It would be helpful to define what you mean by "
self-generated noise" here. Is it like a white noise hiss? Or perhaps it's a 60Hz "buzz" or "hum"?
If it sounds like a white noise hiss, then this is likely the noise floor of the device itself, also known as the "Johnson–Nyquist noise", or simply "thermal noise". There is no way to completely eliminate this particular kind of noise. However, operating the equipment at lower temperatures can reduce it, as the noise power density is a function of temperature multiplied by the Boltzmann constant. (Avg. Power Density = 4*
*T*Δ where
= 1.380649 × 10-23 m2 kg s-2 K-1)
To work around the thermal noise, generally it's wise to keep signal levels at a much higher dB level than the noise, and adjust gain on the amplifier or powered speakers such that the noise is not audible or barely audible compared to the desired audio signal level.
If the noise is more like a "buzz" or "hum", then it is likely due to some external electromagnetic interference on the audio signal lines. Most likely, this is due to a ground loop and the electro-Magnetically induced EMF and current in a loop of wire enclosing the changing magnetic flux lines. Usually it's either 50Hz or 60Hz plus harmonic multiples of those frequencies, which comes from the AC mains current from nearby premises wiring or power cables.
Sometimes there can be other noise sources in the audio range also. For example, if there are powerful nearby radio transmitters or even hobbyist RF transmitters close enough nearby, noise due to these sources can also be picked up in audio lines.
To remedy electromagnetic noise issues on the audio lines, usually you can use "balanced" (as in "balanced wheatstone bridge") interconnections to carry the audio signal. Additionally, differential signaling can also help with this. XLR connections or balanced mono-TRS cabling generally does both of these things, as long as the equipment is designed correctly. In the worst case scenario where unbalanced (RCA, single stereo-TRS, or mono-TS) connections are needed, an inline audio transformer (a.k.a. "ground loop isolator") can be used. Using an audio transformer satisfies the requirements of "balancing the bridge" of the "wheatstone bridge" circuit formed by interconnecting two pieces of audio gear by simply pushing the impedance on the receiver end into the MegaOhm range. This effectively makes the much lower transmitter-side impedance (and slight imbalances due to component tolerance) less significant. Therefore the ratio between receiver-side and sender-side impedances is effectively balanced across the bridge circuit lines.
Finally, a few general rules of thumb:
- Avoid coiling audio signal cables
- The number of turns can increase electro-Magnetic coupling, just like in a transformer winding!
- Even a single loop can enclose magnetic flux lines, resulting in an induced EMF around the loop
- Use the shortest cable between the two points as possible
- If a cable is still too long, wrap it back and forth as an S-turn (two U-turns at each end) to reduce the possible loop area and reverse the direction of current flow such that fields and induced EMF cancel out as best as they possibly can.
- For more information about directionality of the fields & currents, look into Faraday's Law and Lenz's Law & the "right-hand rule".
- Keep audio cables away from any nearby power cables (if possible)
- The electromagnetic field strength is proportional to distance away from the noise source
- Avoid parallel cable runs between audio and power cables
- If you are constrained by space and geometry to run audio cables near to AC power cables, do so at right angles
- Right angles will reduce the electromagnetic coupling between the cables
- Shielded cables (without drain wire) are better against noise than unshielded cables
- Twisted pair cables also perform better than those without twisted pair signal wires
Hope this helps!
