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Hum and buzz in audio systems and home theaters

What effect does ‘hum’ and ‘buzz’ have?

‘Hum’ and ‘buzz’ can cause major noise issues with our high performance audiovisual systems.

  • Hum is a superposition of the 60Hz mains AC frequency on the audio or video signal.
  • Buzz  is a superposition of the harmonics of the 60Hz (120Hz, 180Hz, etc) mains AC frequency on the audio or video signal.

How is hum and buzz caused?

There are three main mechanisms that cause hum and buzz:

  • Interchassis currents between pieces of equipment with OR without a saftey ground as a result of ‘stray’ capacitance in the power supply
  • Ground loops – more specifically differences in the voltage of the safety ground wire between interconnected equipment
  • Electromagnetic coupling of AC and signal cables

For a more detailed discussion we suggest reading the Jensen Transformers guides below.

How do I solve hum and buzz?

A common root cause of hum issues are ground loops caused by equipment being on different electrical circuits or being plugged into different outlets on the same electrical circuit. The solution to this is to use good grounding practices – i.e. having a single grounding point for equipment and connecting all equipment to this with short, high gauge (low impedance) power leads. Powerbridges (in wall electrical circuits that are not always connected to the home electrical system; they are essentially normally de-energized electrical circuits that are energized when one end is plugged into the outlet of a power conditioner or UPS) can be used for subwoofer and projector in wall runs.

In most other cases the root cause of hum and buzz can be tracked down to a single interface between two pieces of equipment. We suggest using the Isomax Troubleshooting Guide to identify the root cause of the hum and buzz issue. The solution is generally to isolate the two components as follows:

Whatever you do, do not float the ground using a cheater plug! The ground is there to protect you from electrocution.

References and further reading:

Understanding, finding and eliminating AV ground loops, Bill Whitlock, Jensen Transformers.

Balanced lines in audio systems: fact, fiction and transformers, Bill Whitlock, Journal of the Audio Engineering Society, Vol 43, June 1995

Hum and buzz in unbalanced interconnect systems, Bill Whitlock, Jensen Transformers application note AN-004.

Isomax troubleshooting guide, Bill Whitlock, Jensen Transformers

6 thoughts on “Hum and buzz in audio systems and home theaters”

  1. Check out products by Equi=Tech. "Balanced" 120 VAC power delivery, unlike ordinary single-circuit-of 120-0-120 Volt stuff which is inherently unbalanced. Their equipment is used in professional audio/video environments. j_sehring@yahoo.com

    1. Hi John,

      Thanks for your comment! We’ve found that the issues that cause hum and buzz aren’t generally ones that an isolation transformer can resolve.

      We use and sell isolation transformers from Torus Power: http://store.acousticfrontiers.com/cart.php?m=productvendorlist&v=13. Conceptually they are very similar to the Equi=Tech transformers with the exception that the output side is not balanced and is a straight 120V-0V.

      Balanced power is restricted by the National Electrical Code to commercial and industrial facilities – see page 26 in the Middle Atlantic power paper (http://www.middleatlantic.com/resources/white-papers.aspx) for more info.

      Balanced power has the theoretical advantage of reducing electrical noise. Torus Power use a form of balancing in their ‘BAL’ designation transformers. Here, however, the balancing is done on the primary side of the transformer – two 120V legs are used to create a single 120V output.

      Nyal

  2. This may be after the fact since this data is 2 years old. I have found that hissing and hum have a simple thing in common, the separation of power cords and line level interconnect cables. You can go out and break the bank on fancy overpriced cables (the snake oil salesman has been getting fat for years) or you can be honest with your ears and not your ego. There is a difference with bench testing, but who is really able to tell the difference in a double blind comparison? The odds are the same as flipping a coin 100 times. The average will be pretty close to 50/50.

    So what really matters? Long runs of high AWG interconnect cable will have a greater impedance, than short runs of a low AWG interconnect cable thus contributing to hiss and hum. When a high AWG interconnect cable is located near a power cable at 117 to 120 volts, the result is often hiss or hum due to inter-frequency crosstalk. The hum is frequently at the 60Hz level or frequency doubling at 120Hz. Electricity in both line level and 120 volts applications absolutely hate 90 degree angles. An electrician would never do it because of increased impedance resulting in heat and possibly a fire. On the other hand, when running interconnect cables and power cables at 90 degrees from each other a cancelling effect will be the result, thus not allowing a full sine wave to develop, which is what you are really hearing. Here is the trick, run power cables low and interconnect cables high and at right angles to each other. This causes frequency rejection, thereby cancelling the hiss and hum and keeps you out of hot water with your Wife because you believed the snake oil salesman. We call this electrical hygiene, or purposeful and planned cable management. I suggest making all electrical power connections first, because their lengths are frequently odd lengths (example 3ft, 5ft, 9ft) giving you less flexibility in placement. Interconnect cables can be of custom lengths from 1 foot to 15 feet and so on, giving you more flexibility with cable management. NEVER cheat by using an extension cord or cheater plug to lift the ground from an electrical component. If you do, that funny smell of burning wires and your smoke alarm going off in the middle of the night is your house on fire. I have been doing home theaters since 1984, and the number of instances where I have seen extension cords and cheater plugs has never failed to amaze me. I have seen lightning strikes, cooked circuit boards and about 8-10 actual house fires.

    So in summary, always practice good electrical hygiene. Plan you power runs first and your interconnect runs last. Use as many right angles as you can when power and interconnect cables cross. Finally, be patient, use moose tags to identify cables and do a simple line drawing of your setup. Keep it in a notebook, or in my case a ziplock bag that I tape to the back of my HDTV. The best part of trying this method is that it costs you nothing other than a little time (I know I just pissed off the snake oil salesman).
    Hope this helps someone.

    1. Thank you for your detailed comment! We agree that the importance of “audiophile wire” is over rated. We generally use high quality “installer grade” bulk wire from ICE cable, and for higher end projects Belden (typical broadcast grade). High priced audiophile wires are only worth worrying about if you’ve optimized all other aspects of your system. Most people have much to do in the area of acoustics, which together with speaker quality is the main arbiter of sound quality in most installs. In fact the tolerances on things like balanced interconnects are much tighter on machine vs man made cables (and a lot of the high priced audiophile cables are hand made).

  3. Looking for help solving a hum/buzz coming from one speaker in a 5-channel home theater setup. The hum/buzz only happens when the system is off. Only coming from the rear left speaker. The system has been in place for over 10 years and the problem just started a couple of days ago. I have changed speakers and the noise still comes from that one speaker location – so it’s not the speaker. Also noticed that the volume of the noise goes up/down as I brighten or dim the room lights with the dimmer switch. But this switch has also been in place for over 10 years. I’m baffled on why this problem just popped up since nothing has changed, and the noise only happens when the system is off. Any help would be much appreciated!

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