Hi Abdul.
This question is not so easy to answer because you have not given us all the information needed.
1) Are you using one or more amplifiers and passive speakers or are you using active speakers (with the amp built-in)?
2) What kind of cabling/connectors are you currently using (XLR speaker, XLR signal, Jack-Jack, SpeakOn, Bananaplugs, heavy duty speaker cable, signal cable)?
3) What is the reason you need such long cable runs? This would indicate a very large area and a lot of people in which case renting a PA would make more sense and having the PA people set it up, including the right cabling.
Or do you need to make announcements heard along a race track or soccer field or something. In which case choosing for a different kind of speakers (100Volt) will give you more flexibility in length.
In general terms I can say this:
A) Amp with passive speakers. Depending (a lot!) on the cable thickness, if it’s a one-piece cable (connectors make you lose signal strength) and the speaker/amp impedance load, you can run very long cables. But you have to count on pretty strong losses. If you have a 4 Ohm system and use 2.5mm2 cable (AWG10), you lose about 20% at a distance of 70 meters and 50% at a distance of 250 meters.
B) Active speakers. Assuming both your speakers and the amp support balanced (either TRS Jack or XLR) connections and you use a good quality signal cable, there is no real official maximum length. I have tried often with 100m cable and have seen 200m runs. Of course this is with a good source signal (Master out from mixer or controller at the right levels). The only problem here CAN be a ground hum or other noise picked up along the way.
Hope that helps some.
.
