{"id":91,"date":"2019-08-22T22:59:33","date_gmt":"2019-08-22T22:59:33","guid":{"rendered":"http:\/\/iconoclastcable.com\/blog\/?p=91"},"modified":"2019-08-22T22:59:33","modified_gmt":"2019-08-22T22:59:33","slug":"xlr-design-brief","status":"publish","type":"post","link":"https:\/\/iconoclastcable.com\/blog\/xlr-design-brief\/","title":{"rendered":"XLR Design Brief"},"content":{"rendered":"\n

1.0 Conductors
1.1 Copper Size
2.0 Dielectric Materials
3.0 Dielectric geometry
4.0 Shield Material and design considerations
5.0 Jacket design and material considerations<\/p>\n\n\n\n

1.0 Conductors.<\/strong><\/p>\n\n\n\n

  1. Copper Size. <\/strong><\/li><\/ol>\n\n\n\n

    BOTH of the copper conductor\nand size considerations were answered when we started the RCA cable. We don\u2019t\nwant to change the current coherence with a differing conductor diameter if we\nare to mirror the reactive variables, too. We need the same exact wire to\nshield reactive L and C parameters in each cable in the end configuration\ndesign. The geometry of each cable is entirely different so how to you do that?\nThat is, assuming you want<\/em> to match\nthe RCA and XLR properties and maintain the same signal quality\u2026and we\ncertainly do.  There is no reason to copy\na bad sounding RCA cable when designing an XLR, so the RCA is designed FIRST. <\/p>\n\n\n\n

    • Dielectric material(s).<\/strong><\/li><\/ul>\n\n\n\n

      One difference in the\nXLR is that we are going to use FOUR wires in a star quad configuration. (Note:\nin our “Gen 2” XLR product, there are sixteen wires — four wires\nmaking a star quad in place of each single wire in the design shown below.  For more detail, see the last paper in this series.)  Four wire XLR cables use two cross-connected\nwires for each polarity, which doubles-up the wire AWG for lower attenuation.\nTwo 25 AWG have the DCR of a single 22 AWG yet has way better signal coherence\nby using smaller wire.<\/p>\n\n\n

      \n
      \"\"<\/figure>\n<\/div>\n\n\n

      I\ncould have used a cheaper and easier two wire XLR design but the inductive and\nsignal coherence benefits of a star quad are too good to pass-up. If I can get\nthe materials and quad design to achieve a high enough level of performance it\nis a better cable design. <\/p>\n\n\n\n

      Star\nquads have a higher degree of CMRR (Common Mode Rejection Ratio) when properly\nsignal balanced. There are three primary reasons for this;<\/p>\n\n\n\n

      • The two or four wire stranding \u201ctwist\u201d.<\/li>
      • The differential encoding.<\/li>
      • The outer shield properties, but only at RF frequencies.<\/li><\/ul>\n\n\n\n

        Two\nwires of a star quad are a \u201cpositive\u201d voltage, and two wires are a \u201cnegative\u201d\nvoltage (180 degrees out of phase), hence the term \u201cbalanced\u201d.  If the cable were a teeter-totter, it would\nsit level. Some call this differential mode since each signal is equal but\ndifferent. <\/p>\n\n\n\n

        Differential Mode Transmission<\/strong><\/td><\/tr>
        Perfect Wire Balance Equals Less Noise<\/strong> <\/td><\/tr>
        \"\"<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

        In the example above we show two\nwires, but the system is the same in a star quad. The signal we WANT is encoded\nas +2 volts and -2 volts. The noise can\u2019t \u201cchange its spots\u201d relative the\ncable\u2019s twisted pairs and shows up as the same voltage on each wire, +1V noise\nin this example. The TWIST ratio helps make sure that the wires see the noise\nthe same amount of time and this is vital to the function of the circuit. <\/p>\n\n\n\n

        Here is where the balance is so\nimportant; the signal IDEALLY becomes the superposition of ALL the voltages, or\n+3 volts and -1 volt. No more, no less. The signal voltages are STILL exactly 4\nvolts \u201capart\u201d from each other; +2 to -2 with no noise and +3 to -1 volts with\nthe noise.  The signals are fed into a\ndifference amplifier that, you guessed it, looks at the \u201cdifference\u201d between\nthe two voltages and see\u2019s 4 volts with, or without, the noise. The noise is\nabsent in a perfect world at the difference amplifier\u2019s output.<\/p>\n\n\n\n

        In order to do this, every wire\nhas to be presented to the noise in the exact same way via the cable twist and\nhas to be the same length so the signal stays TIME aligned down the wire and\nhas to have the same attenuation. The difference amplifiers need to be nulled\nperfectly between gain halves. Believe it or not, this gets done really well\nwith good quality products. <\/p>\n\n\n\n

        The control tolerance of the\ncopper is 0.0005\u201d, so attenuation issues are mitigated and CUB (Capacitance\nUnBalance) tests insure we see MIL standard quality in the finished cable. All\nquality types of copper can be used in the XLR design. It is the overall\nstructure that is the most \u201cmagic\u201d and not as much the copper itself, although\nthe copper draw process does influence the sound. <\/p>\n\n\n\n

        We have several variables that\naren\u2019t present in a coaxial cable design to contend with;<\/p>\n\n\n\n

        • CUB, Capacitance Unbalance or, each wire shows a\ndiffering capacitance to ground.<\/li>
        • DCR unbalance, each wire has to be the same DCR.<\/li>
        • CMRR remainder, the differential signs have to NULL to\nthe exact same point neither above nor below reference ground.<\/li><\/ul>\n\n\n\n
          1. Dielectric geometry.<\/strong><\/li><\/ol>\n\n\n\n

            Lots of words, time for a picture;<\/p>\n\n\n\n

            ICONOCLAST\u2122 XLR END VIEW<\/strong><\/p>\n\n\n\n

            \"\"<\/figure>\n\n\n\n

            The above CAD drawing is what we have\ninside our XLR design so far (well, I ignored two wires in the drawing).<\/p>\n\n\n\n

            Remember I wanted to make L and C\nreactive variables EXACTLY the same for each cable with EXACTLY the same wire\nsize and draw science? What else do we know? I also said that CAPACITANCE is\nsensitive to the distance to a conductive plate area, and that means ALL the\nway around the wire. The coaxial cable is easy; we purposefully put a ground\naround the wire at a known distance that defines the capacitance ground plane\nreference distance and inductive loop area.<\/p>\n\n\n

            \n
            \"\"<\/figure>\n<\/div>\n\n\n

            In the coaxial cable, the center of\nthe wire to the inside of the tube is 0.098\u201d \/ 2 = .049\u201d.  Ok, so what? This is what. The capacitance is\na squared law property and predominantly sees the ground closest to the wire.\nThe shield on the opposite side of the XLR cable, to a first approximation,\nfalls a way. We actually measure the capacitance BETWEEN the two cross paired\nwires but the ground location still influences the capacitance. Also, we have\nfour wires that are capacitors. <\/p>\n\n\n\n

            This doesn\u2019t \u201csound\u201d good, does it?\nWe have four times as many wires and all have capacitance. Somehow this is\nsupposed to come out around 12 pF\/foot (with connectors), same as the RCA!<\/p>\n\n\n\n

            Now for the inductance part, L.\nInductance is loop area defined. It could care less about the dielectric, but\nthe graph above shows a HUGE ~0.170\u201d loop area! How is THAT going to get to the\n0.15 uH\/foot inductance of the coaxial cable? I could make something up, but\nthat isn\u2019t as neat as what\u2019s really going on.<\/p>\n\n\n\n

            To get capacitance as low as I need\nit to be to match the coaxial cables, I use DISTANCE between the wires. And\nyes, this DIRECTLY sets what the inductance will do\u2026hold on a minute.  By using AIR, I can set the C-C of the wires\nto meet my capacitance target needed for the final tested value with two cross\nwires connected and tested between them. AIR lessens this distance for a given\nvalue of C so I can also manage inductance now. For inductance, L, the smaller\nthe wire loop area the better for a given value of total capacitance. Air gets\nme far closer than any other dielectric. <\/p>\n\n\n\n

            How much air? Well, EXACTLY the same\nas the coaxial cables! How do we do that? The standard answer is, \u201cvery\ncarefully\u201d. Let\u2019s look at a drawing;<\/p>\n\n\n\n

            ICONOCLAST\u2122 XLR CHAMBER VOLUME<\/strong><\/p>\n\n\n

            \n
            \"\"<\/figure>\n<\/div>\n\n\n

            Still, so what? Yep, I agree, until\nwe compare this area to the area in in the RCA cable air dielectric; 0.00754 in2<\/sup>.\nOK it isn\u2019t exact; I missed by ~0.000009\u201d in2<\/sup>.  I use the exact same thread design around\neach identical wire so it\u2019s all the same area in the chamber as in the RCA.<\/p>\n\n\n\n

            \"\"<\/figure>\n\n\n\n

            Let\u2019s do some reality checking as to\nwhat it SHOULD be based on MEASUREMENTS and calculations.<\/p>\n\n\n\n

            • We have the EXACT (can I say that as close as it is?)\nsame velocity of propagation based on the composite (air and plastic inside the\nground plane) dielectric; 87% at RF reference. <\/li>
            • I measured the IMPEDANCE at RF @ 100 ohms, same as the\ncoaxial cable.<\/li>
            • The dielectric constant can be calculated and from that\nthe VP, VP = 1\/ SQRT (E). <\/li>
            •  And from that\ncomposite dielectric I also know what the capacitance has to be.<\/li><\/ul>\n\n\n\n

              Capacitance (remember that chart on\ndielectric value and capacitance earlier?) is directly linked to the group\ndielectric constant. I know VP, and I know the impedance, so I can calculate\nthe capacitance and then get the dielectric constant from that.<\/p>\n\n\n\n

              101670 \/ (C * 87) = 100 ohm<\/p>\n\n\n\n

              C = 11.68 pF\/foot.<\/p>\n\n\n

              \n
              \"\"<\/figure>\n<\/div>\n\n\n

              What does the cable actually measure\non capacitance? The chart below shows 11.767 pF\/foot. Notice that the\ncapacitance values between each of any two wires has to be ~ 5 pF\/foot to\n\u201cdouble-up\u201d the two wires capacitance and still to arrive at a final ~11\npF\/foot! Yep, that\u2019s LOW capacitance. Capacitance adds in parallel so this is a\nsignificant issue when a design uses four wires.<\/p>\n\n\n

              \n
              \"\"<\/figure>\n<\/div>\n\n\n

              Below is the measured and calculated\nimbalance of the capacitance between 1-3 and 2-4 cross wires\u2019 conductors as a\n\u201cpair\u201d; 2.02% unbalance, very low. <\/p>\n\n\n\n

              \"\"<\/figure>\n\n\n\n

              We seem to have the capacitance and\nVP looking much like the coaxial cable. Remember, measurements include ALL the\napproximations in the soup. <\/p>\n\n\n\n

              So what about inductance with that\nWAY larger loop area? Isn\u2019t that going to really kill this thing?  No, because of some properties of magnetic\nfields. Magnetic fields CANCEL if they see each other in OPPOSITE directions.\nInductance is the \u201creactance\u201d or \u201cresistance\u201d to instantaneous flow of current.\nIf we can REDUCE the magnetic field lines, we can directly reduce the measured\ninductance.<\/p>\n\n\n\n

              We also know from the basic equations\nthat DISTANCE between the two wires is important. Keeping BOTH distance and\nmagnetic field line magnitude small lowers inductance, and removes the noise.<\/p>\n\n\n\n

              The picture below shows what\u2019s going on\u2026sort\nof. For now, we\u2019ll pretend the field\u2019s ONLY go \u201cinwards\u201d, or inside the wire,\nand stop there (they don\u2019t). If the lines that extend outside each wire do the\nOPPOSITE as the field INSIDE the wires, they reinforce the field!  It is generally accepted that the flux lines\nconcentrate substantially BETWEEN the wires.<\/p>\n\n\n\n

              \"\"<\/figure>\n\n\n\n

              If we draw arrows that represent the\nDIRECTION of the circumferential magnetic field waves AROUND each wire we get\nwhat is shown below for a NOISE signal hitting the wire. We have TWO different\nvoltage polarities so we have TWO different current directions for the SIGNAL,\nbut the NOISE is the SAME direction in all the wires. <\/p>\n\n\n\n

              If you grasp a wire with all four of\nyour fingers, and point your right hand THUMB in the CURRENT direction, your\nfingers will point in the field\u2019s circumferential direction around each wire.\nThe arrows are a \u201cpart\u201d of the noise current field lines \u201cinside\u201d the four-wire\ngroup.<\/p>\n\n\n\n

              NOISE FIELDS (all the same direction)<\/strong><\/p>\n\n\n\n

              \"\"<\/figure>\n\n\n\n

              Where the arrows are OPPOSITE each\nother in direction between any two wires, the field lines cancel. For NOISE\nevery field theoretically cancels. ADJACENT or ACROSS from any TWO wires we\ninduce field cancellation with a star quad design. <\/p>\n\n\n\n

              For the SIGNAL, we now have TWO equal\nbut opposite current directions.<\/p>\n\n\n\n

              This allows larger wire-to-wire\nspacing in order to lower capacitance and also keeps inductance low. Inductance\nis managed with field line cancellation geometry.<\/p>\n\n\n\n

              Now we know why I didn\u2019t use a\ntwo-wire system, you can\u2019t manage CMRR. <\/p>\n\n\n\n

              Let\u2019s look at the situation for the signal. Below is a simple picture of the field cancellation between four wires with opposite polarities wired as a star quad.<\/p>\n\n\n\n

              SIGNAL FIELDS (opposite directions)<\/strong><\/p>\n\n\n\n

                 Minus = Current INTO the page (CW rotation)<\/p>\n\n\n\n

                 Plus = Current OUT of the page (CCW rotation)           <\/p>\n\n\n\n

              \"\"
              Reduce Signal Loop Area to Reduce Inductance<\/figcaption><\/figure>\n\n\n\n

              What do we see? The all the signal\nfield lines DO NOT cancel. Adjacent wires reinforce, and opposites wires\ncancel. Reducing loop area is the best way to manage inductance because we\ncan\u2019t cancel all of the field lines, only some of them. This theoretical field\nrelationship limits the ability to reduce capacitance for a given inductance.\nUsing low dielectric constant materials to lower capacitance (Air!) allows\ncloser spacing needed for low inductance.<\/p>\n\n\n\n

              Is there a design that can, in theory\ndo BOTH, reduce signal and noise fields to \u201czero\u201d? Within the limits of DESIGN,\nyes there is. The ICONOCLAST series II<\/em>\nreduces both noise and signal field cancellation. The wires, in practice aren\u2019t\nEXCATLY the same distance apart and EXACTLY the same resistance, so we say \u201cin\ntheory\u201d. But, reducing the nose to 1000 or more times less and reducing the\ninductance 27% is indeed achievable. <\/p>\n\n\n\n

              So, after all that explaining, how\ndoes the star quad ICONOCLAST cable measure up? Tests at 1 KHz show the\nfollowing values below. The inductance between the two cross wire pairs of the\nstar quad are 0.15 uH\/foot inductance\u2026same as the RCA. <\/p>\n\n\n

              \n
              \"\"<\/figure>\n<\/div>\n\n\n

              So what does the \u201creactive\u201d\npicture look like comparing the RCA and XLR? How close are they to being the\nsame? This swept test is the real deal. There are no approximations to fudge.<\/p>\n\n\n

              \n
              \"\"<\/figure>\n<\/div>\n\n\n

              What we see above is impedance \/\nphase for the XLR and RCA superimposed one on top the other. Note that there\nare four separate lines. We have two identical cables with exceptionally low\nreactive variables.<\/p>\n\n\n\n

              • Shield material and design considerations.<\/strong><\/li><\/ul>\n\n\n\n

                There is\nyet one last thing to consider in the XLR design; the outer shield. A 95% BC\n(Bare Copper) braid is used. Audio cables are not RF designs, and the braid\nshield will NOT shield low frequency magnetic interference. The CMRR of the XLR\nis going to do that for us. Excellent CUB, DCR unbalance and twist ratio all\naid CMRR. The braid DOES knock down RFI by 80 dB, so that\u2019s a given. The shield\nisolation @ RF mitigates NULL balance at high frequencies only. <\/p>\n\n\n\n

                Like it\nor not, 20-20K is a predominantly magnetic field frequency range where the\nB-fields decay at a ratio of 1\/x^3. DISTANCE is the best solution for isolation\nof cables with magnetic properties.
                \n
                \n5.0 Jacket design and material\nconsiderations.<\/strong><\/p>\n\n\n\n

                All\nICONOCLAST cables use FEP as the jacket to reduce UV sensitivity, plasticizer\nmigration and provide chemical resistance. \nThe cables are designed to last decades. <\/p>\n\n\n

                \n
                \"\"<\/figure>\n<\/div>\n\n\n

                I hope that this design summary of ICONOCLAST RCA and XLR\ninterconnect cables shows how important good design is for ALL your audio\ncables, and that every manufacturer has to manage all the same variables to\nproduce these results. There is little \u201cmagic\u201d in the design of good cables.\nThere are indeed tertiary variables that we can\u2019t measure, but those should not\ninfluence the ones we can measure, or at least not excessively so. Mother\nNature abhors complexity, so the better managed the known variables in a cable\nare, the more properly it may highlight \u201cunknowns.\u201d  To put it another way, the more we put knowns\ninto their proper place, the better we may distinguish the effects of the\nunknown. Wire draw science, for instance, can be heard better, and more fairly,\nin a superior electromagnetic design. <\/p>\n\n\n\n

                Belden appreciates your interest in how quality\ninterconnects are made, and how \/ why ICONOCLAST RCA and XLR cables were\nphysically derived as you see them in their production form. We have no special\nsauce or magic in our products, and I think that the cables perform as well as\nthey do BECAUSE we did not design around \u201cunknowns\u201d and then make it appear as\nthough we had unique influence on those unknowns in the design. <\/p>\n\n\n\n

                Truly low R, L and C cables are difficult to make when\nconsideration is given to all three variables to manage them in a truly\nbalanced fashion. The designs can be frustratingly simple looking but hard to\nmanufacture, as processes are pushed to the limits of current capabilities.\nBelden\u2019s focus is to make real measured values as low, and properly balanced,\nas we can. ICONOCLAST interconnects represent the pinnacle of low frequency\nmeasurements and electrical balance between the RCA and XLR (same\nelectromagnetic properties).<\/p>\n\n\n\n

                The next design analysis will look at the SPEAKER cable.<\/p>\n","protected":false},"excerpt":{"rendered":"

                1.0 Conductors 1.1 Copper Size2.0 Dielectric Materials3.0 Dielectric geometry4.0 Shield Material and design considerations5.0 Jacket design and material considerations 1.0 Conductors. Copper Size. BOTH of the copper conductor and size considerations were answered when we started the RCA cable. We don\u2019t want to change the current coherence with a differing…<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[13,14,15],"tags":[],"class_list":["post-91","post","type-post","status-publish","format-standard","hentry","category-xlr-cables","category-xlr-interconnects-gen-1","category-xlr-interconnects"],"_links":{"self":[{"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/posts\/91","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/comments?post=91"}],"version-history":[{"count":0,"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/posts\/91\/revisions"}],"wp:attachment":[{"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/media?parent=91"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/categories?post=91"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/iconoclastcable.com\/blog\/wp-json\/wp\/v2\/tags?post=91"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}