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Re: arsclist Ground Impedance for Sound Studio

How do you ground something effectively if you're on the 12th floor of a building? In the case you describe, a faraday cage is a far better approach. In fact, most equipment is in a faraday cage except that it is breached by signal input/output leads. Addressing interference on these and proper bypassing of a shield's noise signals to the cage and not to the circuitry works. We're trying to get the voltage differential (at all frequencies of interest) to a minimum within the system and then worry about external interfaces to the system as a separate part of the analysis.

In fact, when you're talking about a good ground, you're trying to minimize the voltage drop across some part of a circuit. I'd like to better understand the circuit that you're working with.

As an example, how come, at a shortwave relay station if I turn down the RF gain of my Sony ICF2010 receiver, the receiver still works without a ground wire? It's all relative and needs to be understood as a system. I still hold that going crazy over the impedance of a ground for anything other than lightning protection, power line safety grounding, or unbalanced antenna counterpoise grounding is an exercise in illusion. I have seen too many facilities that followed some of the sacred myths of grounding that failed. Once we got back to basics, it worked.

Also, the control rooms at the stations that I'm familiar with are effectively faraday cages.

While I'm shooting at sacred cows, the isolated ground (IG) receptacles are now considered ill-advised by the latest edition of the IEEE Emerald Book on Grounding.

As a reference, I'd suggest Grounding and Shielding in Facilities by Ralph Morrison, and Grounding and Shielding in Instrumentation, also by Morrison.

Also, there are some people who suggest that a separate grounding conductor is useful and they wonder why it doesn't work for RF. Consider the following comparison of possible grounding conductors:

Impedance of conductors takes into account inductance. At 60 Hz:
  --- #2 - 156 mohms/1000 ft & 572 microH/1000 ft; Z=266mohms
  --- #0000 - 49 mohms/1000 ft & 540 microH/1000 ft; Z=210mohms
Now, looking at some RF values
  --- #2 - 1kHz  Z=3.6ohms/1000 ft
  --- #2 - 1MHz  Z=3.6kohms/1000 ft
Long grounding conductors are illusory
 --- Think of them as antennas

Cheers,

Richard

At 09:42 AM 10/26/2001 -0700, you wrote: 
Bonding alone does not support shielding. Guarding against radiated or
conducted (via power lines, etc.) external interference works only with
a solid ground.

Jerry
Media Sciences, Inc.

Richard L. Hess wrote:
>
> At 08:10 AM 10/25/2001 -0400, José Llufrío wrote:
>
> This happens to be an area that I have spent some time studying. In order
> to get you in the correct frame of mind for what follows, remember
> satellites work fine without being grounded. Think about the image of
> geostationary satellites with 22,300 mile long ground conductors! Ok now on
> to what we're trying to do.
>
> When we say grounding, we mean a lot of things. There is bonding
> (connecting everything together to form an equi-potential plane) and
> grounding (connecting that equi-potential plane to the center of the earth).
>
> The actual grounding is really only important so that you don't fry
> yourself as you step from the real world into the facility.
>
> Everything else is bonding. The goal here is to minimize the potential
> difference among all the points that are connected together. The design
> here is very dependent on the power system design and the overall building
> design.
>
> If you have a central computer room using an access floor the #2 copper
> wire grid (signal reference grid) is a very useful way of achieving a good
> equi-potential plane.
>
> Is RF present? If so, then surface area is more important than cross
> sectional area. Copper strips are often used (and mis-used) as ground
> references.
>
> Don't be afraid of ground loops. In fact, a ring ground around the
> perimeter of the building is often a very good place to start.
>
> I'm sorry there is no one answer, and answering the question of what
> "impedance" ground is only really useful to determine if the power
> utility's circuit breakers will trip if there is a ground fault on the
> incoming feeder.
>
> The most important function of a ground is personnel safety. Bonding helps
> equipment work better.
>
> Also, there are papers for the "pin one problem" that describes common
> impedance sharing. The noise voltage's drop across the common impedance
> becomes superimposed on the signal.
>
> Hope this helps.
>
> Cheers,
>
> Richard
>
> >Hello, everybody.
> >
> >Sorry for any duplicates/cross-posting.
> >
> >In a posting a couple of month past, at ARSCLIST, Graham Newton replied to
> >Kurt Nauck:
> >"Be sure there is a heavy contiguous ground wire available that goes
> >directly to a
> >solid earth ground at the electrical entry to the building. Ground all your
> >equipment to this."
> >
> >I am now involved in the design/construction of a sound recording and mixing
> >studio for one of our production units (animated films).
> >
> >There's much discussion going on among our engineers, about the correct
> >impedance for grounding the equipment. Recording and mixing will be mostly
> >digital, but analog equipment will be eventually used too.
> >
> >What would be the right way to ground the sound studio?
> >
> >If the DAWs are networked with the rest of the computers in the building,
> >should everything be connected to a common ground, or should they have
> >separate grounding with different impedances?
> >
> >What is the acceptable impedance for grounding sound equipment?
> >
> >Is the ground to be independent from the grounding in the electrical mains
> >feed (transformer chamber belonging to the power company)?
> >
> >I plead to the many experienced people on the list.
> >
> >Thanks very much in advance.
> >
> >José E. Llufrío
> >llufrio@xxxxxxxxxxxx
> >Technical Advisor
> >ICAIC Cuban Film Institute
> >Havana, Cuba
> >
> >


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