Can anyones tell me how to design good passive crossover and loudspeaker box?
I also want to know advantage and disadvantage of two-way or three-way system when use with my amp.
As you are going for a bass sub definitely go for a two way system rather than three way. Two way is simpler, cheaper and has less cross over problems. Crossing over from one speaker to another is always undesirable.
Ported cabinets are currently favored rather than closed box (infinite baffle). Besides, a ported cabinet can easily be turned into an infinite baffle, but not the other way around, at least not easily.
There are heaps of suitable designs for speaker systems on the net.
The most critical aspect is what speaker chassis you can access and afford. HiFi speaker chassis are very expensive
In terms of tweeter there is a broad choice to be made: bright or smooth; at one end there is the metal dome types and at the other end there are the soft (silk) dome tweeters. I favor the former, but it is a matter of taste.
And there is also a choice to be made in bass/mid driver: fast and articulate or powerful sounding. I prefer the former, but again it is a matter of choice.
Your best bet would be to buy secondhand speakers, rather than make your own.
As I have said before, don't worry too much about matching the speaker power rating to the amplifier. For example a 100W amplifier driving 20W speaker will be OK. The other way around will not. Bass subs need more power capability though, perhaps 40W. But you do need to match the sound of the amplifier and speakers. For example, a fast articulate amplifier driving fast articulate bass/mids coupled to bright tweeters, would be very revealing and may emphasis any shortcomings in the source material or other components in the audio chain. On the other hand, a smoother system may be more forgiving and easier on the ear.
At the end of the day, it is all down to taste.
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PS: don't worry too much about speaker impedance either: the impedance varies greatly through the audio spectrum. In terms of your amplifier there are roughly four Ohm and roughly eight Ohm speakers.
You will also see a load of stuff about low amplifier output impedance and damping. The fact of the matter is that the equivalent circuit of an eight Ohm speaker chassis, for example, is approximately a six Ohm resistor in series with a motor. In this case the effective output impedance of any amplifier can never be lower than six Ohms, never mind how astonishingly low the actual output impedance of the amplifier is. Some speakers do have very low loading impedances at certain frequencies though, even as low as two Ohms.