Breaking dipole symmetry adds a monopole component that dramatically increases sound output

Evidence

In order for the cancellation to be nearly complete, the sources must be almost equal but opposite in phase. Anything done to reduce the equality or symmetry of the two parts (such as partially blocking one source) can add a monopole component to the radiated sound field, making it much louder. We shall meet this strategy in connection with the violin family of instruments, for example. — Eric J. Heller, Why You Hear What You Hear- An…, 607

Categorization

• XREF: Directly relevant to answering why we hear what we hear — connects dipole radiation theory to violin acoustics later in the book.
• SEED: Angle: how the violin’s soundboard exploits deliberate symmetry-breaking to convert a weak dipole source into a loud monopole.