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Small ported 12 for PA use

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  • #16
    Re: Small ported 12 for PA use

    So, after looking for plans that would fit my design needs I decided to check out what Eminence themselves recommended for the LAB12 I have laying around for now!

    Heres my take on the "med vented subwoofer cabinet" (http://www.eminence.com/pdf/LAB_12_cab.pdf)

    Click image for larger version

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    Hopefully a little over 115dB with 400 Watts with an F3 of 33Hz!

    the only issue is that the design calls for 3.5" ports. WHAT THE!? I havent seen anythign with a 3.5" ID ANYWHERE!!!

    If I were to change that to a standard size of PVC, say 3" or 4" nominal, where can I find a formula to calculate a vent length?

    I have used an online calculator before but when I input the values from the plans, the port length does not match up with thiers so I would like to match thier design as closely as possible!

    Thanks guys

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    • #17
      Re: Small ported 12 for PA use

      Hey Bill, should this LAB12 reflex box placed in a corner be able to outrun my 16" wide premium 8" driver Autotuba?

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      • #18
        Re: Small ported 12 for PA use

        Originally posted by chips and palsa View Post
        Hey Bill, should this LAB12 reflex box placed in a corner be able to outrun my 16" wide premium 8" driver Autotuba?
        It may go lower, but with that low sensitivity I doubt if it will go louder. You won't get the predicted maximum SPL, as that prediction doesn't account for power compression.
        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

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        • #19
          Re: Small ported 12 for PA use

          Originally posted by chips and palsa View Post
          So, after looking for plans that would fit my design needs I decided to check out what Eminence themselves recommended for the LAB12 I have laying around for now!

          Heres my take on the "med vented subwoofer cabinet" (http://www.eminence.com/pdf/LAB_12_cab.pdf)

          [ATTACH=CONFIG]50980[/ATTACH]

          Hopefully a little over 115dB with 400 Watts with an F3 of 33Hz!

          the only issue is that the design calls for 3.5" ports. WHAT THE!? I havent seen anythign with a 3.5" ID ANYWHERE!!!

          If I were to change that to a standard size of PVC, say 3" or 4" nominal, where can I find a formula to calculate a vent length?

          I have used an online calculator before but when I input the values from the plans, the port length does not match up with thiers so I would like to match thier design as closely as possible!

          Thanks guys
          The Eminence box designs are theoretical & computer-generated. I doubt that any of them have been built & tested by the company. If you want a little more flexibility, download a free prediction program (like WinISD, for example) & run your own numbers. You can adjust things like vent dimensions. If you want to crunch the numbers yourself, Keele has an old calculator method that's still valid today. Your design doesn't need to be exactly, precisely the same as someone else's, there's room to fudge.

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          • #20
            Re: Small ported 12 for PA use

            Originally posted by Cuppa Joe View Post
            If you want a little more flexibility, download a free prediction program (like WinISD, for example) & run your own numbers. You can adjust things like vent dimensions. If you want to crunch the numbers yourself, Keele has an old calculator method that's still valid today. Your design doesn't need to be exactly, precisely the same as someone else's, there's room to fudge.
            I actually do have WinISD and have been playing around with it lately and even did a check this morning now that you've mentioned it!

            Using the same numbers from the Eminence design sheet for volume (before ports and driver) in WinISD I found very similar response graph to theirs so now I would feel better focusing on the ports.

            I think I saw somewhere that as long as vent Mach is kept to under .16 there shouldn't be "chuffing". Using a much more easily available 3" ID port, vent Mach was still only .04. However are 2 - 3" ports getting too small for a 12 inch driver?

            Is there an advantage to using larger ports?

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            • #21
              Re: Small ported 12 for PA use

              Three inch ports do chuff when using Series 2 12's in a ported car app. LAB12's would be even worse. When going to dual 4", they get loooong but it does improve things. That's why slot ports are popular - a lot more area to work with and you can make them long (even folded) if you need to. Tweaking the tuning is a bit harder, but make the first one out of expendable OSB...

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              • #22
                Small ported 12 for PA use

                Originally posted by wg_ski View Post
                Three inch ports do chuff when using Series 2 12's in a ported car app. LAB12's would be even worse. When going to dual 4", they get loooong but it does improve things. That's why slot ports are popular - a lot more area to work with and you can make them long (even folded) if you need to. Tweaking the tuning is a bit harder, but make the first one out of expendable OSB...
                I'm not sure what you mean by series 2. Is this chuffing going on much below Fb or just below? I would be high passing at 30Hz with a 35Hz tuned box.

                Also, I would rout the baffle side opening with a 3/8" round over bit and I could even round the internal port end on a lathe if that 1-8 to 1/4" radius would help

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                • #23
                  Re: Small ported 12 for PA use

                  WHOA. After downloading the newest version of WinISD, I will be slot porting. 2x 3" ports would put me at about 35m/s at 35Hz! [emoji51] Thanks to Solidworks these volume calculations are a breeze! I'll post pics of the build ASAP

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                  • #24
                    Re: Small ported 12 for PA use

                    "I'm not sure what you mean by series 2." I believe he's referring to the Dayton line of woofers called Series II. I have one of their 15s in my home stereo system. It's a decent driver overall, tho not suited to SR (sound reinforcement).

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                    • #25
                      Re: Small ported 12 for PA use

                      Gotcha that makes sense. I'm pretty excited to hear how this one I'm putting together will sound. Newest WinISD program rocks, gives a great plot for port air velocity and it shows a 2x14.5" slot (although close to the 8:1 danger zone ratio) still has a lower port velocity than 2 - 4" ID PVC tubes. Will post results and pics soon!Click image for larger version

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                      • #26
                        Re: Small ported 12 for PA use

                        Just some build pictures. Gonna attach the side to side bracing dowels the same time that I put the last panel on. Until then have been taking ideas from the Fitzmaurice school of cabinet assembly building up from one side [emoji57]
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                        Solidworks was a champ at letting me deduct all bracing volume and play with a box volume to plug into WinISD to give me a vent length to deduct from box volume to plug into WinISD to find a vent length to... You get the idea! Should be right on goal of 35Hz tuning.

                        As far as damping goes (polyfill and such) is it better to add big handfuls of cotton candy like stuffing or mattress topper foam? I read somewhere that adding this material "increases" box volume by slowing the air as it travels? I know I'm not looking for a complete fill of stuffing material but around how much for a ported box?? Thanks guys!

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                        • #27
                          Re: Small ported 12 for PA use

                          Never fill a ported box. Line it with an inch or two of damping.
                          Until then have been taking ideas from the Fitzmaurice school of cabinet assembly building up from one side
                          I only do that with folded horns, as it's the only method that works well.
                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

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                          • #28
                            Re: Small ported 12 for PA use

                            You da man Bill. I'll get the egg crate padding tomorrow. And I can't imagine another way of doing horns! This brought me back to the AutoTuba assembly days. Click image for larger version

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                            Wouldn't call it ideal but plenty loud at noise-complaint o'clock

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