have others than just for TLs) replicating as best I could your vented box. Same gross volume of 9.4 liters with a system tuning frequency of 45-46 Hz. For the 1.5" diameter port, I ended up with a port length of 5.5". I increased the input power to 40 watts, which caused the driver to reach Xmax at ~37 Hz and just short of Xmax at 70 Hz. The driver was generating an output of ~105 dB SPL and the port's velocity peaked at 28 m/s at a frequency of ~32 Hz. F3 was 51-52 Hz. Clearly the vent velocity I got, while still too high, is a lot lower than what you got. I suppose this only confuses the issue some, but FWIW, there it is.
                        Paul

                        Comment


                        • #13
                          Re: My modeling results...

                          Originally posted by Paul K. View Post
                          Just out of curiosity I modeled a vented box with one of Martin's worksheets (he does have others than just for TLs) replicating as best I could your vented box. Same gross volume of 9.4 liters with a system tuning frequency of 45-46 Hz. For the 1.5" diameter port, I ended up with a port length of 5.5". I increased the input power to 40 watts, which caused the driver to reach Xmax at ~37 Hz and just short of Xmax at 70 Hz. The driver was generating an output of ~105 dB SPL and the port's velocity peaked at 28 m/s at a frequency of ~32 Hz. F3 was 51-52 Hz. Clearly the vent velocity I got, while still too high, is a lot lower than what you got. I suppose this only confuses the issue some, but FWIW, there it is.
                          Paul
                          I am a bit bewildered, the I thought the Alpair was going to be used as a midrange with 12" woofers. If this is the case, why are we talking about port velocity at 32 Hz? Is this just to experiment with using it full-range?
                          Click here for Jeff Bagby's Loudspeaker Design Software

                          Comment


                          • #14
                            Re: Vent velocity

                            It is going to be used with the 12's Jeff. This is simply a chance to use a full-range driver where I've never used one before and to break-in the drivers a bit.

                            After this they will be used in the yet to be named cabinets with the lab12 and (probably) LD25X. Even with all the speakers I took to InDIYana, I am now speakerless in my little man-cave/listening room:o
                            https://www.facebook.com/Mosaic-Audi...7373763888294/

                            Comment

                            Working...
                            X