On an 8 ohm speaker load, 15 meters is the safe max when using lamp cords or 16 ga wires. When using 12ga wires, you can go 30 meters. 10ga up to 60 meters. But even if you exceed these pressuambly safe limits, the combined resistance, conductance and inductance that result for such long runs start to significantly attenuate frequencies only above 10khz at levels in fractions of decibels. See if you can hear that even in aggregate amounts. A 10ga cable has a resistance of 0.001 ohm per foot. So that's around 0.2 ohms for 200 feet or around 60meters. You would have to have a cable run that will result in an effective impedance in the same magnitude as your speaker load to even hear any audible degradation of sound, say around half or 4 ohms. You can compute how long the cable will be to reach that.
(Speaker impedances that are fairly stable across the freqeuncies and don't widely dip to 2 ohms or less can tolerate longer cable runs than speakers with wild swings. Because if at a certain frequency the speaker impedance goes down to 2 ohms, and the cable resistance is in that same magnitude, you can expect significant attenuation at that frequency. )
