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  • Acoustic centers too far apart?

    In my Lambda build (ala Sunflowers) the XO is at 2500hz and the centers are 9 inch apart. According to calculation they should be no more than 1 wavelength? thats 5.7 inch. I can get them about 6.25 inch apart. IS that good enough? The problem is I am using a Peerless 830883 which is 6.5 inch dia so it doesn't leave me a lot of room. The tweeter is a SB29. advice?

  • #2
    Re: Acoustic centers too far apart?

    Don't get too hung up on CTC spacing. There are myriad other little things that affect SQ perception far more.
    Don't listen to me - I have not sold any $150,000 speakers.

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    • #3
      Re: Acoustic centers too far apart?

      http://techtalk.parts-express.com/sh...56#post1873856

      Maybe some of my ramblings (posts #4 and #5) will help... or maybe not.

      Depending on the orientation of the drivers involved (vertical/horizontal), this might not be an issue.
      ~Marty

      Baby Eidolons
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      • #4
        Re: Acoustic centers too far apart?

        Originally posted by johnnyrichards View Post
        Don't get too hung up on CTC spacing. There are myriad other little things that affect SQ perception far more.
        Agree completely. There's nothing special about 1 wavelength CTC spacing either. Even at 1 wavelength, there's still a null. Ideally, you'd want less than 1/2 wavelength to avoid the null. The crossover basic design and voicing has a far greater impact on overall sound, as well as box stiffness and damping.

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        • #5
          Re: Acoustic centers too far apart?

          Originally posted by jimangie1973 View Post
          Agree completely. There's nothing special about 1 wavelength CTC spacing either.
          Sure, nothing special if you don't care about off-axis response. The farther apart the sources, the narrower the pattern around the crossover point. Closer is better - I shoot for 1/2 wavelength. For this reason I try to never cross over above 2kHz.

          YMMV.

          -Charlie
          Charlie's Audio Pages: http://audio.claub.net

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          • #6
            Re: Acoustic centers too far apart?

            Ok so I went back to the model (using Jeff B's software) and the one thing that DOES make a big difference believe it or not is my baffle height. It is 11 inch wide by 46 inch high. When i reduce it to 40 inch high it smoothed out a lot. Now I can easily do it based on the way i designed my test baffle!!

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            • #7
              Re: Acoustic centers too far apart?

              Originally posted by charlielaub View Post
              Sure, nothing special if you don't care about off-axis response. The farther apart the sources, the narrower the pattern around the crossover point. Closer is better - I shoot for 1/2 wavelength. For this reason I try to never cross over above 2kHz.

              YMMV.

              -Charlie
              I care deeply about off-axis response, but having heard many systems struggle at a crossover point arrived at by considering a single metric, I believe it better to make a compromise towards a higher crossover point, if the drivers in hand do not want to play nice at a lower crossover point.

              To head off the inevitable response, not everyone can afford to go through driver after driver finding "that one tweeter". Not saying you would do that Charlie, just throwing it out there. Sometimes, a guy just wants to use what he has.

              Distortion is the ugliest artifact in a speaker system, and making the compromise of a higher crossover point to avoid distortion at the expense of some lobing is a time-tested budget friendly approach to design work. Distortion is far uglier than lobing, IMHO and YMMV
              Don't listen to me - I have not sold any $150,000 speakers.

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              • #8
                Re: Acoustic centers too far apart?

                Originally posted by charlielaub View Post
                Sure, nothing special if you don't care about off-axis response. The farther apart the sources, the narrower the pattern around the crossover point. Closer is better - I shoot for 1/2 wavelength. For this reason I try to never cross over above 2kHz.

                YMMV.

                -Charlie
                I don't disagree with you, although only the vertical off axis is affected, assuming vertical driver alignment. I'm not saying it's irrelevant, only that it will most likely have much less effect than other design choices.

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                • #9
                  Re: Acoustic centers too far apart?

                  One addendum - if the tweeter is capable of playing cleanly at intended output at a crossover point low enough to minimize lobing, then that is the direction I would go with and recommend to others.

                  In this case, I think the SB29 can probably be pushed significantly lower than 2500 hz, and IMHO a lower crossover point being very feasible should be attempted.
                  Don't listen to me - I have not sold any $150,000 speakers.

                  Comment


                  • #10
                    Re: Acoustic centers too far apart?

                    Originally posted by charlielaub View Post
                    Sure, nothing special if you don't care about off-axis response. The farther apart the sources, the narrower the pattern around the crossover point. Closer is better - I shoot for 1/2 wavelength. For this reason I try to never cross over above 2kHz.

                    YMMV.

                    -Charlie
                    +1

                    I used to blow of CTC spacing but now consider it a high priority. My current design uses a 950hz cross over and about 9" driver spacing.
                    https://www.youtube.com/channel/UCm2...oSKdB448TTVEnQ

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                    • #11
                      Re: Acoustic centers too far apart?

                      Originally posted by jimangie1973 View Post
                      ... Even at 1 wavelength, there's still a null.
                      well… it depends where the microphone is located. The geometry is the key to this issue.

                      Two Vertical woofers:
                      If you have two woofers both playing the same frequencies, and you place the microphone exactly between them, you won't see a null. But, as you move the mic up or down, the geometry dictates that the path lengths will not be identical... thus at some frequency there will be cancellation. The thing to remember though is that this is typically far above the listening axis and it won't be much of a problem. However...


                      Two Horizontal woofers:
                      In this configuration, (which is often seen in center channel speakers,) the two woofers will produce cancellation as you move left and right (with respect to the center seat). In this orientation the cancellation is going to pose a problem for people sitting left and right of the center seat. The solution is to try to mount the two Horizontal woofers as close as you can and cross them over as low as you dare (without distortion or risking your tweeter's life.)
                      ~Marty

                      Baby Eidolons
                      Sapphos
                      Cables (Post #54)
                      Other speakers (Post #21)
                      Design Thoughts (Posts: 6,10,13,33,35)
                      Boundary Augmentation
                      Dispersion/Interference

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                      • #12
                        Re: Acoustic centers too far apart?

                        ReissM, your correct that the null will be way off axis. Although the null won't affect the direct waves, it will affect the reflections, which in a real world room will have an effect, although potentially (and in my experience) minor. This null would effect the overall power response.

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                        • #13
                          Re: Acoustic centers too far apart?

                          Originally posted by jimangie1973 View Post
                          ReissM, your correct that the null will be way off axis. Although the null won't affect the direct waves, it will affect the reflections, which in a real world room will have an effect, although potentially (and in my experience) minor. This null would effect the overall power response.
                          I agree... my advice is to figure out the geometric implications of using two woofers and the resulting frequencies of the nulls, then design the speaker to not have the nulls at all.

                          No nulls? How you going to do that?
                          By picking a crossover frequency low enough, the wavelengths would be long enough to avoid the nulls completely.


                          This would be easy to obtain in a three way center channel design that utilized 2 horizontally mounted woofers only up to 150Hz. Then, a midrange driver could handle 150Hz up to about 1800Hz before handing off to a tweeter. (The tweet could be vertically mounted above the midrange. See the pic)

                          Click image for larger version

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                          ~Marty

                          Baby Eidolons
                          Sapphos
                          Cables (Post #54)
                          Other speakers (Post #21)
                          Design Thoughts (Posts: 6,10,13,33,35)
                          Boundary Augmentation
                          Dispersion/Interference

                          Comment


                          • #14
                            Re: Acoustic centers too far apart?

                            Originally posted by charlielaub View Post
                            Sure, nothing special if you don't care about off-axis response. . . . Closer is better - I shoot for 1/2 wavelength.
                            +1

                            Speaker builders seem rarely to look up. If they did perhaps they'd care more about vertical polars . . .
                            "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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                            • #15
                              Re: Acoustic centers too far apart?

                              My system is not an MTM. WMT I'll look at a lower XO point. I am currently 2nd order.

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