I tried to extend my hometheater speaker to fit my hall size, but after connecting (soldring) the extra wire the speaker volume has reduced. This is not the same for the speaker which is not extended.
Longer speaker wire will increase resistance and that resistance can cause a slight change in speaker volume, but unless you added a hundred extra feet, I seriously doubt you would notice the change without testing equipment. I find it to be a safer bet that it's the added distance you put between the speakers and the listener that caused them to sound more quiet. While low frequencies can travel further without sound reduction, the volume of high frequencies will roll off much more quickly. Speakers are made to fit rooms of specific sizes. It could very well be that the speakers you have are designed to fit in a smaller room, or to at least be listen to at a closer range than where you have them now. Without taking away any speaker wire, try moving the speakers back to their original position and see if the volume returns. If it does, then you know it's not the added speaker wire causing the drop in volume.
This is normal due to the signal lost over the longer transmission. This can be fixed by adding equal amounts of wire to the shorter run or simply adjusting the balance on the receiver.
