The info below was taken from this website:
http://www.dt4u.com/dtsystems/speakertech.phpSpeaker Drivers - More = Better....MYTHMany speakers are built with a bass driver and separate tweeter to get better sound. Some take this further to add a third and even fourth driver. The idea is to split up the audio spectrum and to let each driver handle the part it is best at reproducing. This is another idea that sounds fine in theory but is fatally flawed in practice - See Point Source Speakers below. Another factor which makes multiple drivers worse from a hifi perspective is that each speaker has to be connected via a crossover network and each network adds errors. See Crossover discussion for more detailed information.
Point Source Speakers are Better....FACTThe next time you see a duck (sat on a pond) take two or three pieces of bread and throw them in the pond so that they land close together and at the same time. Watch the ripples produced and how they spread out - you will see they are very confused - hard to follow. Wait for the water to settle, then throw in a single piece of bread (away from the duck!) and observe how uniformly the ripples spread out in a pure circle.
This is an EXACT analogy of how sound waves travel in air. A single source (one speaker) produces a series of vibrations (ripples) that travel out from the speaker in a coherent (all together) fashion. The result - beautiful clear, direct sound with no confusion. Multiple speakers (2 or more) produce vibrations exactly like the confused ripples you saw when throwing multiple objects into the pond and produce lots of incoherent (confused) vibrations.
This is complicated by the fact that as you change position (even slightly) in front of a multiple speaker, you hear different combinations of ripples (vibrations) that affect your perception of the sound - you lose focus.
Given the pond illustration, a single speaker must have the edge when it comes to producing a focused, coherent sound front and this is true.
The difficulty is that no single driver can reproduce the full range of sounds contained within the audio spectrum and we need both a woofer and tweeter to achieve this. The point source problem is solved very cleverly by mounting the tweeter at the center and on the same exact axis as, the woofer. This Dual Concentric approach CAN and DOES produce the same clearly focused pattern as a single speaker, but crucialy, now across the whole audio spectrum. Hence we get the best of both worlds.
Speaker ConstructionAll closed areas vibrate at certain frequencies - blow across the top of a milk bottle and see what happens. Change the enclosed volume (add water to the milk bottle) and the frequency of vibration (resonance) will change. This is true of ANY closed space, be it your speaker cabinet, fridge or living space itself. The larger the space, the lower the resonace produced. This is another law that cannot be changed. However, steps CAN be taken to control or reduce the effect of the resonance.
Make the cabinet stronger - use thicker material
Get the cabinet dimensional ratios right and try to eliminate edges
Paint the cabinet inside and out with sound absorbing material - ie bitumin
Put sound absorbing materials within the cabinet
Add critically tuned ports to cancel out the last remnants of any cabinet resonance
Make sure the cabinet cannot move about
So the trick is to minimise resonance by optimising the variables above. A sucessful well designed cabinet produces no unwanted or additional sounds - period. Sorry if that is a bit basic but.....
