difference sub Vs. speaker

[camacazi]

whats the difference between a normal speaker and a subwoofer (and not that it is just a deeper noise) but the mechanical and electrical/ component differences

 

[mechie]

Subwoofer

Not a lot !!!
All loudspeakers use the same basic idea, they just pump air around.

A tweeter can be small as it moves fast, effectively generating 'shock waves' in the atmosphere, the wavelength of a high frequency (inverse of frequency) is short and so a small pump (moving fast) can transmit the required energy to your ears.

A woofer has to be physically bigger as its cone moves much more slowly and so the pressure front generated will dissipate more readily. By pumping a much larger volume of air a similar energy level will be recieved by your ears.
Take this to the extreme --- a door being opened will pump a great deal of air but most of it will have time to leak from one side of the door to the other. Wasted energy. Your ears will only work with a range of frequencies starting at maybe 40Hz (depends on age, sex, environment, previous exposure, etc.). Move the door fast enough and energy may be transmitted to your ears - but better efficiency can be obtained by ...
Seal the door so that you can open it without allowing air to leak round it (like a bellows ?) and much more energy will be available to you ears.
If this door is into a small space such as a cupboard then the pressure inside the cupboard will vary significantly - retarding the door's movement - the room on the other side of this door will not see such a big change in pressure as the same volume being pumped will have further to spread.
This is the basic idea of a loudspeaker cabinet - it stops the air leaking around the 'speaker but it can make the 'speaker harder to drive. The volume of air inside the cabinet is important in defining the 'speaker's overall sound, efficiency and lower frequency limit, "a good big one is always better than a good small one".
Cabinet design is a subject in itself !

Electrically, any subwoofer (or woofer) will be seen as a reactive load - it is a coil of wire, just the same as a mid-range 'speaker but will be unable to respond as fast due to its sheer mass of cone and the amount of air in contact with it. It will therefore probably be a bigger reactance (more inductive).
A typical loudspeaker cabinet with a tweeter, mid-range and woofer will contain a crossover network to steer only low frequencies towards the woofer - this is all it can reproduce, anything extra will be wasted energy from the amplifier and potential heat in the woofer's voice coil.