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  • Re: "Rock Its" Build Thread

    Originally posted by Paul K. View Post
    The Walmart polyester fiberfill is just fine. BTW what is the length of the port representing the impedance measurement you made most recently? Is it the length I modeled or have you increased the length?
    Paul
    Its the length you modeled with a 1" round over on 1/2" MDF, so it is slightly flared.
    It does look like it may be a couple of Hz above what you modeled, but I really don't understand what raising or lowering the tuning will do. If I were to lower it to much will that put a dip in the response eventually or if I raise it to much will that put a hump in the respones? I just don't get what to shoot for when tuning.
    I could make up a new inner section to the port and lengthen it and also remove the round over if you don't think it is necessary.
    Dave
    http://www.pellegreneacoustics.com/

    Trench Seam Method for MDF
    https://picasaweb.google.com/101632266659473725850

    Comment


    • Re: "Rock Its" Build Thread

      You may not need to lower the tuning frequency but the TL was modeled with a tuning frequency that optimized the overall response (according to what I consider optimal) affecting both the flatness of the response above the knee in the curve and F3. If the roundovers you used on both ends of the port have raised the tuning frequency above what I modeled, lengthening the port, while keeping the roundovers, will restore the original predicted response, presumably making it flatter and having a bit lower F3. In a real room, you may not be able to tell any difference, however. I have no reason to believe making the tuning frequency be as I modeled it will cause a dip anywhere.
      Paul

      Originally posted by davepellegrene View Post
      Its the length you modeled with a 1" round over on 1/2" MDF, so it is slightly flared.
      It does look like it may be a couple of Hz above what you modeled, but I really don't understand what raising or lowering the tuning will do. If I were to lower it to much will that put a dip in the response eventually or if I raise it to much will that put a hump in the respones? I just don't get what to shoot for when tuning.
      I could make up a new inner section to the port and lengthen it and also remove the round over if you don't think it is necessary.
      Dave

      Comment


      • Re: Dave, here's your tuning answer...

        The best way to show you what would likely happen is to simply model it. So, first, I set up the model as I originally did for your design and that system response is shown in the first graph I've attached. Second, I shortened the port's length, to simulate what is likely going on with your port as constructed, until I got about the same, somewhat higher tuning frequency you're seeing with your impedance measurement. The second graph I've attached, then, shows the expected system response with the higher tuning frequency of ~43 Hz instead of 40 Hz. You can see there are two effects from the higher tuning frequency; F3 is 1-2 Hz higher, and a sort of high-Q type peak has developed at the knee in the response curve. You can also see that no new dips have developed. I'll leave it up to you, of course, to decide if you want to modify your port's dimensions to get back to the original response.
        Paul

        Originally posted by davepellegrene View Post
        Its the length you modeled with a 1" round over on 1/2" MDF, so it is slightly flared.
        It does look like it may be a couple of Hz above what you modeled, but I really don't understand what raising or lowering the tuning will do. If I were to lower it to much will that put a dip in the response eventually or if I raise it to much will that put a hump in the respones? I just don't get what to shoot for when tuning.
        I could make up a new inner section to the port and lengthen it and also remove the round over if you don't think it is necessary.
        Dave
        Attached Files

        Comment


        • Re: Dave, here's your tuning answer...

          Originally posted by Paul K. View Post
          You can see there are two effects from the higher tuning frequency; F3 is 1-2 Hz higher, and a sort of high-Q type peak has developed at the knee in the response curve. You can also see that no new dips have developed.
          Paul
          Paul,

          Can you estimate how this will affect the sound? Might the bass be boomier or might it be just a slight effect?

          Thanks,

          Darren

          Comment


          • Re: Dave, here's your tuning answer...

            That's really difficult for me to estimate. The peak is about 1.5-2 dB high. I suppose some people might be able to hear its effect and, of course, there would have to be some musical content at that frequency even then. I really don't know.
            Paul

            Originally posted by dian1511 View Post
            Paul,

            Can you estimate how this will affect the sound? Might the bass be boomier or might it be just a slight effect?

            Thanks,

            Darren

            Comment


            • Re: Dave, here's your tuning answer...

              Originally posted by dian1511 View Post
              Paul,

              Can you estimate how this will affect the sound? Might the bass be boomier or might it be just a slight effect?

              Thanks,

              Darren
              Different Paul, but...
              It's not an "in your face" difference, but it's noticeable. Sometimes I tune my vented designs to have a 1-2 dB peak just before roll off (as you see in that diagram). I find this gives the bass a bit more "authority" down low.
              It's sort of the opposite of a sealed sound, where you tend to get more attack, but the fundamental is a bit subdued.
              Isn't it about time we started answering rhetorical questions?

              Paul Carmody's DIY Audio Projects
              Twitter: @undefinition1

              Comment


              • Re: Dave, here's your tuning answer...

                Originally posted by Paul K. View Post
                The best way to show you what would likely happen is to simply model it. So, first, I set up the model as I originally did for your design and that system response is shown in the first graph I've attached. Second, I shortened the port's length, to simulate what is likely going on with your port as constructed, until I got about the same, somewhat higher tuning frequency you're seeing with your impedance measurement. The second graph I've attached, then, shows the expected system response with the higher tuning frequency of ~43 Hz instead of 40 Hz. You can see there are two effects from the higher tuning frequency; F3 is 1-2 Hz higher, and a sort of high-Q type peak has developed at the knee in the response curve. You can also see that no new dips have developed. I'll leave it up to you, of course, to decide if you want to modify your port's dimensions to get back to the original response.
                Paul
                Thanks for taking the time to remodel that and explain what to expect. I will make a new port at the longer length if for nothing to see and hear the difference.
                I honestly don't know if I would be able to hear it. Maybe in a couple of ZZ Top songs that I know well that extend pretty low.
                I got a chance this morning to put together a few xo parts that I had laying around to get close to what I have modeled and with some low level listening to one speaker I am really liking what I hear from the TB W4 656 as a mid. Hard to tell yet on the bass but definitely not bad. Hard to tell at low levels.

                I head up to Akron tomorrow to defend my State Championship water ski jumping title. Then next weekend off to Illinois to defend my Mid West title. Then Following week back to Illinois for the nationals, so time is going to be tight for the next few weeks.
                I have been working with my measuring set up and seem to be getting some good results. I think next I am going to set up outside and see how that goes.

                Meanwhile I may get started on the other cabinet with the pour on epoxy. Hopefully I can have that one ready so I can drop in my somewhat final xo then tear the other apart and finish it.
                Dave
                http://www.pellegreneacoustics.com/

                Trench Seam Method for MDF
                https://picasaweb.google.com/101632266659473725850

                Comment


                • Re: Dave, here's your tuning answer...

                  Some people would prefer tuning even lower than I did originally; that would increase the output a bit in the 20-30 Hz range while decreasing the output above 30 Hz some.

                  Good luck with your water ski contests.
                  Paul

                  Originally posted by davepellegrene View Post
                  Thanks for taking the time to remodel that and explain what to expect. I will make a new port at the longer length if for nothing to see and hear the difference.
                  I honestly don't know if I would be able to hear it. Maybe in a couple of ZZ Top songs that I know well that extend pretty low.
                  I got a chance this morning to put together a few xo parts that I had laying around to get close to what I have modeled and with some low level listening to one speaker I am really liking what I hear from the TB W4 656 as a mid. Hard to tell yet on the bass but definitely not bad. Hard to tell at low levels.

                  I head up to Akron tomorrow to defend my State Championship water ski jumping title. Then next weekend off to Illinois to defend my Mid West title. Then Following week back to Illinois for the nationals, so time is going to be tight for the next few weeks.
                  I have been working with my measuring set up and seem to be getting some good results. I think next I am going to set up outside and see how that goes.

                  Meanwhile I may get started on the other cabinet with the pour on epoxy. Hopefully I can have that one ready so I can drop in my somewhat final xo then tear the other apart and finish it.
                  Dave

                  Comment


                  • Re: "Rock Its" Build Thread

                    I hate to be the one asking the box building for dummies question, but I'll do it anyway. You show a pic of the baffle during construction. It has the roundovers and paint and looks wonderful. I have never had a board look so flat, or the roundovers take paint so evenly, to match what you have done. How did you do this? Obviously not a seam method here.

                    Steve

                    Comment


                    • Re: Dave, here's your tuning answer...

                      Originally posted by Paul K. View Post
                      Some people would prefer tuning even lower than I did originally; that would increase the output a bit in the 20-30 Hz range while decreasing the output above 30 Hz some.

                      Good luck with your water ski contests.
                      Paul
                      These will be for music only so I can't see tuning them much lower. I think I would rather have them stronger at 30 Hz and above.
                      Dave
                      http://www.pellegreneacoustics.com/

                      Trench Seam Method for MDF
                      https://picasaweb.google.com/101632266659473725850

                      Comment


                      • Re: "Rock Its" Build Thread

                        Originally posted by skatz View Post
                        I hate to be the one asking the box building for dummies question, but I'll do it anyway. You show a pic of the baffle during construction. It has the roundovers and paint and looks wonderful. I have never had a board look so flat, or the roundovers take paint so evenly, to match what you have done. How did you do this? Obviously not a seam method here.

                        Steve
                        I sanded the baffle with 150 grit paper. For under two dollars I bought a small plastic tray with a sponge roller with a plastic handle. The tray has a lid that clips on top of the tray, so you can keep the roller wet until you are done.I rolled oil base Bin 123 over the entire baffle with a sponge roller. I let it sit 12 hours lightly sanded the round overs and hit the round overs again. Let set again, lightly sanded the round overs then hit them again. I left the baffles dry 24 hours after the third coat. I then sanded with 220 until I started to see through the primer, but did not actually go through. Its best to take it outside and look close to make sure you have sanded off all orange peel. The surface will only be as flat as what you can see with good light. If you sand through the primer it is best to touch up and resand. I blew the baffle off with an air hose and then wiped with a tack rag. I then spray all edges first including the round overs. Let sit about 10 minutes then spray all the edges then the entire baffle. let it sit until you can touch it. Then spray the whole baffle including edges with a medium coat. Then spray again 90 degrees from the direction you sprayed last time. Turn 90 degrees and spray again. Turn 90 degrees and spray again. I let it sit for two hours. At this point if you have dirt or imperfections let it dry 24 hours then resand. probably with 320. I didn't have any imperfections so I resprayed using the same process as above. make sure on the last coat it has a real nice wet look to it.

                        Its 95% prep work 5% painting. Just get the paint on even and wet looking by the time you are done spraying and you should get the same results.
                        Hope that helps
                        Dave
                        http://www.pellegreneacoustics.com/

                        Trench Seam Method for MDF
                        https://picasaweb.google.com/101632266659473725850

                        Comment


                        • Re: "Rock Its" Build Thread

                          Originally posted by davepellegrene View Post
                          Then spray again 90 degrees from the direction you sprayed last time. Turn 90 degrees and spray again. Turn 90 degrees and spray again. I let it sit for two hours. At this point if you have dirt or imperfections let it dry 24 hours then resand. probably with 320. I didn't have any imperfections so I resprayed using the same process as above. make sure on the last coat it has a real nice wet look to it.

                          Its 95% prep work 5% painting. Just get the paint on even and wet looking by the time you are done spraying and you should get the same results.
                          Hope that helps
                          Dave
                          Dave, When you spray, is the board lying horizontal or is it upright? I'm just wondering about drips.

                          Darren

                          Comment


                          • Re: "Rock Its" Build Thread

                            Originally posted by dian1511 View Post
                            Dave, When you spray, is the board lying horizontal or is it upright? I'm just wondering about drips.

                            Darren
                            I sprayed these laying flat and you can put it on pretty heavy. Just be careful around the round overs. You need to be careful spraying vertical surfaces. Start with lighter coats and just keep an eye on it. Spray cans dry pretty fast so that helps. Best to just try to keep a slight wet look and let it flow. Still spray both directions especially with metallic paints. I will even go diagonally. The more directions you go the more even the metallic will come out. Another tip don't get to close. Roughly about 8" to 12" trying to keep the exact same distance back as you spray across a peice. Helps too if it is dead calm.
                            Dave
                            http://www.pellegreneacoustics.com/

                            Trench Seam Method for MDF
                            https://picasaweb.google.com/101632266659473725850

                            Comment

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