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Quiet by Design: How to De-noise the Electrical Environment of Your Media System
Many factors contribute to the noise environment of your media room; unfortunately, your home’s electrical system can be a primary factor. The nature of the electrical system, how that system is hooked up, and the individual pieces of equipment it contains, can all contribute to noise problems.
This noise comes from both the electrical power supplied by your power company and from noise-generating equipment and wiring within your home. The noise can easily affect the performance of audio/video components, adding to the noise floor, limiting power available for transients, or allowing breakthrough of GB or AM radio.
Determining what the noise sources are and eliminating or overcoming them will give you an electrically quiet media room in which the only signal you receive will be the one you want to hear.
Some sources of noise have been with us for many years; refrigerators, air conditioners, and fluorescent lamps are common sources. However, new sources of noise are beginning to come on line from equipment within the home (such as personal computers) and from the surges that result when a community’s electrical load-management system remotely starts or stops numbers of central air conditioners or other large devices at once.
Some types of noise, such as the repetitive, narrow-band noise produced by some domestic appliances, are readily filtered. But many other noises are more difficult to filter and should be eliminated at their source.
Solid-state lamp dimmers, for example, are a common source of electrical noise. Although they are very popular, they are extremely noisy and it is very difficult to filter out their noise once it is on the audio/video power line. These solid-state dimmers can also transmit their noise as radio signal, invading sensitive audio/video circuits and corrupting the signal.
Surprisingly, some noise can come from audio/video components themselves. Most televisions today use a type of power supply that has a poor power factor. Power factor, technically defined as the true power in watts divided by the apparent power in volt-amperes, or the cosine of the current/voltage phase angle, indicates how a component draws power. The power factor rating can be anywhere from 0 to 1.0; a rating at the low side of the scale is poor and 1.0 is ideal. A poor power factor suggests that the component utilizes a switching- mode power supply that does not draw energy in a consistent or efficient manner, but rather pulls current in surges. This distorts the power-line waveform and causes noise on the electrical lines.
SEPARATE ELECTRICAL FEEDS
Ideally, the electrical feeds for the media room should be derived from separate circuit feeds off the main breaker. In most cases, they should be passed through high- attenuation electrical filters. There are a number of brands of these filters: Corcom is probably the largest U.S. supplier; another prominent company is Delta.
High-attenuation filters will form a first line of defense against noise getting into the electrical service line. They also help pre vent whatever noise is on the line from getting out to the rest of the system. These filters, which generally should be installed by licensed electricians, must have voltage and current ratings at least equal to the circuit-breaker ratings for each of the electrical feeds to the media room.
According to the National Electrical Code (NEC), a feed rated at 15 amperes is good for about 1,440 watts, while a 20-amp feed is good for 1,920 watts. That’s less than you might calculate by multiplying the current by the nominal line voltage of 120 V; this is because the NEC allows only 80% utilization of the service rating, not 100%.
The use of isolated-ground outlet receptacles should also be considered. These outlets are differentiated from normal grounded outlets by their orange color- coding; note that a separate ground return wire must be run back to the service panel and that the conduit is not used as the ground return.
All media rooms have to be lit. However, it’s important to determine what lighting is suitable, not only from the point of view of generating light, but also to avoid generating noise.
The rule is “incandescent lights only” and to be even more particular, low-voltage (6 to 24 V a.c.) incandescent lighting that uses step-down transformers, because the electrical noise generated is almost imperceptible. Such low-voltage systems use different electrical principles than low-voltage incandescent lighting utilizing solid-state supplies, and do not generate noise. As an added benefit, the light output of low- voltage, incandescent lamps is greater than that of standard 120-volt lamps of equal wattage. They are available in a variety of formats, including round ceiling-mount light cans for track lighting. Another acceptable type of low-voltage system uses a single incandescent bulb, a step-down transformer, and a variable potentiometer to control the brightness from off to 100%. It does not generate perceptible noise.
Needless to say, fluorescent lights, neon lights, or any other gas-discharge lamps are not recommended. These lamp types create electrical noise. Halogen lamps, however, are simply incandescent lamps filled with halogen gas to increase the lifetime and brightness of the bulb.
The use of dimmers in residential and commercial properties has been very popular for quite a while. With the advent of the silicon-controlled rectifier and the triac, inexpensive solid-state lamp dimmers became a reality.
Unfortunately, these devices are among the worst generators of electrical noise. Because they are most frequently produced with an eye on competitive pricing, they are rarely filtered to the degree necessary for a quiet media room.
Although the NEC requires these devices to be filtered, the basis for this requirement and the standards set for this date back to the early 1970s or before. They only ad dress the interference these devices cause to AM radios operating in the 500- to 1600- kHz radio band. But the frequency of the noise that these dimmers generate ranges into the tens of megahertz.
In fact, the only reason noise generated by dimmers was regulated at all was be cause they came out in the heyday of AM, and they made AM noise. Audio, on the other hand, was such an infant industry at the time that a dimmer’s effect on audio components was not even considered.
Solid-state dimmers control incandescent lamps by a method technically known as “phase control?” Instead of allowing the 60-cycle current to flow continuously, these devices turn it off each half cycle and then turn it on again after so many milliseconds of delay from the beginning of the cycle. What you end up with is an electronic device that is switching on and off 120 times per second. Because the device turns on so quickly, and the rise of current is limited solely by the lamp and other circuit parasitics, a noise pulse is generated each time these devices turn on.
As you can see, this is not exactly the type of device you would want in a media room. The question comes up, if you have to dim, how can you dim and not create noise?
The answer is, use the venerable old variable-voltage isolation transformer. Manufactured by a number of companies, these devices have been used for many years in recording studios’ dim lamps with out generating the “nasties” associated with solid-state dimmers.
These devices are perhaps 10 times more expensive than solid-state dimmers and are larger (they may require a two- or three- gang conduit box). They are also available with motor drives, should you want to remotely control them from a convenient location. In that case, the devices that actually dim the lamp can be located back at the service panel, and the devices that control the motor drive can be placed where the light switch normally is.
INSULATE INCOMING POWER
If incoming electric service is routed through metal conduit pipe, noise will be kept to a minimum. The metal conduit was a safety requirement in residential and commercial properties for many years and is still required in commercial properties in many states. But you generally do not see this type of electrical wiring in new houses today. If it has not been installed in your house, then you will have to make do with what you have.
If we are talking about a house that has not yet been constructed, I strongly urge the use of steel electrical conduit pipe rather than Romex wiring. Although it may cost a good deal more money, you have the increased benefit of protection from fire, the ability to more easily replace broken or worn-out wire, and the obvious shielding benefit of the steel conduit pipe.
You may be tempted to do your own electrical wiring and, in some states, you are allowed to wire your own house, but you still must meet the NEC codes that pertain to this work. I think it best to call in a professional. Not only are professionals trained, but they are also familiar with all the minute details of the NEC regarding electrical hookups in the residential environment. They are licensed by their states and counties to do electrical work and have the advantage of being legally recognized as qualified.
Further, if you ever want to sell your house and it is not up to code, you would have to bring in a professional anyway. Perhaps most important, if the wiring you install yourself results in problems, you would be liable for all damages.
POWER IN YOUR COMMUNITY
In the past, the quality of electrical power had not been a concern for audiophiles. But the marketing of more and more electronic devices using microprocessors, especially the personal computer and other devices that use SMPS (switch-mode power supplies), necessitates that consumers take a closer look at the effect these devices have on the quality of the electrical line power.
For a long time, power factor was some thing only electric utilities were concerned with. However, because of the proliferation of computers and other devices that use switching power supplies, it now also affects us. Further, these switching-mode power supplies have had, until recently, poor power factors, so they are capable of distorting the power-line feed and could make the effective quality of the power worse than it was previously.
Because there is so much switching- mode equipment in use that does not have an adequate power factor, there have been electrical fires in commercial offices with a concentration of these devices. Because of this, safety agencies throughout the world, such as Underwriter’s Laboratories in the U.S., have now set new standards governing the power factor of switching-mode power supplies. As devices with adequate power factors of 0.9 and above proliferate, they will greatly reduce the distortion in the power-line waveforms coming into the home from the utility company. This will provide the residential user with power of higher quality, unaffected by devices with poor power factors. Other devices can also have poor power factors. Generally, the power company is responsible for arid interested in seeking out loads with poor power factors. It is in their interest not to have to generate excess power.
If you are curious, have the necessary test equipment at hand, and are knowledgeable working around open fuse panels, the following method, proposed by The John Fluke Co. in a pamphlet entitled Sources of Harmonic Distortion, can be used to detect if harmonic distortions are present on the power line.
You will need two pieces of test equipment—an average-responding clamp-on current meter and a clamp-on current meter with true rms response. With each meter, measure the current being drawn through the circuit that will feed your audio/video system. Divide the average cur rent by the rms current. A value of 1 would indicate little or no distortion. If, upon per forming this test, you obtain a value of 1, you can hook up your hi-fi system without fear of distortion. However, an indication of 0.5 or lower would indicate substantial harmonic distortion. Since you are measuring the circuit feed to which the hi-fi will be connected, you must disconnect, one at a time, each of the devices currently connected to that feed. After disconnecting each device, perform these two measurements and calculate the product. You will be able to determine which of the devices is causing the problem.
Of course, this test assumes that the feed coming into the panel itself is reasonably clean, and that the source of the distortion is equipment you are plugging into the circuit. Unfortunately, this may not be the case. Other devices, which are drawing current from the fuse panel but are not on that circuit feed, may be the cause of the distortions. To determine whether any of the de vices in your house are causing the distortion, perform the same two measurements on the main feed wires coming into the panel itself. If they indicate less distortion, then one or more appliances within the house is causing the problem.
Tests by some colleagues using high-end audio systems reveal a definite sonic difference between listening during the day and listening at night. Measurements undertaken by these colleagues during day and night have shown that harmonic distortion in a power line can vary from as little at 0.5% in the nighttime to as much as 3% or 3.5% during daylight hours. This change in distortion level is directly attributable to the various industrial loads with poor power factors that are present during the day but not used at night.
Some high-end audiophile companies are aware of this problem and are bringing out devices to address it. These plug into the same electrical outlet as your other equipment and are, in effect, connected in parallel with your devices, in an attempt to correct the power factor problem. The makers of these devices do not go into great detail in public about how these devices work. Much of the technology is proprietary or patent-pending, but I believe that most of these devices attack the problem via power-factor correction.
You can use a portable, battery-operated AM radio to seek out amplitude-based noise interference. By tuning the radio through its band and placing it close to suspected noise-inducing electrical devices, you’ll be able to hear, through the radio, the impulse noise these devices create. Even the turning on of a light switch should show up on a radio. By bringing the AM radio close to fluorescent light fixtures while they are operating, you will be able to hear the noise the devices create. The same goes for placing the radio near solid-state lamp dimmers.
Remember, the noise may only be present in a certain area of the AM radio band. Therefore, you must continuously tune in order to locate the noise. In other cases, the noise is repetitive and of such a broad-band nature that tuning the AM radio is unnecessary.
An unusual source of noise are items called “carrier current devices.” These de vices send coded pulses over the a.c. power line, giving you control over the lights and lamps plugged into the 120 V a.c. line. They can generate noise that may get into your media room sound system. Because these devices operate only when you want them to, it is not critical that we look at them as a potential continuous noise source, but be aware of them.
In some cases, carrier-current devices are interfered with by high noise levels on the a.c. power line. Should this be the case, you should seek out the devices that are making the carrier-current devices inoperable. These same devices would most assuredly affect the quality of electrical lines in the media room.
In conclusion, let me hope that you have good luck in hunting down any sources of electrical noise you encounter in your media room, and wish you quiet listening.
About the Author: James Evert, an analog design engineer at gammaelectronics.xyz, wrote this piece with the company’s entire engineering. gammaelectronics.xyz contract-designs a variety of systems and accessories for custom-installed multi-room and multimedia entertainment systems.