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Thread: Dispelling ground myths

  1. #61
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    Quote Originally Posted by jkeny View Post
    They also will likely tell you nothing about AC voltage as multimeters are very limited in the frequency range for which they can give an accurate ac measurement
    So who said anything about using a cheap multi-meter?

    With good modern test equipment, making measurements at -120 to -130 dB's is common.

    You measure the signal to noise ratio at the loudspeaker terminals.

    Measurements done by skilled engineers/scientists using the correct test equipment for the task at hand.
    Kevin

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    Quote Originally Posted by Speedskater View Post
    So who said anything about using a cheap multi-meter?
    Folsom mentioned using a multimeter - maybe you or he can you give some examples of multimeters with a relevant accurate measurement across the frequency range we may be interested in?

    With good modern test equipment, making measurements at -120 to -130 dB's is common.

    You measure the signal to noise ratio at the loudspeaker terminals.

    Measurements done by skilled engineers/scientists using the correct test equipment for the task at hand.
    That would be great - can you give us an example of SNR measurement differences at speaker terminals which show a difference in noise that RogerD is perceiving as audibly improved sound as a result his PEC techniques?
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    I had a similar conversation with Don Herman about chassis grounding...aka PEC

    "Same principles apply to controlling noise currents/voltages on the ground/shield paths.

    Chassis grounding in audio is no different than for any other circuit sensitive to noise. Keeping a good chassis ground relatively independent of signal ground can do anything from nothing to profound improvements in the noise floor depending on the circuit design and implementation. You generally want the "noise" path to ground to be different than the signal return path, and often that means a heavy chassis ground to provide the lowest impedance path for noise while the signal return goes through the signal cables.

    strap everything so all ground noise is common-mode
    , then shielded cables for low-level signals and only low-impedance (e.g. speaker) or isolated (e.g. power) connections should control noise for the vast majority of folk.

    Like many things, conceptually simple, straight-forward good engineering practice, but not well known or recognized and can be unexpectedly difficult to implement well. There are numerous texts and courses teaching noise control."

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    Quote Originally Posted by DaveC View Post
    I'd expect broadband AC noise from 60 Hz on up. Possible sources are induced ground loops, leakage currents, local emf...

    It seems obvious that certain substances can actually serve as a "sink" for noise. Silicon carbide, quartz, tourmaline and carbon, probably many more. Hearing what a Furutech GTX receptacle sounds like in regular vs NCF versions is astounding...
    It's not obvious to me how "Silicon carbide, quartz, tourmaline and carbon" act a a sink for electrical noise?
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    Quote Originally Posted by jkeny View Post
    Folsom mentioned using a multimeter - maybe you or he can you give some examples of multimeters with a relevant accurate measurement across the frequency range we may be interested in?
    Are you a skilled scientist/engineer? It's not about the tools, it's about how the craftsman uses the tools.

    That would be great - can you give us an example of SNR measurement differences at speaker terminals which show a difference in noise that RogerD is perceiving as audibly improved sound as a result his PEC techniques?
    How would I know what RogerD heard?
    The measurements and the listening test need to be done on the same setup at the same time. But if the noise measurement differences are great enough, you might not need to do the listening test.
    Kevin

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    Quote Originally Posted by Speedskater View Post
    Are you a skilled scientist/engineer? It's not about the tools, it's about how the craftsman uses the tools.
    Part of being skilled is knowing what tools are not suitable due to their limitations & a multimeter is just not suitable for doing what was suggested


    How would I know what RogerD heard?
    I expect by his reports of the audible improvements.

    The measurements and the listening test need to be done on the same setup at the same time. But if the noise measurement differences are great enough, you might not need to do the listening test.
    I agree but the opposite also applies - if listening reveals audible changes which measurement doesn't you may discount the measurements as using inappropriate equipment or techniques to reveal what is audible
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    Quote Originally Posted by jkeny View Post
    Part of being skilled is knowing what tools are not suitable due to their limitations & a multimeter is just not suitable for doing what was suggested
    A person with skill would not need to ask that question.

    I expect by his reports of the audible improvements.
    How can we test his situation, without testing his situation?

    I agree but the opposite also applies - if listening reveals audible changes which measurement doesn't you may discount the measurements as using inappropriate equipment or techniques to reveal what is audible
    Then we need to find a person with greater skill or get the correct test equipment. Because there will be measurable differences.
    Kevin

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    Quote Originally Posted by Speedskater View Post
    A person with skill would not need to ask that question.
    I was pointing out that a multimeter is not suitable measurement device for this application as Folsom seemed to suggest - I asked for an example of such a multimeter measurement if this was under dispute.
    You specifically stated that a multimeter could be usefully used
    Yep it is. Common Impedance Coupling noise is when two chassis are at different leakage current potentials and use the interconnect shields to equalize. So short Safety Ground wires or chassis-to-chassis PEC wires wire reduce the leakage potentials.

    More likely measurements will reveal problems the are not easily audible.
    So when you talk about "More likely measurements will reveal problems the are not easily audible." you include this in the same post as suggesting using a multimeter.
    How can we test his situation, without testing his situation?
    You mean test his reports of audibility?


    Then we need to find a person with greater skill or get the correct test equipment. Because there will be measurable differences.
    Right & as I asked before to back up your claim but I'll change my request slightly as you focused on a particular aspect that avoids answering "That would be great - can you give us an example of SNR measurement differences at speaker terminals which show a difference in noise" which shows a change due to PEC being applied? Not something which is a ground loop hum or buzz - these are gross intrusion of electrical noise into signal ground.

    I mentioned RogerD's reports specifically as he did not hear any ground loop hum or buzz prior to his beginning this PEC technique.

    Just a question - do you believe that there are other audible effects from such electrical noise intrusion into signal grounds, besides the typical hum & buzz?
    Last edited by jkeny; 08-13-2017 at 07:08 AM.
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    Quote Originally Posted by jkeny View Post
    It's not obvious to me how "Silicon carbide, quartz, tourmaline and carbon" act a a sink for electrical noise?
    These materials are known for its high microwave absorption - it is why I always unsuccessfully ask for a rigorous specification of bandwidth when debating noise ...
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    Quote Originally Posted by microstrip View Post
    These materials are known for its high microwave absorption - it is why I always unsuccessfully ask for a rigorous specification of bandwidth when debating noise ...
    Ok, yes I agree electrical noise needs to be characterised as regards spectrum, amplitude & temporal aspects & not treated as one amorphous blob
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