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  • #16
    Originally posted by billfitzmaurice View Post
    You can't discuss what you don't understand. Emails of that sort tend to get answered by a customer service rep working off a standard script.
    "Thank you for your puzzling inquiry. Just buy it, you'll like it!"
    Francis

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    • #17
      "Pay no attention to that man behind the curtain!"
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #18
        It's actually super simple to make a servo driver. At work we built a few different iterations of servo drivers all using different principles of operation or different configurations (some used capacitive and some used optical sensing to determine cone position). I think we may even have gotten a patent on something (I can't remember). Anyways, it all amounted to nothing. Even exquisite servo control of the drivers had almost no audible improvement.

        Now, just to be clear, the environment we were looking at was a car or SUV. So we were using drivers that were not larger than about 10" (we even applied servo control to the mids). Maybe in a home environment you can get some audible improvement, but I wouldn't bet on it. Apparently the ear/brain is just not that sensitive to small (<10%) amounts of distortion at low frequencies. Or maybe we're just so used to hearing a little distortion at low frequencies that without it the brain just "fills it in". I dunno. I do know that we wrecked a lot of otherwise nice Italian drivers a couple of years ago building prototypes ;-)

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        • #19
          Originally posted by LIDAR View Post
          I it all amounted to nothing. Even exquisite servo control of the drivers had almost no audible improvement.
          That's what one would expect. There was a time when real servo drive subs made sense. That time was 1987. Tom Danley's Intersonic Servo Drive sub woofers had an Xmax of 12.5 to 16 mm, depending on the unit, when most woofers had an Xmax of around 4mm, so the advantages were huge. There simply were no traditional voice coil driven cone speakers with Xmax anywhere near what the Servo Drive units had then. That hasn't been the case for roughly 20 years.
          Last edited by billfitzmaurice; 01-08-2021, 01:58 PM.
          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

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          • #20
            Originally posted by tvrgeek View Post
            So, I have pushed my sub build within the very tight space and budget limits about as far as I can. I thought I would look at more advanced technology, servo, as my issue is distortion not SPL or extension.
            I heard the old Phillips, heard Velodyne's, and some others years ago and was very unimpressed. Seemed dull as far as transient response.
            I'm curious. Describe what you mean by "Seemed dull as far as transient response.".
            dlr
            WinPCD - Windows .NET Passive Crossover Designer

            Dave's Speaker Pages

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            • #21
              OK, yes, they do sell their drivers and amps separately and as kits.
              They use a secondary sense coil, not quite like a DCV. I agree the mutual inductance and phase delay would seem to make it not the best solution. Using just a DVC would make for a very inefficient system.

              I attempted to do an optical based resolver many years ago but my ability to make a stable tapered slit/aperture accurate enough was not successful. The linear motors are not quite "linear" enough. I then thought about some sort of optical amplification using a curved mirror ( dustcap) with a laser hitting a CCD, but again, precision was a problem. I do not know exactly how the cheap digital calipers work, but they have resolution to the .001 inch which should be accurate. It is some sort of two phase pickup. Again, you need a secondary zero-offset reference as thy drift.

              Philips used the accelerometer method and was marginally effective. I suspect newer transducers are far more accurate. But, the main issue with them is determining a baseline. They are too susceptible to drift.

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              • #22
                Originally posted by dlr View Post
                I'm curious. Describe what you mean by "Seemed dull as far as transient response.".
                dlr
                Neither the little Phillips bookshelf speaker nor the big Velodynes seemed to have any life to them. Sounded like a ported speaker with a Q of 1. I am accustomed to critical Q subs. You will only notice this on some percussion. Some jazz, some classical. You are not going to notice it on organ or even a plucked bass.

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                • #23
                  Originally posted by LIDAR View Post
                  It's actually super simple to make a servo driver. At work we built a few different iterations of servo drivers all using different principles of operation or different configurations (some used capacitive and some used optical sensing to determine cone position). I think we may even have gotten a patent on something (I can't remember). Anyways, it all amounted to nothing. Even exquisite servo control of the drivers had almost no audible improvement.

                  Now, just to be clear, the environment we were looking at was a car or SUV. So we were using drivers that were not larger than about 10" (we even applied servo control to the mids). Maybe in a home environment you can get some audible improvement, but I wouldn't bet on it. Apparently the ear/brain is just not that sensitive to small (<10%) amounts of distortion at low frequencies. Or maybe we're just so used to hearing a little distortion at low frequencies that without it the brain just "fills it in". I dunno. I do know that we wrecked a lot of otherwise nice Italian drivers a couple of years ago building prototypes ;-)
                  I buy the "accustomed to" but I think the 10% is being too generous for everyone. As with any single number though, misleading. Masking depends on both the F-L curve as well as there being content at the harmonic frequencies. As usual, everyone has different sensibilities. If I go by the cars with subs going down the street, I would gather 100% not to bother some. Of course at the levels, I suspect the drivers are half deaf in the first place. More subtle is the variability of our sensitivity based on the most recent sound levels. FR and Q may be more important.

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                  • #24
                    Originally posted by tvrgeek View Post
                    Neither the little Phillips bookshelf speaker nor the big Velodynes seemed to have any life to them. Sounded like a ported speaker with a Q of 1. I am accustomed to critical Q subs. You will only notice this on some percussion. Some jazz, some classical. You are not going to notice it on organ or even a plucked bass.
                    The Velodynes were closed box. I've never heard a closed box sound like ported. The ULD line used an accelerometer attached to the driver that required the amp to be tuned to that driver, IIRC. They were sold with the lowpass set second order at 85Hz. They could be "adjusted" by the merchant according to the literature. However, when I bought my ULD15-II in 1990, I called Velodyne and spoke at some length with one of the designers. He provided me with the info that I needed to experiment with the filter settings. 8 pin (more I think, recall not up to snuf) dip chips held the resistor networks that determine the slope and Fc. Ultimately I set mine first order at 45Hz to allow me to run may mains full range without the provided passive highpass in the Velodyne.

                    AFA distortion, the ULD line provided (and measured by Stereophile at the time I believe) less than 1% THD at maximum output. The ULD15-II amp is 400W rated. In my discussion with the designer he gave me some recommendations on improving the amp, primarily replacing the power capacitors from 4700 to 10000 micro, again IIRC. I did that. Made an improvement, especially since the accelerometer feedback loop did require, I'm sure, a lot of current. If it provided less than 1% THD with the original caps, it may have been better with the new ones. I could easily hear the improvement in any case. I would simply describe the sound as "more solid". Thumps such as drums were really thumps.

                    If you thought of the Velodynes as having "no life", maybe the problem was using them as set at the factory. In any decent full range system I ever used them with, 85Hz second order lowpass would have been the wrong filter to use unless it was some underperforming 2-way system. Or if used with the passive highpass, since that always detracted from the mains response and didn't blend well with the sub no matter how I set the filters.

                    I still have that sub, purchased in 1990, and use it occasionally, although I find it mostly unnecessary with my main system, a dipole with two 12" drivers a side. But for something with really low "thump" I may want, the Velodyne does it. I'm not quite sure how a sub can have no "life to them", at least with one such as the Velodyne. But I don't hear "life" in my sub, I either hear the music content or not, but in my case it's never a case of not hearing it nor is it dull. It requires a subtle volume setting to prevent it being overpowering and artificial, though.

                    In another post you said that your target is "1% @ 80 dB, 30 Hz". That's well within the rating of the Velodyne ULD series back then, even the little 12" version I believe. I found an old review with stats at Stereophile.com. Taken from the manufacturer data it is "Velodyne ULD-15 subwoofer system. Similar system using 15" cone, 5/8" linear travel. Frequency response: 18Hz–85Hz, ±3dB, 104dB at 20Hz with less than 1% THD." The ULD-18 is the same, except its THD is < 0.5%. The article does point out that the amp and driver must be tuned together. The amp won't even operate without the driver connected.

                    Other improvements had to do with the accelerometer feedback. The system came with a 25' RCA cable. I was using 10 gauge cable from amp to speaker box. I bumped the connection at the amp one day with no music playing and the driver made a "thump" sound. I found that the RCA sockets on both box and amp were, in a word, cheap. I replaced both the RCAs and the driver connectors with high quality ones. The connector change also improved the response subtly. Amazing at times how those little things can be an issue. Since then I've always replaced RCAs and connectors with high quality ones any time I could in any electronics.

                    dlr
                    WinPCD - Windows .NET Passive Crossover Designer

                    Dave's Speaker Pages

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                    • #25
                      Dave,
                      Quite informative. I only heard them in show-rooms so I am sure they were as-shipped.
                      I think you misread my description. To me the sounded like a high Q ( 1 or so) sealed system rather than a critical Q .5Qtc system.
                      Doubling the filter bank quite likely helped. Easy for me to believe.
                      Cool if my target was not unreasonable. I did not miss it by much, but that is why I was thinking servo. Always set targets that you may not reach. Sometimes you do.

                      As this was all pre-DSP, it could be how they rolled off to match the room gain. Showrooms being much bigger than most living rooms. Could be simple level matching resulted in a very poor FR. Back then, our most advanced tool was the Gold Line octave RTA. We thought it was amazing as a real RTA, like a HP and an instrument mic was well over 10K. Now an iPhone app is almost laboratory quality.

                      If we ever get rid of COVID, I may try to track down a dealer. Not for the HT as I think I will leave it be, but for my living room where I run a single Peerless XLSS 12 inch. I am very space constrained there too and had to give up the second one.

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                      • #26
                        Ouch, $4K for the 15. Well, back to the drawing board. Retired civil servant you know.

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                        • #27
                          Originally posted by tvrgeek View Post
                          Dave,
                          Quite informative. I only heard them in show-rooms so I am sure they were as-shipped. I think you misread my description. To me the sounded like a high Q ( 1 or so) sealed system rather than a critical Q .5Qtc system.
                          Doubling the filter bank quite likely helped. Easy for me to believe.
                          Cool if my target was not unreasonable. I did not miss it by much, but that is why I was thinking servo. Always set targets that you may not reach. Sometimes you do.

                          As this was all pre-DSP, it could be how they rolled off to match the room gain. Showrooms being much bigger than most living rooms. Could be simple level matching resulted in a very poor FR. Back then, our most advanced tool was the Gold Line octave RTA. We thought it was amazing as a real RTA, like a HP and an instrument mic was well over 10K. Now an iPhone app is almost laboratory quality.
                          Since they were +/-3db down to 20Hz, it was probably some room mode issue and/or the integration with the mains. I've only been to a couple of shows, quite a few showrooms at dealers. Few seem to know or care about the room setup. Surprisingly, the worst setup I heard was at dealer showrooms.

                          dlr
                          WinPCD - Windows .NET Passive Crossover Designer

                          Dave's Speaker Pages

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                          • #28
                            Originally posted by tvrgeek View Post
                            Ouch, $4K for the 15. Well, back to the drawing board. Retired civil servant you know.
                            Dude. Buy an RSS390HF-4 and put it in the Parts Express knock-down box. I added a little extra bracing, but mainly because it was fun.
                            Francis

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                            • #29
                              Originally posted by dlr View Post
                              I've only been to a couple of shows, quite a few showrooms at dealers. Few seem to know or care about the room setup. Surprisingly, the worst setup I heard was at dealer showrooms.
                              By and large dealers don't know diddly. In a similar vein when shopping for a new car don't talk to salesmen. Talk to mechanics who work on them.
                              www.billfitzmaurice.com
                              www.billfitzmaurice.info/forum

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