matze79 wrote on 2020-03-10, 19:53:
would it not better to couple them over a opamp with some sort of summing amplifier ?
i tried that with resistors and the impact on sound quality with only resistors is hear able.
i simply would purchase a cheap stereo mixer ^^
What do you think happens in the mixer? 😉 To sum inputs, you isolate them with resistors, then buffer the result with an op-amp (or discrete amplifier if you're into hand-selecting transistors, etc.). With a "passive" mixer, you .... isolate the inputs with resistors, then feed it to your speakers. The first stage of which will be a buffer amp. That's basically a mixer.
The variability comes down to -- what R values did you choose? What's the input topology of the speakers? Is there a DC-blocking cap? (hint: yes, there is) What's its value and its effect on the bandpass filter you've just created?
Basically, you can try 1K, 10K, 22K resistors and pick the combination that works best. If you were going to design a fancy mixer, you might buffer the individual inputs straight away, then mix them (with resistors -- always with resistors), then buffer again. This helps you eliminate any variable interactions. But, many cheap mixers do not go to such lengths. (E.g., common Rolls utility knife boxen and such -- they just use resistors followed by potentiometers followed by a buffer amp.)