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  • The real world importance of cabinet bracing is?

    Hi Gang,

    The title pretty much says it all. I am currently building a pair of Carmody Hitmakers which use a 1/2 CF cabinet which includes a U brace joining the sides and back. The cabinet is small enough that it is hard for me to imagine that there would be enough resonance in 3/4 MDF to actually be audible. In the High End audio magazines they measure cabinet resonance and imply that a "dead" cabinet is vital, but there is so much BS in those magazines that I do not take their opinion unquestioingly.
    I can see where a speaker with large panels could benefit from braces, but wonder based on your personal experience, if with speakers of 1 CF or less volume there is an audible (or measurable) difference between braced and un-braced. Also, at what point, in your experience, does bracing become of real world audible significance.

    Best,
    Jay

  • #2
    Panel resonance can be an issue in cabs of less than 1 cu ft. That said, a U brace is one of the least effective bracing methods, as it does not directly connect opposing panels where they flex the most, in their middles.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

    Comment


    • #3
      Thickness, span, material all play a part. If that "U" is connected through the middle you really have some effective bracing. I sometimes use battons to stiffen, though not eliminate, panel resonance. Just depends on the project.

      If I truly am building out a project, I try to not have over 1 sq ft of panel not broken up by some kind of bracing to somewhere near the middle of the panel. And then sometimes I just go overkill but take it into account with cabinet volume.

      This helped create a dead cabinet (and completely and utterly overkill):




      On that note, it puts me at peace of mind that I have created the best product I could, instead of leaving a little doubt if it would could sound any better. And knowing what I know now, I'm sure you could obtain the same thing using sticks throughout, but I really wanted to push the envelope since I knew I would have those cabinets a long long time (7 years now and still satisfied).

      Mustang, corvette, porsche, lamborghini, bugatti.....at what point are you satisfied.

      I had a speaker in a cardboard box for poops and giggles and I grabbed it while it was playing one day and noticed an incredible improvement in the sound quality of midrange and down. Extreme example but I think illustrates the point.

      PS. someone posted testing data of unbraced areas of panels, though I have zero recollection of results or conclusions.
      Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

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      • #4
        I like post braces every 6 inches in 3/4 MDF. I've only noticed cabinet issues with 1/2 MDF and that was braced every 8 inches.
        John H

        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

        Comment


        • #5
          There was an interesting thread on this:

          http://techtalk.parts-express.com/fo...ation-validity

          You can skip much of the debate and focus on using the equations to attempt to calculate frequencies of panel resonance with, and without bracing.

          If it seems like the bracing might move the panel frequencies up into a range where your ear is more sensitive, you could then decide whether the effort of bracing is worthwhile.

          Comment


          • #6
            If the panel can't vibrate sufficiently to create audible coloration its resonant frequency doesn't matter. By the same token if the panel does vibrate sufficiently to create audible coloration it still doesn't matter what its resonant frequency is.
            www.billfitzmaurice.com
            www.billfitzmaurice.info/forum

            Comment


            • #7
              I've often wondered if a low Q, compliant or even flexible cabinet would work. The charts I've seen of various cabinet bracing methods seem to all return a lot of energy right where you don't want it.

              Comment


              • #8
                And of course it's all relative. If you're using $5 drivers and an off the shelf crossover, panel resonance probably isn't a big deal. If you're going for perfection, it is.
                Francis

                Comment


                • #9
                  I've really enjoyed some of my sub builds that were really poorly (if at all) braced. Could I hear the difference in harmonic distortion from panel resonances if compared against a better built box?... maybe.

                  Ultimately I with Joey... it's a best practice that can and does make measurable differences in the final product performance. If you're taking the time to build, take the time to add bracing as you see fit. I'd go for simple between panel braces with dowels or window cuts, and use damping material as well.
                  Electronics engineer, woofer enthusiast, and musician.
                  Wogg Music
                  Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat

                  Comment


                  • #10
                    Originally posted by wogg View Post
                    it's a best practice that can and does make measurable differences in the final product performance. If you're taking the time to build, take the time to add bracing as you see fit. I'd go for simple between panel braces with dowels or window cuts, and use damping material as well.


                    It's ultimately a sum of the parts (which drivers, cabinet construction, crossover design, crossover parts, room placement, furnishings, etc.)
                    Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                    Comment


                    • #11
                      Originally posted by fpitas View Post
                      And of course it's all relative. If you're using $5 drivers and an off the shelf crossover, panel resonance probably isn't a big deal. If you're going for perfection, it is.
                      And this.
                      Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                      Comment


                      • #12
                        Originally posted by Drjay View Post
                        The title pretty much says it all. I am currently building a pair of Carmody Hitmakers which use a 1/2 CF cabinet which includes a U brace joining the sides and back. The cabinet is small enough that it is hard for me to imagine that there would be enough resonance in 3/4 MDF to actually be audible. In the High End audio magazines they measure cabinet resonance and imply that a "dead" cabinet is vital, but there is so much BS in those magazines that I do not take their opinion unquestioingly.
                        There is a lot of nonsense about bracing cabinets in both magazines and, I am afraid, forums. To many it seems obvious that bracing which makes a cabinet stiffer so it deflects less under a static load must also make a cabinet vibrate less and radiate less sound. Although true for competent subwoofer cabinets which don't contain cabinet resonance within the passband of the drivers this isn't the case for most speaker cabinets like your Hitmakers which do. In this case the increased stiffness shifts the resonances to higher frequencies where it requires a smaller deflection to radiate an equal level of sound negating the effect of the increased stiffness. The sound radiated by the braced and unbraced cabinets tend to be around the same level.

                        What makes resonant cabinets dead is not bracing but effective damping. At a resonance the forces due to stiffness and mass are exactly the same size but 180 degrees out of phase and cancel. It doesn't matter how stiff the cabinet is at resonance. The only force acting to oppose the resonant motion is damping and so this is what needs to be increased to make a resonating cabinet quieter.

                        If you skip to page 10 of this KEF marketing bumpf you can see evidence of the effect of bracing and effective damping on a well engineered commercial speaker cabinet around the size of your Hitmakers. Bracing has raised the resonant frequencies but left the level of sound radiated about the same. Whereas effective damping has reduced the level by 30 dB.

                        Comment


                        • #13
                          Originally posted by andy19191 View Post
                          There is a lot of nonsense about bracing cabinets in both magazines and, I am afraid, forums. To many it seems obvious that bracing which makes a cabinet stiffer so it deflects less under a static load must also make a cabinet vibrate less and radiate less sound. Although true for competent subwoofer cabinets which don't contain cabinet resonance within the passband of the drivers this isn't the case for most speaker cabinets like your Hitmakers which do. In this case the increased stiffness shifts the resonances to higher frequencies where it requires a smaller deflection to radiate an equal level of sound negating the effect of the increased stiffness. The sound radiated by the braced and unbraced cabinets tend to be around the same level.

                          What makes resonant cabinets dead is not bracing but effective damping. At a resonance the forces due to stiffness and mass are exactly the same size but 180 degrees out of phase and cancel. It doesn't matter how stiff the cabinet is at resonance. The only force acting to oppose the resonant motion is damping and so this is what needs to be increased to make a resonating cabinet quieter.

                          If you skip to page 10 of this KEF marketing bumpf you can see evidence of the effect of bracing and effective damping on a well engineered commercial speaker cabinet around the size of your Hitmakers. Bracing has raised the resonant frequencies but left the level of sound radiated about the same. Whereas effective damping has reduced the level by 30 dB.
                          Thank you Andy for pointing out what everyone is missing.
                          I used to think too that maximum stiffness is what is desired from a panel in a cabinet.
                          What is actually desired is a stiff, but sufficiently damped panel.

                          I agree that the KEF white paper has been totally lost on most people. The paper lays it out very clearly.

                          Effective noise and vibration control can be achieved through four (4) main methods; absorption, use of barriers or enclosures, structural damping, and vibration isolation.
                          KEF uses three of these four:

                          The first is free-layer or extensional damping or constrained layer damping.
                          The mechanism for this is that energy is dissipated through shear-layer deformation in materials that are capable of storing strain energy when deformed and then dissipating it through hysteresis.
                          So KEF does use a brace, but uses a viscoeleastic layer between the brace and the panel, effectively creating a constrained layer system. The damping layer needs to be affixed using a high-shear adhesive, less the energy be absorbed through the shearing of the adhesive.
                          This can be achieved by using epoxy and butyl rubber. This moves panel resonances up, but also damps them. Constrained layer damping has also been proven to damp higher panel modes most effectively.

                          Bracing without damping is all well and good, but is rather brute-force rather than well thought out. The idea that you can constrain something not to move is simply misguided. We're not talking static-load deflection, we're talking vibration and resonances.

                          A second method KEF uses is vibrational isolation by not rigidly affixing the driver to the baffle or the enclosure. It is sandwiched between the baffle and the bracing using the viscoelastic pads. Since the reactive force of the driver motor is a source of vibrational energy, by isolating it from the system it limits the methods of panel excitement to internal pressure variations.

                          Then finally you can damp through absorption using good old acoustic foam.

                          KEF achieves all of this through a very cost-effective and manufacturable solution of using one X-brace and a bunch of mastic pads.
                          It looks simply, but is very well thought out.
                          Good engineering.

                          Comment


                          • #14
                            Lots of interesting info here. In the past I designed small human powered boats and found out that what looked like significant hydrodynamic factors made no discernible real world performance difference. So, while minimal cabinet panel vibration seems theoretically desirable, has anyone done an auditory A B comparison of braced vs. un-braced cabinets in the .25 to 1 CF size. I am going to build more speakers in this size range and want to minimize work on factors which have no "real world" auditory performance.
                            The KEF white paper showing that an X brace was vibrationally worse than un-braced was especially interesting, but a further question is, would there be an audible difference between an un-braced version of the LS 50 and the actual production model?
                            It seems to me that the actual sound output from panel resonance in any 1CF or less two way speaker made of 3/4" MDF would be so minimal that it would be totally masked by the output from the drivers. If you were sitting 8 feet or more from the speakers and someone was playing the same track (at the speaker position) which you were listening to at a 40 db lower volume that the speaker output (which should be much more than the worst case panel vibration) would even that have an audible effect on the sound?
                            Again, I'm a total beginner in this field and just trying to find out where to best focus my efforts, so please forgive my ignorance...

                            Jay

                            Comment


                            • #15
                              We use a box in a box technique with 1/8" of silicone separating the 2 with the mid-bass
                              and tweet only fastened to the inner cab, cheap, easy and effective. No braces with a
                              small box like that (1 5/8 thick total).
                              Guess xmax's age.

                              My guess: 15. His grammar is passable. His trolling is good.

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