None. Ohms is your speakers impedance. A 4 ohm speaker is harder to drive than a eight ohm speaker. If your amp is four ohm stable, then you'll get more power from it in a four ohm speaker and it will get louder than an eight ohm speaker assuming the two speakers have the same efficiency. Efficiency is how loud a speaker gets with one watt of power applied to it. If a speaker is 88 dB/watt, then it will put out 88 dB's of loudness when you put one watt into it. If a speaker is 93 dB/watt, then it will put out 93 dB when one watt of power is put into it.
The amount of bass a speaker puts out is more dependent on driver size, cabinet design, and crossover design. Not to mention room interaction being probably the number one factor of how a speaker sounds in any given room.
Television: Mitsubishi WD65737 DLP
Processor: Emotiva UMC-200
Amps: Carver AV 806x/Behringer EP4000
Mains: DCM TimeFrame 600 Center: AT 453C
Surrounds: AT 251.1 Sub: Danley DTS-10
Blu Ray: Panasonic DMP-BD655