John is right of course but lets see if we can make this a bit less complicated (and apologies to electronics purists if I over-simplify TOO much!)
First, the two make microphone types, dynamic or condenser.
Dynamic mics work by attaching either a coil of wire or a magnet to a diaphragm. Your sound waves hit the diaphragm, wiggle the magnet inside the coil of wire or vice versa. This acts like a tiny generator and creates an electric current, effectively converting the sound waves to electrical energy. Because of the way this happens, the amount of electricity involved is tiny so dynamic mics are less sensitive than condensers--which can be an advantage in a noisy environment.
Condensers work like a capacitor in an electric circuit...in fact they ARE a capacitor. Don't worry if you don't know how these work but what you have is a diaphragm (again) this time wiggling in front of a charged plate--charged because some electricity is applied to it. Since you're not generating electricity, just controlling its flow, condensers are more sensitive (and many would say more accurate) but they DO pick up more background sound which, from what you say, is part of your problem.
Second, pick up patterns.
The design of the mic controls how much sound is picked up from various directions.
At one end of the spectrum is an "omni" (omnidirectional) mic that picks up sound equally from all directions. In a nice room these can sound really nice...but are awkward in a less than perfect room because they pick up everything.
The next step up is the cardioid you were asking about. This picks up most of its sound from one side (the front) and is fairly insensitive to the rear. If you plot out the sensitivity on a circular graph, it looks (in theory) a bit like a valentines day hear. Well, if you have a good imagination!
Moving up from there you have all the variants John mentioned--hyper cardioid, super cardioid and so on. These names designate how wide an area in front of the mic is in the sensitive "
sweet spot" vs. how soon the less sensitive part starts. Things like super cardioid are commonly called shotgun mics and used for location recording in film, TV and so on.
Now, the thing is that both dynamic and condenser mics can have any of these patterns. For example,
the Shure SM58 (that mic with a ball shaped head you see on lots of vocalists in rock bands) is a dynamic hypercardioid, used to cut out as much of the stage noise as possible. Similarly, those big mics you see in studios tend to be large diaphragm cardioid condensers...often a lovely sound but sensitive to room noises.
In treated studios, most voice overs are done on large cardioid condensers but at least some are done on large dynamic cardioid mics. In your situation, the ideal would be to do some room treatment. Otherwise, try a cardioid or hypercardiod dynamic...but, for best results, this'll have to be "in your face" in the way you don't want.
Finally, if you mean "on camera" when you say "voice over" then either a hyper or super cardioid (form of shotgun) would be one option...or maybe the sort of clip on mini lavalier mic you see on lots of TV announcers...but these are hard to find except in radio mic form.
Hope I haven't confused you too much!
