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Re: Comparison Question

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  • mark.fouxman
    ... I wish I knew how to make a 1/4 diaphragm capsule with a true tension (as a function of stiffness) controlled system, with adequate noise performance...
    Message 1 of 17 , Jan 31, 2008
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      > it would make sense to have a custom diaphram.
      > That mod would probably work, I would think the large mfgs would
      > balk at really severe mods to the tooling on their capsules for
      > relatively small amounts of business.

      I wish I knew how to make a 1/4" diaphragm capsule with a "true"
      tension (as a function of stiffness) controlled system, with
      adequate noise performance...

      > I knew Dave Blackmer (never
      > met his son) he was really into the ultra-sonic content of music
      > like James Boyk at Performance Recordings.

      Sorry I am not familiar who is James Boyk. As for Dave
      Blackmer's "ultra-sonic content of music" theory, I sympathize it,
      but in many cases also find it only "half of true", as far as
      microphones are concerned.
      You see, for me it is not about ultrasonic extension, but how that
      ultrasonic extension was achieved. The main factor is not how far up
      the mic can go, but the phase shift on the top of audio band.
      For example, just compare sonically Gefell MK201 vs. MK221, or
      B&K4133 vs. B&K4134, capsules. Sure, immeditely there will be
      winners--MK221 and B&K4133. Immediately people would "blame" it on
      the HF extension... And it will be true. But... that is true because
      it will be a function of diaphragm tuning--the higher the tenison--
      the higher the frequency of the phase shift--easy.

      Now let's see what's going on with the something like resonance
      controlled system (as most cheap electrets are), where due to small
      size and a highly resonant chambers we easily achieve something like
      50K HF extension.
      If in this capsule the phase shift occures at let's say, 10K,
      sonically you will always find MK221 much superior, even though it
      has "only" 20K extension, but 14K phase shift point.

      > Mr. Boyk uses ribbons on
      > piano now I think. Going by sheer size I would guess the thermal
      > noise of the air load would be pretty low on a ribbon. Matching to
      > the ultra-low noise resistance of the ribbon is another problem.
      No
      > one ever answered my question about the theoretical self noise
      limit
      > of ribbons. Even I'm not quite sure how to measure the thermal
      noise
      > of a milli-Ohm.

      I never thought about self noise of the ribbon itself. Indeed,
      considering the natural fig8 plot, the loading mass of the air is
      too big and random, and the thermal noise is way diffused... My
      guess, the noise of ANY space you take your measurements of IDEAL
      RIBBON SYSTEM would be larger, so the "real life" resistance is the
      major factor. Considering we ALWAYS use "real life" transformers
      with ribbons, those milliohms will be a part of the transformer
      ratio and dead copper resistance, which are a MAJOR part of
      equation.

      Best, Mark (aka Marik)
    • mark.fouxman
      ... Assuming there is some thermal noise, wouldn t it cancel itself as the air load from both sides of the ribbon is the same (of course, if we are talking of
      Message 2 of 17 , Feb 1 9:04 AM
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        --- In micbuilders@yahoogroups.com, "userno232000" <scott.wurcer@...>
        wrote:
        > Going by sheer size I would guess the thermal
        > noise of the air load would be pretty low on a ribbon.

        Assuming there is some thermal noise, wouldn't it cancel itself as the
        air load from both sides of the ribbon is the same (of course, if we
        are talking of fig8)?...

        or would it add?...

        Just thinking out loud.

        Best, M
      • William Morris
        Mark: I should think the thermal noise would self cancel because the impulse on the reverse side on the diaphragm element would be 180 degrees out of phase
        Message 3 of 17 , Feb 1 11:19 AM
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          Mark: I should think the "thermal noise" would self cancel because the impulse on the reverse side on the diaphragm element would be 180 degrees out of phase with the front side (opposite) therefore cancelling itself out as you suggest...correct me mic builders if this is incorrect....
          Bill

          "mark.fouxman" <mark.fouxman@...> wrote:
          --- In micbuilders@yahoogroups.com, "userno232000" <scott.wurcer@...>
          wrote:
          > Going by sheer size I would guess the thermal
          > noise of the air load would be pretty low on a ribbon.

          Assuming there is some thermal noise, wouldn't it cancel itself as the
          air load from both sides of the ribbon is the same (of course, if we
          are talking of fig8)?...

          or would it add?...

          Just thinking out loud.

          Best, M






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        • userno232000
          ... because the impulse on the reverse side on the diaphragm element would be 180 degrees out of phase with the front side (opposite) therefore cancelling
          Message 4 of 17 , Feb 1 12:31 PM
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            --- In micbuilders@yahoogroups.com, William Morris
            <classicaudioservice@...> wrote:
            >
            > Mark: I should think the "thermal noise" would self cancel
            because the impulse on the reverse side on the diaphragm element
            would be 180 degrees out of phase with the front side (opposite)
            therefore cancelling itself out as you suggest...correct me mic
            builders if this is incorrect....
            > Bill
            >
            > "mark.fouxman" <mark.fouxman@...> wrote:
            > --- In micbuilders@yahoogroups.com, "userno232000"
            <scott.wurcer@>
            > wrote:
            > > Going by sheer size I would guess the thermal
            > > noise of the air load would be pretty low on a ribbon.
            >
            > Assuming there is some thermal noise, wouldn't it cancel itself as
            the
            > air load from both sides of the ribbon is the same (of course, if
            we
            > are talking of fig8)?...
            >
            > or would it add?...
            >
            > Just thinking out loud.
            >
            >

            I meant the Brownian motion noise of the air molecules, it limits
            the noise floor of any mike. It's a thermodynamic thing proportional
            in some way to KT (like 4KTR for a resistor). The B&K paper in the
            files section shows a preamp quiet enough to easily resolve it.
          • Richard Lee
            ... I think you ll find that ALL small omni capsules rely on tiny backchamber which sets the resonance. In fact, cheap electrets will have a slack film
            Message 5 of 17 , Feb 1 11:15 PM
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              >The LF extension is not surprising. What I suspect, to get that 50K HF extension and still good noise figure from 1/4" capsule they should rely not on the diaphragm tension, but heavy damping/tiny backchamber.

              I think you'll find that ALL small omni capsules rely on tiny backchamber which sets the resonance. In fact, cheap electrets will have a "slack" film diaphragm so even more prone to having the back chamber dominate.

              Damping is a different matter and is what makes a B&k 4133 or 4134

              But the reason for the HF cutoff on most cheap electrets is nothing to do with the resonance. It's the cavity and hole in front of the diaphragm which is a resonant HP filter. The felt in that hole provides the damping and is the main inconsistency.

              >No one ever answered my question about the theoretical self noise limit of ribbons.

              I'm stung by Guru Wurcer to write a short note about Ribbon noise. I'll put it on my MicBuilders folder when done.

              >Even I'm not quite sure how to measure the thermal noise of a milli-Ohm.

              The electrical noise of a ribbon is still given by rt(4kT R f) as Baxandall et al

              You can measure milli-Ohms by 4 wire method as done in Skul daze. But don't put too many Amps through your 4038 ribbon or it'll spoil your day.

              >For example, just compare sonically Gefell MK201 vs. MK221, or B&K4133 vs. B&K4134, capsules. Sure, immeditely there will be winners--MK221 and B&K4133.

              The 4dB @ 10kHz and 10dB @ 20kHz difference between 4133 & 4134 might have something to do with it.

              >But... that is true because it will be a function of diaphragm tuning--the higher the tenison-- the higher the frequency of the phase shift--easy.

              4133 & 4134 have exactly the same diaphragm & tension.



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            • mark.fouxman
              ... B&K4133 vs. B&K4134, capsules. Sure, immeditely there will be winners--MK221 and B&K4133. ... might have something to do with it. Duh!!! I connot believe I
              Message 6 of 17 , Feb 2 1:13 PM
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                > >For example, just compare sonically Gefell MK201 vs. MK221, or
                B&K4133 vs. B&K4134, capsules. Sure, immeditely there will be
                winners--MK221 and B&K4133.
                >
                > The 4dB @ 10kHz and 10dB @ 20kHz difference between 4133 & 4134
                might have something to do with it.

                Duh!!!
                I connot believe I posted that nonsense!
                Indeed, there is very little sense comparing free-field vs. pressure
                type capsules.
                Obviously, I meant B&K 4165, which is "official" equivalent of
                MK221. Also, I screwed up the winners as well, as it would be a
                MK201 (istead of MK221), which is a close analog of 4133. It is
                always a very bad idea to start posting after a nice evening and
                bottle of wine :(.
                Sorry for the confusion.

                --- In micbuilders@yahoogroups.com, Richard Lee <ricardo@...> wrote:

                > I think you'll find that ALL small omni capsules rely on tiny
                backchamber which sets the resonance. In fact, cheap electrets will
                have a "slack" film diaphragm so even more prone to having the back
                chamber dominate.
                >
                > But the reason for the HF cutoff on most cheap electrets is
                nothing to do with the resonance. It's the cavity and hole in front
                of the diaphragm which is a resonant HP filter.
                >

                Yes. In the thread on ECM8000 I described the positive sonic impact
                of cutting off that front resonator, despite the fact it limits HF
                extension.
                Personally, I am against resonator system as means of extending
                frequency response. IMO, sonically it does more harm than good.

                Best, Mark (aka Marik)
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