A general question but inspired by a specific example so framed as such.
I have powered studio monitors attached to a computer's unbalanced headphone port, and there is some amount of underlying noise, either from the computer's DAC or induced along the unbalanced cable or some combination. Overall not particularly surprising. With headphones plugged in instead, I don't hear the same noise at all.
My thought is that the likely cause of this difference is that the headphones, being a relatively low impedance load (64 ohm in this case) act to short out the noise so it's not heard. Basically the noise, wherever it's coming from, isn't strong enough to drive the headphones' drivers enough to be audible.
When the powered speakers are plugged in instead, they have a very high input impedance that then goes into their amplifiers (10k ohm). Now the same noise can drive the input easily, and is then amplified and played through the speaker.
So, the question is, if I were to put a resistor in parallel with the speaker input, or even plug the headphones in in parallel for that matter, would this decrease or eliminate the noise? Am I thinking about some part of this wrong?