Today I purchased 4 speakers. 2 Mackie S215's and 2 Mackie S218's.

I need an amp to run them and the man in the shop suggested the QSC RMX 2450.

The satellites are 8ohm's with 350 watts RMS long term and 1400 watts peak power handing and the subs are 8ohm's with 500 watts RMS long term and 2000 watts peak power handling.

The amp kicks out 2x500 watts @ 8ohm's and 2x750 watts @ 4ohm's. Will this amp be suitable to run just the satellites and both the satellites & subs.

The amp would be suitable for powering just the tops OR the bass bins. You'll get sound out of the whole lot together with the amp but those subs want around 750w+ each really (although the passive crossover may not take that much) to get going.

Using the subs and tops together each cab will see 375w.

The RMX is a fine amp though, and a worthy purchase.

Subs are 500w RMS @ 8ohms, so you want an amp that will push that out...
Tops are 350w RMS @ 8ohms, so same principle here... thats the level at which your sound is going to be best.... i would use 2 of those amps, if i were you... run them with a crossover...

But you could run all four off the one Amp... would just push the amp... well i think

Hope that helps...

Now here is where i get confused... if you have 4x 8 ohm speakers, and run them off 1 amp, 2 speakers per channel, does that make each cab 4 ohms?

No but 2 x 8 ohm cabs in parallel will present a 4ohm load to your amp.

An amp doesn't know what the rating of your speakers is, only the total impedance they present to it. The power is divided equally between any cabs connected to that channel.

So 2 8R cabs in parallel will be a 4R load. If your amp gives 600w per channel at 4R then each cab will receive 300w. [edit - which is what you just said...oops!

As Welshy said, you'd be best off running the whole lot through an active crossover using 2 amps, one for the tops, and one for the bass bins. If possible you should bypass the passive crossover in the bass bins as they suck power and aren't required if used with an active crossover.

For the price of 1 RMX2450 you could buy a Behringer EP1500 and EP2500 and a crossover! Run the tops off the 2500 (2x450w at 8R) and run the EP1500 bridged into the bass bins in parallel (1x1500 at 4R, giving each cab 750w - which is just about perfect...)

I run all QSC amps now (mixture of PLX's and RMX's) but I did have EP's previously and they got a fair hard time (bridged mono at 4R flat out for 12 hour periods) on my system with no problems. The only reason for the change was weight and resale value (and a silly good price!!)

The reason why you don't see many subs with passives in is because once you get close to 500w power handling, passive crossover networks get big and heavy and expensive to produce, where it is often more cost effective to buy an active crossover.

Thanks for all the advice, I'll look into some of the options

If I did run all 4 speakers with that amp would it cause any problems ?

I'm with Norty on this one