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  • Damping Driver Baskets

    Frank Van Alstine has been after me to try wrapping the baskets for the drivers used in Jim Salk's speakers with clay to damp vibrations. He swore it made a difference even on high quality drivers, and he finally wore me down. So today I experimented with applying mortite to the various basket elements of the Seas CA12 midwoofer-midrange units I've been working with recently. This is what I posted in the Salk Audio Circle site:

    First I installed two Seas CA12 4.5" midbass-midrange speakers in extremely rigid double walled cabinets that I had built to help develop a midrange design for the as-yet unfinished HT4. I measured each (they were almost identical), and lugged them into my listening room to see if I could hear any difference between the two unmodified speakers. I have a comparison preamp machine with a remote control that allows instantaneous, volume compensated (though that wasn't necessary in this test) comparisons between up to 4 speakers. The two Seas units sounded the same to me, and not as good as the HT3 sitting next to them. But pretty darn good for raw drivers running full range. I then removed one of the Seas and wrapped mortite tightly around as much of the basket as I could without interferring with the spider or cone surround (that wasn't easy, and I can't swear that I succeeded 100%). I then listened to the same music slections as before (mostly a variety of stuff on the Iowa DIY2007 test disc and some Tchaikovsky at full cry). This was not a blind test. I obviously knew which was which. I didn't expect to hear anything, because the Seas frame is quite rigid to start with, and it's small. But there was an obvious difference this time around. It wasn't really that subtle, and I'll keep this experiment set up in case anyone else in the area wants to hear it. The modified unit had more presence. In comparison, the unmodified Seas sounded somewhat hollow. Maybe that was due to some kind of basket resonance. I'm not sure everyone would say the modified Seas sounded better, although I think it did. But there was a distinct difference, and there wasn't before. I thought it was probably just a change in frequency response due to some ill-placed mortite, so I measured that unit again in the same position as before. Really no difference, except at the very top, and in a direction that wouldn't explain the character or magnitude of the difference I heard, and was probably due to a slight difference in the mic position. Am I 100% sure the effect was due to mortite damping vibrations rather than just restricting cone movement? No--and I would have to repeat the experiment with a larger driver that was easier to work with. But I'm pretty sure. Unfortunately, I can't write to Jim telling him to wrap clay around all of the baskets, because it could very well come loose in the field or during shipping, and that would be a disaster. So I'm not sure this can be implemented as a post-mod. But it's certainly worth exploring (after I expermiment some more, which won't be anytime reall soon due to other demands.) If someone will remind me how to post images here, I would be happy to show you the relevant plots. Thanks for the suggestion, Frank.
    ______________________________________________

    I think anyone who's read very many of my posts will know that I'm highly skeptical of mods like designer caps, resistors, coils , and just about anything else. But this was kind of a jaw dropper for me.

  • #2
    Re: Damping Driver Baskets

    Originally posted by framus View Post

    I think anyone who's read very many of my posts will know that I'm highly skeptical of mods like designer caps, resistors, coils , and just about anything else. But this was kind of a jaw dropper for me.
    You may well have heard a difference, perhaps even a fairly major one. But for every person who accepts a non-scientific listening test alone as gospel two more will write it off to placebo effect. Measurements that back up the listening results would go a long way to giving credence to your observations.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

    Comment


    • #3
      Re: Damping Driver Baskets

      Hi Dennis:

      I suspect that if you can hear a difference as a result of damping out parasitic resonances in the frame, you can also measure that difference. You might try:

      (1) measuring and comparing distortion products (not just FR) of the treated and untreated woofers.

      (2) measuring resonances directly with a piezo accelerometer, the way JA does in Stereophile. If possible, measure both the resonances of the treated and untreated driver frames, and of the enclosures with the drivers mounted in them.

      It would be interesting to see what you find. The idea of damping stamped steel frames with strips of lead glued to the struts has been around for a long time. The more rigid cast frames of the SEAS drivers "should" be inherently less resonant than stamped steel, but apparently can still benefit from some damping.

      The main problem I would forsee is making sure the damping material remains firmly adhered to the driver. At some later date it could conceivably work loose and fall off -- or worse, fall into the frame and come in contact with the back of the cone and the spider.

      Comment


      • #4
        Re: Damping Driver Baskets

        Originally posted by framus View Post
        Frank Van Alstine has been after me to try wrapping the baskets for the drivers used in Jim Salk's speakers with clay to damp vibrations. He swore it made a difference even on high quality drivers, and he finally wore me down. So today I experimented with applying mortite to the various basket elements of the Seas CA12 midwoofer-midrange units I've been working with recently. This is what I posted in the Salk Audio Circle site:

        First I installed two Seas CA12 4.5" midbass-midrange speakers in extremely rigid double walled cabinets that I had built to help develop a midrange design for the as-yet unfinished HT4. I measured each (they were almost identical), and lugged them into my listening room to see if I could hear any difference between the two unmodified speakers. I have a comparison preamp machine with a remote control that allows instantaneous, volume compensated (though that wasn't necessary in this test) comparisons between up to 4 speakers. The two Seas units sounded the same to me, and not as good as the HT3 sitting next to them. But pretty darn good for raw drivers running full range. I then removed one of the Seas and wrapped mortite tightly around as much of the basket as I could without interferring with the spider or cone surround (that wasn't easy, and I can't swear that I succeeded 100%). I then listened to the same music slections as before (mostly a variety of stuff on the Iowa DIY2007 test disc and some Tchaikovsky at full cry). This was not a blind test. I obviously knew which was which. I didn't expect to hear anything, because the Seas frame is quite rigid to start with, and it's small. But there was an obvious difference this time around. It wasn't really that subtle, and I'll keep this experiment set up in case anyone else in the area wants to hear it. The modified unit had more presence. In comparison, the unmodified Seas sounded somewhat hollow. Maybe that was due to some kind of basket resonance. I'm not sure everyone would say the modified Seas sounded better, although I think it did. But there was a distinct difference, and there wasn't before. I thought it was probably just a change in frequency response due to some ill-placed mortite, so I measured that unit again in the same position as before. Really no difference, except at the very top, and in a direction that wouldn't explain the character or magnitude of the difference I heard, and was probably due to a slight difference in the mic position. Am I 100% sure the effect was due to mortite damping vibrations rather than just restricting cone movement? No--and I would have to repeat the experiment with a larger driver that was easier to work with. But I'm pretty sure. Unfortunately, I can't write to Jim telling him to wrap clay around all of the baskets, because it could very well come loose in the field or during shipping, and that would be a disaster. So I'm not sure this can be implemented as a post-mod. But it's certainly worth exploring (after I expermiment some more, which won't be anytime reall soon due to other demands.) If someone will remind me how to post images here, I would be happy to show you the relevant plots. Thanks for the suggestion, Frank.
        ______________________________________________

        I think anyone who's read very many of my posts will know that I'm highly skeptical of mods like designer caps, resistors, coils , and just about anything else. But this was kind of a jaw dropper for me.
        I can understand coating a stamped steel basket with something that would mass-load it and damp vibrations. In this case I would use something that would harden and be permanent, maybe even something like a thick layer of silicone.

        However, I share your concern that the mortite would become loose and cause more problems than it could possibly solve. I also know that "sounds different" does not always translate into "better" (I know you are aware of this too). I think tweaks like this have as good of a chance of going in the wrong direction. What would really be a significant objective test would be to see is the distortion spectrum changed significantly after treating the frame. I think that might be the only way to definintively say that it "improved" driver performance. Maybe, if some could place an accelerometer on the back of the magnet or on the frame and tested with and without the fram damping it would show us something too. It is interesting though that you hear a difference but do not pick it up in the frequency response.

        I have been working with the CA18 on a new version of the HTS Series, and the cast Seas frame on a small driver sure looks like it would be robust enough to do the job.
        Click here for Jeff Bagby's Loudspeaker Design Software

        Comment


        • #5
          Re: Damping Driver Baskets

          Originally posted by brianp View Post
          Hi Dennis:

          I suspect that if you can hear a difference as a result of damping out parasitic resonances in the frame, you can also measure that difference. You might try:

          (1) measuring and comparing distortion products (not just FR) of the treated and untreated woofers.

          (2) measuring resonances directly with a piezo accelerometer, the way JA does in Stereophile. If possible, measure both the resonances of the treated and untreated driver frames, and of the enclosures with the drivers mounted in them.

          It would be interesting to see what you find. The idea of damping stamped steel frames with strips of lead glued to the struts has been around for a long time. The more rigid cast frames of the SEAS drivers "should" be inherently less resonant than stamped steel, but apparently can still benefit from some damping.

          The main problem I would forsee is making sure the damping material remains firmly adhered to the driver. At some later date it could conceivably work loose and fall off -- or worse, fall into the frame and come in contact with the back of the cone and the spider.
          Ha! we were apparently think exactly the same things as the same time. How close our two posts were is almost as interesting as the mortite test.
          Click here for Jeff Bagby's Loudspeaker Design Software

          Comment


          • #6
            Re: Damping Driver Baskets

            Dynamat Xtreme works really well. Deadens/dampens the basket really well, won't eat your drivers like silicone, and won't fall off.

            As for Mortite, it works great as a gasket material, it couples the driver with the cabinet.
            "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

            http://www.diy-ny.com/

            Comment


            • #7
              Re: Damping Driver Baskets

              Originally posted by Face View Post
              Dynamat Xtreme works really well. Deadens/dampens the basket really well, won't eat your drivers like silicone, and won't fall off.

              As for Mortite, it works great as a gasket material, it couples the driver with the cabinet.
              Thanks for the all the interesting replies. I did this test on the fly because Frank was getting irritated that I never tried his suggestion. I'm out of time for further testing this weekend, but I will try distortion plots at some point. I don't have the equipment for the other suggestions. As for this being a "subjective" comparison--yes it is, but the conditions were pretty darned controlled, and the listener was pretty darned skeptical. If anyone wants to see the frequency response plots, they'll be posted on the Salk AuioCircle site shortly.

              Comment


              • #8
                Re: Damping Driver Baskets

                [QUOTE=Jeff B.;1547456]I can understand coating a stamped steel basket with something that would mass-load it and damp vibrations. In this case I would use something that would harden and be permanent, maybe even something like a thick layer of silicone.

                Modeling clay damps metal frames/baskets real well. If it hardened up it wouldn't be any good.

                I happen to be fond of the peel and stick stuff PE sells. Kind of like DYNAMAT only affordable.

                Comment


                • #9
                  Re: Damping Driver Baskets

                  You may be able to see the changes in frame resonance in the impedance plots also. I found that two small irregularities I thought were just part of a DC250's curve were actually buzzes in the test frame I had them mounted on.

                  The MLS tests showed the anomalies, and a sine sweep let me hear them.

                  I realize the vibration you are trying to verify is going to be harder to see, but it may be worth a shot.

                  Also, I think John Stockman has done something similar with a more permanant material.
                  Jay T
                  http://sites.google.com/site/lhwidgetssite/home

                  Comment


                  • #10
                    Re: Damping Driver Baskets

                    This is just a guess, but I would suspect that any changes due to driver frame vibrations would have to show up as linear distortion in a measurement, but that's just my hunch.
                    RJB Audio Projects
                    http://www.rjbaudio.com

                    Comment


                    • #11
                      Re: Damping Driver Baskets

                      Originally posted by romanbednarek View Post
                      This is just a guess, but I would suspect that any changes due to driver frame vibrations would have to show up as linear distortion in a measurement, but that's just my hunch.
                      And I certainly will check that out. This is just a first trial, and I don't blame anyone for being skeptical. I still am myself. I'll have to repeat this with other drivers and make sure there's something going on.

                      Comment


                      • #12
                        Re: Damping Driver Baskets

                        Hi Dennis, I'm assuming that you're using the "switchboxes" that Neil Davis made a while ago, but correct me if I'm wrong. I've made a few different similar devices in the past (but not quite as nice as what I saw from Neil) and I would like to add that devices like this are extremely handy when making comparisons. I find that I have a pretty short "acoustic memory" when it comes to comparing anything from speakers to amps and having the ability to make a quick switch really takes a lot of the uncertainty out of the comparison. The additional ability to match the levels of two devices during a comparison is also very important but this is common knowledge. I've often done blind comparisons in the past by putting tape over the selection indicator, rapidly switching until the selected device is unknown and then trying to determine which is which.

                        Anyway, the point that I'm trying to make is that I think that your method of comparison is one that is least likely to be corrupted by false interpretation and I would have more confidence in other comparisons that have been discussed in the past if "switchbox" devices like this were used. I think that every DIY'er should have something like this because I've used mine several times to compare older, tweaked designs to new projects still in the tweaking phase in order to see if there are any obvious flaws (not to make the new speakers sound like the old ones but to sort of freshen my ears after they've gotten used to the sound of the new speakers).

                        I've read your posts for years and it is good to have you around again doing experiments such as this. Your current name, "framus", reminds me of a guitar that I got from my uncle that needs some neck work (it is German made Framus, a thin hollow body 12-string electric guitar that my dad bought for his brother back in the 1960's... It has an amazingly full and deep sound for a 12 string electric but the warped neck makes it difficult to play).
                        RJB Audio Projects
                        http://www.rjbaudio.com

                        Comment


                        • #13
                          Re: Damping Driver Baskets

                          Originally posted by romanbednarek View Post
                          Hi Dennis, I'm assuming that you're using the "switchboxes" that Neil Davis made a while ago, but correct me if I'm wrong. I've made a few different similar devices in the past (but not quite as nice as what I saw from Neil) and I would like to add that devices like this are extremely handy when making comparisons. I find that I have a pretty short "acoustic memory" when it comes to comparing anything from speakers to amps and having the ability to make a quick switch really takes a lot of the uncertainty out of the comparison. The additional ability to match the levels of two devices during a comparison is also very important but this is common knowledge. I've often done blind comparisons in the past by putting tape over the selection indicator, rapidly switching until the selected device is unknown and then trying to determine which is which.

                          Anyway, the point that I'm trying to make is that I think that your method of comparison is one that is least likely to be corrupted by false interpretation and I would have more confidence in other comparisons that have been discussed in the past if "switchbox" devices like this were used. I think that every DIY'er should have something like this because I've used mine several times to compare older, tweaked designs to new projects still in the tweaking phase in order to see if there are any obvious flaws (not to make the new speakers sound like the old ones but to sort of freshen my ears after they've gotten used to the sound of the new speakers).

                          I've read your posts for years and it is good to have you around again doing experiments such as this. Your current name, "framus", reminds me of a guitar that I got from my uncle that needs some neck work (it is German made Framus, a thin hollow body 12-string electric guitar that my dad bought for his brother back in the 1960's... It has an amazingly full and deep sound for a 12 string electric but the warped neck makes it difficult to play).
                          How did you know I have a warped neck? Or perhaps brain. Anyhow, thanks very much for the comments. I would never have posted anything if I didn't have the magic comparo box. If poor Neil Davis had time to devote to it, I'm sure he could sell dozens of these things to DIY'ers. It's really an essential tool. But I agree that none of this means much unless my impressions can be backed up with some relevant measurements or a proper double-blinded A-B test with enough people to achieve adequate statistical power.

                          Comment


                          • #14
                            Re: Damping Driver Baskets

                            A wedge pack of Dynamat Xtreme goes a long way, it's just as affordable as the peel and stick stuff from PE, and sticks much better.

                            "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

                            http://www.diy-ny.com/

                            Comment


                            • #15
                              Re: Damping Driver Baskets

                              Originally posted by romanbednarek View Post
                              This is just a guess, but I would suspect that any changes due to driver frame vibrations would have to show up as linear distortion in a measurement, but that's just my hunch.
                              This would have to be the case, unless it is some change that might only show up as an alteration of distortion due to changes being down in level to small to be readily apparent in FR responses.

                              The other thing to consider is the MLS resolution. It's possible that changes in the midrange aren't made apparent with our typical 3-4msec impulse response windows. A sine wave sweep, though it may show some audible differences, doesn't work well for documenting changes when not done in an anechoic enviornment. A close-mic MLS might work to some degree by partially swamping reflections, even though the FR response won't correlate well to the far-field. The difference might be made more apparent.

                              dlr
                              WinPCD - Windows .NET Passive Crossover Designer

                              Dave's Speaker Pages

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