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The Current Trend Toward Multiple Tweeter Designs

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  • The Current Trend Toward Multiple Tweeter Designs

    I started a thread about some Tekton Pendragons recently and someone pointed out that there was a current trend toward multiple tweeters. Well, I think these may squeeze into that category. They're designed by Ken Kreisel, who was formerly with M&K. I have no idea what these sound like, but they sure seem to be outside the realm of most conventional speaker designs.

    Has anyone seen a speaker with more than 4 tweeters other than a line array? I thought the Pendragons were over the top with 3 tweeters.



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  • #2
    Re: The Current Trend Toward Multiple Tweeter Designs

    They're intentionally designing the speakers to beam with a very narrow dispersion pattern. This is usually intended for multiple speaker home theater systems. I doubt they would appeal to many people as a music speaker. There would be a much greater than normal drop in high frequencies off-axis compared to more conventional speaker designs, so highs would be much more position dependent and the power response would be fairly dark.
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    • #3
      Re: The Current Trend Toward Multiple Tweeter Designs

      .........but as a benefit to some, there would be less impact from early reflections from the room. It really depends on the preference of the listener.

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      • #4
        Re: The Current Trend Toward Multiple Tweeter Designs

        Originally posted by Mayhem13 View Post
        .........but as a benefit to some, there would be less impact from early reflections from the room. It really depends on the preference of the listener.
        From an acoustics perspective I would question that. Reflections are generally an issue at lower frequencies, but not so much in a tweeter's range.
        Click here for Jeff Bagby's Loudspeaker Design Software

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        • #5
          Re: The Current Trend Toward Multiple Tweeter Designs

          What about a Bessel Array? It allows multiple similar drivers to act similarly to a point source in dispersion by amplitude-shading the outer drivers. McIntosh has used them before - see below.

          Click image for larger version

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          (McIntosh XLS360)

          It seems to me like you could do the same by frequency-shading the outer drivers to roll off at lower frequencies to provide the horizontal dispersion you want. You just need a way to calculate the phase difference for a given frequency between multiple spaced sound sources at off-axis angles.

          Also, an X-shaped array of tweeters could provide similar pattern control to the larger square arrays with fewer drivers needed. Of course, the means of pattern control would be self-interference, but you could adjust it by rolling off the outer drivers as stated.

          What I'm not sure about would be the effect on impulse response.

          I think the reason why Bessel arrays aren't used more commonly is that it's easier and cheaper to just integrate a horn-loaded HF section with one driver.
          Best Regards,

          Rory Buszka
          Product Manager, Dayton Audio

          The best way to predict the future is to create it.

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          • #6
            Re: The Current Trend Toward Multiple Tweeter Designs

            With my Genesis 350's, which have 3 tweeters in front and one rear firing, all but the center one is low passed.

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            • #7
              Re: The Current Trend Toward Multiple Tweeter Designs

              Originally posted by doctormorbius View Post
              Has anyone seen a speaker with more than 4 tweeters other than a line array? I thought the Pendragons were over the top with 3 tweeters.
              Even two tweeters vertically aligned are a line array, as they will act as a line source, though only at the upper end of the spectrum. The more you use the lower the frequency to which it acts as a line source. The Kreisel four tweeter array is an odd duck, as few users would want to reduce both the horizontal and vertical high frequency dispersion. IMO using that arrangement is more of a marketing than an engineering decision.
              From an acoustics perspective I would question that. Reflections are generally an issue at lower frequencies, but not so much in a tweeter's range.
              Early reflections can be an issue in the highs, usually from ceiling bounce. But it's seldom an issue with wall bounce, toe-in takes care of that, so I really don't see the need to halve the horizontal high frequency dispersion with that arrangement.
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

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              • #8
                Re: The Current Trend Toward Multiple Tweeter Designs

                Originally posted by [email protected] View Post
                What about a Bessel Array? It allows multiple similar drivers to act similarly to a point source in dispersion by amplitude-shading the outer drivers. McIntosh has used them before - see below.

                [ATTACH=CONFIG]49688[/ATTACH]

                (McIntosh XLS360)

                It seems to me like you could do the same by frequency-shading the outer drivers to roll off at lower frequencies to provide the horizontal dispersion you want. You just need a way to calculate the phase difference for a given frequency between multiple spaced sound sources at off-axis angles.

                Also, an X-shaped array of tweeters could provide similar pattern control to the larger square arrays with fewer drivers needed. Of course, the means of pattern control would be self-interference, but you could adjust it by rolling off the outer drivers as stated.

                What I'm not sure about would be the effect on impulse response.

                I think the reason why Bessel arrays aren't used more commonly is that it's easier and cheaper to just integrate a horn-loaded HF section with one driver.
                That's a real interesting photo there, I'm trying to wrap my head around the benefits of this arrangement over a vertical array. What you get here is narrow horizontal dispersion, and wide vertical dispersion, which is the exact opposite of most design philosophies, my own included. This is like taking a tall ribbon or AMT (AMTPRO-4 for example) and installing sideways. Usually you would want the wide horizontal dispersion to avoid the laser beam sweet spot, and limiting the vertical dispersion can be of some benefit to reduce interaction from floor/ceiling.

                I guess the idea is to match the dispersion of the midrange below that tweeter array.
                "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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                • #9
                  Re: The Current Trend Toward Multiple Tweeter Designs

                  Originally posted by dcibel View Post
                  That's a real interesting photo there, I'm trying to wrap my head around the benefits of this arrangement over a vertical array. What you get here is narrow horizontal dispersion, and wide vertical dispersion, which is the exact opposite of most design philosophies, my own included. This is like taking a tall ribbon or AMT (AMTPRO-4 for example) and installing sideways. Usually you would want the wide horizontal dispersion to avoid the laser beam sweet spot, and limiting the vertical dispersion can be of some benefit to reduce interaction from floor/ceiling.

                  I guess the idea is to match the dispersion of the midrange below that tweeter array.
                  In theory, when wired properly a five element bessel array acts exactly like a single point source with improved power handling and a slight increase in efficiency being the primary benefits. As mentioned earlier, there's certainly cheaper ways to accomplish the same goals. The untapped potential of bessel arrays over horn loaded drivers is the reduced center to center spacing allowing for less lobing and combing. If we use five 1" domes as the example with a need to cross to an eight inch or larger woofer, a typical waveguide would have a min c to c spacing of 7 inches which limits the point of crossover to avoid those artifacts. Let's not forget the crowd that absolutely hates the sound of so called 'honking' horns.

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                  • #10
                    Re: The Current Trend Toward Multiple Tweeter Designs

                    I disagree with the subject premise. I see no "trend" toward the use of multiple tweeters. In domestic applications, only a small fraction of designs use tweeter arrays of any sort.
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                    • #11
                      Re: The Current Trend Toward Multiple Tweeter Designs

                      I agree with JRT but there has been increasing discussion and interest on this board. It is an interesting topic, and beside McIntosh and M+K, Dynaudio and the old Polk SDA systems use tweeter arrays for a variety of reasons.

                      Given the current interest in matching the directivity of large mid-woofers to tweeters using waveguides, I think the multi-tweeter approach should be explored. It is far easier and cheaper to use a few tweeters in an array than design and test a waveguide. The CTC spacing is an extra benefit.

                      Today we have access to inexpensive tweeters with excellent performance and low resonance points. There's an ongoing thread here about making an 8" 2 way, and directivity mismatches are for me, the reason why this otherwise splendid approach doesn't wash. The bass of an 8" driver is often all you need for satisfying musical performance, and if a tweeter array helps match with a good midwoofer, it might be a really practical design. Not to say there aren't other issues, but I honestly don't see why people aren't open to exploring it, especially given the precedents set by M+K and so on.

                      Also - I was thinking of what Jeff said about a 'dark' presentation. He is certainly correct in this characterization. However it seems to me that directivity preferences are very personal. I see basically four approaches - the dipole response, aiming for similar dispersion from all drivers, with a null to the sides. The typical hifi response, of a 2 way with a directivity mismatch at the crossover region - but tuned to the preferences of the listener. The smoothed hifi response, where you go from omni to very directional with higher frequency, with no dramatic lumps between drivers - a 3 or 4 way design. Finally, the CD response, where you have a whole bandwidth from upper midrange to mid treble that has identical, presumably narrow dispersion. This minimizes early reflections, but can lack some sparkle. It is important to note which effect you are aiming for in a design.

                      If you order them by intrinsic cost, you have:
                      $ 2 way hifi response
                      $$ 2 way CD
                      $$$ 3-4 way hifi response
                      $$$$ Dipole response - normally a 4 way design, often with active filters

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                      • #12
                        Re: The Current Trend Toward Multiple Tweeter Designs

                        Originally posted by civit View Post
                        Today we have access to inexpensive tweeters with excellent performance and low resonance points. There's an ongoing thread here about making an 8" 2 way, and directivity mismatches are for me, the reason why this otherwise splendid approach doesn't wash. The bass of an 8" driver is often all you need for satisfying musical performance, and if a tweeter array helps match with a good midwoofer, it might be a really practical design. Not to say there aren't other issues, but I honestly don't see why people aren't open to exploring it, especially given the precedents set by M+K and so on.
                        I honestly think that a lot of people nowadays spend too much time staring at charts and graphs instead of listening. The debate of the 8" 2-way is a great example. Many shy away from this because the polar response is worse than a 6.5" 2-way design. But you must listen...I've done a few 8" two ways, and believe me the benefit of an 8" woofer over 6.5" trumps the slightly worse polar response by far. Along similar lines, I recently read a thread where someone didn't want to use a 4 ohms version of the same driver because someone measured the 4 ohm version to have slightly worse distortion. This is one of those "give me a break" moments, seriously plug in a 4 ohm model and an 8 ohm model of the same driver and tell me you can tell them apart. That's my rant for today, I'm done now. ;)
                        "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
                        exactly a Fc 3K for both drivers, anybody can do it." -Xmax

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                        • #13
                          Re: The Current Trend Toward Multiple Tweeter Designs

                          Originally posted by billfitzmaurice View Post
                          Even two tweeters vertically aligned are a line array, as they will act as a line source, though only at the upper end of the spectrum. The more you use the lower the frequency to which it acts as a line source. The Kreisel four tweeter array is an odd duck, as few users would want to reduce both the horizontal and vertical high frequency dispersion. IMO using that arrangement is more of a marketing than an engineering decision.
                          Early reflections can be an issue in the highs, usually from ceiling bounce. But it's seldom an issue with wall bounce, toe-in takes care of that, so I really don't see the need to halve the horizontal high frequency dispersion with that arrangement.
                          additionally, the side wall reflections are known to increase AWS. so not all reflections are evil.

                          plus, what are we defining early as? 10ms? 30ms (haas window)? To verge near the Haas window where the reflection is detracting as an echo, your speaker would have to be very far from the side wall. therefore, in typical home use, the side walls are a contribution to the soundstage rather than a detriment. so, I don't really see an issue with "early" reflections.
                          ErinsAudioCorner.com

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                          • #14
                            Re: The Current Trend Toward Multiple Tweeter Designs

                            The problem with using two side by side drivers to control directivity is that it doesn't actually work like we want it to. In reality the polar response is fairly poor and extremely narrow up high and omni down low. Simply measure a pair of drivers next to each other and you'll see quickly it's not a magic remedy.
                            https://www.youtube.com/channel/UCm2...oSKdB448TTVEnQ

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                            • #15
                              Re: The Current Trend Toward Multiple Tweeter Designs

                              Originally posted by dcibel View Post
                              I honestly think that a lot of people nowadays spend too much time staring at charts and graphs instead of listening. The debate of the 8" 2-way is a great example.
                              Funnily enough I am listening to a pair of EPI 8" 2-ways right now. Very elegant design to say the least.

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