Physics teaches the larger the instrument, the more capable it is of volume because the amplitude of the wavelength can be larger. So technially your bass voices such as tuba, string bass, bass drum, contrabass clarinet and so forth can produce the loudest sound. It is one reason why the larger instrument are placed in the back of ensembles.
Actually acoustically a smaller instrument will be louder. I know a trumepet can play louder than a tuba. A flute is louder than a bass clarinet. longer waves do not transform into louder sounds.
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