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How do I Visualize the Width of an Audio Frequency? . . .

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  • How do I Visualize the Width of an Audio Frequency? . . .

    . . . I understand that audio frequencies (Sine Waves) have length as emanated from the source but how do I understand/visualize their width/height?

    My current dilemma concerns baffle step/horns.

    How wide is 55 Hz?

    How wide is 800 Hz?

    How wide is 4KHz?

    Thanks for any methods to visualize these phenomenon.

  • #2
    13550/F = length in inches.
    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
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    • #3
      So, 13,550 is the constant and F (Frequency) is the Variable, right?

      If so, thanks Mr. Wolfy.


      • #4
        Then after a search concerning Wolf's response I get this thread -->


        • billfitzmaurice
          billfitzmaurice commented
          Editing a comment
          Much in that is incorrect, especially where driver spacing is concerned. It should be less than 1 wavelength CTC for a uniform wavefront at the source, but other than studio nearfield monitors there's no real need for that. At normal listening distances separate wavefronts will have integrated into one even with considerably more than 1 wavelength CTC.

        • Steve Lee
          Steve Lee commented
          Editing a comment
          Thanks, Bill - this makes good sense.

      • #5
        270 cm(32hz) overlaps perfectly with90 cm (96hz ) in parallel ‘TL’s converging to same exit . (neat stuff to play with


        • #6
          The math here is super basic. Speed of sound is 343m/s…Frequency is the number of cycles per second so the math is simply (1/F)*343 for wave length in meters.
          I'm not deaf, I'm just not listening!


          • #7
            Originally posted by dcibel View Post
            The math here is super basic. Speed of sound is 343m/s…Frequency is the number of cycles per second so the math is simply (1/F)*343 for wave length in meters.
            343 m/s (1125.3 ft/sec) is true for dry air at 18.85C (65.93_degF). Temperature and humidity change that.

            Here in western Massachusetts, the air temperature outside of my backdoor is cureently 78 degF, and indoor temp is 72 degF with windows open (no A/C). Not sure about the humidity, but it does feel more humid than usual (sky is overcast and it is supposed to rain later this afternoon).

            At 72 degF (22.22C) in dry air, speed of sound increases to 1130.6 ft/sec (344.6 m/s), and 50% relative humidity increases that another 1 ft/sec.

            12*1131.6= 13579.2 inches per second

            I more usually use 69 degF and 50% relative humidity, which gets to
            1130 ft/sec, 13560 in/sec, 344.4 m/s.

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            • #8
              Pressure variables such as temperature, humidity affect the speed of sound. The other variable is altitude.


              • #9
                Sorry, 344.4m/s, I’m off by 0.4%, back to the drawing board!

                Trying to keep it simple for someone who just wants to know how long 100Hz wave is, does it matter much if it’s 3.43meters long or 3.444 meters long?
                I'm not deaf, I'm just not listening!


                • #10
                  ^ NO!

                  C-C spacing --> less than 1 wave length at the XO Freq is GOOD ENOUGH.
                  Last edited by Steve Lee; 09-12-2022, 09:27 PM.


                  • #11

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                    • #12
                      Originally posted by Steve Lee View Post
                      C-C spacing --> is it 1/4 wave or less than 1 wave length at the XO Freq?
                      There are several threads at that will say the same thing....Planet10 will talk about how it SHOULD be 1/4 wave but that is impractical for almost all designs unless you have a coaxial, so a rule of thumb (ROT) is to have C-t-C spacing no more than 1 wavelength at the xo point...then some people will talk about how they have heard speakers that sound great that break the rule.

                      More recently Kimmo Saunisto (author of VituixCAD) has suggested that 1.2 x one wavelength often sounds the best to him. (This is an over-generaliztion of what he says.)

                      Bottom line...its a rule of thumb, good to think about, but don't take it all too seriously. What I have been doing lately is figure out close to where I think I will xo, keep track of the length of 1 wavelength and 1.2 times that wavelength and then mess around in Sketchup for what will actually look okay.

                      One place it becomes restrictive is if you are using a relatively large woofer then some large-faceplate tweeters may get ruled out if you aren't able to cross quite low.


                      • #13
                        ^ Thanks for the clarification, Sir!

                        I am crossing a 12" woofer at 800 Hz to a 12" x 4" midrange horn and then that to a 4" x 4" Tweeter horn at 4KHz.

                        After running the numbers it looks like it should be fine if I overlap the tweeter horn rim over the mid horn.


                        • #14
                          The ROT a4e mentions really applies to flat faceplate tweeters and 4th order LR filters. It's a ROT for the most common type of speaker design.

                          Best solution is to measure your horn on a baffle full horizontal and vertical response sets, horizontal only is okay if the horn is round or square, but ellipse or rectangles should include both axis of data. You can then observe the balance of driver separation in VituixCAD extremely easily. Just pound the response into shape with active blocks and adjust filter knee and driver spacing y axis dimension until you get a good smooth slope of in-room and power response between the horns and woofer. This is a good exercise to go through with any drivers, it will show easily that placing drivers as close together as possible can possibly provide the worst result.
                          I'm not deaf, I'm just not listening!


                          • #15
                            dcibel, thanks for your continued support to this hobby - for now I will work with what I have and see what happens - all this measurement stuff is complex and time consuming and I really don't have suitable facilities to take this to the degree suggested - but in the effort I will come to understand what you are proposing.

                            The reality is that I don't need these speakers - it is just a WANT and another experiment to satisfy my addiction to speakers so that I stop mentally designing and buying drivers and start building and learning again.