If you want the sound to be louder, you add more force. To make a guitar louder, you would hit the strings harder. To make a piano louder, you would strike the keys harder. Loud sounds differ from soft sounds in their amplitude. Hold the comb in one hand and the cardboard in the other.
Sound does travel through matter.
To prove this, I will arrange four objects on a table in front of the class. I will let you name each object. Then you will rank them according to which one sound travels through fastest. Write your responses on your paper. After singing it in the usual manner one time, try singing the song at a different pitch.