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Basic questions about a 2-way 12" & horn PA top

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  • #31
    Re: Basic questions about a 2-way 12" & horn PA top

    Originally posted by Paul O View Post
    What is the black dot on the top of the cab? Is that the handle? If so that won't help you place the cab up on a pole.. better to have 1 handle on each side. I like this style handle, you can buy these things in plastic but I have also carved something similar into the side of cabs too.
    [ATTACH=CONFIG]52102[/ATTACH]
    Those multi way handles are pretty neat looking

    Here's the revised setup:
    Click image for larger version

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    How would you guys recommend bracing this? I'm guessing it's not as heavily braced as a subwoofer gets. I will also be using mattress topper for damping/lining

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    • #32
      Re: Basic questions about a 2-way 12" & horn PA top

      Originally posted by chips and palsa View Post
      Those multi way handles are pretty neat looking

      Here's the revised setup:
      [ATTACH]52118[/ATTACH]

      How would you guys recommend bracing this? I'm guessing it's not as heavily braced as a subwoofer gets. I will also be using mattress topper for damping/lining

      To be honest, I don't like the profile of that design.

      Here's a suggestion - replace the two round ports with triangular ones, located at each corner of the bottom of the front baffle. Then decrease the height and increase the depth of the box. This should also allow you to use longer and larger vents. Try to get the internal dimensions close to one of the golden ratios, e.g. 0.6:1:1.6 or 0.8:1:1.25. This should also provide enough space to insert a shelf brace for the back panel.
      Brian Steele
      www.diysubwoofers.org

      Comment


      • #33
        Re: Basic questions about a 2-way 12" & horn PA top

        Originally posted by Brian Steele View Post
        To be honest, I don't like the profile of that design.

        Here's a suggestion - replace the two round ports with triangular ones, located at each corner of the bottom of the front baffle. Then decrease the height and increase the depth of the box. This should also allow you to use longer and larger vents. Try to get the internal dimensions close to one of the golden ratios, e.g. 0.6:1:1.6 or 0.8:1:1.25. This should also provide enough space to insert a shelf brace for the back panel.
        I was actually wondering about those ratios. I tried to make sure there was at least a port diameter's clearance to the back of the cab but what other benefit is there to following those ratios?

        Comment


        • #34
          Re: Basic questions about a 2-way 12" & horn PA top

          Originally posted by chips and palsa View Post
          I was actually wondering about those ratios. I tried to make sure there was at least a port diameter's clearance to the back of the cab but what other benefit is there to following those ratios?
          It's supposed to spread any resonances caused by the cabinet dimensions. In this case the primary advantage is likely that with the increased depth of the cab you'll be able to have enough space to put shelf braces between the panels. The triangular corner ports will also act as braces.
          Brian Steele
          www.diysubwoofers.org

          Comment


          • #35
            Re: Basic questions about a 2-way 12" & horn PA top

            Okay understood. As far as calculating triangular port area/length, am I just simulating a square port in WinISD and using half of it for each port?

            Also, if this cab sims as 96dB / watt and the OTop12 is around 102-103, does that really mean that it will take 2 of these to equal one OTop in output?

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            • #36
              Re: Basic questions about a 2-way 12" & horn PA top

              Originally posted by chips and palsa View Post
              Also, if this cab sims as 96dB / watt and the OTop12 is around 102-103, does that really mean that it will take 2 of these to equal one OTop in output?
              It does. I wouldn't have made the OTop construction as complicated as I did if there wasn't a very good reason for doing so.
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

              Comment


              • #37
                Re: Basic questions about a 2-way 12" & horn PA top

                Originally posted by chips and palsa View Post
                Okay understood. As far as calculating triangular port area/length, am I just simulating a square port in WinISD and using half of it for each port?
                Better if you sim it as two ports with equivalent cross-sectional area. Be prepared to adjust actual vent length when built however - these tools can sometimes over-estimate the vent length required to achieve a target Fb.
                Brian Steele
                www.diysubwoofers.org

                Comment


                • #38
                  Re: Basic questions about a 2-way 12" & horn PA top

                  Originally posted by billfitzmaurice View Post
                  It does. I wouldn't have made the OTop construction as complicated as I did if there wasn't a very good reason for doing so.
                  No free lunches I do suppose. As this builds #1 priority is economy and simplicity, I sure hope my friend can settle for ~125+dB @ 1m. (2 96dB cabs @300W) and if he needs the low 130's+ then maybe we can drop the drivers into a horn loaded mid like JBell's HS12. (Looking on Bill's forum the PA310 isn't recommended in the OTop)

                  Will start simming triangular equivalent ports in ISD and adjusting the box into more of an ideal ratio.

                  Pretty excited to hear these 18" subs =) was playing around with PEQ & HP filters on ISD today. Not sure if I will ever try it but it looks like I can get a good bit of extra extension by boosting EQ @Fb with a corresponding HP (B6 assisted alignment that no one seems to discuss much except Tony Wilkes of speakerplans)

                  Comment


                  • #39
                    Re: Basic questions about a 2-way 12" & horn PA top

                    Originally posted by chips and palsa View Post
                    Looking on Bill's forum the PA310 isn't recommended in the OTop.
                    Since it does not have rising response into the midrange it's not going to work well in any horn above 1kHz or so.
                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

                    Comment


                    • #40
                      Basic questions about a 2-way 12" & horn PA top

                      Originally posted by billfitzmaurice View Post
                      Since it does not have rising response into the midrange it's not going to work well in any horn above 1kHz or so.
                      Wow a 5dB rise on my Deltalite indeed. I didn't know that's what dealt with the horn's filtering.

                      When it comes to crossing these boxes with the 18" BR's we're putting together, is a 100Hz LR on both boxes acceptable? Using both 4th order filters looks like a 4dB dip at the xover freq but 4th order BW filters looks like only a 1-2 dB dip. Is that the point of the LR filters to stop the responses from summing to a peak at 100Hz?

                      Comment


                      • #41
                        Re: Basic questions about a 2-way 12" & horn PA top

                        Originally posted by billfitzmaurice View Post
                        Since it does not have rising response into the midrange it's not going to work well in any horn above 1kHz or so.
                        Wow a 5dB rise on my Deltalite indeed. I didn't know that's what dealt with the horn's filtering.

                        When it comes I crossing these boxes with the 18" BR's were putting together, is a 100Hz LR on both boxes acceptable? Using both 4th order filters looks like a 4dB dip at the xover freq but 4th order BW filters only look like only a 1-2 dB dip. Is that the point of the LR filters to stop the responses from summing to a peak at 100Hz?

                        Comment


                        • #42
                          Re: Basic questions about a 2-way 12" & horn PA top

                          Originally posted by chips and palsa View Post
                          Is that the point of the LR filters to stop the responses from summing to a peak at 100Hz?
                          The point of LR filters is less bandwidth overlap, more protection for the high-passed cab, and no phase issues.
                          www.billfitzmaurice.com
                          www.billfitzmaurice.info/forum

                          Comment


                          • #43
                            Re: Basic questions about a 2-way 12" & horn PA top

                            Had anyone suggested this instead?
                            http://www.diysoundgroup.com/wavegui...ion12-kit.html

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