The reason the dog jumps up more when your husband shouts or says 'down' more or more loudly is that your husband is giving the dog attention, so the dog percieves his jumping up as a way to get attention. He might be jumping up because he is excited or thinks your husband is going to take him out, but the reason here doesn't really matter.

To gett he dog to stop jumping up, your husband needs to turn his back to the dog (using a wall to steady himself if he needs to) and stay slient and ignore the dog. Eventually the dog will stop jumping or sit down. The second the dog stops jumping, your husband must reward him with attention and possibly also a treat. The aim of the exercise is to teach the dog that the ONLY way ot get attention it to behave in a calm way, and jumping up gets him nothing and is a waste of energy.

Your husband will have to be 100% consistent and bear in mind it may take some time as the dog has effectively inadvertantly already been 'taught' to jump up. In other words, your husband saying 'down' tot eh dog has reinforced the jumping up behaviour.