The sound waves then hit the listener's ear drum causing it to vibrate. Sounds consist of waves of air molecules that vibrate at different frequencies. It will vibrate easily at those frequencies, and less so at other frequencies. They vibrate, pulse, and quiver. These vibrate to produce sound inside the body. It will easily vibrate at those frequencies, and vibrate less strongly at other frequencies. Cylindrical brasses do not naturally vibrate at this frequency. To produce the croaking sound, special muscles vibrate against the swim bladder. If they are pulled farther apart, they do not vibrate and so produce voiceless phones. Using sonic waves, he could rapidly vibrate himself or other masses at will. Sonic and ultrasonic scalers are powered by a system that causes the tip to vibrate. A glass has a natural resonance, a frequency at which the glass will vibrate easily. Low depth gauges will also cause the saw to vibrate excessively. These spasms make it difficult for the vocal folds to vibrate and produce voice. Built-in mutes may be made from foam, which reduces the length that notes can vibrate.