A sound system consist of four basic kinds or components: inputs, amplifiers, attenuators (volume controls) and outputs. (Feedback occurs when an amplified signal output is presented as an input and gets amplified again. For any given length of "feedback loop", some family of frequencies is going to be in synch, and the amplitudes (volumes) at those frequencies will rapidly build toward infinity.) "Hum" refers to an extraneous input into the system. Michael Faraday discovered that it was easy to turn a fluctuation electrical current into a moving magnetic field, and vice versa. In the case of most hum, the fluctuating AC power from a wall outlet is producing a weak magnetic field which int turn induces a small fluctuating current in wires carrying the sound signal (which is ALSO a small fluctuating current). This won't usually be noticeable unless it occurs on the input side of one or more amplification stages. If these are powered speakers, then there is an amplifier built into one or more of the speakers, and so it may be the speaker *wire*, not the speaker itself, that is passing too close to a power cord or other device. (A fluorescent light could be the culprit.) David Gillett On 7 Sep 2003, at 16:11, Brady C Burke wrote: > I put to together a system epox mobo kl133 750mhz everything ran ok I > delivered it and they called me with bad hum in the speakers. The sound in > built into the mobo and I was using the drivers downloaded from epox. I > made sure the speakers are not next to the monitor or electrical wiring I > rebooted the system using a boot disk to dos and I still have this hum > when the speakers are turned up all of the way. I even installed a new pci > sound card same problem. Any and all ideas on how to proceed appreciated. > > Brady > > The NOSPIN Group provides a monthly newsletter with great > tips, information and ideas: NOSPIN-L, The NOSPIN Magazine > Visit our web site to signup: http://freepctech.com PCBUILD maintains hundreds of useful files for download visit our download web page at: http://freepctech.com/downloads.shtml