I am assuming you don't know what ohms measures. So I will tell you. Ohms is the measurement of electrical resistance. So the lower the number means that the amp has less resistance and can send the current with greater ease. Keep in mind though if you want to ever use two cabinets that you want to choose a higher ohms like 8 or 16. When you combine two 16 ohm cabs it equals 8 ohms. When you combine two 8 ohm cabs it equals 4 ohms. Most amplifiers I have seen can accommodate all three ohms. However you should refer to you owners manual. I have a single cab that is 16 ohms that way I can use more than one in the future. As far as tone goes I don't think it affects it one bit, but I could be wrong. I have never done a comparison. Hopefully that answers your question.