How are AC signals combined?

[Blenton]

Ok I've got an output from a mp3 player which has two channels (L & R) however the device I'm connecting it to can only output mono sound, so what I did was merely connect the left and right channel wires together but what I'm wondering is AC signals are not so clear cut to me, I'm currently studying Electrical Engineering (2nd year), but it hasn't clicked in my head previously that AC signals are not simply additive. Would I really be getting both channels combined? And would there be cancellation or some other problem that would be detrimental to the sound quality?

Thanks.

 

[vk6kro]

You should probably use combining resistor networks.

If you are taking speaker outputs and combining them, the problem is that they will sometimes be out of phase and one will feed power into the other. The output impedance of even small amplifiers is very low and can look like a short circuit to another speaker output.

It is safer (and probably sounds better) to put a 10 ohm resistor across each speaker output, then take a 1 K resistor from each speaker output to the same 10 K resistor to ground.
You can then take this output to the input of an amplifier as a mono signal.

This way, you will get minimum interaction between the two stereo channels.

 

[oswaler]

I can provide an explanation for how AC signals are combined. When two AC signals are combined, they undergo a process called superposition. This means that the individual signals will add together to create a resultant signal. In the case of audio signals, this means that the left and right channels will add together to create a mono signal. However, this process is not as simple as just connecting the wires together as you have described. There are a few factors that can affect the quality of the combined signal.

One factor is the phase difference between the two signals. AC signals have a frequency and a phase, which determines where the signal is in its cycle. If the two signals have a significant phase difference, they may cancel each other out or create interference, resulting in a distorted or weaker combined signal. This is why it is important to properly match the phase of the signals before combining them.

Another factor is the impedance of the circuit. Impedance is the measure of resistance to an AC signal, and it can affect how the signals combine. If the impedance of the individual channels is not matched, it can cause reflections and distortions in the combined signal.

In summary, combining AC signals is not as simple as just connecting wires together. It requires careful consideration of factors such as phase and impedance to ensure a high-quality combined signal. As an electrical engineering student, it is important to understand these concepts in order to properly design and troubleshoot audio systems.