How Can Opera Singers Be Heard Above the Orchestra?

One of the most important abilities for a singer is to be heard singing above an orchestra. Wise voice teachers over the years have taught that the key to achieving this feat is not by singing louder, but with greater vocal resonance, meaning a more diverse signature of higher frequencies. This is the type of sound a singer makes that causes your ears to ring even though the singer is not necessarily singing loudly.

In a recent Scientific American, a reader asks the question "Why can an opera singer be heard above the much louder orchestra?". SA's answer provides a scientific basis for this vocal wisdom:

Usually, the fundamental frequency has the greatest acoustic power, but the very high harmonics, although less powerful, have the advantage of residing in a range above about 3,000 Hz, where the orchestral accompaniment provides less competition. Sopranos have an advantage over lower voices, such as the bass and tenor: Due to their higher range, the auditory frequency at which they sing, as represented by their f_o, lies in the neighborhood of frequencies to which the ear is most sensitive. In contrast, the lower fundamental frequencies of male voices cannot compete as easily with the power of an orchestra; male singers, therefore, must often rely on their higher harmonics in order to be heard.

Learning this concept requires more than simple understanding. Voice teachers have a host of exercises and concepts to teach the actual physicality of developing a sound with a wide resonance signature since the singer's voice must be actually built step-by-step (via correct daily practice) inside their body.

The parting words from the column give an evolutionary hint as to why we respond so viscerally to singing (italics are mine):

Furthermore, it is quite likely that there has been considerable selection pressure to pay attention to very loud sounds produced by people in any context, as such sounds can be a warning of impending danger.

If you're interested in reading more about the technical foundations of singing, I recommend Richard Miller's The Structure of Singing: System and Art of Vocal Technique.