The main difference between an instrument cable and a speaker cable is that an instrument cable is shielded and a speaker cable is not. This is due to each cables specific function. That being said you would not want to use a speaker cable as an instrument cable. The same applies, you would not want to use an instrument cable as a speaker cable.
An instruments output is relatively weak compared to an amp’s output. That is the reason they are shielded to keep out noise-causing interference. Speaker cables have signals that are so strong they will not get interrupted by interfering signals.
Using an instrument cable as a speaker cable can be harmful to your amp and speakers. This is because the signal is too strong for the shielded cable. In this situation, the amp will have to work very hard to push the signal through the cable. On the other hand, using a speaker cable as an instrument cable will allow unwanted interference noise into your signal. This is due to the lack of protective shielding
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