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  • Arx A5c response

    For another installment of Arx measurements, we'll review the A5, in this case an A5 modded with the "c" tweeter with level-trimming.

    The C variant of each Arx model, as some already know, indicates upcoming models whose upgrade consists of a second generation planar magnetic tweeter, the "third gen" tweeter since Acculine's original BG Neo3.

    The C tweeter offers three benefits:

    1. It is more efficient. While still a six ohm device - with a dead-flat impedance magnitude constituting a purely resistive load - we could get roughly 3dB more out of it.

    2. This added level has to be reduced to match each model's response and in so doing we add about double the thermal power handling. A change in the tweeter filter circuit cuts power to the tweeter approximately in half.

    3. Tied in with all of this is a shortened bandwidth from the C device that means better crossover integration.

    I'd also like to touch on measuring as a whole. Long-time readers will recall that TAI does not hold final system measurements in as high esteem as others may. Where measurements are crucial to the design process, and while they absolutely confirm the complete design, they have little pertinence to the listener's overall experience aside from minor after-the-fact correlations of data and experience. (I've written before about measuring and if a reader would like to link those posts into this thread I'd appreciate it.)

    Measurements also add outside influences to the data to conflict with what it is assumed to represent. Very good acoustical models will often reveal important elements of a design that measuring will completely miss. The design process must therefore include a good deal of perspective beyond what appears to be objective measurement in theoretical analysis.

    With this in mind following are a pair of measurements of the Arx A5 with a C tweeter fitted.

    The first is a conventional on-axis response plot. Because we want this information to actually pertain to real-world conditions of use, it is an in-room capture but without the A5 toed in normal use. The response above roughly 300Hz is actual, 1/6 octave averaged output of the A5. In order to capture the design center which includes the tweeter's response, the microphone is positioned on vertical axis just above the bottom edge of the tweeter's diaphragm.

    The response below 300Hz is too colored by the room so it is acoustically modeled output; the response nearfield measurement of just the woofer(s) will resemble to a high degree.

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    The challenges of in-room measurements are well known and this response is not immune to those effects either. First, the 400Hz bobble is boundary bounce.

    Second, the 1400 dip is the midrange - which is a very energetic paper-coned 5" driver - entering cone breakup, a region above which experience says level has to be carefully dealt with. You can see the A5's response is shelved down slightly in the region between 1500Hz and 3500Hz. The bottom end of the tweeter's response is also in the upper-middle of this region and it too has to be contoured for full dynamic output.

    Third, the bobble centered at 4kHz is diffraction; this being an on-axis response doesn't do much to camouflage the phenomenon.

    Lastly, the new tweeter has even more very high frequency energy than the existing tweeter and is near reference up to 20kHz. The raw measurement extending to 50kHz show this tweeter has output - even in-speaker, through the crossover - beyond 30kHz.

    A second measurement was taken approximately 15 degrees below the first.

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    All of the little artifacts of in-room measuring still appear, however the entire spectral balance of the speaker, so to put it, has shifted. An imaginary line drawn through 200Hz and 17kHz has nearly the same response as the first measurement, only the speaker's response is tilted down on top.

    This second response plot tells us that the A5 has the uniform off-axis power response the design called for, even with a simple seven element crossover plus one conjugate and treble attenuation. The careful design that went into both of the two crossover points and filters has preserved the speaker's response characteristic for a linear, predictable response off axis.

    Given the A5's reputation, measurements for the sake of simply comparing measurements appear to be no substitute for ears-on time with the product. Many times a speaker known for a natural tonal balance, good transient response, and a focused, expansive, and believable soundstage will not show us any of those traits in a simple on-axis response.

    The A5 appears to be built to be brighter in the treble than the other models too but the A5 (and the A3/A3c too) are floorstanding speakers with appreciable bass output and a propensity to be pushed back toward walls. Doing so elevates the bass output to which a slight corresponding treble lift is needed to balance the presentation. Remember too that a floorstanding speaker set perpendicular to the floor and many times square without toe in the room - as the second plot shows - may or may not always be heard on-axis. A bookshelf speaker, by contrast, can always be adjusted for sound on the vertical axis.

    And so on and so on. Speaker design is dependent on measurement, but good sound depends on a series of design choices that allow visible deviations from a simple line on a screen. When the A5 was turned on and heard for the first time - after tens of thousands of models in the computer - it predictably sounded unlistenable, at least to the music lovers who first heard it. After subjective decisions to eliminate colorations the speaker start to get out of the way and let the music through. Weeks later we felt the design suitable for production.

    The C tweeter can be retrofit into existing A5s. A kit is being developed with the new tweeter and a simple attenuation network for field fitment. Modified A5s will have improved power handling and a better and more extended response. We'll post those details as this affordable product comes to market.

    The A5 is a relatively compact, affordable product. Naturally it won't do things it cannot do. It's not perfect and it's not going to please every listener. The point of bringing this information out is to show its in-room response - including off-axis in its power field - and to begin a conversation about the trade-offs a design must include along with the further compromises every listening environment will impress on the sound.

  • #2
    Jon, I'm signed in and I can't seem to view the images. I tried three different browsers but can't view them, not sure if it's just me...

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    • #3
      Its not just you, I can't view them either. Tried IE and Firefox.

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      • #4
        It appears to be a server security measure, folks. Depending on if Bernie the webmaster is in this weekend or not, we'll do our best to make these visible.

        Meanwhile I'm going to start a series of posts in another thread about related topics.

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        • #5
          I can see the plots now. Jon how do these plots compare with the original A5s that I own?

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          • #6
            Originally posted by newspeakers
            I can see the plots now. Jon how do these plots compare with the original A5s that I own?
            Quite similar. The current tweeter just has less output and therefore less attenuation in the crossover. The hotter tweeter required a filter to drop it down to the original level. Both designs were voiced alike.

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            • #7
              Originally posted by newspeakers
              Jon how do these plots compare with the original A5s that I own?
              Originally posted by Jon Lane
              Quite similar. The current tweeter just has less output and therefore less attenuation in the crossover. The hotter tweeter required a filter to drop it down to the original level. Both designs were voiced alike.
              Jon, I don't quite understand the point. Most of the power to drive a speaker goes into the bass. The tweeter requires very little power by comparison. So why bother making the tweeter more efficient if there is no improvement in the sound? Why would anyone want to upgrade? I'm not arguing with you, I just don't understand.

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              • #8
                Originally posted by newspeakers
                Jon, I don't quite understand the point. Most of the power to drive a speaker goes into the bass. The tweeter requires very little power by comparison. So why bother making the tweeter more efficient if there is no improvement in the sound? Why would anyone want to upgrade? I'm not arguing with you, I just don't understand.
                I'll answer. Pick me! Pick ME! *Raises hand extra high*

                Efficiency, in this case, also brings headroom before the onset of clipping AND even lower distortion at all volume levels.

                So, there IS improvement in the sound....and, also, MORE sound as well.

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                • #9
                  I'll add that this new tweeter is not going to be offered to fix any problems or shortcomings of the current gen2 Arx tweeter. But, lower distortion, more efficiency, and higher power handling are ALWAYS good things to have...and especially good things to get more of when zero tradeoffs have to be made (other than cost).

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                  • #10
                    Originally posted by newspeakers
                    Jon, I don't quite understand the point. Most of the power to drive a speaker goes into the bass. The tweeter requires very little power by comparison. So why bother making the tweeter more efficient if there is no improvement in the sound? Why would anyone want to upgrade? I'm not arguing with you, I just don't understand.
                    The tweeter being more efficient means we can pad it down electrically in the crossover more than the current tweeter. This in turn means that while we've never had one fail, we can put more power into the entire speaker it's in. We're burning up more power in the resistive crossover elements than in the tweeter itself.

                    This gives us more thermal headroom - basically more loud and less heat - in the tweeter, which for parametrically bigger systems like the A5 and above means we can continue to use this tweeter in the presence of a gang of heavy duty SplitGap woofers. It's not a concern in A1-A3, but about the time Buford convinced me to try 3x SplitGaps in a tower, I started thinking about just where the tweeter's limits lied.

                    After his videos of attempted apocalypse Arx, I really thought about it...

                    Tweeter 3G also allowed us to tighten our supply chain and tighten the crossover design, so basically we get some added advantages too that help us potentially hold cost in a wildly fluctuating market.

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                    • #11
                      Where have I been, anything happening with this new developement? I haven't heard anything about the LRs lately either, what's up?
                      Cheers Jeff

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