Audio Systems: about passive crossover

Question
Namaste sir,
i am running professional public address music rental company and i want to ask that if i had 4 ohms 2way passive crossover of 1800hzs frequency 1000watts RMS and 2000 watts programme power. This passive crossover i used in 15" 300 watts 2 nos midbass speker and 1" 60 watt hize. Then my question is that can i use this passive crossover at 8 ohms for 15" 300 watts 1 speker and 1" 60 watts hize?
and i request to explain in detail that one passive crossover of 4 ohm is also use for 8 and 16 ohm or vice versa. i hope you should answer in simple language so that non technical also can understand.
thanks for your heartly supports.

Answer
Well, you stated using a 2-way passive crossover but you are using it in a 3-way example.

http://www.diyaudioandvideo.com/FAQ/Crossover/

The tutorial above will help explain a little more about basics of crossover usage and multi-way examples.

For a 15" subwoofer, 1800Hz is a very high crossover point.  Normally, it would be expected to be down in the range of 100 to 150Hz.  And for crossover into a 1" tweeter it would likely be more like 2500 Hz or more.  You must study the specifications of each driver/speaker in the system and select the crossover point according to its performance area.  And, further, due to different sensitivities the speaker power level may need to be tuned to match the same loudness as the other speakers in the system.

As a rule, crossovers are intended for unique performance characteristics for a specific system and not used in a general way.

Crossovers are designed for the specific impedance and if used with different impedance than intended the performance will change significantly.  

I suggest you study more about crossover design and applications.  It is not a simple application.  In fact speaker system engineers spend hours in listening tests setting the correct components in order to obtain best wound quality performance.  Many loudspeaker manufacturers give technical specifications on how to design or select the proper crossover information.

Hope this helps you get started.  You have a long ways to go!