The volume going to each speaker is halved, so make sure you can turn it way up.
Actually, the volume may not be reduced at all, and if it is it probably won't be anywhere near 50%.
When you split a signal like this, you're increasing the load on the output amplifier. Depending on the output circuitry, it might be able to drive both loads with the same current, meaning that you might actually get the same volume levels.
Even if the output power were cut in half, that would not result in a 50% drop in volume. You would need to drop the power by a factor of 10 to decrease the volume by 50%.
Generally speaking, you can split a single output like this into two loads without significant signal loss or degradation.
OK, I was exaggerating a bit. But from what I've observed, using a splitter decreases the volume from each speaker significantly.
Not necessarily, because the power output of the amplifier is likely to change when you change the load. When you connect two 8 ohm speakers in parallel, you are placing a 4 ohm load on the amplifier. Depending on the design of the amp, you may simply get more current instead of half power to each speaker. Ever notice that power amp specs vary depending on the load? For instance, the following link lists the specs for a Carvin power amp that puts out 425W @ 8 ohms, 750W @ 4 ohms:If you're using the splitter to two sets of unpowered speakers (say iPod earphones) then yes, volume will drop by half because the power is split.