The jacks are for daisy-chaining to a further set of speakers. You should never plug two different amplifier outputs into a single speaker - you will probably end up with two blown amplifiers.

There are a couple of things you have to take into account when thinking about plugging in a second set of speakers. The first is the combined impedance. Your original speaker set is 8 Ohm, and if you add another set of 8 Ohm, you present a 4 Ohm load to the amplifier, which it may or may not be happy to drive. If the mixer's output says "8 Ohm speakers", don't try to operate the mixer with a 4 Ohm load.

Secondly, even if it's OK to plug a 4 Ohm load into the mixer, there is no guarantee that it will deliver any more power to the combined load than it did to one set of speakers.

The mixer's amplifier specifications will give you the necessary information.

Excellent. Thanks

Also, keep in mind that if they are not the same make and model of speakers, they'll likely have different sensitivity and frequency response characteristics. That means that if you get one set sounding good, the other might not sound as good with the same EQ/volume settings, and vice-versa (assuming paralleled output using the same settings for both sets, and your powered mixer doesn't have mains/monitors outputs with separate output level and EQs so you can adjust each set independently). You may get both sets sounding "OK", but may not be getting the optimum sound out of either set because you had to compromise something on each.

And as Boswell already said, those 2 jacks are likely for daisy-chaining. The only speakers you might see separate "input jacks" on are speakers designed to accomodate bi-amping with an external crossover/power amps where one jack goes to the lows, and one to the mid/highs...or possibly a multi-spekar guitar cab like some Marshall 4-12s that can run 4/16 ohms mono, or 8 ohms stereo by setting a switch and plugging in two amps, or a stereo power amp.

ALL of those speakers should be clearly marked for those purposes (and will certainly be in the manual). In the case of the PA speaker with bi-amp inputs, you may see something like one input labelled "Full-range/Low Input", while the other may be something like "Mid-High Input". These may contain an internal passive crossover that is bypassed when using bi-amped with an external crossover. For instance, plugging a full-range signal directly from your powered mixer into the "Full-range/Low Input" will send the signal to the large low end speaker, and also through the internal crossover to any mid-hi speakers. But, if you have an external crossover and two power amps to divide the lows and highs, with that speaker, you'd plug the output of the lows from the crossover and through the amp into the "Full-range/Low Input", while plugging the output from the external crossover's mid-hi through that amp into the "Mid-High" input of the speaker. It may be designed so that plugging into the "Mid-Hi Input" of the speaker interrupts the connection of the speaker's internal crossover so that it is out of the path.

You'll likely not see those on smaller PA/Monitor speakers, though. They'll more likely be on some larger PA speakers with at least 15" low-end drivers. I've seen Peavey PA speakers like that.

But, again, NEVER connect two power amps to a paralleled speaker input. ALWAYS check the manual, if you are not sure, or have someone more clued-in check it out.

And, don't forget to remember. Learning about this mundane stuff comes in handy at times.

Kapt.Krunch