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Re: Experience with Smith Micro?

From J Burns <burns4@nowhere.com>
Newsgroups comp.sys.mac.system, alt.engineering.electrical
Subject Re: Experience with Smith Micro?
Date 2014-02-10 11:39 -0500
Organization A noiseless patient Spider
Message-ID <ldavch$5fa$1@dont-email.me> (permalink)
References (7 earlier) <k-2dnfBzu9elyGjPnZ2dnUVZ8jadnZ2d@giganews.com> <ld3p6g$3t1$1@dont-email.me> <SalmonEgg-A260CA.15490609022014@news80.forteinc.com> <ld9bu9$lo$1@dont-email.me> <SalmonEgg-1599B4.00261810022014@news80.forteinc.com>

Cross-posted to 2 groups.

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On 2/10/14, 3:26 AM, Salmon Egg wrote:
> In article <ld9bu9$lo$1@dont-email.me>, J Burns <burns4@nowhere.com>
> wrote:
>
>> If the impedance of my phones varied from 20 to 170 ohms depending on
>> frequency, I could say a 220-ohm resistor in series had the effect of
>> negative current feedback.  With my resistor network, the amplifier saw
>> more than 20 ohms, but the phones saw 1.8 ohms, meaning 99.2% less
>> negative current feedback than from the standard resistor.
>
> I do not fully understand this point.
>
> The impedance phones present at its terminals is from a combination of
> factors. There is the actual impedance of the internal driving network
> (voice coil) with the transducer blocked as modified by the loading of
> the diaphragm and the acoustic load of the air it drives. Adding large
> series resistance R turns a voltage feedback amplifier into a current
> source. That is, for an output voltage V the current through your phones
> approaches V/R as R increases no matter what the impedance of the phones
> are. It is the Norton equivalent resistance of the amplifier and the
> attached R. This is not negative current feedback because the current
> flowing in the output has no effect on the signal that ends up getting
> amplified.
>
> Depending upon the details of the phones, constant current drive may or
> may not end up giving improved performance over constant voltage drive.
> One thing the series resistance will do is prevent blowout of a low
> impedance voice coil when a loud passage occurs.
>
> Because a watt or two of sound is pretty loud in confined regions, a
> practical tradeoff is to have high power amplifiers with low efficiency
> speakers if the dissipation in the speaker circuitry improves (flattens)
> frequency response.
>
I'm not used to the phrase "negative current feedback." I supposed it 
could be used to protect the power transistors in an amplifier: if more 
output current were sensed, the signal would be reduced in the preamplifier.

If you put a resistor in series with a loudspeaker and the signal 
voltage coming from the amplifier were constant, and the speaker 
impedance changed, the voltage at the speaker would vary inversely with 
the current.  That sounds like the effect of negative current feedback.

I have connected a sine-wave generator to an amp to check loudspeakers 
and phones.  All were louder at certain frequencies.  Current was 
minimal at those same frequencies.  In other words, they produced sound 
more efficiently at resonance.  Negative current feedback would mean 
increased voltage at resonant points, making them harsher and more 
mechanical sounding.

That observation led me to make a low-impedance source for phones, as is 
normal for loudspeakers.  I was rewarded.

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Thread

Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-04 21:56 -0800
  Re: Experience with Smith Micro? Doug Anderson <ethelthelogremovethis@gmail.com> - 2014-02-04 22:14 -0800
    Re: Experience with Smith Micro? Savageduck <savageduck1@{REMOVESPAM}me.com> - 2014-02-05 05:03 -0800
      Re: Experience with Smith Micro? Doug Anderson <ethelthelogremovethis@gmail.com> - 2014-02-05 06:22 -0800
        Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 12:24 -0500
          Re: Experience with Smith Micro? Michelle Steiner <michelle@michelle.org> - 2014-02-05 10:52 -0700
            Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 12:53 -0500
            Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 13:04 -0500
          Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 13:34 -0500
          Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 17:48 -0500
          Re: Experience with Smith Micro? Lewis <g.kreme@gmail.com.dontsendmecopies> - 2014-02-05 23:40 +0000
            Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 20:14 -0500
            Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 21:59 -0500
              Re: Experience with Smith Micro? JF Mezei <jfmezei.spamnot@vaxination.ca> - 2014-02-05 22:18 -0500
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 23:12 -0500
        Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 11:02 -0800
          Re: Experience with Smith Micro? Doug Anderson <ethelthelogremovethis@gmail.com> - 2014-02-05 11:16 -0800
            Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 17:54 -0500
          Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 15:39 -0500
          Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 17:53 -0500
            Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 21:56 -0500
              Re: Experience with Smith Micro? billy@MIX.COM - 2014-02-06 18:12 +0000
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-06 17:59 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-06 18:18 -0800
                Re: Experience with Smith Micro? billy@MIX.COM - 2014-02-07 03:09 +0000
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-08 16:51 -0800
                Re: Experience with Smith Micro? billy@MIX.COM - 2014-02-09 03:51 +0000
                Re: soured vibrations J Burns <burns4@nowhere.com> - 2014-02-07 10:10 -0500
                Re: soured vibrations Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-07 16:39 -0800
              Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-07 16:50 -0500
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-07 18:11 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-09 15:49 -0800
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-09 21:01 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-10 00:26 -0800
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-10 11:39 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-10 16:51 -0800
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-13 05:48 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-08 22:53 -0800
                Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-09 09:16 -0500
            Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 19:16 -0800
              Re: Experience with Smith Micro? JF Mezei <jfmezei.spamnot@vaxination.ca> - 2014-02-05 23:09 -0500
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-06 00:27 -0500
                Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-06 01:20 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-08 16:42 -0800
                Re: Experience with Smith Micro? Jim Gibson <jimsgibson@gmail.com> - 2014-02-06 12:38 -0800
              Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-07 16:52 -0500
    Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 06:20 -0800
      Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 12:13 -0500
        Re: Experience with Smith Micro? Michelle Steiner <michelle@michelle.org> - 2014-02-05 10:47 -0700
          Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 11:36 -0800
            Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 15:39 -0500
            Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 18:10 -0500
              Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 22:14 -0500
                Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-07 16:45 -0500
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-07 23:38 -0500
                Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-08 09:34 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-09 16:15 -0800
                Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-09 21:52 -0500
        Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 11:22 -0800
          Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 15:39 -0500
            Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 18:36 -0800
              Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 21:43 -0500
        Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 18:04 -0500
          Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 18:19 -0500
            Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 21:03 -0500
              Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 21:40 -0500
                Re: Experience with Smith Micro? Savageduck <savageduck1@{REMOVESPAM}me.com> - 2014-02-05 23:21 -0800
                Re: Experience with Smith Micro? android <here@there.was> - 2014-02-06 08:47 +0100
                Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-07 16:55 -0500
                Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-07 18:43 -0500
                Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-07 18:48 -0500
                Re: Experience with Smith Micro? Jolly Roger <jollyroger@pobox.com> - 2014-02-08 02:09 +0000
                Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-07 22:23 -0500
                Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-07 22:23 -0500
                Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-08 09:32 -0500
                Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-08 12:54 -0500
                Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-09 16:32 -0800
                Re: Experience with Smith Micro? JF Mezei <jfmezei.spamnot@vaxination.ca> - 2014-02-09 22:38 -0500
                Re: Experience with Smith Micro? JF Mezei <jfmezei.spamnot@vaxination.ca> - 2014-02-07 19:48 -0500
      Re: Experience with Smith Micro? Michelle Steiner <michelle@michelle.org> - 2014-02-05 10:25 -0700
        Re: Experience with Smith Micro? J Burns <burns4@nowhere.com> - 2014-02-05 12:58 -0500
          Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 11:48 -0800
        Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 13:34 -0500
          Re: Experience with Smith Micro? Michelle Steiner <michelle@michelle.org> - 2014-02-05 12:13 -0700
            Re: Experience with Smith Micro? Doug Anderson <ethelthelogremovethis@gmail.com> - 2014-02-05 11:18 -0800
            Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 15:39 -0500
              Re: Experience with Smith Micro? "John Varela" <newlamps@verizon.net> - 2014-02-05 22:34 +0000
                Re: Experience with Smith Micro? Jolly Roger <jollyroger@pobox.com> - 2014-02-05 23:10 +0000
                Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-05 18:19 -0500
                Re: Experience with Smith Micro? "John Varela" <newlamps@verizon.net> - 2014-02-06 23:56 +0000
    Re: Experience with Smith Micro? Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-05 17:45 -0500
  Re: Experience with Smith Micro? Jim Jaeger <jimjaeger@example.com> - 2014-02-04 23:04 -0800
    Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-05 06:28 -0800
      Re: Experience with Smith Micro? Jim Jaeger <jimjaeger@example.com> - 2014-02-05 11:04 -0800
    Re: Experience with Smith Micro? billy@MIX.COM - 2014-02-05 20:47 +0000
  Re: Experience with Smith Micro? Alan Ralph <alan.ralph@gmail.com> - 2014-02-05 18:22 +0000
    Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-08 16:09 -0800
      Re: Experience with Smith Micro? nospam <nospam@nospam.invalid> - 2014-02-08 20:01 -0500
        Re: Experience with Smith Micro? Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-09 16:46 -0800
      Re: Experience with Smith Micro? billy@MIX.COM - 2014-02-09 01:26 +0000
  Re: Experience with Smith Micro? me@home.spamsucks.ca (Kiraly) - 2014-02-05 23:49 +0000
  Re: Experience Smith Micro Progress maybe Salmon Egg <SalmonEgg@sbcglobal.net> - 2014-02-11 15:56 -0800
    Re: Experience Smith Micro Progress maybe Alan Browne <alan.browne@FreelunchVideotron.ca> - 2014-02-11 19:13 -0500

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