What's this stuff I hear about "noise/hum" on the ground from the Sound Guys. I was just speaking to a Sound Guy in LA yesterday (they call him the Hum Buster) and he was telling me something that scared me; to solve the "hum" they disconnect the equipment ground wire from the electrical system and connect it to a separate ground rod.
Answer No. 1
This is the same problem that instrument techs and engineers in the industrial side of the business do and design. This is supported and encouraged by the Honeywell's, Foxbough's, other instrument companies. Check their web sites and see what they show for grounding.... watch out on how they show the common and ground coming from the transformer....they don't and leave the reader to believe figure out that it is a high resistance ground.
Harmonic current that circulates via the ground path and inductive/capacitive couple to the signal circuit creates the hum. This is the reason that thermocouples and other instrument signal have only one end of the shield grounded. Petrochemical plants will put in a separate "quite ground triad" for instrument/computer ground reference. This is somewhat addressed in the section of the NEC that allows the ground cable to be run with the non-grounded conductors and terminated at the power system ground. However Foxbough show on its web site that the final solution is to run the instrument ground wire a different path to a different ground rod on the ground triad. This is wrong in that it allows higher impedance during a ground fault when the grounding conductor is not closed bundled to its ungrounded conductors.
Reference Chapters Chapter 3 (3.9) and Chapter 4 of William D. Stevenson Jr. book "Elements of Power System Analysis" and Westinghouse's Electrical Transmission and Distribution Reference Book, and Dr. Mack Grady, U. of Texas on Harmonics. Since he is a personal friend of my from the Power Distribution Conference (I am on the Executive Planning Committee and Chairman of the Industrial Section of the Conference) and Mack is world expert on harmonics. Mack wrote the IEEE Harmonic Standard now in use. These references should help you if additional questions come up. This is a good topic to publish and clear up for both the commercial and industrial sides of the business.
John D. Rowland Sr. PE, John.Rowland@GDSeng.com
Answer No. 2
The first thing to do is to put all of the audio equipment onto the same transformer, which should be isolated rated (Square D is an excellent source of this stuff) and run isolated grounds and isolated grounded outlets for all equipment. This puts the entire audio system onto the same ground plane and helps to prevent the inducing of hum into the system in the first place. This can be a pain in a large building. The techniques around
this is if various equipment is on different power sources (remote speaker clusters on remote amp racks) then the signal is fed via fiber or isolation transformers so that the 2 grounds are separated and will prevent potentials (voltage).
About balanced systems, this is not the same thing as 530-G. In the audio low voltage world, you can have balanced and unbalanced signals, unbalanced is a + signal and uses the ground or shield for return (typical of home audio systems, uses only 2 wires) where a balanced will have a + and - for the signal and the ground or shield is separate for noise attenuation. Another practice in the audio world is to only terminate the shield and the source end, which would help to eliminate the connection of potentials. If it is an existing system, isolation audio transformers, ground lifts, etc, are all that you have. You try to everything onto the same ground plane or isolate it from the rest.
P.S. Sources to look up some of this stuff would be the Audio Engineering Society (a little to techno for me), but are located at aes.org. There are also numerous books; I would have to go digging for some info.
Bill Ellis, IESNA, firstname.lastname@example.org
Answer No. 3
Mike there is a solution, which is allowed for in the 1999 edition of the NEC -250-6 or 250-21 in the 1996 edition in my opinion. Typically noise is not considered an "objectionable current" relatively speaking so other standards would be required for this application. IEEE emerald or green books, FIPS 94, "Ground Loop Causes and Cures" - Moore Ind. and other pubs written on the subject. I have had personal experience with the problem on several occasions and have seen some installers and designers do the same thing. There are several solutions (alternatives) to the situation. The solution would be based on several factors such as frequency, location, voltage and design. Alternative grounding techniques and / or filtering are typical solutions. Without more information an accurate solution would not be possible. However we can definitely agree that his present solution would not be acceptable.
Mike - I assumed that the sound guy has used the proper equipment to diagnose his problem. If not, he must us a Pink Noise Generator, Analyzer & Equalizer in that order. This test procedure usually filters out any audio noise he may have. Removing the ground just opens his ground loop and does not fully solve his problem. An equalizer is a series of LCR filters, Tank Circuits and Isolators.
I hope this helps - inform the technician that this is not the first time that this event has occurred and it can be solved, just be tenacious.
DAVID R. CARPENTER, email@example.com
Answer No. 4
Hum is a common problem with regards to the installation of sound systems. The method you described is sometimes referred to (incorrectly in my opinion) as "Sudo-Balancing."
Sharing grounds with equipment that is not part of your "audio" system, such as refrigerators, air conditioners, and other appliances and equipment most commonly causes it.
The ideal and best way to "power" up a sound system is to give it it's own "dedicated" Power source which is separate from any other power in the building.
This allows it to have it's own "grounding" (scheme) system separate from all Non Audio related equipment, and prevents that "other" equipment from introducing" the ground loops into your sound system.
One way to resolve this type of problem is to put everything on the same "grounding scheme, which can be accomplished by either grounding everything or lifting the ground from any "offending" piece of equipment. My strong suggestion is once again, that a "Balanced system" be used, up to and including an UPS which is solely dedicated for the entire audio system.
I am an electronics technician by trade, and have made a living for over 16 years by installing and maintaining Pro Audio Sound Systems and Recording Studios here in the US. I hold several degrees on Design and Estimating of P.A systems as well.
I think a good source for those that question my comments is to have them contact NSCA (National Association of Sound Contractors) and NAB (National Association of Broadcasters). The NSCA holds classes and seminars on all levels of audio design and installation.
Answer No. 5
Your audio "HUM" is caused by ground loops there are several ways to solve this depending on your install. Solving ground loops on DC or automobile installs is as easy as this. Common point - Return ALL of your amps/stereos/and CD players to the same point. This will solve the problem most of the time.
Solving this on Home is just as easy go to "Radio Shack" (not my first choice) and buy a ground loop isolator. This is just really a pair of 1-1 isolation transformers that go in line with the incoming audio (you will lose some audio but it's safe.) This should solve your problems.
Answer No. 6
The dilemma is that solving "noise" problems is an art within itself. Since it doesn't come up every day, we all have limited practical experience. This has spawned an industry for those who are now specialize in solving noise problems. I noted several types of audio hum buster gear on the Internet for sale. All references cited at the end of the article are available on the Internet.
However, audio studios have their own set of unique problems. Here is a quote from one of the references below--Audio Noise and AC Systems by Martin Glasband. If you want to fully understand the problems and solutions of audio hum you must read all his article.
The basics of all noise problems on the grounding system boils down to what is objectionable current. With the exception of hospital systems, the definition is vague at best. The standard electrical grounding system throughout the building isn't designed to have current constantly flowing through it--and yet it does, you cannot stop it. The reason a ground will not and never be perfectly noise free is that the grounding electrode conductor
is nothing more than a long wire from point A to point B. And the longer the wire the more noise it will pick up. If you have electricity you will have electromagnetic lines cutting through the air and anytime one of the lines cross any conductor in the ground system; it will produce an unwanted voltage. And then you have direct feeds from faulty equipment, ill-designed, and poor installation.
References: All available on the Internet
Audio Noise and AC systems By Martin Glasband Lifting the "Grounding Enigma" by Martin Glasband The How's and Why's of Isolated Grounding--Thomas M. Gruzs, Liebert Corporation, Columbus, Ohio Equitech Technical Support Bulletin Audio Wiring and Grounding
Answer No. 7
When you have two active devices are on difference power (110v +) phases (transformer secondary) phase in the power panel. Sound systems want to be on the same leg of the power transformer.
Primarily finding out the power routing from the electrician and rerouting the power feeds or have the electrician pull a new feed to the external sound equipment or use isolation (1:1) audio transformers on audio circuits between two different devises (my preferred method). The ground lift and stake is only used on a rental setup when the equipment would be shelved later in the day or week. (Non permanent installations)
John Lasher, firstname.lastname@example.org
Mike Holtís Final Comment
Answer No. 6 states "Donít violate the Code. A building is to have one and only one grounding system. He can drive an extra rod if he so desires but he must tie it into the whole building grounding system."
I though and taught for many years that the NEC contained this requirement, but it doesnít (never did as far as I know). As a matter of fact the NEC [250-54] recognizes the use of a supplement grounding electrodes, which is often required by CNC machine instructions, RF grounding grids, etc. The key is that the earth itself cannot be used for equipment grounding, but a supplement electrode can be installed without bonding it to the building grounding electrode system.
1999 NEC Section 250-54. Supplementary Grounding Electrodes
Supplementary grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in Section 250-118, but the earth shall not be used as the sole equipment grounding conductor.
If after reading this, you would like to make any updates, comments, corrects, etc. please let me know. I want to keep this question and answer updated to the current standard.
God Bless,Mike Holt
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