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How to Shield an inductor?

Discussion in 'Radio and Communications' started by Cluene, Mar 12, 2012.

  1. duffy

    duffy New Member

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    Not the guy who dislikes single-note bass thumpers, not the guy disgusted with the "Loudness War" reducing the dynamic range of digital recordings to eight bits, not the guy changing the driver and port on a speaker and checking the spectrum.

    It's these guys - http://gizmodo.com/305549/james-ran...iles-can-prove-7250-speaker-cables-are-better
     
  2. RichTheDude

    RichTheDude Active Member

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    I have been tempted to QUANTITATIVELY (i.e. measurements and plots rather than “this sounds better” ) prove or disprove many things that are going on the audiophile market.

    Mounting coils and magnetics carefully is good practice, so no quibbles there assuming you have the board space :). I have seen mains transformers mounted in old scopes such that they was directly under the CRT, in the null of magnetic field such not to cause any stray deflection of the beam.

    Examples of things that irk me in the audio market:

    * Mullard ECC83's with with different coloured writing fetch different prices due to their “differing sound characteristics”. I personally believe there is no difference between them, or some some of the reproduction valves which fetch much more sane prices.

    * Point to point wiring over PCB's in audio amps. I severely doubt at audio frequencies there will be any real measurable benefit, assuming a decently designed PCB of course. I have worked on old point to point gear (HF transceivers, amps) and I really do not enjoy it.

    * Super audio quality electrolytic caps – if you get the spec of capacitor you require does it matter if it says “Audio Quality” with some fancy logo on it? From a design perspective keeping a digital circuit quiet is a lot more challenging, yet we use everyday capacitors with everyday prices there with no problems (or I do anyway).

    As an engineer, when I hear or read about audiophiles measuring things with their “golden ears” (without a double blind test) it infuriates me to be honest. I build an amp, guess what I do? I measure the THD and bode plot, (all you need is a scope, sig gen and some way of viewing the spectral content – spectrum analyser or FFT on your scope).

    You can then measure a percentage improvement (if any), and see if those incredibly expensive coupling capacitors, HT caps, ECC83's with yellow writing, etc, was really worth their money.

    end rant hehe
     
    Last edited: Mar 20, 2012
  3. cachehiker

    cachehiker New Member

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    Quantitative measurements were made with and without the aforementioned attenuation network but only after the woofer's surround was replaced, the high pass crossover components (20 year old electrolytics) were replaced, and low pass crossover components were added. They were not made with anything like the Dayton Omnimic system but a frequency generator and audio spectrum analyzer. The system was designed to measure noise produced by an appliance, not speaker fidelity, so I have no fancy graphs, just a few notes. Although I wouldn't stand behind the analysis to within ±1dB, it did utilize a measurement quality microphone.

    Once I pulled it apart to fix it, subsequent analysis of the speaker's construction indicated "design compromises". The most important of these were crossover frequency too close to tweeter resonance and no low pass crossover for a woofer clearly capable of reproducing higher frequencies. Adding an attenuation network to componsate for the former knocked down a 4 to 5dB midrange hump to around 0 to -1dB. The low pass crossover didn't seem to change much, at least not at the resolution I figured I had.

    All of this just represents common sense speaker building and the result was clearly audible.
     
  4. dave

    Dave New Member

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  5. RichTheDude

    RichTheDude Active Member

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    None of my rambling was really aimed at you cachehiker, I have seen things like ECC83s with yellow writing go for truly absurd prices on the well known auction site.

    Also I was referring to audiophile magazines that make reviews based upon their "golden ears", rather than actually having a go at doing some real engineering. The most amusing one I witnessed was $700 USB cables for DAC’s that “improved the sound”, as “binary bits are not just one’s and zeros”. Assuming the DAC has a good PSU and whatever cable you use maintains signal integrity (be it a $1 cable or the $700 one) such claims are truly ludicrous - it’s digital after all.

    I just want to give such magazines and websites a good run for their pseudo science money :p
     
  6. duffy

    duffy New Member

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    My favorite's the 24k gold-plated wall outlet.
     

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