Audio System Noise

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Audio System Noise and the S1 Pro System

S1 Pro  This information is applicable to the S1 Pro system

The S1 Pro System is different from the L1 and F1 Model 812 Flexible Array Loudspeaker families of products because you can remove the AC power plug and run on the internal batteries.

Hints:

  • Removing the AC Power isolates the AC Line Noise and Ground Loops.
  • If you have a hum or buzz or excessive hiss try unplugging the AC power.

Related conversation:

Feedback hum on channel 3 in the Bose Portable PA Community



Audio System Noise and the L1

Most L1 owners rarely experience audio system noise since a typical L1 setup is composed of a minimal number of electrical/electronic devices. Nonetheless, there is always a possibility of occasionally having noise issues arise unless an L1 owner only uses his/her system in a fixed controlled location.

Avoiding having to troubleshoot a noise problem (the easy way):

  • Know your system
  • Have a variety of spare cables
  • Perform routine maintenance on your system
  • Keep your setup as simple as possible
  • Arrive early
  • Avoid adding a new piece of equipment in the audio chain at a gig without having pretested the new setup
  • Qualify the site's AC power
  • Avoid Ground Loops
  • Use proper protective bags and/or cases

Know your system

Read the owner's manual for every piece of equipment you use in your system. Understand each of the functions for each piece. Understand how best to interconnect the system. The better your understanding of each piece in your system the easier faults can be isolated should a problem arise.

Have a variety of spare cables

Cables are usually the most abused components in the audio chain, especially when the gigs are in different venues. Spare cables can bring piece of mind and allows for quick troubleshooting. Spare cables can be stored under the seat of the vehicle until they are called into action.

Perform routine maintenance on your system

Implementing a routine maintenance schedule for your equipment can go a long way in helping you avoid the dreaded last minute problems. Some tasks may be performed monthly while other would be well served on a yearly basis. Check the owner's manuals for manufacturer's recommended maintenance. Make yourself a list of your gear and itemize areas that may be most prone suffer from wear.

Inspect all your cables for wear and external damage. Treat the connectors with a premium contact oxidizer/enhancer. Inspect the connectors internal contact terminals (solder, crimp or screw). Learn to properly roll your cables. The over/under method is one of the best for longer cables.

Keep your setup as simple as possible

Fewer pieces of gear in an audio chain helps minimize eventual problems. If you need it and use it then keep it. Keep the cables as short as possible. Consider custom length cables. Consider different length cables for very different setups.

Arrive early

It can be very stressful to have to locate and eliminate the source of unwanted audio noise moments before the show is to start. Arriving early to setup for a gig whenever possible can help one keep a clear mind and to calmly follow basic troubleshooting steps.

Avoid adding a new piece of equipment in the audio chain at a gig without having pretested the new setup

Need we say more??

Qualify the site's AC power

It is important to ensure that your equipment is connected to good quality AC power of the correct voltage and properly wired. The use of a simple three light AC receptacle tester in conjunction with a basic AC voltmeter is an absolute minimum step that should be taken before connecting equipment to a power outlet. Ground, Hot and Neutral lines should be present and wired to their respective terminals. The AC receptacle tester can provide quick verification of this. For the USA and Canada, the voltages should be: 120VAC* between Hot and Neutral, 120VAC* between Hot and Ground and 0VAC between Ground and Neutral. If the power does not meet your requirements, find a different outlet. *120VAC is a nominal reading and can safely range from 115VAC to 125VAC It is important to know if any or all your equipment can be safely operated outside of this voltage range. Read the owner's manuals.

Ground Loops

cheater plug

Safety Note

NEVER use a cheater plug or cut the ground plug off an ac power cord.

From the Owners Manual

Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades with one wider than the other. A grounding-type plug has two blades and a third grounding prong. The wider blade or third prong is provided for your safety. If the provided plug does not fit into your outlet, consult an electrician for replacement of the obsolete outlet.


Diagnosing / Troubleshooting

System Owner DT recently posted the following:[1]

To troubleshoot ground loops problems, listen to the audio signal at the mixer with headphones. If the buzz exists at the mixer then do the following:

One by one, disconnect the inputs and outputs to and from the mixer and note if the buzz decreases. If the buzz slowly diminishes with each input or output that is disconnected including those connected directly to microphones and devices not powered from an AC wall plug, then the buzz may be caused by the snake running too close to a noisy AC power line. If the hum reduces dramatically only when inputs or outputs are disconnected which are connected to devices that are AC powered, then it is likely caused by a ground loop.

If the hum is not present in the mixer headphones but only audible from the L1™s, try adding direct boxes between the mixer and the L1™s.

Usually if all equipment powered from AC power is plugged into the same AC wall plug, there will be little or no problem with ground loops. Because the mixer is usually at the back but other equipment powered by AC is at the front, it is impractical to use the same AC wall plug (long extension cords do not qualify as the same wall plug). Try using a direct box with ground lift and connect between the mixer or other audio devices which are AC powered that seem to be responsible for the ground loop. AC devices with 3-prong plugs are most suspect but 2-prong AC powered devices can also cause ground loops. Do NOT modify or isolate the ground pin of devices that have 3-prong AC power cords.

I helped two churches with L1™s reduce hum to acceptable levels by using direct boxes at the audio output of the electric organ and at the audio input to the L1™s . We used a Radial PRODI for the electric organ. I recommend a balanced line-level to balanced line-level direct box for the L1™ inputs. The Radial Twin ISO is a two channel line to line direct box. If the two channels are used on two separate L1™s put the two channel direct box close to the mixer. Alternately, have your local pro audio store help you select single channel line to line or line to mic direct box to be used with each L1™. Be sure that the ground lift switch is in the "lift" position.

The direct boxes can be expensive, check to see if you can return them if they don't solve your problem or if you find that you don't all of them.

In some cases ground loops or buzz in the presence of certain light dimmers can be difficult to completely solve and some residual hum may be audible. There are some types of light dimmers that produce less electrical noise. One technology is known as "zero crossing" switching which generate less electrical interference.

Hopefully some of this info is relevant and helpful.

Dave

Dave also recommended reading Ground Loops at Radial Engineering.

Ground Loops (article excerpt)

This is an excerpt of an article www.rane.com Sound System Interconnection [2]

Almost all cases of noise can be traced directly to ground loops, grounding or lack thereof. It is important to understand the mechanism that causes grounding noise in order to effectively eliminate it. Each component of a sound system produces its own ground internally. This ground is usually called the audio signal ground. Connecting devices together with the interconnecting cables can tie the signal grounds of the two units together in one place through the conductors in the cable. Ground loops occur when the grounds of the two units are also tied together in another place: via the third wire in the line cord, by tying the metal chassis together through the rack rails, etc. These situations create a circuit through which current may flow in a closed "loop" from one unit's ground out to a second unit and back to the first. It is not simply the presence of this current that creates the hum -- it is when this current flows through a unit's audio signal ground that creates the hum. In fact, even without a ground loop, a little noise current always flows through every interconnecting cable (i.e., it is impossible to eliminate these currents entirely). The mere presence of this ground loop current is no cause for alarm if your system uses properly implemented and completely balanced interconnects, which are excellent at rejecting ground loop and other noise currents. Balanced interconnect was developed to be immune to these noise currents, which can never be entirely eliminated. What makes a ground loop current annoying is when the audio signal is affected. Unfortunately, many manufacturers of balanced audio equipment design the internal grounding system improperly, thus creating balanced equipment that is not immune to the cabling's noise currents. This is one reason for the bad reputation sometimes given to balanced interconnect.

A second reason for balanced interconnect's bad reputation comes from those who think connecting unbalanced equipment into "superior" balanced equipment should improve things. Sorry. Balanced interconnect is not compatible with unbalanced. The small physical nature and short cable runs of completely unbalanced systems (home audio) also contain these ground loop noise currents. However, the currents in unbalanced systems never get large enough to affect the audio to the point where it is a nuisance. Mixing balanced and unbalanced equipment, however, is an entirely different story, since balanced and unbalanced interconnect are truly not compatible. The rest of this note shows several recommended implementations for all of these interconnection schemes.

Please see the full text: Sound System Interconnection

Related Discussions

Download: Sound System Interconnection.pdf


  1. DT talks about ground loops in Major BUZZ problem
  2. Excerpt of Article at www.rane.com Sound System Interconnection


Line Noise

RFI from Light Dimmers

The following is an excerpt from lutron.com

WHAT IS RADIO FREQUENCY INTERFERENCE (RFI)?

RFI is a buzzing noise which may occur in some audio and radio equipment when solid-state dimmers are used nearby. Although every Lutron dimmer contains a filter to suppress RFI, additional filtering may be required in some applications. Typical examples of RFI-sensitive equipment are AM radios, stereo sound systems, broadcasting equipment, intercom systems, public address systems, and wireless telephones.

RFI can be transmitted in two ways: * Radiated * Conducted

Note: The suggestions in this application note will help minimize RFI: however, they do not guarantee that RFI will be completely eliminated.


Radiated RFI

Any sensitive equipment that is in close proximity to dimming equipment can pick up the RFI and generate noise into its system.

The following are three possible ways to minimize the radiated RFI:

  • Physically separate the RFI-sensitive equipment from the dimmer and its wiring.
  • Run dimmer wiring in its own metal conduit.
  • Use a lamp debuzzing coil (available from Lutron) to filter the RFI.
Conducted RFI

In some cases, RFI is conducted through the building wiring and directly into the AC power supply of the sensitive equipment.

To minimize the conducted RFI, follow these guidelines:

  • Feed sensitive equipment from a circuit without a dimmer on it.
  • Add a power-line filter to the sensitive equipment.
  • Add shielded wire for all microphones and input cables. Also, use low-impedance balanced microphone cables, which are less susceptible to interference than high-impedance types.
  • Make sure all the equipment is grounded. Connect all shields to the ground at one point. Ground lighting fixture metal housings properly.
  • Use a lamp debuzzing coil (available from Lutron) to filter the RFI. Lamp Debuzzing Coils Lamp debuzzing coils (LDCs) are the most effective way to reduce RFI. One LDC is required for each dimmer. Select the LDC according to the connected lighting load. The LDCs may be wired in series on either the line side or the load side of the dimmer. For maximum RFI suppression, keep the wiring between the LDC and the dimmer as short as possible.

Since the LDC itself make an audible buzz, mount in a location where the noise will not be objectionable (e.g., an electrical closet, a basement, or above a drop ceiling). LDCs are designed to easily mount onto a standard 4"x4" junction box. They are UL listed and thermally protected.

The following LDCs are available from Lutron: Model # LDC-10-TCP LDC-16-TCP Rated Capacity: 600-1200W 1201-1920W.

See also: Ground Loop



Laptop Hum

From the Dell Audio Faq

"How do I eliminate the buzzing noise from my speakers or headphones that occurs only when my system is connected to AC power?"

Ensure that both the computer and any external speakers are plugged into the same outlet or power strip. This should eliminate or minimize the buzzing associated with a ground loop. You should not assume that all outlets in a single room are on the same circuit. Outlets may be on different circuits, even when they are close to each other. In studio type situations where buzzing associated to a ground loop is unacceptable, an isolation transformer can be used. An isolation transformer should eliminate the problem, but is typically expensive. While a three to two prong wall outlet adapter (removing ground) will eliminate the noise, for safety concerns this solution is definitely not recommended. "



DI boxes

Laptop (notebook computer) power supplies are notoriously noisy. The quick test to find out whether this the culprit, is to simply unplug the power and run off battery. If the noise goes away, you know it's the power supply.

Your best bet is a two-channel passive DI box with a ground lift switch such as this:

http://www.audiopile.net/products/DI_Boxes/FDB-202/FDB-202_cutsheet.asp

Hope that helps Hilmar

See it in context

There are several reports on the Bose® Pro Portable PA Community that the EBTECH Hum Eliminator works for removing hum when using a laptop power supply.

See: search results for Ebtech on the forum


Taylor ES System Noise

I've had some troubles with dimmers and airborne hum (especially those carbon coiled cosy bulbs in some restaurants) on my Taylor with an ES-system.

All was due to a blown micro fuse behind the battery in the guitar. It grounds the strings to earth, and without it the single coil in the fretboard acts like an antenna! I replaced the fuse, and the guitar now sounds wonderful! These fuses are available from Taylor Store, or your local dealer may find them.

My Taylor is a 426 ltd with the 9V 2 body sensor system. I think it is a 2007 or 2008 guitar (can't check it right now...).

Here is one link from loads of Taylor fuse questions: Acoustic Guitar Forum discussion

String Ground Replacement Fuses

Source: Taylor 310 Problems - Bifuel


TC-Helicon VoiceLive 2

Are you hearing excessive noise (hum or hiss) when you connect your TC-Helicon VoiceLive 2 to your L1®? Here is a tip.

You certainly shouldn't be hearing excessive noise when using your VoiceLive 2.
Firstly, can you check the level of the Aux and Guitar inputs and if they are not being used, set them to off (please note that 0dB is not off - this is full gain).

— Source: Joey @ TC-Helicon

— Thanks to SunDog


Use proper protective bags and/or cases

Properly maintained gear will perform for many years longer when properly protected in transportation.