What do I do if the soundpost falls down?

A soundpost is absolutely crucial in getting a violin to sound well. A cheap commercial violin with a properly placed soundpost will sound much better than a Stradivarius with a soundpost down. Aside from the poor tone, you can tell when the soundpost is down when you hear something rattling around on the inside of the instrument. This can happen for a variety of reasons. It may occur if you drop the instrument or bang it into something. The soundpost could fall if you take all the strings off the instrument at once when you are changing them. It also tends to happen during great fluctuations of humidity. The top and back swell when it is warm and humid and the soundpost simply becomes too loose and falls. Take the instrument in to your repairperson. It will only take a few minutes to set the post back up, but it is very much a job for a professional and a difficult and risky job for an amateur. I have seen many instances of torn up treble f holes as the result of inexperienced soundpost setting. For the better violins it is essential that it is positioned correctly.