So it cannot travel through a vacuum because there is no medium. It travels faster through solid wood but why?

Before you can answer these questions you have to first understand that there are two categories of waves that generate sound. The two groups are Electromagnetic Waves and Mechanical Waves. Electromagnetic waves include most of the waves people are familiar with: Microwaves, X-Rays, Infrared Waves, Visible Light, Radio Waves, etc... These kinds of waves pass through different media as they project from their source. The more dense the media it passes through, the more the wave is slowed down. So it makes sense that cell phone signals are great when out in the open but worse when surrounded by solid walls. The second kind of waves are mechanical waves. Your voice, created by the vibration of your vocal chords, would be an example of a mechanical wave. Mechanical waves are different in the way that they travel. Rather than passing through different media as they travel, they use the particles inside the media to travel. Think of it like this...You say something, the sound waves is absorbed by an air molecule, which passes it to another and another until it gets where it is going. By themselves sound waves cannot travel, just like the wave can't cant happen at the football game without the people. The more dense the media the better, becuase the waves just have an easier time jumping from one particle to the next one. They travel fastest in solids and slow down as the particles get further apart. Now, to answer the final part of your question, "why doesn't sound travel in space?" Your voice would not be able to travel in space because it has no air particles to travel on. However, a radio, sending out electromagnetic waves doesn't need any particles to travel. In fact, the empty space of a vacuum is the ideal setting because nothing gets in the way to slow the wave down. I hope this helps....best of luck.

as far as scientific today concern, there is no such thing as absolute vacum space, hence there is a finite particles per volume units, and since you mentions that sound waves realized on the vibration of particles to pass on it energy, then in theory sound should be able to get around in space. however, because of the density in space, such sound energy can only be detected at plank scale. so and since we compute at macro level, we ussually aproximate such a small energy as zero.