This for sure can be done. Although I always wondered how much of the power is lost in this case. I mean, say you have a headphone jack going to a headphone that does not have its own power. And you use one of those simple splitters, Would overall volume decrease? Like the max volume?
Generally speaking, for audio we think in terms of voltage, since audio is represented by voltage. And then if current is not enough then it clips and distorts lor. Which happens often but people actually don't notice.
So assuming your source has nearly unlimited current capability for your application, like a decent headphone amp out, then you can split dunno how many load and it doesn't care.
And, while the exact behavior can become complicated and require knowing the impedances of various parts involved, the prediction can be simplified. You connect to one headphone load and another active speaker or amplifier? An analogy is like a car with one 200kg BBFA (the headphone) and then you add one more teddy bear plushie (active speaker or amp), we can predict the teddy bear doesn't change anything noticeably. But if you add one more BBFA, then yes, start to worry. And can the car still run normally? That's your output voltage. Is the car on fire? That's your current being insufficient to sustain the output voltage. Is your car not on fire but the car is slow? Not enough output voltage.
