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  • Acoustic centre calculations?

    Say my acoustic centres are 44mm between woofer and tweeter at 1m (It's a horn tweeter). The centres of the drivers on the vertical plane are 267mm apart. What would the acoustic centres be at 2.5mtr?
    Is there a calculation for this? Or do I have to draw It out on the floor

  • #2
    Just drew It out on the floor (not very accurately though). At 2.5mtr, would my acoustic centres now be 24mm apart, rather than 44mm?

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    • #3
      Huh?

      I'm not sure what you're doing exactly, but it sounds like to are measuring from the speaker to mic? In that case, the math is Pythagorean theorem. a^2 + b^2 = c^2. That said, "acoustic centre" to me is a z-axis measure, so if its 44mm from one driver to the other then it's 44mm no matter how far away you are.


      Don't waste your money on a new set of speakers, you get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

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      • #4
        Originally posted by fatmarley View Post
        ...Is there a calculation for this?...
        If you can lay it out as triangles - yes

        "Not a Speaker Designer - Not even on the Internet"
        "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

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        • #5
          Originally posted by dcibel View Post
          Huh?

          I'm not sure what you're doing exactly, but it sounds like to are measuring from the speaker to mic? In that case, the math is Pythagorean theorem. a^2 + b^2 = c^2. That said, "acoustic centre" to me is a z-axis measure, so if its 44mm from one driver to the other then it's 44mm no matter how far away you are.

          Yes, speaker to mic on the tweeter axis.

          The acoustic centre would stay the same If It were measured half way between the mid and tweeter.

          Pythagorean - I can hardly spell It, let alone understand It.

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          • #6
            Originally posted by Sydney View Post
            If you can lay it out as triangles - yes
            Yes, that's what I did on my kitchen floor. Just wanted to know If there was an easier way of doing It.

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            • #7
              Originally posted by fatmarley View Post
              Pythagorean - I can hardly spell It, let alone understand It.
              Pythagoras did stagger us, and our reason encumber, with irrational number.

              Comment


              • #8
                Originally posted by fatmarley View Post
                ... Just wanted to know If there was an easier way of doing It.
                https://www.triangle-calculator.com/
                I've also used Sketchup
                "Not a Speaker Designer - Not even on the Internet"
                "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                Comment


                • #9
                  Oh yea, Sketchup. I did try it a couple of times but found it a bit confusing. I'll have to download it again and have another go.

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                  • #10
                    Acoustic center generally refers to the sound from 2 drivers (or more) arriving at your ear at the same time,
                    people often think of the voice coil being the "acoustic center" but it never is in the real world, and it changes
                    with frequency! When you see a step in a speakers baffle like the tweeter being set back further than the
                    mid, it is done to try and align the acoustic centers in the time domain.

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                    • #11
                      I'm surprised none of the gurus have chimed in. I'm hoping that means my measurements on the kitchen floor are about right. If they're not, It's going to cost me a hell of a lot of time, hassle, and a bit of money.

                      For anyone who's wondering why I'd like to know what the acoustic centre Is at 2.5mtr, It's because I can't get the phase tracking right on my horn speakers (within 90 degrees at the crossover). I get a weird phasey, cuppy, hollow type of sound with some speech, that I don't get with headphones. If all I have to do to get the phase tracking right Is to bring the tweeter forward 24mm, then I'm happy to do It.

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                      • #12
                        Originally posted by xmax View Post
                        people often think of the voice coil being the "acoustic center" but it never is in the real world, and it changes
                        with frequency!
                        Phase changes with frequency, acoustic centre is a constant.
                        Don't waste your money on a new set of speakers, you get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

                        Comment


                        • #13
                          Originally posted by dcibel View Post
                          Phase changes with frequency, acoustic centre is a constant.
                          In theory yes, in practice however you will find optimum "time alignment"
                          between 2 drivers will also change with frequency.

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                          • #14
                            Under time alignment
                            Notice they specify 2-3K region.

                            http://www.sbacoustics.com/index.php/technical-notes/

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                            • #15
                              Originally posted by xmax View Post
                              Under time alignment
                              Notice they specify 2-3K region.

                              http://www.sbacoustics.com/index.php/technical-notes/
                              That's quite the lacklustre document you've found there. Tell me, did it tell you why the 2-3kHz range was chosen?

                              I'd suggest that you try designing a speaker employing time alignment, or even phase alignment, before you proclaim yourself an expert on the subject. Acoustic centre is a constant, entered as the z-axis dimension when analyzing the polar performance of a system. It is simply minimum phase + distance (delay) to correlate the physical relation between drivers, or if you want to look at it in the terms of the document you linked to, it is "the group delay of the excess phase". In the SB doc, details of the measurement method are not given, but I can go out on a whim and say the 2-3kHz range was used because its a range where both the tweeter and midwoofer have significant output.

                              Originally posted by xmax View Post
                              In theory yes, in practice however you will find optimum "time alignment"
                              between 2 drivers will also change with frequency.
                              I've practised plenty, and I think perhaps you are confusing time alignment and phase alignment.




                              Don't waste your money on a new set of speakers, you get more mileage from a cheap pair of sneakers. Next phase, new wave, dance craze, anyways it's still rock and roll to me!

                              Comment

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