How can a speaker be a barrier to effective listening?

Since listeners are also taking in the way a speaker looks, the speaker needs to be dressed in neat, clean unobtrusive clothing (for example, not low cut or otherwise revealing) and jewelry. If the language is not clear, as it can be with foreign speakers, or loud enough, that may impede the understanding of the listeners also. Finally, if the speaker does not employ either the format at the beginning (tell them what you are going to tell them, tell them, tell them what you told them), or some other form of organization (power point), then the main ideas may not be taken in by the listeners.