The phrase "capable of being heard" refers to the ability of sound to travel and be audible to the human ear. Synonyms for this phrase may include "audible", "perceivable", "discernible", and "hearable". These words indicate the capacity of sound to be heard or detected by a person. Other synonyms may include "sonorous", "resonant", and "loud". These words may convey a sense of power or intensity in the sound being produced. Finally, the phrase "capable of being heard" may also be expressed as "acoustic" or "aural", indicating the relationship between sound and the human ear.