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Understanding Sub-woofer SPL

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  • Understanding Sub-woofer SPL

    I am in the process of designing some PA sub-woofers and I am not understanding the results that my modeling software is spitting out. With one (1) B&C 18TBW100 in an 8ft^3 cabinet tuned to 38Hz, I am hitting 129dB @ 50.7Hz. If I make a cabinet with two (2) 18TBW100 in an 16ft^3 cabinet tuned to 38Hz, I am hitting 134.8dB @ 50.7Hz. I always thought (and forgive me if I'm wrong), that every time surface area is doubled, there is a 3dB gain. Should I not be doubling the input power to 3KW when using the two (2) speaker method? I feel as thought I am missing something very simple here and need a sanity check from my fellow members. Any help would be greatly appreciated!
    two (2) 18TBW100 in a single box @3KW one (1) 18TBW100 in a single box @1.5KW
    "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

  • #2
    Your second graph does show 3000w input power.
    Paul O

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    • #3
      You are doubling your surface area and doubling your power, each provides a 3 db gain for a total of 6 db.

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      • #4
        Originally posted by Billet View Post
        You are doubling your surface area and doubling your power, each provides a 3 db gain for a total of 6 db.
        So everything is accurate in the 2nd graph?
        "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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        • #5
          The graph looks fine, I have to question the enclosure size you picked however.. why so big? My simulation in WinISD suggest that the driver will be well over xmax at 1500w which isn't ideal but it can handle it.
          Paul O

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          • #6
            Originally posted by Paul O View Post
            The graph looks fine, I have to question the enclosure size you picked however.. why so big? My simulation in WinISD suggest that the driver will be well over xmax at 1500w which isn't ideal but it can handle it.
            Paul -- For some reason it's not letting me upload anything tonight without getting an error. At 8ft^3 tuned to 38Hz, running 1500W RMS to the driver, Bass Box Pro is telling me I have almost 2mm to spare. I could be doing something wrong though. Is there any difference in results between the two (2) programs?
            "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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            • #7
              The programs should produce the same results if we are both using the same driver TS parameters. Where did you get yours?
              Paul O

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              • #8
                Originally posted by Paul O View Post
                The programs should produce the same results if we are both using the same driver TS parameters. Where did you get yours?
                Mine were in the database of the program, but I always verify them with the specs on the website.
                "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

                Comment


                • #9
                  Anyone have any experience with B&C speakers (specifically the 18TBW100). I am designing a set of 18" PA sub-woofers right now and am torn between the Eminence KappaProLF 18" vs the B&C mentioned earlier. Any recommendations? The Eminence looks like I can get away with a slightly smaller enclosure tuned a couple Hz higher. Output is nearly the same, but with much less power required from the Eminence. I currently have a set of SigmaPro 18" from Eminence and have been less than impressed with them. Are B&C going to sound better? Any help is appreciated
                  "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

                  Comment


                  • #10
                    Dude,
                    I can't help you with driver choices, but I'm pretty sure that for PA use, you need to be looking a bass "horns" or "scoops".
                    Because you will def run out of SPL using direct radiator boxes.

                    Like one of the designs from Bill Fitzmaurice:

                    I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                    "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                    High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                    SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                    My Voxel min sub Yet-another-Voxel-build

                    Tangband W6-sub

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                    • #11
                      Originally posted by donradick View Post
                      Dude,
                      I can't help you with driver choices, but I'm pretty sure that for PA use, you need to be looking a bass "horns" or "scoops".
                      Because you will def run out of SPL using direct radiator boxes.

                      Like one of the designs from Bill Fitzmaurice:
                      I appreciate the advice, but I don't have any interest in horns or scoops. I don't care for their directivity and complexity in construction. I will not disagree that you can get a lot of output out of a horn with a small speaker, but I don't care for the response curve or directivity. This is not a slam on Bill or anyone else that uses these products. I simply prefer direct radiating.

                      I am looking for some advice on driver selection at this point.
                      "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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                      • #12
                        Originally posted by STIchris722 View Post

                        I appreciate the advice, but I don't have any interest in horns or scoops. I don't care for their directivity and complexity in construction. I will not disagree that you can get a lot of output out of a horn with a small speaker, but I don't care for the response curve or directivity. This is not a slam on Bill or anyone else that uses these products. I simply prefer direct radiating.

                        I am looking for some advice on driver selection at this point.
                        Fair enough, rock on Wayne

                        I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
                        "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

                        High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
                        SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
                        My Voxel min sub Yet-another-Voxel-build

                        Tangband W6-sub

                        Comment


                        • #13
                          i've not heard any of B&Cs 18's , but this is Jbrunner's B&C 21 in 13^3ft . it was amazing !

                          Click image for larger version

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                          Paper Towers
                          RS180P/28F surrounds
                          Boombox

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                          • #14
                            Originally posted by STIchris722 View Post
                            I am designing a set of 18" PA sub-woofers right now and am torn between the Eminence KappaProLF 18" vs the B&C mentioned earlier.
                            You're comparing a top shelf driver to a mid level driver so they're not really in the same ballpark, even a Definimax doesn't compare to the B&C when it's being pushed. Have you modeled the 18TBX100? I'm also seeing 5.5 cu/ft per driver as the optimum for power handling.
                            Paul O

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                            • #15
                              Originally posted by donradick View Post

                              Fair enough, rock on Wayne
                              What is this supposed to mean?
                              "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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