|Bring On The Noise|
|Home Theater Feature Articles Other|
|Written by Kim Wilson|
|Thursday, 13 December 2007|
Bring On The Noise
Most of us take electricity for granted. We plug in a device and flip the switch and expect it to work perfectly. However, as home theater systems feature increasingly more complex and sophisticated configurations, there are more instances of nasty 60 Hz hums, buzzes and other EMI (electro-magnetic interference) related noises which affect the performance of our sound system.
The sophistication of your individual system will determine which measures are most appropriate for you, but there are several preventative measures you can employ to combat these problems and greatly improve your A/V system.
To get the scoop on eliminating AC source problems, I called upon Michael Fuschi of Michael Fuschi Designs, who has installed dedicated music and theater and 35 millimeter film systems priced at over $1,000,000 in residences, motor yachts and aircraft on four continents.
According to Mr. Fuschi, the first step is to install orange, isolated ground receptacles in the wall outlets you plan to use for your home theater equipment. Those outlets should be on separate circuit breakers so no other electrical devices in your household are drawing power off the same circuit.
This method is sometimes mistakenly referred to as a 'dedicated line.' In fact, a dedicated line is a separate line of electricity running from the street that you would use for only your home theater. This, in most cases, is completely unnecessary. Most circuit breakers in the average home are rated at twenty amps which should be adequate even though it's not a bad idea to upgrade those to thirty amps when running multiple high powered amplifiers.
These are simple fixes for any qualified electrician and shouldn't cost more than a few hundred dollars (depending on the number of outlets and circuits in your system). Unfortunately, doing all this doesn't guarantee a noise free sound system, but at least now you know you're getting clean and uncorrupted power from the source.
The next step is to insure you have a true earth ground. For those of you with some extra time and a desire to roll up your sleeves for some manual labor, the absolute best way to get a true earth ground is to drive a metal rod 10 to 20 feet into the ground. Then take copper wire and connect the rod to the panel of the circuit box. This will ground anybody, although personally, I would have my electrician put this upgrade in the bid.
A less extreme method, used successfully for decades, is to ground the chassis of the offending device to something already grounded in the room. Another easy solution that often works is to use a ground lifter--these are those three-to-two prong adapters you've seen at the hardware store. Sometimes these 39 cent lifts are all you need to eradicate demon-like hums and noise from a component.
At this point, if you still encounter any noises, it's probably one of your A/V components. When products leak RF (radio frequencies) into the audio signal, ground loops are created, resulting in audible hums and buzzes. Ground loops are all too common due to the various shielding practices of even high end equipment manufacturers.
A handy accessory to have around is the Xantech Ground Breaker, it knows how to solve this problem. Unfortunately we can try to keep RF from infiltrating our audio signal, but it is sadly an inherent trait in video signals. The Ground Breaker, however, isolates the ground potential differences within a video signal without affecting the RF signal.
Single-ended RCA type connectors are the most common in consumer audio. These are known as unbalanced lines. Generally speaking, unbalanced lines are perfectly suitable for most home theater installations. However, many high-end audio manufacturers incorporate balanced connectors into their equipment.
There are good reasons for you to consider using balanced lines, however, trying to explain the differences between the two can be pretty heady stuff. So, for now I want to keep it very simple and explain the basic concept of both using these two illustrations to graphically demonstrate a glance at the key differences.
In an unbalanced line, the single wire carries the audio signal. The shield acts as ground and signal reference (return path of signal). Since the signal reference also functions as the ground, it becomes imperative that both the sending and receiving paths are properly grounded.
When both ends of the line are at the same potential (this means they have equal voltage), you should have no problem, but when the potential varies, even a few millivolts between the sending and receiving paths will give you a dreaded ground loop.
Balanced lines use XLR, 3-pin connectors. The two wires carry the audio signal and signal reference. The shield is still grounded, but it has no other function in this configuration.
Balanced lines are based on a concept known as "common mode rejection." Even when noise energy strikes the two wires, the electrical potential on both wires stays equal. Remember I said earlier that there are no grounding problems when the signal and the signal reference are of the same potential. When proper wiring techniques are employed, there should be no voltage differential, in which case all noise is effectively rejected.
A relatively new technique, balanced power, is perfectly suited for complex home theaters. Originally conceived by Martin Glasband, a long time veteran of the recording and broadcast industry, balanced power works on principle of common mode rejection (like an XLR). This may very well become a new standard in electrical wiring as his method for balanced power is included in the latest edition of the National Electrical Code, which governs accepted electrical practices in the U.S.
Balanced power virtually eliminates intermodulation distortion (IM), which occurs when AC noise is present in the audio signal. Balanced power prevents AC interference into the audio signal that can reduce the signal to noise ratio. Balanced power has been known to increase dynamic range by an amazing 16 dB or more and reduces the noise floor by as much as 20 dB.
Martin Glasband's company EquiTech, markets balanced power line conditioners as does Cinepro who will also be offering a line conditioner this year featuring balanced power. This is a concept we will be hearing much more about in the next few years.
Finally, using the high quality interconnect and speaker cables will help to increase the odds of reducing noise in your system. There is a lot of controversy over the relative value of expensive cables, so I recommend good common sense. The quality of cable should be commensurate with the level of quality you can expect from the components themselves. No matter how good the cables, they can't improve a given component's quality beyond its design. You wouldn't put a $4000 set of Pirelli P-Zero racing tires on a 1992 Honda Accord, would you? By the same token, you should invest in cables that make good connections and don't add tonality or noise to your system.
With regard to speaker cables, the smaller gauge numbers signify greater thickness. The longer the run, the heavier the cable should be. The shorter the cable length, the better, however, that's usually not going to be the case with your increasingly demanding surround loudspeakers due to the specs of Dolby Digital and DTS.
No matter the gauge, bare stranded wire, your basic `lamp cord' style MUST be avoided at all costs. It is very prone to corrosion with a relatively high inductance (resistance to signal flow). It comes back around to shielding when we talk about low grade cables. Noise and interference can be transmitted along the wires of cheap cables. You will notice more resonance with a grittier sound when using these types of cables.
A cable's ability to minimize signal resistance and deliver the original signal intact without any degradation determines its quality. If the first thing you do after outfitting your system with quality cables is turn down the overall volume level, you know more signal is reaching the amplifier, requiring less gain from the preamp.
There are a lot of different high end cables to choose from and the claims made by some can be confusing. Find a retailer who has a try-before-you-buy policy, allowing you to take a few different cables home and listen to what they can do for your system.
You should have a dedicated circuit with isolated ground receptacles in the wall outlets used by your home theater equipment. Get a true earth ground. No matter how much money you spend on cables and power 'conditioning' apparatus, if you have poor grounding at the wall, you'll always be plagued by hum and buzz. Always use high quality interconnect and speaker cables and when possible use balanced interconnect cables and balanced power.
Ensuring the integrity of the AC and your audio signal can be a time consuming and sometimes expensive process, but lowering the noise level of your system by 5 to 20 dB or more will result in amazing clarity and greatly improved performance of your equipment.