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To de, or not to de: that is the question....

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  • #16
    Originally posted by 1100xxben View Post
    In your video, are both your test setups just resting on the table top? I'm assuming they are just sitting there and not clamped/bolted down. I would think that if you added a significant amount of mass to your test assemblies, the results would be closer to the same. If the transducer is rigidly coupled to the baffle, of course it's going to transfer more energy and the baffle will move more if it's not rigidly fixed or loaded with enough mass. When you begin to decouple it with something that gives, you won't transfer as much energy to the baffle and you've added loss to your system. Whether the loss of acoustic energy output is measurable/noticeable is up for debate. In your fixed woofer setup (at 30 Hz), you're transferring more energy in phase to your baffle test assembly and it's physically moving up and down more. With your decoupled setup, the resonant system you've created with your isolation material is allowing the frame of the woofer to move more and transfer less energy into your test baffle. Ideally, the way the woofer makes sound is by having the frame in a fixed physical position and moving only the cone to create pressure waves.

    So, let's take a step back and look at the bigger picture... Presumably, you have a problem that the woofer is transferring energy into the baffle and the baffle is vibrating/resonating. What you're experimenting with is decoupling the woofer from the baffle so it does not transfer as much energy into the baffle and excite this resonance. IMO, this is similar to the guy who brags about how much power his car makes that allows him to do a burnout. As an engineer, I say that's cool that you make that much power, but it's actually a problem of lack of traction . In this case, instead of decoupling the woofer, why not address the problem of having resonant panels? Add extra bracing and/or increase the mass of the walls.

    Just my 2 cents on this topic. I've had plans to get some accelerometers and run some experiments on box bracing, but I can't get the projects done I'm working on now
    Excellent observations!

    Comment


    • #17
      DE = Diatomaceous Earth, if you maintain swimming pools.

      Comment


      • #18
        Since the accelerometer comment was brought up, someone who I know works in the field of measuring resonances once explained that accelerometers are problematic since they add their own mass. You could argue though in this case the mass of an inexpensive one from digikey, mouser, etc is small in comparison to the panel/woofer system mass. If you want to do it right you need a laser vibrometer accordng to him. However, that was many years ago and there are tiny accelerometers today that were not around back 7-10 years ago.

        Decoupling also causes some loss of output, I am curious how much is lost. Maybe it is negligible?

        But there is also a another way to decouple also suggested by linkwitz here, where he suggests mounting the driver by clamping the magnet. This has a couple of cool things:
        http://linkwitzlab.com/frontiers_2.htm#N
        1) Clamping is done at the center of mass (maybe this is beneficial?)
        2) The energy transfer is to a smaller panel and possibly absorbed instead of transmitted through the front baffle.

        Comment


        • #19
          I never understood the idea of decoupling, much. If you could actually get the frame to perfectly "float" (w/out it transferring ANY energy to the baffle), wouldn't the cone just sit there (along w/the baffle) while only the frame vibrated? Doesn't that just seem like not a good idea?

          Comment


          • #20
            How about using a sprinkling of salt instead of water on your black background? You can observe vertical and lateral motion.

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            • #21
              Originally posted by Kevin K. View Post

              ​I agree with a lot of what you've said and realize not having the baffles anchored is certainly affecting the test. This was the reason I stated the next test would be done with them mounted to enclosures (significant amount of mass). Not to argue, but I've seen very few cabinets built with braces attached to the front baffle. As you know, there's not a lot of room left between a woofer and tweeter to add a brace which is why most builders focus their efforts of bracing on the sidewalls (larger panels) or other panels of the cabinet. With that being said, I suspect the results of the test to stay the same once the baffles are mounted in enclosures but that's just a guess on my part. There's much more to this than just the simple test I've performed here. Where is the energy going and how is it affecting the output of the driver. Hoping to be able to measure some of those things in the next round and I'm open to any suggestions you guys might have on test you would like to see.

              For the record, the title of my thread is "To de(couple) or not to de(couple)" meaning I'm asking, not trying to convince anyone one way or the other, it's just a test spurned out of curiosity. Kind of hoping in the end there's no benefit because it sure makes things much easier to build without all of this stuff.
              First, please don't take any of my comments as negative, I'm just trying to have a friendly discussion about "tech talk". Again, as an engineer, I geek out on technical/academic discussions. I think your experiments will have some cool results. I wish I had the time to do some more experimentation with accelerometers.

              A summary of what I was trying to say is that I don't know that your setup shows a true resonance IN the baffle. I think you're just showing the entire assembly rattling around, which isn't really realistic. Also, you don't have any sides mounted perpendicular to your baffle which will stiffen them up exponentially and that should make the biggest difference of all in such a narrow baffle.

              In regards to bracing against the front baffle, you've obviously never looked inside cabinets that I've built . The speakers I'm working on now will have significant bracing against the front baffle because it spans a 12.5" gap and has a heavy 10" woofer mounted to it. Of course the baffle is a minimum of 1.25" thick as well.

              Comment


              • #22
                Originally posted by Chris Roemer View Post
                I never understood the idea of decoupling, much. If you could actually get the frame to perfectly "float" (w/out it transferring ANY energy to the baffle), wouldn't the cone just sit there (along w/the baffle) while only the frame vibrated? Doesn't that just seem like not a good idea?
                ​If you could achieve 100% decoupled, what you are saying makes sense. Although this is referred to as decoupled, it's really just another form of damping IMO.
                My "No-Name" CC Speaker
                Kerry's "Silverbacks"
                Ben's Synchaeta's for Mom
                The Archers
                Rick's "db" Desktop CBT Arrays
                The Gandalf's

                Comment


                • #23
                  Originally posted by marvin View Post
                  How about using a sprinkling of salt instead of water on your black background? You can observe vertical and lateral motion.
                  Great idea Marvin, will give that a shot on the next round.
                  My "No-Name" CC Speaker
                  Kerry's "Silverbacks"
                  Ben's Synchaeta's for Mom
                  The Archers
                  Rick's "db" Desktop CBT Arrays
                  The Gandalf's

                  Comment


                  • #24
                    Originally posted by durwood View Post
                    Since the accelerometer comment was brought up, someone who I know works in the field of measuring resonances once explained that accelerometers are problematic since they add their own mass. You could argue though in this case the mass of an inexpensive one from digikey, mouser, etc is small in comparison to the panel/woofer system mass. If you want to do it right you need a laser vibrometer accordng to him. However, that was many years ago and there are tiny accelerometers today that were not around back 7-10 years ago.
                    There's another issue that is probably a bigger factor with accelerometers. I have one, bought it 10+ years ago to experiment. The problem is attaching it to what you want to test in a manner that is both consistent and provides accurate results. In short, I was not able to do that. It needs to be attached such that how it is attached does not damp any vibration. That means very secure attachment, like permanent glue. I needed to be able to re-use it, so I tried very thin blue-tac, but that isn't very repeatable. Two-sided tape might have been a better choice, I didn't test that.

                    The other issue is...where do you attach it? I tried detaching/reattaching at the same point and got very different results. Then I tried attaching at various points on a box panel and got wildly different results, not so surprising since panel resonances will have nodes all over it. The only option remotely consistent was attaching it and leaving it alone and making tests with other changes to the box. Attaching to a driver is far more problematic if it's not going to be a permanently fixed.

                    A laser vibrometer is probably the only truly accurate means to measure.

                    dlr
                    WinPCD - Windows .NET Passive Crossover Designer

                    Dave's Speaker Pages

                    Comment


                    • #25
                      Originally posted by 1100xxben View Post
                      In your video, are both your test setups just resting on the table top? I'm assuming they are just sitting there and not clamped/bolted down. I would think that if you added a significant amount of mass to your test assemblies, the results would be closer to the same. If the transducer is rigidly coupled to the baffle, of course it's going to transfer more energy and the baffle will move more if it's not rigidly fixed or loaded with enough mass. When you begin to decouple it with something that gives, you won't transfer as much energy to the baffle and you've added loss to your system. Whether the loss of acoustic energy output is measurable/noticeable is up for debate. In your fixed woofer setup (at 30 Hz), you're transferring more energy in phase to your baffle test assembly and it's physically moving up and down more. With your decoupled setup, the resonant system you've created with your isolation material is allowing the frame of the woofer to move more and transfer less energy into your test baffle. Ideally, the way the woofer makes sound is by having the frame in a fixed physical position and moving only the cone to create pressure waves.

                      So, let's take a step back and look at the bigger picture... Presumably, you have a problem that the woofer is transferring energy into the baffle and the baffle is vibrating/resonating. What you're experimenting with is decoupling the woofer from the baffle so it does not transfer as much energy into the baffle and excite this resonance. IMO, this is similar to the guy who brags about how much power his car makes that allows him to do a burnout. As an engineer, I say that's cool that you make that much power, but it's actually a problem of lack of traction . In this case, instead of decoupling the woofer, why not address the problem of having resonant panels? Add extra bracing and/or increase the mass of the walls.

                      Just my 2 cents on this topic. I've had plans to get some accelerometers and run some experiments on box bracing, but I can't get the projects done I'm working on now
                      Do a search for the Kef LS50 white paper and read it. It addresses your post.

                      Comment


                      • #26
                        Originally posted by 1100xxben View Post

                        First, please don't take any of my comments as negative, I'm just trying to have a friendly discussion about "tech talk". Again, as an engineer, I geek out on technical/academic discussions. I think your experiments will have some cool results. I wish I had the time to do some more experimentation with accelerometers.

                        A summary of what I was trying to say is that I don't know that your setup shows a true resonance IN the baffle. I think you're just showing the entire assembly rattling around, which isn't really realistic. Also, you don't have any sides mounted perpendicular to your baffle which will stiffen them up exponentially and that should make the biggest difference of all in such a narrow baffle.

                        In regards to bracing against the front baffle, you've obviously never looked inside cabinets that I've built . The speakers I'm working on now will have significant bracing against the front baffle because it spans a 12.5" gap and has a heavy 10" woofer mounted to it. Of course the baffle is a minimum of 1.25" thick as well.
                        ​Ben, I didn't mean for my last response to come across as defensive, sometimes my wording can seem that way. I appreciate any input.

                        When I was referring to most builders not bracing the front baffle, I was generally speaking of 2-ways where there wouldn't be a lot of room left between the drivers to attach a brace. There were sidewalls in the test, not very deep ones, they were 5" tall. Both test baffles were placed on top of a piece of 1/2" Sonic Barrier Foam. You made some very good points in your first response and I plan to follow up on this and try some different things. Looks like the one thing everyone agrees on is "what is the trade off". The first test only demonstrated less vibration in the panel. Need to set up the mic and see what else is going on with some near-field measurements. I'll run an impedance sweep also to see if anything shows up there.
                        My "No-Name" CC Speaker
                        Kerry's "Silverbacks"
                        Ben's Synchaeta's for Mom
                        The Archers
                        Rick's "db" Desktop CBT Arrays
                        The Gandalf's

                        Comment


                        • #27
                          Some of you may be members of Javad's Facebook Group where I also posted this test. Sorry for this being repetitive if you are but there are members here that are not.

                          As a disclaimer guys, I'm not trying to talk anyone into doing this. It was done out of curiosity with the hopes that there be some kind of results to show a difference. I'm in the middle of a pretty intense build right now and thought about trying to incorporate something like this but will pass on it this time since there are so many variables that could impact how it works. I do think there has to be a DIY solution that could show some benefits (less coloration of the overall sound). dcibel provided this link earlier in the thread (http://www.linkwitzlab.com/Driver%20Decoupling.doc), Andrew Jones put together a very interesting study on the subject. Am I even close to pulling off what they've done, heck no but where's the fun in not trying.
                          My "No-Name" CC Speaker
                          Kerry's "Silverbacks"
                          Ben's Synchaeta's for Mom
                          The Archers
                          Rick's "db" Desktop CBT Arrays
                          The Gandalf's

                          Comment


                          • #28
                            Originally posted by durwood View Post
                            Since the accelerometer comment was brought up, someone who I know works in the field of measuring resonances once explained that accelerometers are problematic since they add their own mass. You could argue though in this case the mass of an inexpensive one from digikey, mouser, etc is small in comparison to the panel/woofer system mass. If you want to do it right you need a laser vibrometer accordng to him. However, that was many years ago and there are tiny accelerometers today that were not around back 7-10 years ago.

                            Decoupling also causes some loss of output, I am curious how much is lost. Maybe it is negligible?

                            But there is also a another way to decouple also suggested by linkwitz here, where he suggests mounting the driver by clamping the magnet. This has a couple of cool things:
                            http://linkwitzlab.com/frontiers_2.htm#N
                            1) Clamping is done at the center of mass (maybe this is beneficial?)
                            2) The energy transfer is to a smaller panel and possibly absorbed instead of transmitted through the front baffle.
                            Anchoring the driver at both ends instead is a good idea. If you think of the motion of the frame, when the front of the frame that is attached to the baffle pushes, the rear end where at the motor is pulling, so anchoring the motor is providing a lot of extra stability to prevent it from moving in the first place. It may be somewhat difficult to get the construction just right so everything fits and is still serviceable.
                            "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

                            Comment


                            • #29
                              Originally posted by Chris Roemer View Post
                              If you could actually get the frame to perfectly "float" (w/out it transferring ANY energy to the baffle), wouldn't the cone just sit there (along w/the baffle) while only the frame vibrated?
                              This statement is incorrect, think about the differences in mass between the cone and the motor/frame, they are not equal.

                              Besides, decoupling doesn't necessarily mean not attaching the frame to anything, i think the well nuts and sorbothane gasket is more about providing absorption of engergy rather than transmission through a rigid fixture.
                              "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

                              Comment


                              • #30
                                Originally posted by Kevin K. View Post
                                Some of you may be members of Javad's Facebook Group where I also posted this test. Sorry for this being repetitive if you are but there are members here that are not.

                                As a disclaimer guys, I'm not trying to talk anyone into doing this. It was done out of curiosity with the hopes that there be some kind of results to show a difference. I'm in the middle of a pretty intense build right now and thought about trying to incorporate something like this but will pass on it this time since there are so many variables that could impact how it works. I do think there has to be a DIY solution that could show some benefits (less coloration of the overall sound). dcibel provided this link earlier in the thread (http://www.linkwitzlab.com/Driver%20Decoupling.doc), Andrew Jones put together a very interesting study on the subject. Am I even close to pulling off what they've done, heck no but where's the fun in not trying.
                                What you assembled in your OP appears to be a very close description of the decoupling assemblies used in the documents I posted. What you've already shown show much promise in greatly reducing cabinet panel vibrations. I encourage you to continue your research on the subject.
                                "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

                                Comment

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